Room: Track 4
Purpose: specific membrane antigen positron emission tomography imaging (PSMA-PET) has demonstrated potential for lesion localization. We addressed the question: when escalating dose to PSMA-PET lesions, what is the effect on dose to the underlying cancer defined on corresponding histology?
Methods: registered annotated prostatectomy mid-gland histology sections from 10 patients to pre-prostatectomy PSMA-PET/MRI scans. We segmented PSMA-PET volumes using our previously developed guidelines, with the intent to delineate underlying dominant intra-prostatic lesions (DILs). To simulate realistic high-dose-rate brachytherapy (HDR-BT), we registered PSMA-PET defined segmentations and underlying cancer to two trans-rectal ultrasound images of other HDR-BT patients previously treated with a 15-Gy whole-gland prescription. We used clinical inverse planning to optimize dwell times for focal dose escalation to the segmentations, with a target dose of 20 Gy. We compared histopathology dosimetry on whole-gland treatment plans versus PSMA-PET targeting. Histopathology was broken down into two sub groups: high-grade cancer (Gleason score 7 or greater) and low-grade cancer (Gleason score less than 7).
Results: analyzed 20 simulated HDR-BT plans using PSMA-PET for DIL targeting. For the analysis we calculated the minimum dose 98% of the histology received (D98). For high-grade histology the whole-gland plans achieved a median [IQR] D98 of 15.22 [14.56–16.35] Gy, while the targeted plans achieved a D98 of 16.48 [15.04–18.97] Gy. Low-grade histology for the whole-gland plans achieved a D98 of 15.88 [14.88–16.93] Gy and the targeted treatment plans achieved 16.26 [14.77–19.21] Gy. The D98 for high-grade histology received a significantly higher dose within the targeted treatment plans (p = 0.0068).
Conclusion: study is the first to use digital histology to test the effectiveness of PSMA-PET HDR-BT dose escalation using automatically generated contours. Based on the findings of this simulation study, PSMA-PET dose escalation to DIL segmentations leads to increased dose to the high-grade ground truth histology.
Funding Support, Disclosures, and Conflict of Interest: This research was funded by Prostate Cancer Canada, Natural Sciences and Engineering Research Council, Canadian Institutes of Health Research, Ontario Institute for Cancer Research, and Cancer Care Ontario.
TH- Brachytherapy: Imaging for brachytherapy: development and applications