Cold spot mapping inferred from MRI at time of failure predicts biopsy-proven local failure after permanent seed brachytherapy in prostate cancer patients: Implications for focal salvage brachytherapy

Abstract

Background and purpose To establish a method to evaluate dosimetry at the time of primary prostate permanent implant (pPPI) using MRI of the shrunken prostate at the time of failure (tf). To compare cold spot mapping with sextant-biopsy mapping at tf. Material and methods Twenty-four patients were referred for biopsy-proven local failure (LF) 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 (VCF) as a function of time from time of pPPI (t0). An isotropic expansion to both prostate volume (PV) and seed position (SP) coordinates determined at tf was performed using a validated algorithm using the VCF. Results pPPI CT-based evaluation (at 4 weeks) vs. MR-based evaluation: Mean D90% was 145.23 ± 19.16 Gy [100.0–167.5] vs. 85.28 ± 27.36 Gy [39–139] (p = 0.001), respectively. Mean V100% was 91.6 ± 7.9% [70–100%] vs. 73.1 ± 13.8% [55–98%] (p = 0.0006), 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.

GGEMS-Brachy: GPU GEant4-based Monte Carlo simulation for brachytherapy applications

“…These results are in agreement with previous studies: mean −6.4% (range: −1.8%,−14.1%) reported in Collins-Fekete et al (2015) and a mean difference of −7% corresponding to the results of Carrier et al (2006). Similarly to all theses studies, dose within the prostate region is overestimated using the TG43 formalism relative to the MCS whichcan in turn lead to potential local recurrences (Crehange et al 2013, Sasaki et al 2014.…”

“…In LDR brachytherapy, a high precision in the positioning of the seeds is essential in order to avoid areas of tumor under-dosage (cold spots) due to the limited penetration of the low-energy radiation, while at the same time ensuring the minimum dose in the organs at risk. As reported by a recent clinical study (Crehange et al 2013, Sasaki et al 2014, patients with biopsy-proven local recurrence had poorer implantation quality with underdosed areas corresponding to the positive biopsy sites. There is therefore increasing evidence of a strong relationship between local recurrence and dose cold spots.…”

Clinical and technical challenges of cancer reirradiation: Words of wisdom

“…Conversely, if the progression-free interval is shortened, the reRT should be maximally aggressive (McAvoy et al, 2014). Early local recurrence may be a sign of underdosing during the first irradiation, for example, after prostate brachytherapy (Crehange et al, 2013), or a sign of radioresistance. In the latter case, the reRT could allow to consecutively increase the dose at the target volume and therefore potentially improve the local control.…”

Natural History after Biochemical Failure Following Dose-escalated External Beam Radiation: An Opportunity to Improve Outcomes?

“…As a result, the dogma that ''after radiotherapy you cannot have additional radiation'' is increasingly being proven wrong. This body of work, combined with contemporary imaging approaches, appears to identify some parameters that physicians can use to help in determining which patients might be most likely to benefit from additional local therapy [6][7][8]. For patients with intermediate to high risk of regional and/or distant failure, more aggressive imaging and therapeutic strategies may be indicted, but more data and longer follow-up are needed to confirm the initial optimism [9,10].…”