R Alfano^1,3*, C Smith^1,3, D Hoover^1,2,3, K Surry^1,2,3, D D'Souza^2,3, J Thiessen^1,3, I Rachinsky^1,3, W Pavlosky^1,3, J Butler³, M Moussa¹, J.A. Gomez¹, M Gaed¹, S Pautler^1,3, J Chin^1,3, G Bauman^1,2,3, A Ward^1,2,3, (1) University of Western Ontario, London, ON, CA, (2) London Regional Cancer Program, London, ON, CA, (3) London Health Sciences Centre, London, ON, CA

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  R Alfano

(Thursday, 7/16/2020) 10:30 AM - 12:30 PM [Eastern Time (GMT-4)]

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.

Keywords

PET, Prostate Therapy, HDR

Taxonomy

TH- Brachytherapy: Imaging for brachytherapy: development and applications

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