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

Abstract

Purpose: We aimed to probe the clinical value of 18F-PSMA-1007 and 68Ga-PSMA-11 PET/MRI in the GTV delineation of radiotherapy for prostate cancer (PCa). Methods: 69 patients were retrospectively enrolled (57 in 18F subgroup and 12 in 68Ga 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 18F subgroup: (1) GTV-PET/MRI and GTV-PET60% had significant correlation and difference with the reference GTV-MRI (p<0.05). (2) DSC between GTV-MRI and GTV-PET/MRI was>0.7. (3) The GTV-MRI (R2=0.462, p<0.05) was the influencing factor of the DSC, and positively affected the DSC. In 68Ga subgroup: (1) GTV-PET/MRI, GTV-PET30% had significant correlation and difference with the reference GTV-MRI (p<0.05). (2) DSC between GTV-MRI and GTV-PET/MRI were>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.

Lesion Dosimetry for [177Lu]Lu-PSMA-617 Radiopharmaceutical Therapy Combined with Stereotactic Body Radiotherapy in Patients with Oligometastatic Castration-Sensitive Prostate Cancer

“…The 2 main components of the uncertainty in RPT dosimetry are the variability associated with contour delineation and the volume-and sphere-based RC (25,39). A 50% threshold on PET was chosen because it was previously reported to result in the smallest mean differences from morphologic volume measurements (Bland-Altman analysis (40)) and most closely corresponds to volumes delineated on a PSMA PET/MRI scan (41). PETderived volumes also closely correspond in size to CT-derived volumes; however, in 2 cases, the lesions were not seen on the CT.…”