Contrast-enhanced ultrasound parameters for predicting complete response after neoadjuvant chemoradiotherapy in rectal cancer

Contrast-enhanced ultrasound parameters for predicting complete response after neoadjuvant chemoradiotherapy in rectal cancer | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Contrast-enhanced ultrasound parameters for predicting complete response after neoadjuvant chemoradiotherapy in rectal cancer Jie Zhang, Mengjia Liu, Yun Dai, Yu He, Ningyi Cui, Yong Wang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8700611/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Background Accurate identification of complete responders before neoadjuvant chemoradiotherapy (nCRT) is essential for organ-preservation strategies for rectal cancer. However, current preoperative radiological assessment methods lack sufficient accuracy. The purpose of this study is to evaluate the diagnostic value of contrast-enhanced ultrasound (CEUS) in distinguishing complete response (CR) in patients with rectal cancer after nCRT. Methods In this prospective study, 100 patients with rectal cancer treated between January 2023 and February 2025 underwent endorectal ultrasound (ERUS) and CEUS examinations before and 6–8 weeks after nCRT. Quantitative perfusion parameters were derived using time–intensity curve analysis. Surgical histopathology served as the reference standard for pathological CR, and multimodal clinical evaluation defined complete CR. Diagnostic performance was assessed using logistic regression and receiver operating characteristic curve analysis. Result A total of 100 participants (mean age, 57 ± 11 years; 77 men) were included. Pathological CR occurred in 29 (29.0%) participants, and clinical CR in 13 (13.0%), yielding an overall CR rate of 42%. Post-nCRT CEUS parameters—relative area under the time–intensity curve (rAUC*), relative enhancement intensity, and enhancement intensity difference—were significant predictors of CR (all p < 0.05). The AUCs were 0.72 (95% CI: 0.617, 0.829), .76 (95% CI: 0.665, 0.858), and 0.76 (95% CI: 0.695, 0.875), respectively. Combined models achieved AUCs of 0.80 (95% CI: 0.708, 0.887) and 0.82 (95% CI: 0.741, 0.903), respectively. Conclusion Quantitative contrast-enhanced ultrasound (CEUS) parameters, including enhancement intensity (EI), relative AUC*, and their derived ratio values (rEI, rAUC*) and difference (ΔEI), demonstrated robust discriminative capacity in complete response participants after nCRT. The CEUS-based diagnostic model also demonstrated a high level of diagnostic efficacy. The clinical diagnostic model constructed from the above parameters demonstrated higher diagnostic value. rectal cancer ERUS CEUS nCRT Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Background According to recent epidemiological data, colorectal cancer is the third most commonly diagnosed cancer and the second leading cause of cancer-related mortality globally [ 1 ]. Therapeutic strategies are individualized according to the tumor–node–metastasis staging system. The National Comprehensive Cancer Network recommends neoadjuvant chemoradiotherapy (nCRT) followed by total mesorectal excision (TME) as the standard treatment for rectal cancer [ 2 ]. nCRT effectively reduces tumor size, increases surgical resectability, increases the rate of pathological complete response (pCR)—defined as the absence of viable tumor cells on full pathologic examination (ypT0N0)—and reduces surgery-related complications, including postoperative anastomotic leakage [ 3 , 4 ]. Pathological examination after nCRT demonstrates that approximately 15–27% of patients achieve pCR [ 5 ]. For patients with mid-to-low rectal cancer, sphincter preservation is a critical clinical goal, and nCRT significantly improves the likelihood of achieving it [ 4 ]. Patients achieving a clinical complete response (cCR) after nCRT may be managed using a watch-and-wait strategy [ 6 , 7 ]. Systematic reviews indicate comparable long-term outcomes, including non-regrowth recurrence and overall survival, between the watch-and-wait approach and immediate surgery [ 8 , 9 ], supporting organ preservation without compromising oncological safety. Current clinical CR assessment relies on multimodal evaluation, including MRI, and digital rectal examination [ 10 ]. Endoscopy effectively assesses mucosal response but cannot determine the tumor invasion depth, whereas MRI provides regional assessment of residual disease within the rectal wall, mesorectum, and pelvic lymph nodes. However, posttreatment MRI accuracy is limited, with reported sensitivity as low as 50.4% for restaging [ 11 ]. Endorectal ultrasonography (ERUS) enables high-resolution visualization of the five-layer rectal wall. It allows accurate assessment of invasion depth, although post-nCRT changes, including tumor regression, inflammatory edema, fibrosis, and necrosis, reduce diagnostic accuracy [ 12 ]. Contrast-enhanced ultrasound (CEUS) is a blood pool imaging technique that enables dynamic assessment of tumor perfusion and microvascular characteristics. CEUS has significant diagnostic value in several malignancies, including breast and primary liver cancers [ 13 , 14 ]. However, its application in rectal cancer after nCRT remains exploratory. We hypothesized that quantitative CEUS parameters can accurately identify CR. Accordingly, the purpose of this research is to explore the diagnostic value of CEUS in distinguishing CR in participants with rectal cancer after nCRT. Methods Participants We prospectively recruited 158 participants with rectal cancer treated at our hospital between January 2023 and February 2025. The inclusion criteria were biopsy-confirmed rectal cancer; lower tumor margin <15 cm from the anal verge; consent to receive nCRT; and completion of ERUS and CEUS examinations before nCRT and surgery. Exclusion criteria included lack of definitive clinical or pathologic diagnosis after nCRT; tumor bleeding, obstruction, intestinal stenosis, or incomplete ERUS examination; failure to undergo timely ERUS and CEUS examinations before or after nCRT; and contrast allergy. Notably, all participants underwent ERUS and CEUS before and 6–8 weeks after nCRT (2 weeks before surgery). Participants evaluated as having achieved clinical CR underwent ERUS follow-up every 3 months. Instruments ERUS and CEUS examinations were performed using GE LOGIQ E11 (GE Healthcare, WI, USA) with an IC5-9-D end-fire endorectal probe operating at a 5–9 MHz. Collection of clinical data Participants’ data included sex, age, and pretreatment tumor markers (carcinoembryonic antigen and carbohydrate antigen 19-9). Tumor characteristics, including length, thickness, invasion depth, and lymph node metastasis, were assessed using ERUS. Reference standard CR was determined as follows: (1) for surgical participants who underwent TME, postoperative pathology served as the reference standard; (2) for non-surgical participants, clinical complete remission based on comprehensive multimodal (pelvic MRI, CT, and endoscopy) judgment was used. Participants were classified as CR if pathology confirmed ypT0N0 or if evaluation indicated a clinical CR [10, 15, 16]. All others were classified as non-complete response (NCR). ERUS examination Participants received enemas to clear the rectum before the ERUS. They were positioned in the left lateral decubitus position, and approximately 100–150 mL of coupling gel was instilled to visualize the five layers of the rectal wall and tumor. Tumors were evaluated for location, length, thickness, echo pattern, color Doppler flow, and depth of rectal wall invasion [17]. Ultrasound T-staging followed Beynon criteria [18]: Stage 0, no visible tumor with intact wall layers; stage 1, tumor confined to the mucosa or submucosa; stage 2, tumor invading muscularis propria but not adventitia; stage 3, tumor penetrating muscularis propria to serosa; and stage 4, tumor invading adjacent tissues or organs. Dynamic and static images were recorded on a workstation. Two experienced sonographers (10 and 20 years of experience) jointly performed the assessments, resolving disagreements by consensus. CEUS examination After ERUS, CEUS was performed using a dual grayscale display. A 2.4 mL dose of sulfur hexafluoride lipid-coated microbubble contrast agent (SonoVue, Bracco SpA, Milan, Italy) was diluted in 5 mL 0.9% saline and administered via the antecubital vein. A 3-minute video captured the maximal tumor cross-section and adjacent normal