Correlation Between Toxicity and Dosimetric Parameters in Patients Treated with Adjuvant Intensity-Modulated Radiation Therapy for Breast Cancer: The Results of a Prospective Study.

Abstract Background. In the treatment of breast cancer, intensity-modulated radiation therapy (IMRT) reportedly reduces the high-dose irradiation of at-risk organs and decreases the frequency of adverse events (AEs). Comparisons with conventional radiotherapy have shown that IMRT is associated with lower frequencies of acute and late-onset AEs. Here, we extended a prospective, observational, single-center study of the safety of IMRT to a second investigating center. Methods. Patients scheduled for adjuvant IMRT after partial or total mastectomy were given a dose of 50 Gy (25 fractions of 2 Gy over five weeks), with a simultaneous integrated boost in patients having undergone conservative surgery. Results. 300 patients were included in the study, and 288 were analyzed. The median follow-up period was 2.1 years. Most AEs were mild. The most common AEs were skin-related - mainly radiodermatitis (in 266 patients (92.4%)) and hyperpigmentation (in 178 (61.8%)). Smoking (odds ratio) [95%CI] = 2.10 [1.14–3.87]; p = 0.017), no prior chemotherapy (0.52 [0.27–0.98]; p = 0.044), and D98% for subclavicular skin (1.030 [1.001–1.061]; p = 0.045) were associated with grade ≥ 2 acute AEs. In a univariate analysis, the mean dose, (p < 0.0001), D2% (p < 0.0001), D50% (p = 0.037), D95% (p = 0.0005), D98% (p = 0.0007), V30Gy (p < 0.0001), and V45Gy (p = 0.0001) were significantly associated with grade ≥ 1 acute esophageal AEs. In a multivariate analysis, D95% for the skin (p < 0.001), D98% for the subclavicular skin and low D95% for the internal mammary lymph nodes were associated with grade ≥ 1 medium-term AEs. Conclusions. The safety profile of adjuvant IMRT after partial or total mastectomy is influenced by dosimetric parameters. Trial registration: ClinicalTrials.gov NCT02281149