Room: AAPM ePoster Library
Purpose: Post-radiotherapy prostate cancer recurrence often occurs at dominant intraprostatic lesions (DILs), motivating focal dose escalation. Multiparametric magnetic resonance imaging (mpMRI) has demonstrated potential for DIL localization. We addressed the question: when targeting dose escalation to mpMR-defined DILs, what is the dose to the cancer defined on corresponding histology?
Methods: We registered pathologist annotated prostatectomy mid-gland histology sections from 12 patients to pre-prostatectomy mpMRI scans that were each interpreted by four radiologists. To simulate realistic high-dose-rate brachytherapy (HDR-BT) treatments, we registered each observer’s interpretation of mpMRI to two transrectal ultrasound images of other HDR-BT patients, thus registering mpMRI-defined DILs and underlying cancer histology to treatment plans with a 15-Gy whole-gland prescription. We used a clinical inverse planning system to optimize dwell times for focal dose escalation to 20 Gy for the mpMRI-DILs. We compared the dose that the histopathology would have received if treated with whole-gland treatment plans to the dose that would have been achieved through mpMRI targeting. The histopathology was broken down into two subgroups: high-grade cancer (Gleason 4 or greater) and low-grade cancer (Gleason 3).
Results: We analyzed 212 mpMRI-targeted HDR-BT plans. For high-grade histology the whole-gland plans achieved a median [IQR] D98 dose of 16.93 [15.83-17.71] Gy, while the mpMRI-targeted plans achieved a significantly higher median D98 dose of 18.16 [16.73-19.45] Gy (p = 0.01). Low-grade histology for the whole-gland plans achieved a D98 of 15.26 [14.62-15.76] Gy and the targeted treatment plans achieved 15.36 [14.86-16.23] Gy.
Conclusion: Based on the findings of this study, mpMRI dose escalation does lead to increased dose to the high-grade ground truth histology, but not to low-grade disease, therefore mpMRI lesion-targeted therapy may only be useful for patients who present with high grade cancer and that patients with only low-grade cancer should receive the current clinically standard whole-gland treatment plans.
Funding Support, Disclosures, and Conflict of Interest: Ontario Early Researcher Award (ER15-11-095)