bowel wall. For NCR, a 5-mm circular region of interest (ROI) was placed on the area of most stable enhancement, avoiding necrotic regions. For CR, the ROI was placed at the original tumor bed. A corresponding 5-mm ROI was placed on the normal bowel wall. During CEUS image analysis, the starting and ending frames of the ROI were adjusted according to the actual inflow of the contrast agent. Time–intensity curves were generated using the Gamma Variate model. The parameters derived were arrival time (time for contrast microbubbles to initially enter the ROI, in seconds, ArT); time to peak (time from contrast arrival to peak intensity, in seconds, TtoP); peak intensity (maximum intensity of the contrast agent within the, in decibels, PI); time width at half maximum (time from contrast arrival to half of the peak intensity, in seconds, TWH); area under the intensity–time curve (AUC*); background intensity (baseline contrast intensity); and the wash-in gradient (ascending slope of the time–intensity curve, Grad.). Enhancement intensity (EI) was calculated as the difference between the tumor's peak and background intensities, with rEI and rAUC* derived relative to the normal bowel wall. ΔEI was defined as the difference in EI between the tumor and the adjacent normal bowel wall. CEUS images were analyzed by two board-certified radiologists (10 and 20 years of experience), with disagreement resolved by consensus. Statistical analysis Statistical analyses were performed using SPSS version 27.0(SPSS version 27.0, IBM Corporation, Armonk, New York, United States). Continuous variables are presented as the mean ± standard deviation and compared using Student’s t-test or ANOVA for normally distributed data, Mann–Whitney U or Kruskal–Wallis H tests for non-normal data. Categorical variables were compared using the chi-square test. Postoperative pathology and comprehensive clinical assessment served as the reference standard for diagnostic performance. Receiver operating characteristic curves were plotted to evaluate the diagnostic performance of time–intensity curve parameters. The area under the receiver operating characteristic curve (AUC) was used to quantify discrimination, distinct from the TIC-derived area under the curve (AUC*). A P-value ≤0 .05 was considered statistically significant. Results Participant characteristics Between January 2023 and February 2025, 158 eligible participants with rectal cancer were prospectively recruited at our tertiary referral center. Of the initial 158 participants, 58 were excluded because of loss to follow-up (n=29), lack of timely examination (n=17), or absence of a definitive diagnosis (n=12). Consequently, a total of 100 participants were enrolled (Figure 1), consisting of 77 men (mean age: 56.7 ± 10.8 years) and 23 women (mean age: 57.2 ± 11.4 years). Overall, 42 participants achieved CR after nCRT, including 28 men (67%) and 14 women (33%). All participants received short-course radiotherapy followed by chemotherapy, with or without immunotherapy. A significant sex-based difference in tumor-free response was observed, with women achieving a higher CR rate than men (61% vs. 36%, p< 0.05; Table 1). Post-treatment tumor thickness differed between the CR and non-CR groups (p<0.05; Table 1). Postoperative pathological and clinical diagnoses A total of 87 participants underwent TME after nCRT. Postoperative pathology revealed pathological CR (ypT0N0) in 29 participants. The remaining pathological stages were ypT0N+ (n=1), ypTisN0 (n=2), ypT1N0 (n=2), ypT1N+ (n=1), ypT2N0 (n=20), ypT2N+ (n=4), ypT3N0 (n=13), and ypT3N+ (n=15). Additionally, 13 participants achieved clinical CR, and the mean follow-up time was 21.4 months. ERUS examination Table 2 summarizes the diagnostic performance of ERUS for post-nCRT tumor staging compared with the reference standard. Overall, 54 participants (54/100, 54%) were correctly staged. The accuracy of ERUS for predicting CR was 50% (21/42). Among participants with non-CR, 21 were overstaged. ERUS identified 87 participants without lymph node metastasis and 13 with metastasis. The overall accuracy for metastasis detection was 84%, with a sensitivity of 69%, specificity of 86%, positive predictive value of 43%, and negative predictive value of 95%. Notably, one participant with no residual primary tumor after TME was found to have metastatic lymph node involvement on histopathological examination. CEUS examination Quantitative CEUS parameters declined after nCRT. The rAUC* decreased from 2.47±2.10 to 1.89±1.42 after nCRT (p=0.004). Similarly, rEI decreased from 1.82±0.56 to 1.44±0.52 (p<0.001), and ΔEI decreased from 12.29±6.77 to 8.04±5.26 (p0.05). In contrast, post-nCRT CEUS parameters were independent predictors of residual tumor. Univariate logistic regression results are presented in Table 3. Receiver operating curve analysis using post-nCRT ΔEI, rEI, and rAUC* demonstrated diagnostic value for identifying residual tumors (Table 4, Figure 2). The optimal cut-off values were 8.25 dB for ΔEI, 1.38 for rEI, and 1.36 for rAUC*, yielding AUCs of 0.79 (95% CI: 0.695, 0.875), 0.76 (95% CI: 0.665, 0.858), and 0.72 (95% CI: 0.617, 0.829), respectively. A ΔEI < 8.25 dB yielded a sensitivity of 66% and specificity of 76%, whereas rEI < 1.38 yielded a sensitivity of 72% and specificity of 71%. An rAUC* < 1.36 provided higher sensitivity (86%) but lower specificity (57%). Combined diagnosis The accuracy for identifying CR was 50% (21/42) using ERUS alone, increasing to 67% (28/42) when combined with rAUC*, 71% (30/42) when combined with rEI, and 76% (32/42) when combined with ΔEI. As shown in Figure 3, the combined diagnostic model_1 (rAUC* plus ΔEI) achieved an AUC of 0.80 (95% CI: 0.708, 0.887), whereas model_2 (ΔEI plus lesion thickness) yielded an AUC of 0.82 (95% CI: 0.741, 0.903). Neither combined model demonstrated superior diagnostic performance compared with the single parameter (p>.05). Discussion Accurate restaging of rectal cancer after neoadjuvant chemoradiotherapy (nCRT) is crucial as pathological complete response (pCR) occurs in approximately 15–27% of patients [ 5 ]. In our cohort, 33% (29/87) of participants achieved pCR after nCRT, a higher rate than previously reported, potentially reflecting advances in systemic therapy, incorporation of immunotherapy, and precise delineation of radiation therapy target volumes. For participants achieving pathological CR or clinical CR, the “watch and wait” strategy offers the potential for sphincter preservation and improved quality of life [ 19 ]. ERUS is well established for initial tumor staging but is limited after nCRT because of treatment-induced fibrosis, edema, and inflammatory changes [ 12 ]. CEUS, a safe pure blood pool imaging technique, allows the dynamic assessment of tumor perfusion and vascularity and has demonstrated value in evaluating treatment response across several malignancies, including breast, pancreatic, and cervical cancers [ 20 – 22 ]. Quantitative CEUS parameters, including peak intensity, AUC, slope, and arrival time, are essential for assessment, with peak intensity and AUC being particularly valuable for the diagnosis and prediction of tumors [ 23 , 24 ]. However, prior studies on rectal cancer after nCRT have relied largely on CEUS or elastography, and quantitative post-nCRT evaluation remains largely unexplored [ 25 ]. Our prospective study design and moderate sample size strengthen the validity and generalizability of the findings. Post-nCRT quantitative CEUS parameters—rAUC*, rEI, and ΔEI—declined significantly, reflecting reduced tumor perfusion and microvascular density consistent with necrosis and vascular regression induced by therapy [ 25 , 26 ]. Pre-nCRT parameters did not predict CR, whereas post-nCRT measures demonstrated effective discrimination, with receiver operating characteristic–AUC of 0.72, 0.76, and 0.79 for rAUC*, rEI, and ΔEI, respectively. Lower post-nCRT values correlated with greater therapeutic response, consistent with prior reports linking reduced EI and AUC* to pathological CR [ 24 ]. This is because nCRT induces tumor cell necrosis, vascular atrophy, and rupture, thereby reducing the vascular network. This reduction disrupts the angiogenic support essential for tumor growth and survival. As EI acts as a visual marker of microvascular density, it effectively demonstrates these pathophysiological alterations [ 27 ]. In participants with CR, the time–intensity curves from previously involved tumor site closely