Abstract: PNFBA-10
Sources of Funding: The project described was supported by Award Number R01CA158627 from the National Cancer Institute; Jean Perkins Foundation; Steven C. Gordon Family Foundation.

Introduction

Focal therapy of prostate cancer (partial gland ablation, PGA) is of keen interest. To determine treatment margins required for complete tumor ablation, we studied men who were eligible for PGA, but underwent radical prostatectomy. The present work differs from prior studies in that accurate co-registration between pre-op multiparametric MRI (mpMRI) slices and whole-mount findings was enabled through use of patient-specific prostate molds to obtain uniform, standardized processing of specimens. _x000D_

Methods

35 men with localized, organ-confined prostate cancer (CaP) who underwent 3 Tesla mpMRI prior to radical prostatectomy from 2013 to 2015 were subjects. Mean patient age was 63 yrs; median PSA 6.7 ng/ml; and mean prostate volume 37.6 cc. Criteria for focal therapy eligibility were Gleason score ≤4+3 within MRI-visible index tumor, pathologic stage ≤T3a, and no contralateral clinically significant disease. Using T2-weighted images from pre-operative mpMRI, the prostate capsule and suspicious regions of interest (ROIs) were contoured. 3D patient-specific molds, printed in advance of prostatectomy from MRI specifications, were then used to align prostatectomy specimens with mpMRI (Priester et al., J. Urol, 2016). Digitized whole mount sections, sliced at 4.5 mm intervals, provided 3D reconstruction of prostate tumors. Tumors were matched with ROIs and the relative 3D surfaces were compared to determine appropriate treatment margins. _x000D_

Results

39 of 62 (63%) prostate tumors found on whole-mount sections were detected by MRI. 90% of tumors were in PZ, 10% in TZ. Of the 23 tumors not MRI visible, 22 were low volume, Gleason score 3+3. Mean index tumor volume on MRI was 0.59 cc and 1.59 cc on prostatectomy specimen (p<0.001). Median treatment margin required was 10.7mm (FIGURE). Average treatment volume required for complete tumor ablation was 11.4 cc, which comprised 30% of average prostate volume. All subjects would have been successfully treated with hemi-gland ablation. _x000D_

Conclusions

MRI consistently and dramatically underestimates the extent of prostate tumors. In this population, uniformly employing 1cm treatment margins during focal therapy would have resulted in incomplete tumor ablation in 50% of patients. A patient specific treatment plan incorporating tumor size, geometry, and adjacent tissue sampling is a future research priority. _x000D_

Funding

The project described was supported by Award Number R01CA158627 from the National Cancer Institute; Jean Perkins Foundation; Steven C. Gordon Family Foundation.