The Prognostic Value of the Size and the Sub-Site of the Local Failure at DCE-MRI before Salvage Radiotherapy for Prostate Cancer

Abstract

<h3>Purpose/Objective(s)</h3> To investigate predictors of biochemical failure after salvage radiotherapy (sRT) in the context of a presumed local failure at dynamic contrast-enhancement-magnetic resonance imaging (DCE-MRI) post radical prostatectomy (RP). <h3>Materials/Methods</h3> All patients referred for sRT at our Institution with a biochemical failure after RP have been consistently offered restaging with both PET/CT and multiparametric MRI since January 2014. Those with a presumed local failure at DCE-MRI as well as no regional/distant disease at PET/CT (either choline and/or PSMA) were selected for the present study. Exclusion criteria were history of androgen deprivation (AD) before sRT and positive nodes at RP. All patients underwent 3T DCE-MRI without endorectal coil and the lesion(s) transferred to the planning CT after co-registration. sRT consisted in 73.5 Gy to the presumed local lesion and 66-69 Gy to the prostatic bed in 30 fxs. Pelvic nodes (PN) were covered to 54 Gy/30 fxs in selected patients. The endpoint of the study was the development of a biochemical failure after sRT defined as a 0.2 ng/ml PSA rise above the nadir. Various covariates (age, pre-RP PSA, pT and pN stages at RP, margins status at RP, ISUP grade group, time from RP to sRT, PSA doubling time, PSA detectability after RP, PSA at sRT, the location, number and volume of the detected recurrence(s), AD use, PN coverage, EUA risk category) were investigated at univariate analysis (UVA) on the time to biochemical failure (bNED-survival). Covariates with a p value <0.2 at UVA were entered a Cox proportional hazards regression analysis. <h3>Results</h3> Up to June 2020, 146 patients satisfying all selection criteria have been treated with sRT. Median (IQR) PSA at sRT was 0.60 ng/ml (0.38-1.05 ng/ml) and only 17 patients (11.6%) received AD along with sRT. A total of 168 local lesions have been detected, 92 (54.8%), 40 (23.8%) and 36 (21.4%) at the vesicourethral anastomosis (VUA), the bladder neck and the retrovesical space, respectively. At the median (IQR) follow-up of 48.1 months (31.3-60.6 months), 22 biochemical failures have been observed for a 4-yr bNED survival of 84.4% (95%CI: 77.9-90.9%). On UVA, bNED-survival after sRT was significantly more likely for patients with VUA-only lesions (VUA-only vs others, HR=0.307, 95%CI: 0.120-0.784, p=0.014) and with smaller lesions (for every cc, HR: 1.071, 95%CI: 1.025-1.119, p=0.002). These associations remained significant (p< 0.01) on multivariate analysis as well. For patients with VUA-only disease or with lesions smaller than 0.5cc, 4-yr bNED survival rates were 90.7% (95%CI: 83.4-98.0%) and 90.6% (95%CI: 83.9-97.3%), respectively. The 46 patients with both favorable features had a 4-yr bNED rate of 94.6% (95%CI: 87.3-100%). <h3>Conclusion</h3> These data support local restaging with DCE-MRI before sRT in the setting of a biochemical failure after RP. Patients with VUA-only and/or small volume lesions have an excellent outcome after dose-escalated sRT.