approximated those of adjacent normal bowel wall. This convergence was reflected in comparable peak intensities, similar time-to-peak values, and analogous washout patterns, suggesting nearly identical perfusion kinetics between the two regions(Fig. 4, Fig. 5). This pattern provides a clear imaging correlate of complete pathological response, reflecting the replacement of tumor tissue with fibrotic tissue and restoration of a normal microvascular architecture. While this convergence may serve as a qualitative adjunct for identifying potential CR, its assessment remains subjective. It depends on precise region-of-interest placement, posing challenges for standardization and reproducibility across observers. Future studies should aim to quantify this “convergence index” to enhance its objectivity and diagnostic utility. Tumor thickness, but not length, differed between the CR and nCR groups, indicating radial regression is a more reliable indicator of response than longitudinal extent, which may be confounded by peritumoral edema from radiation. Multivariate analysis identified rAUC*, rEI, and ΔEI as independent predictors of CR. Combined models incorporating CEUS parameters with lesion thickness modestly improved discrimination (AUC 0.80 and 0.82 for models 1 and 2, respectively), though Delong’s test showed no statistically significant improvement over single-parameter models. This suggests that CEUS provides the majority of predictive information, and combined approaches offer limited incremental value in our sample. ERUS alone demonstrated 50% accuracy for CR identification, consistent with previous research [ 28 ]. Overstaging occurs due to post-nCRT fibrosis and edema, whereas understaging reflects residual tumor not apparent on imaging. Integrating ERUS with CEUS improved CR identification to 67–76%, with ΔEI and rEI providing superior accuracy than rAUC*, likely because EI directly reflects peak perfusion and is less affected by operator-dependent curve fitting. Persistent diagnostic errors may arise from tumor “fragmentation,” wherein residual tumor cells disperse microscopically, evading CEUS detection [ 29 ]. CEUS cannot reliably identify microscopic tumor residues within the muscularis propria or the serosa. This limitation directly contributes to the decreased accuracy in CR. ERUS detected lymph node metastasis with 84% accuracy (sensitivity 69%, specificity 86%, positive predictive value of 43%, and negative predictive value 95%). The high negative predictive value indicates that negative ERUS reliably excludes nodal involvement. Nevertheless, one participant with CR had ypT0N+ disease, highlighting the need for multimodal assessment of lymph nodes due to post-nCRT morphological changes and limited field of view for nodal detection (Fig. 6). These alterations create a complex and heterogeneous echotexture that is difficult to distinguish from active metastatic deposits, thereby reducing the diagnostic accuracy of ERUS for lymph node assessment [ 30 ]. The wash-in gradient, representing the ascending slope of the time–intensity curve, serves as a quantitative biomarker reflecting flow resistance within the tumor microenvironment. Tumor vasculature is typically disorganized and heterogeneous, with newly formed pathological microvessels exhibiting increased permeability and lacking normal regulatory mechanisms, resulting in altered perfusion dynamics [ 31 ]. These vessels have thin, fragile walls and often develop arteriovenous fistulas, producing a steep wash-in slope on the time–intensity curves. In contrast, participants without residual tumors show more organized vasculature with thicker walls, resulting in a slower ascending slope. This difference may help distinguish post-treatment changes from residual tumors. Unlike previous reports [ 32 ], the arrival time and time-to-peak were not significant predictors of CR, likely because they reflect perfusion timing rather than vascular structure. Tumor survival depends on vascular density and blood flow volume, not timing alone. Further research is needed to validate our results. A notable finding was the higher CR rate in female participants, consistent with previous studies linking sex to disease-free survival [ 33 ]. While this may indicate sex-related biological differences, including potential radioprotective effects of estrogen, the observation requires validation in larger, multicenter cohorts. This study has some limitations. First, its single-center design and moderate sample size may limit generalizability. Second, follow-up ≤ 24 months for participants with clinical CR may underestimate late local regrowth, as established in prior literature [ 8 ]. This is further supported by evidence indicating that approximately 25–30% of non-operatively managed participants with clinical CR experience recurrence within 3 years [ 34 , 35 ]. Finally, bowel gas interference may lead to incomplete lymph node visualization. In conclusion, quantitative contrast-enhanced ultrasound (CEUS) parameters—including enhancement intensity, area under the time–intensity curve, and their derived ratio values (rEI, rAUC*) and difference (ΔEI)—demonstrate robust discriminative capacity for identifying after neoadjuvant chemoradiotherapy in rectal cancer. CEUS-based models improved diagnostic performance over endorectal ultrasound alone and may aid the selection of candidates for the “watch-and-wait” strategy. However, its limitations in lymph node assessment highlight the need for multiple imaging modalities. The findings of this study require validation in large-scale, multicenter, prospective cohorts. Abbreviations nCRT: neoadjuvant chemoradiotherapy CEUS: contrast-enhanced ultrasound ERUS: endorectal ultrasound CR: complete response TME: total mesorectal excision pCR: pathological complete response cCR: clinical complete response NCR: non-complete response AUC: the area under the receiver operating characteristic curve ArT: arrival time TtoP: time to peak PI: peak intensity TWH: time width at half maximum AUC*: area under the intensity–time curve Grad.: the wash-in gradient EI: enhancement intensity rEI: ratio of EI rAUC*: ratio of rAUC* ΔEI: difference between EI Declarations Ethics approval and consent to participate The study was approved by the hospital Ethics Committee (NCCH-000194), and all participants provided written informed consent, including consent for publication of potentially identifiable data. Consent for Publication All participants provided consent for publication of anonymized data. No identifying information is included in this manuscript. Availability of Data and Materials The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request. Competing Interests The authors declare that they have no competing interests related to this work Funding This research was funded by the General Program of National Natural Science Foundation of China. Award Numbers are 81974268. The funding agencies had no role in study design, data collection, analysis, or manuscript preparation. Authors’ Contributions Conception and design: Yong Wang, Ningyi Cui Acquisition of data: Jie Zhang, Mengjia Liu, Yun Dai, Yu He Analysis and interpretation of data: Jie Zhang, Mengjia Liu Drafting of the manuscript: Jie Zhang, Mengjia Liu, Statistical analysis: Jie Zhang, Mengjia Liu Obtaining funding: Yong Wang Supervision: Yong Wang All authors reviewed and approved the final version of the manuscript. Acknowledgments. None References Bray, F., et al., Global cancer statistics 2022: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries. CA Cancer J Clin, 2024. 74 (3): p. 229-263. Benson, A.B., et al., Rectal Cancer, Version 2.2022, NCCN Clinical Practice Guidelines in Oncology. J Natl Compr Canc Netw, 2022. 20 (10): p. 1139-1167. Feeney, G., et al., Neoadjuvant radiotherapy for rectal cancer management. World J Gastroenterol, 2019. 25 (33): p. 4850-4869. Li, Y., et al., A Review of Neoadjuvant Chemoradiotherapy for Locally Advanced Rectal Cancer. 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Chadi, S.A., et al., Factors affecting local regrowth after watch and wait for patients with a clinical complete response following chemoradiotherapy in rectal cancer (InterCoRe consortium): an individual participant data meta-analysis. Lancet Gastroenterol Hepatol, 2018. 3 (12): p. 825-836. Tables Tables 1 to 4 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files TABLE1234.