Gross Tumor Volume Delineation in Primary Prostate Cancer on 18 F-PSMA-1007 PET/MRI and 68 Ga-PSMA-11 PET/MRI

Purpose: We aimed to probe the clinical value of 18 F-PSMA-1007 and 68 Ga-PSMA-11 PET/MRI in the GTV delineation of radiotherapy for prostate cancer (PCa). Methods: : 69 patients were retrospectively enrolled (57 in 18 F subgroup and 12 in 68 Ga subgroup). First, three physicians delineated the GTVs by visual method and threshold method with thresholds of 30%, 40%, 50%, and 60% SUVmax. The volume correlation and differences in GTVs were assessed. Second, the DSC was applied to estimate the spatial overlap between GTVs. Then we also evaluated the association between DSCs and clinical parameters (including age, the reference GTV-MRI, PSA, Gleason score, risk classification, and SUVmax). Last, the interobserver variability was evaluated. GTV-MRI was set as a reference. Results: : In 18 F subgroup: (1) GTV-PET/MRI and GTV-PET 60% had significant correlation and difference with the reference GTV-MRI ( p 0.7. (3) The GTV-MRI ( R 2 =0.462, p <0.05) was the influencing factor of the DSC, and positively affected the DSC. In 68 Ga subgroup: (1) GTV-PET/MRI, GTV-PET 30% had significant correlation and difference with the reference GTV-MRI ( p 0.7. (3) There was a significant correlation between GTV-MRI ( r =0.580, p <0.05) and the DSC. There were no significant differences in tumor volume delineated by different observers in both subgroups. Conclusion: It is feasible to visually delineate GTV on PSMA PET/MRI in PCa radiotherapy, we emphasize the GTV delineation on the PET/MRI fusion image. In addition, the overlap degree was the highest between GTV-MRI and GTV-PET/MRI, and it increased with increasing volume.