The association of intraprostatic calcifications and dosimetry parameters with biochemical control after permanent prostate implant

PurposeThe objective of this study was to evaluate the impact of intraprostatic calcifications (IC) on long-term tumor control in patients treated with permanent implant prostate brachytherapy (PIPB).Materials and MethodsData from 609 I-125 patients treated with PIPB were retrospectively reviewed. The presence of IC was determined by reviewing postimplant CT images. Doses delivered were determined using the Monte Carlo (model-based) calculations and the TG43 approach. Biochemical relapses at 7 and 10 years were determined according to Phoenix definition. Long-term biochemical relapse-free survival (bRFS) was determined using Kaplan–Meier estimates with log rank test. Cox proportional hazard models were used for analysis of predictor factors of biochemical recurrence.ResultsIC were observed for 11.1% of patients. Clinical stage, PSA, Gleason score, D'Amico risk group, and ADT use were comparable between IC and no IC groups. The 7- and 10-year bRFS for the entire cohort were 94.1% and 90.6%, respectively. The bRFS at 7 years was 90.5% (with IC) vs. 94.5% (without IC) (p = 0.198); the corresponding values at 10 years were 78.8% vs. 91.8% (p = 0.046). On Cox model, only prostatic calcifications were a significant risk factor for biochemical relapse (HR: 2.30, IC 95%: 1.05–5.00, p = 0.037; and HR: 3.94; IC 95%: 1.00–15.38; p = 0.049 for univariate and multivariate analysis, respectively).ConclusionThe presence of IC in patients treated with PIPB decreases V₁₀₀ and D₉₀ for postimplant Monte Carlo dosimetry (compared with TG43); correspondingly, IC are associated with a lower 10-y bRFS. Model-based dose calculations are critical to evaluate potential cold spots due to calcifications.