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8700611","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":595575342,"identity":"03f7be61-6bdf-4c25-9638-529dc8d1bb7c","order_by":0,"name":"Jie Zhang","email":"","orcid":"","institution":"National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical 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He","email":"","orcid":"","institution":"National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical college","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"He","suffix":""},{"id":595575346,"identity":"4e42014d-216e-4bd4-981d-2a7820e45f80","order_by":4,"name":"Ningyi Cui","email":"","orcid":"","institution":"National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical college","correspondingAuthor":false,"prefix":"","firstName":"Ningyi","middleName":"","lastName":"Cui","suffix":""},{"id":595575347,"identity":"037686fa-a882-4f8a-ba82-b09127a6b364","order_by":5,"name":"Yong Wang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA6ElEQVRIiWNgGAWjYDCCA3AW//cfHwxs7EjRwmAgOaMgLZk0LdI8Hw4xNhDSwXf7jOHngl+H5cz5FyQY2xgcYGZgP3x0Az4tkudyjKVn9h02tpzx4EByjsEdPgaetLQb+LQYnOHdIM3bczhxw42DDYdzDJ4xM0jwmBHSsvk3RMthxmYLg8OMDURo2SbN8wOo5XwbMzMDMVokz/B/s+ZtSDc2uMHDxthjkJbMRsgvfGfYkm/z/LGWMzh/ho3hxx8bO372w8fwagEDxrZmBgaJBAiHjaByMPhTB0wvB4hTOwpGwSgYBSMPAAA18lCgmlw6zwAAAABJRU5ErkJggg==","orcid":"","institution":"National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical college","correspondingAuthor":true,"prefix":"","firstName":"Yong","middleName":"","lastName":"Wang","suffix":""}],"badges":[],"createdAt":"2026-01-26 13:11:04","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8700611/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8700611/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103507456,"identity":"e3ca13fe-46e4-4e61-a391-a61f7ddd61ae","added_by":"auto","created_at":"2026-02-26 13:41:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":137760,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e\u0026nbsp;See image above for figure legend.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8700611/v1/836b9b74a9d7f809725c7221.png"},{"id":103346601,"identity":"5dc2921d-a6c8-4a5e-8aea-0e3b4573fef8","added_by":"auto","created_at":"2026-02-24 16:23:05","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":123432,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;See image above for figure legend.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8700611/v1/9dabb39aef443563903437ca.png"},{"id":103346604,"identity":"2ae3bbc1-ff47-47d5-a928-586c6f4f49d3","added_by":"auto","created_at":"2026-02-24 16:23:05","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":175291,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;See image above for figure legend.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8700611/v1/5db2b229472b043c26d54863.png"},{"id":103507457,"identity":"40746545-1a46-42fa-9324-1084b3fa4fbb","added_by":"auto","created_at":"2026-02-26 13:41:22","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":368038,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;See image above for figure legend.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8700611/v1/5ac8fc2c3e0c5e8fe203f104.png"},{"id":103346606,"identity":"267e52b6-7c8f-41ac-82ab-5d52a045b4f0","added_by":"auto","created_at":"2026-02-24 16:23:06","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":462839,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;See image above for figure legend.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8700611/v1/d0e14d36ca99527cb92ff764.png"},{"id":103346607,"identity":"27b672c8-8833-44ac-b59c-c9e40bb40262","added_by":"auto","created_at":"2026-02-24 16:23:06","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":439139,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;See image above for figure legend.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8700611/v1/93f3135cd854ad6a76243b87.png"},{"id":104780081,"identity":"38b2b2e1-e3ea-4bc5-ac94-0c343b93f536","added_by":"auto","created_at":"2026-03-17 07:50:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2338998,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8700611/v1/89e69b9e-1f82-4492-9176-ae9056c0b81b.pdf"},{"id":103346602,"identity":"97b7560a-e732-406c-8ab7-6957ed2242c0","added_by":"auto","created_at":"2026-02-24 16:23:05","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":145878,"visible":true,"origin":"","legend":"","description":"","filename":"TABLE1234.docx","url":"https://assets-eu.researchsquare.com/files/rs-8700611/v1/5bb3fa165045ead24c06109e.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Contrast-enhanced ultrasound parameters for predicting complete response after neoadjuvant chemoradiotherapy in rectal cancer","fulltext":[{"header":"Background","content":"\u003cp\u003eAccording to recent epidemiological data, colorectal cancer is the third most commonly diagnosed cancer and the second leading cause of cancer-related mortality globally [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Therapeutic strategies are individualized according to the tumor\u0026ndash;node\u0026ndash;metastasis staging system. The National Comprehensive Cancer Network recommends neoadjuvant chemoradiotherapy (nCRT) followed by total mesorectal excision (TME) as the standard treatment for rectal cancer [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. nCRT effectively reduces tumor size, increases surgical resectability, increases the rate of pathological complete response (pCR)\u0026mdash;defined as the absence of viable tumor cells on full pathologic examination (ypT0N0)\u0026mdash;and reduces surgery-related complications, including postoperative anastomotic leakage [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Pathological examination after nCRT demonstrates that approximately 15\u0026ndash;27% of patients achieve pCR [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. For patients with mid-to-low rectal cancer, sphincter preservation is a critical clinical goal, and nCRT significantly improves the likelihood of achieving it [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Patients achieving a clinical complete response (cCR) after nCRT may be managed using a watch-and-wait strategy [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Systematic reviews indicate comparable long-term outcomes, including non-regrowth recurrence and overall survival, between the watch-and-wait approach and immediate surgery [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], supporting organ preservation without compromising oncological safety.\u003c/p\u003e \u003cp\u003eCurrent clinical CR assessment relies on multimodal evaluation, including MRI, and digital rectal examination [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Endoscopy effectively assesses mucosal response but cannot determine the tumor invasion depth, whereas MRI provides regional assessment of residual disease within the rectal wall, mesorectum, and pelvic lymph nodes. However, posttreatment MRI accuracy is limited, with reported sensitivity as low as 50.4% for restaging [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Endorectal ultrasonography (ERUS) enables high-resolution visualization of the five-layer rectal wall. It allows accurate assessment of invasion depth, although post-nCRT changes, including tumor regression, inflammatory edema, fibrosis, and necrosis, reduce diagnostic accuracy [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eContrast-enhanced ultrasound (CEUS) is a blood pool imaging technique that enables dynamic assessment of tumor perfusion and microvascular characteristics. CEUS has significant diagnostic value in several malignancies, including breast and primary liver cancers [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. However, its application in rectal cancer after nCRT remains exploratory.\u003c/p\u003e \u003cp\u003eWe hypothesized that quantitative CEUS parameters can accurately identify CR. Accordingly, the purpose of this research is to explore the diagnostic value of CEUS in distinguishing CR in participants with rectal cancer after nCRT.