Abstract

Background and purpose To establish a method to evaluate dosimetry at the time of primary prostate permanent implant using MRI of the shrunken prostate at the time of failure. To compare cold spot mapping with sextant-biopsy mapping at tf. Material and methods Twenty-four patients were referred for biopsy-proven local failure after pPPI. Multiparametric MRI and combined-sextant biopsy with a central review of the pathology at tf were systematically performed. A model of the shrinking pattern was defined as a Volumetric Change Factor as a function of time from time of pPPI. An isotropic expansion to both prostate volume and seed position coordinates determined at t f was performed using a validated algorithm using the VCF. Results pPPI CT-based evaluation vs. MR-based evaluation: Mean D90% was 145.23 ± 19.16 Gy [100.0-167.5] vs. 85.28 ± 27.36 Gy [39-139], respectively. Mean V100% was 91.6 ± 7.9% [70-100%] vs. 73.1 ± 13.8% [55-98%], respectively. Seventy-seven per cent of the pathologically positive sextants were classified as cold. Conclusions Patients with biopsy-proven LF had poorer implantation quality when evaluated by MRI several years after implantation. There is a strong relationship between microscopic involvement at tf and cold spots. © 2013 Elsevier Ireland Ltd. All rights reserved.