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eParticipants\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;We prospectively recruited 158 participants with rectal cancer treated at our hospital between January 2023 and February 2025. The inclusion criteria were biopsy-confirmed rectal cancer; lower tumor margin \u0026lt;15 cm from the anal verge; consent to receive nCRT; and completion of ERUS and CEUS examinations before nCRT and surgery. Exclusion criteria included lack of definitive clinical or pathologic diagnosis after nCRT; tumor bleeding, obstruction, intestinal stenosis, or incomplete ERUS examination; failure to undergo timely ERUS and CEUS examinations before or after nCRT; and contrast allergy. Notably, all participants underwent ERUS and CEUS before and 6\u0026ndash;8 weeks after nCRT (2 weeks before surgery). Participants evaluated as having achieved clinical CR underwent ERUS follow-up every 3 months.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInstruments\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eERUS and CEUS examinations were performed using GE LOGIQ E11 (GE Healthcare, WI, USA) with an IC5-9-D end-fire endorectal probe operating at a 5\u0026ndash;9 MHz.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCollection of clinical data\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eParticipants\u0026rsquo; data included sex, age, and pretreatment tumor markers (carcinoembryonic antigen and carbohydrate antigen 19-9). Tumor characteristics, including length, thickness, invasion depth, and lymph node metastasis, were assessed using ERUS.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReference standard\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCR was determined as follows: (1) for surgical participants who underwent TME, postoperative pathology served as the reference standard; (2) for non-surgical participants, clinical complete remission based on comprehensive multimodal (pelvic MRI, CT, and endoscopy) judgment was used. Participants were classified as CR if pathology confirmed ypT0N0 or if evaluation indicated a clinical CR [10, 15, 16]. All others were classified as non-complete response (NCR).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eERUS examination\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eParticipants received enemas to clear the rectum before the ERUS. They were positioned in the left lateral decubitus position, and approximately 100\u0026ndash;150 mL of coupling gel was instilled to visualize the five layers of the rectal wall and tumor. Tumors were evaluated for location, length, thickness, echo pattern, color Doppler flow, and depth of rectal wall invasion [17]. Ultrasound T-staging followed Beynon criteria [18]: Stage 0, no visible tumor with intact wall layers; stage 1, tumor confined to the mucosa or submucosa; stage 2, tumor invading muscularis propria but not adventitia; stage 3, tumor penetrating muscularis propria to serosa; and stage 4, tumor invading adjacent tissues or organs. Dynamic and static images were recorded on a workstation. Two experienced sonographers (10 and 20 years of experience) jointly performed the assessments, resolving disagreements by consensus.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCEUS examination\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAfter ERUS, CEUS was performed using a dual grayscale display. A 2.4 mL dose of sulfur hexafluoride lipid-coated microbubble contrast agent (SonoVue, Bracco SpA, Milan, Italy) was diluted in 5 mL 0.9% saline and administered via the antecubital vein. A 3-minute video captured the maximal tumor cross-section and adjacent normal bowel wall. For NCR, a 5-mm circular region of interest (ROI) was placed on the area of most stable enhancement, avoiding necrotic regions. For CR, the ROI was placed at the original tumor bed. A corresponding 5-mm ROI was placed on the normal bowel wall.\u003c/p\u003e\n\u003cp\u003eDuring CEUS image analysis, the starting and ending frames of the ROI were adjusted according to the actual inflow of the contrast agent. Time\u0026ndash;intensity curves were generated using the Gamma Variate model. The parameters derived were arrival time (time for contrast microbubbles to initially enter the ROI, in seconds, ArT); time to peak (time from contrast arrival to peak intensity, in seconds, TtoP); peak intensity (maximum intensity of the contrast agent within the, in decibels, PI); time width at half maximum (time from contrast arrival to half of the peak intensity, in seconds, TWH); area under the intensity\u0026ndash;time curve (AUC*); background intensity (baseline contrast intensity); and the wash-in gradient (ascending slope of the time\u0026ndash;intensity curve, Grad.).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEnhancement intensity (EI) was calculated as the difference between the tumor\u0026apos;s peak and background intensities, with rEI and rAUC* derived relative to the normal bowel wall. \u0026Delta;EI was defined as the difference in EI between the tumor and the adjacent normal bowel wall. CEUS images were analyzed by two board-certified radiologists (10 and 20 years of experience), with disagreement resolved by consensus.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStatistical analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eStatistical analyses were performed using SPSS version 27.0(SPSS version 27.0, IBM Corporation, Armonk, New York, United States). Continuous variables are presented as the mean \u0026plusmn; standard deviation and compared using Student\u0026rsquo;s t-test or ANOVA for normally distributed data, Mann\u0026ndash;Whitney U or Kruskal\u0026ndash;Wallis H tests for non-normal data. Categorical variables were compared using the chi-square test.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePostoperative pathology and comprehensive clinical assessment served as the reference standard for diagnostic performance. Receiver operating characteristic curves were plotted to evaluate the diagnostic performance of time\u0026ndash;intensity curve parameters. The area under the receiver operating characteristic curve (AUC) was used to quantify discrimination, distinct from the TIC-derived area under the curve (AUC*). A P-value \u0026le;0 .05 was considered statistically significant.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eParticipant characteristics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eBetween January 2023 and February 2025, 158 eligible participants with rectal cancer were prospectively recruited at our tertiary referral center. Of the initial 158 participants, 58 were excluded because of loss to follow-up (n=29), lack of timely examination (n=17), or absence of a definitive diagnosis (n=12). Consequently, a total of 100 participants were enrolled (Figure 1), consisting of 77 men (mean age: 56.7 \u0026plusmn; 10.8 years) and 23 women (mean age: 57.2 \u0026plusmn; 11.4 years).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOverall, 42 participants achieved CR after nCRT, including 28 men (67%) and 14 women (33%). All participants received short-course radiotherapy followed by chemotherapy, with or without immunotherapy. A significant sex-based difference in tumor-free response was observed, with women achieving a higher CR rate than men (61% vs. 36%, p\u0026lt; 0.05; Table 1). Post-treatment tumor thickness differed between the CR and non-CR groups (p\u0026lt;0.05; Table 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePostoperative pathological and clinical diagnoses\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA total of 87 participants underwent TME after nCRT. Postoperative pathology revealed pathological CR (ypT0N0) in 29 participants. The remaining pathological stages were ypT0N+ (n=1), ypTisN0 (n=2), ypT1N0 (n=2), ypT1N+ (n=1), ypT2N0 (n=20), ypT2N+ (n=4), ypT3N0 (n=13), and ypT3N+ (n=15). Additionally, 13 participants achieved clinical CR, and the mean follow-up time was 21.4 months.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eERUS examination\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTable 2\u0026nbsp;summarizes the diagnostic performance of ERUS for post-nCRT tumor staging compared with the reference standard. Overall, 54 participants (54/100, 54%) were correctly staged. The accuracy of ERUS for predicting CR was 50% (21/42). Among participants with non-CR, 21 were overstaged.\u003c/p\u003e\n\u003cp\u003eERUS identified 87 participants without lymph node metastasis and 13 with metastasis. The overall accuracy for metastasis detection was 84%, with a sensitivity of 69%, specificity of 86%, positive predictive value of 43%, and negative predictive value of 95%. Notably, one participant with no residual primary tumor after TME was found to have metastatic lymph node involvement on histopathological examination.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCEUS examination\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eQuantitative CEUS parameters declined after nCRT. The rAUC* decreased from 2.47\u0026plusmn;2.10 to 1.89\u0026plusmn;1.42 after nCRT (p=0.004). Similarly, rEI decreased from 1.82\u0026plusmn;0.56 to 1.44\u0026plusmn;0.52 (p\u0026lt;0.001), and \u0026Delta;EI decreased from 12.29\u0026plusmn;6.77 to 8.04\u0026plusmn;5.26 (p\u0026lt;0.001).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBinary logistic regression revealed that pre-nCRT CEUS parameters were not associated with CR (p\u0026gt;0.05). In contrast, post-nCRT CEUS parameters were independent predictors of residual tumor. Univariate logistic regression results are presented in Table 3.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eReceiver operating curve analysis using post-nCRT \u0026Delta;EI, rEI, and rAUC* demonstrated diagnostic value for identifying residual tumors (Table 4, Figure 2). The optimal cut-off values were 8.25 dB for \u0026Delta;EI, 1.38 for rEI, and 1.36 for rAUC*, yielding AUCs of 0.79 (95% CI: 0.695, 0.875), 0.76 (95% CI: 0.665, 0.858), and 0.72 (95% CI: 0.617, 0.829), respectively. A \u0026Delta;EI \u0026lt; 8.25 dB yielded a sensitivity of 66% and specificity of 76%, whereas rEI \u0026lt; 1.38 yielded a sensitivity of 72% and specificity of 71%. An rAUC* \u0026lt; 1.36 provided higher sensitivity (86%) but lower specificity (57%).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCombined diagnosis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe accuracy for identifying CR was 50% (21/42) using ERUS alone, increasing to 67% (28/42) when combined with rAUC*, 71% (30/42) when combined with rEI, and 76% (32/42) when combined with \u0026Delta;EI. As shown in Figure 3, the combined diagnostic model_1 (rAUC* plus \u0026Delta;EI) achieved an AUC of 0.80 (95% CI: 0.708, 0.887), whereas model_2 (\u0026Delta;EI plus lesion thickness) yielded an AUC of 0.82 (95% CI: 0.741, 0.903). Neither combined model demonstrated superior diagnostic performance compared with the single parameter (p\u0026gt;.05).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eAccurate restaging of rectal cancer after neoadjuvant chemoradiotherapy (nCRT) is crucial as pathological complete response (pCR) occurs in approximately 15\u0026ndash;27% of patients [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. In our cohort, 33% (29/87) of participants achieved pCR after nCRT, a higher rate than previously reported, potentially reflecting advances in systemic therapy, incorporation of immunotherapy, and precise delineation of radiation therapy target volumes. For participants achieving pathological CR or clinical CR, the \u0026ldquo;watch and wait\u0026rdquo; strategy offers the potential for sphincter preservation and improved quality of life [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eERUS is well established for initial tumor staging but is limited after nCRT because of treatment-induced fibrosis, edema, and inflammatory changes [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. CEUS, a safe pure blood pool imaging technique, allows the dynamic assessment of tumor perfusion and vascularity and has demonstrated value in evaluating treatment response across several malignancies, including breast, pancreatic, and cervical cancers [\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Quantitative CEUS parameters, including peak intensity, AUC, slope, and arrival time, are essential for assessment, with peak intensity and AUC being particularly valuable for the diagnosis and prediction of tumors [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. However, prior studies on rectal cancer after nCRT have relied largely on CEUS or elastography, and quantitative post-nCRT evaluation remains largely unexplored [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Our prospective study design and moderate sample size strengthen the validity and generalizability of the findings.\u003c/p\u003e \u003cp\u003ePost-nCRT quantitative CEUS parameters\u0026mdash;rAUC*, rEI, and ΔEI\u0026mdash;declined significantly, reflecting reduced tumor perfusion and microvascular density consistent with necrosis and vascular regression induced by therapy [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Pre-nCRT parameters did not predict CR, whereas post-nCRT measures demonstrated effective discrimination, with receiver operating characteristic\u0026ndash;AUC of 0.72, 0.76, and 0.79 for rAUC*, rEI, and ΔEI, respectively. Lower post-nCRT values correlated with greater therapeutic response, consistent with prior reports linking reduced EI and AUC* to pathological CR [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. This is because nCRT induces tumor cell necrosis, vascular atrophy, and rupture, thereby reducing the vascular network. This reduction disrupts the angiogenic support essential for tumor growth and survival. As EI acts as a visual marker of microvascular density, it effectively demonstrates these pathophysiological alterations [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. In participants with CR, the time\u0026ndash;intensity curves from previously involved tumor site closely approximated those of adjacent normal bowel wall. This convergence was reflected in comparable peak intensities, similar time-to-peak values, and analogous washout patterns, suggesting nearly identical perfusion kinetics between the two regions(Fig.\u0026nbsp;4, Fig.\u0026nbsp;5). This pattern provides a clear imaging correlate of complete pathological response, reflecting the replacement of tumor tissue with fibrotic tissue and restoration of a normal microvascular architecture. While this convergence may serve as a qualitative adjunct for identifying potential CR, its assessment remains subjective. It depends on precise region-of-interest placement, posing challenges for standardization and reproducibility across observers. Future studies should aim to quantify this \u0026ldquo;convergence index\u0026rdquo; to enhance its objectivity and diagnostic utility.\u003c/p\u003e \u003cp\u003eTumor thickness, but not length, differed between the CR and nCR groups, indicating radial regression is a more reliable indicator of response than longitudinal extent, which may be confounded by peritumoral edema from radiation. Multivariate analysis identified rAUC*, rEI, and ΔEI as independent predictors of CR. Combined models incorporating CEUS parameters with lesion thickness modestly improved discrimination (AUC 0.80 and 0.82 for models 1 and 2, respectively), though Delong\u0026rsquo;s test showed no statistically significant improvement over single-parameter models. This suggests that CEUS provides the majority of predictive information, and combined approaches offer limited incremental value in our sample.\u003c/p\u003e \u003cp\u003eERUS alone demonstrated 50% accuracy for CR identification, consistent with previous research [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Overstaging occurs due to post-nCRT fibrosis and edema, whereas understaging reflects residual tumor not apparent on imaging. Integrating ERUS with CEUS improved CR identification to 67\u0026ndash;76%, with ΔEI and rEI providing superior accuracy than rAUC*, likely because EI directly reflects peak perfusion and is less affected by operator-dependent curve fitting. Persistent diagnostic errors may arise from tumor \u0026ldquo;fragmentation,\u0026rdquo; wherein residual tumor cells disperse microscopically, evading CEUS detection [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. CEUS cannot reliably identify microscopic tumor residues within the muscularis propria or the serosa. This limitation directly contributes to the decreased accuracy in CR.\u003c/p\u003e \u003cp\u003eERUS detected lymph node metastasis with 84% accuracy (sensitivity 69%, specificity 86%, positive predictive value of 43%, and negative predictive value 95%). The high negative predictive value indicates that negative ERUS reliably excludes nodal involvement. Nevertheless, one participant with CR had ypT0N+ disease, highlighting the need for multimodal assessment of lymph nodes due to post-nCRT morphological changes and limited field of view for nodal detection (Fig.\u0026nbsp;6). These alterations create a complex and heterogeneous echotexture that is difficult to distinguish from active metastatic deposits, thereby reducing the diagnostic accuracy of ERUS for lymph node assessment [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe wash-in gradient, representing the ascending slope of the time\u0026ndash;intensity curve, serves as a quantitative biomarker reflecting flow resistance within the tumor microenvironment. Tumor vasculature is typically disorganized and heterogeneous, with newly formed pathological microvessels exhibiting increased permeability and lacking normal regulatory mechanisms, resulting in altered perfusion dynamics [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. These vessels have thin, fragile walls and often develop arteriovenous fistulas, producing a steep wash-in slope on the time\u0026ndash;intensity curves. In contrast, participants without residual tumors show more organized vasculature with thicker walls, resulting in a slower ascending slope. This difference may help distinguish post-treatment changes from residual tumors. Unlike previous reports [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], the arrival time and time-to-peak were not significant predictors of CR, likely because they reflect perfusion timing rather than vascular structure. Tumor survival depends on vascular density and blood flow volume, not timing alone. Further research is needed to validate our results.\u003c/p\u003e \u003cp\u003eA notable finding was the higher CR rate in female participants, consistent with previous studies linking sex to disease-free survival [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. While this may indicate sex-related biological differences, including potential radioprotective effects of estrogen, the observation requires validation in larger, multicenter cohorts.\u003c/p\u003e \u003cp\u003eThis study has some limitations. First, its single-center design and moderate sample size may limit generalizability. Second, follow-up \u0026le;\u0026thinsp;24 months for participants with clinical CR may underestimate late local regrowth, as established in prior literature [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. This is further supported by evidence indicating that approximately 25\u0026ndash;30% of non-operatively managed participants with clinical CR experience recurrence within 3 years [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. Finally, bowel gas interference may lead to incomplete lymph node visualization.\u003c/p\u003e \u003cp\u003eIn conclusion, quantitative contrast-enhanced ultrasound (CEUS) parameters\u0026mdash;including enhancement intensity, area under the time\u0026ndash;intensity curve, and their derived ratio values (rEI, rAUC*) and difference (ΔEI)\u0026mdash;demonstrate robust discriminative capacity for identifying after neoadjuvant chemoradiotherapy in rectal cancer. CEUS-based models improved diagnostic performance over endorectal ultrasound alone and may aid the selection of candidates for the \u0026ldquo;watch-and-wait\u0026rdquo; strategy. However, its limitations in lymph node assessment highlight the need for multiple imaging modalities. The findings of this study require validation in large-scale, multicenter, prospective cohorts.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003enCRT: neoadjuvant chemoradiotherapy\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCEUS: contrast-enhanced ultrasound\u003c/p\u003e\n\u003cp\u003eERUS: endorectal ultrasound\u003c/p\u003e\n\u003cp\u003eCR: complete response\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTME: total mesorectal excision\u003c/p\u003e\n\u003cp\u003epCR: pathological complete response\u003c/p\u003e\n\u003cp\u003ecCR: clinical complete response\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eNCR: non-complete response\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAUC: the area under the receiver operating characteristic curve\u003c/p\u003e\n\u003cp\u003eArT: arrival time\u003c/p\u003e\n\u003cp\u003eTtoP: time to peak\u003c/p\u003e\n\u003cp\u003ePI: peak intensity\u003c/p\u003e\n\u003cp\u003eTWH: time width at half maximum\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAUC*: area under the intensity\u0026ndash;time curve\u003c/p\u003e\n\u003cp\u003eGrad.: the wash-in gradient\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eEI: enhancement intensity\u003c/p\u003e\n\u003cp\u003erEI: ratio of EI\u003c/p\u003e\n\u003cp\u003erAUC*: ratio of rAUC*\u003c/p\u003e\n\u003cp\u003e\u0026Delta;EI: difference between EI\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was approved by the hospital Ethics Committee (NCCH-000194), and all participants provided written informed consent, including consent for publication of potentially identifiable data.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for Publication\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll participants provided consent for publication of anonymized data. No identifying information is included in this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of Data and Materials\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests related to this work\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was funded by the General Program of National Natural Science Foundation of China. Award Numbers are 81974268.\u0026nbsp;The funding agencies had no role in study design, data collection, analysis, or manuscript preparation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; Contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConception and design: Yong Wang, Ningyi Cui\u003c/p\u003e\n\u003cp\u003eAcquisition of data: Jie Zhang, Mengjia Liu, Yun Dai, Yu He\u003c/p\u003e\n\u003cp\u003eAnalysis and interpretation of data: Jie Zhang, Mengjia Liu\u003c/p\u003e\n\u003cp\u003eDrafting of the manuscript: Jie Zhang, Mengjia Liu,\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eStatistical analysis: Jie Zhang, Mengjia Liu\u003c/p\u003e\n\u003cp\u003eObtaining funding: Yong Wang\u003c/p\u003e\n\u003cp\u003eSupervision: Yong Wang\u003c/p\u003e\n\u003cp\u003eAll authors reviewed and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNone\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBray, F., et al., \u003cem\u003eGlobal cancer statistics 2022: GLOBOCAN estimates of incidence and mortality worldwide for 36 cancers in 185 countries.\u003c/em\u003e CA Cancer J Clin, 2024. \u003cstrong\u003e74\u003c/strong\u003e(3): p. 229-263.\u003c/li\u003e\n\u003cli\u003eBenson, A.B., et al., \u003cem\u003eRectal Cancer, Version 2.2022, NCCN Clinical Practice Guidelines in Oncology.\u003c/em\u003e J Natl Compr Canc Netw, 2022. \u003cstrong\u003e20\u003c/strong\u003e(10): p. 1139-1167.\u003c/li\u003e\n\u003cli\u003eFeeney, G., et al., \u003cem\u003eNeoadjuvant radiotherapy for rectal cancer management.\u003c/em\u003e World J Gastroenterol, 2019. \u003cstrong\u003e25\u003c/strong\u003e(33): p. 4850-4869.\u003c/li\u003e\n\u003cli\u003eLi, Y., et al., \u003cem\u003eA Review of 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X., et al., \u003cem\u003eResearch Progress on Contrast-Enhanced Ultrasound (CEUS) Assisted Diagnosis and Treatment in Liver-Related Diseases.\u003c/em\u003e Int J Med Sci, 2025. \u003cstrong\u003e22\u003c/strong\u003e(5): p. 1092-1108.\u003c/li\u003e\n\u003cli\u003eMaas, M., et al., \u003cem\u003eAssessment of Clinical Complete Response After Chemoradiation for Rectal Cancer with Digital Rectal Examination, Endoscopy, and MRI: Selection for Organ-Saving Treatment.\u003c/em\u003e Ann Surg Oncol, 2015. \u003cstrong\u003e22\u003c/strong\u003e(12): p. 3873-80.\u003c/li\u003e\n\u003cli\u003eGlynne-Jones, R., et al., \u003cem\u003eRectal cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up.\u003c/em\u003e Ann Oncol, 2018. \u003cstrong\u003e29\u003c/strong\u003e(Suppl 4): p. iv263.\u003c/li\u003e\n\u003cli\u003eLiu, M., et al., \u003cem\u003eA prospective study on using shear wave elastography to predict the ypT0 stage of rectal cancer after neoadjuvant therapy: a new support for the watch-and-wait approach?\u003c/em\u003e Front Mol Biosci, 2024. \u003cstrong\u003e11\u003c/strong\u003e: p. 1402498.\u003c/li\u003e\n\u003cli\u003eBeynon, J., et al., \u003cem\u003eEndoluminal ultrasound in the assessment of local invasion in rectal cancer.\u003c/em\u003e Br J Surg, 1986. \u003cstrong\u003e73\u003c/strong\u003e(6): p. 474-7.\u003c/li\u003e\n\u003cli\u003eHabr-Gama, A., et al., \u003cem\u003eOperative versus nonoperative treatment for stage 0 distal rectal cancer following chemoradiation therapy: long-term results.\u003c/em\u003e Ann Surg, 2004. \u003cstrong\u003e240\u003c/strong\u003e(4): p. 711-7; discussion 717-8.\u003c/li\u003e\n\u003cli\u003ePeng, Q., et al., \u003cem\u003ePrediction of neoadjuvant chemotherapy efficacy in patients with HER2-low breast cancer based on ultrasound radiomics.\u003c/em\u003e Cancer Imaging, 2025. \u003cstrong\u003e25\u003c/strong\u003e(1): p. 112.\u003c/li\u003e\n\u003cli\u003eYan, X., et al., \u003cem\u003eDevelopment and validation of a nomogram model based on pretreatment ultrasound and contrast-enhanced ultrasound to predict the efficacy of neoadjuvant chemotherapy in patients with borderline resectable or locally advanced pancreatic cancer.\u003c/em\u003e Cancer Imaging, 2024. \u003cstrong\u003e24\u003c/strong\u003e(1): p. 13.\u003c/li\u003e\n\u003cli\u003eHong, R., et al., \u003cem\u003eThe treatment response evaluation through the combination of contrast-enhanced ultrasound and squamous cell carcinoma antigen in cervical cancer.\u003c/em\u003e Quant Imaging Med Surg, 2024. \u003cstrong\u003e14\u003c/strong\u003e(10): p. 7587-7599.\u003c/li\u003e\n\u003cli\u003eSu, S., et al., \u003cem\u003ePredictive Value of TRUS and CEUS Parameters for Lymph Node Metastasis in Rectal Cancer: A Retrospective Study.\u003c/em\u003e Int J Gen Med, 2025. \u003cstrong\u003e18\u003c/strong\u003e: p. 3335-3345.\u003c/li\u003e\n\u003cli\u003eBai, G., et al., \u003cem\u003eQuantitative analysis of contrast-enhanced ultrasound in neoadjuvant treatment of locally advanced rectal cancer: a retrospective study.\u003c/em\u003e Front Oncol, 2023. \u003cstrong\u003e13\u003c/strong\u003e: p. 1340060.\u003c/li\u003e\n\u003cli\u003eXiao, Y., et al., \u003cem\u003eApplication value of biplane transrectal ultrasonography plus ultrasonic elastosonography and contrast-enhanced ultrasonography in preoperative T staging after neoadjuvant chemoradiotherapy for rectal cancer.\u003c/em\u003e Eur J Radiol, 2018. \u003cstrong\u003e104\u003c/strong\u003e: p. 20-25.\u003c/li\u003e\n\u003cli\u003eAbuliezi, D., et al., \u003cem\u003eCombined transrectal ultrasound and radiomics model for evaluating the therapeutic effects of neoadjuvant chemoradiotherapy in locally advanced rectal cancer.\u003c/em\u003e Int J Colorectal Dis, 2025. \u003cstrong\u003e40\u003c/strong\u003e(1): p. 7.\u003c/li\u003e\n\u003cli\u003eWang, Y., et al., \u003cem\u003eTime-intensity curve parameters in rectal cancer measured using endorectal ultrasonography with sterile coupling gels filling the rectum: correlations with tumor angiogenesis and clinicopathological features.\u003c/em\u003e Biomed Res Int, 2014. \u003cstrong\u003e2014\u003c/strong\u003e: p. 587806.\u003c/li\u003e\n\u003cli\u003ePanzironi, G., et al., \u003cem\u003eEndorectal ultrasonography performance in staging rectal cancer before and after neoadjuvant chemoradiotherapy.\u003c/em\u003e Ann Ital Chir, 2014. \u003cstrong\u003e85\u003c/strong\u003e(6): p. 569-75.\u003c/li\u003e\n\u003cli\u003eHanly, A.M., et al., \u003cem\u003eMulticenter Evaluation of Rectal cancer ReImaging pOst Neoadjuvant (MERRION) Therapy.\u003c/em\u003e Ann Surg, 2014. \u003cstrong\u003e259\u003c/strong\u003e(4): p. 723-7.\u003c/li\u003e\n\u003cli\u003eYan, L., et al., \u003cem\u003eA model based on endorectal ultrasonography predicts lateral lymph node metastasis in low and middle rectal cancer.\u003c/em\u003e J Clin Ultrasound, 2022. \u003cstrong\u003e50\u003c/strong\u003e(5): p. 705-712.\u003c/li\u003e\n\u003cli\u003eSzab\u0026oacute;, B.K., et al., \u003cem\u003eCorrelation of contrast-enhanced ultrasound kinetics with prognostic factors in invasive breast cancer.\u003c/em\u003e Eur Radiol, 2013. \u003cstrong\u003e23\u003c/strong\u003e(12): p. 3228-36.\u003c/li\u003e\n\u003cli\u003eWan, C.F., et al., \u003cem\u003eQuantitative contrast-enhanced ultrasound evaluation of pathological complete response in patients with locally advanced breast cancer receiving neoadjuvant chemotherapy.\u003c/em\u003e Eur J Radiol, 2018. \u003cstrong\u003e103\u003c/strong\u003e: p. 118-123.\u003c/li\u003e\n\u003cli\u003eZhang, H., et al., \u003cem\u003ePrognostic factors in patients with complete response of the tumour (ypT0) after neoadjuvant chemoradiotherapy and radical resection of rectal cancer.\u003c/em\u003e ANZ J Surg, 2021. \u003cstrong\u003e91\u003c/strong\u003e(4): p. E190-e195.\u003c/li\u003e\n\u003cli\u003evan der Valk, M.J.M., et al., \u003cem\u003eLong-term outcomes of clinical complete responders after neoadjuvant treatment for rectal cancer in the International Watch \u0026amp; Wait Database (IWWD): an international multicentre registry study.\u003c/em\u003e Lancet, 2018. \u003cstrong\u003e391\u003c/strong\u003e(10139): p. 2537-2545.\u003c/li\u003e\n\u003cli\u003eChadi, S.A., et al., \u003cem\u003eFactors affecting local regrowth after watch and wait for patients with a clinical complete response following chemoradiotherapy in rectal cancer (InterCoRe consortium): an individual participant data meta-analysis.\u003c/em\u003e Lancet Gastroenterol Hepatol, 2018. \u003cstrong\u003e3\u003c/strong\u003e(12): p. 825-836.\u003cstrong\u003e\u003c/strong\u003e\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 4 are available in the Supplementary Files section.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"rectal cancer, ERUS, CEUS, nCRT","lastPublishedDoi":"10.21203/rs.3.rs-8700611/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8700611/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eAccurate identification of complete responders before neoadjuvant chemoradiotherapy (nCRT) is essential for organ-preservation strategies for rectal cancer. However, current preoperative radiological assessment methods lack sufficient accuracy. The purpose of this study is to evaluate the diagnostic value of contrast-enhanced ultrasound (CEUS) in distinguishing complete response (CR) in patients with rectal cancer after nCRT.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eIn this prospective study, 100 patients with rectal cancer treated between January 2023 and February 2025 underwent endorectal ultrasound (ERUS) and CEUS examinations before and 6\u0026ndash;8 weeks after nCRT. Quantitative perfusion parameters were derived using time\u0026ndash;intensity curve analysis. Surgical histopathology served as the reference standard for pathological CR, and multimodal clinical evaluation defined complete CR. Diagnostic performance was assessed using logistic regression and receiver operating characteristic curve analysis.\u003c/p\u003e\u003ch2\u003eResult\u003c/h2\u003e \u003cp\u003eA total of 100 participants (mean age, 57\u0026thinsp;\u0026plusmn;\u0026thinsp;11 years; 77 men) were included. Pathological CR occurred in 29 (29.0%) participants, and clinical CR in 13 (13.0%), yielding an overall CR rate of 42%. Post-nCRT CEUS parameters\u0026mdash;relative area under the time\u0026ndash;intensity curve (rAUC*), relative enhancement intensity, and enhancement intensity difference\u0026mdash;were significant predictors of CR (all p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The AUCs were 0.72 (95% CI: 0.617, 0.829), .76 (95% CI: 0.665, 0.858), and 0.76 (95% CI: 0.695, 0.875), respectively. Combined models achieved AUCs of 0.80 (95% CI: 0.708, 0.887) and 0.82 (95% CI: 0.741, 0.903), respectively.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eQuantitative contrast-enhanced ultrasound (CEUS) parameters, including enhancement intensity (EI), relative AUC*, and their derived ratio values (rEI, rAUC*) and difference (ΔEI), demonstrated robust discriminative capacity in complete response participants after nCRT. The CEUS-based diagnostic model also demonstrated a high level of diagnostic efficacy. The clinical diagnostic model constructed from the above parameters demonstrated higher diagnostic value.\u003c/p\u003e","manuscriptTitle":"Contrast-enhanced ultrasound parameters for predicting complete response after neoadjuvant chemoradiotherapy in rectal cancer","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-24 16:22:47","doi":"10.21203/rs.3.rs-8700611/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"43420da6-40dd-4952-9ab3-8f3fb0689a0a","owner":[],"postedDate":"February 24th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-03-11T15:26:54+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-24 16:22:47","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8700611","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8700611","identity":"rs-8700611","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}