MRI-based atlas for prostate bed recurrence after radical prostatectomy: consistency of CTV delineation with 7 contouring guidelines.

Abstract

To create a magnetic resonance image (MRI)-based atlas of prostate bed recurrence for prostate cancer patients undergoing salvage radiotherapy (sRT) after radical prostatectomy and to evaluate the consistency of contouring guidelines for the prostatic fossa clinical target volume (PF-CTV). Patients with biochemical recurrence and MRI-detected prostate bed lesions before sRT were included. Each lesion was contoured on T2-weighted MRI, using dynamic-contrast-enhanced sequences for guidance. Lesions were transferred to a reference T2-weighted dataset through deformable co-registration to generate a 3D recurrence incidence map. The volume and the location of the lesions were extracted. 7 PF-CTV contouring strategies were implemented on the reference T2w to assess coverage: European Organization for Research and Treatment of Cancer, Faculty of Radiation Oncology Genito-urinary Group, Francophone Group of Urological Radiotherapy, Radiation Therapy Oncology Group (RTOG), Princess Margaret Hospital (PMH), European Society for Radiotherapy and Oncology-Advisory Committee for Radiation Oncology Practice (ESTRO) and PERYTON. Centroid- and volume-based coverage rates were calculated, and statistical comparisons performed using Cochran's Q or Friedman tests. Correlations were analyzed with phi or Spearman's coefficients. 131 patients with 140 recurrences were identified. The lesions were located at the vesicourethral anastomosis (VUA) (53%), bladder neck (BN) (29%) and retrovesical (RV) (18%). Median volume of the lesion was 0.48 cm³ (range 0.03-40.5 cm³) (VUA), 0.29 cm³ (0.09-3.72) (RV) and 0.49 cm³ (0.02-3.51) (BN). Centroid-based coverage ranged from 65%-93%, with ESTRO, PMH and PERYTON achieving the highest rates (92.1-92.9%). Volume-based coverage ranged from 63,7%-91,2%, again favoring ESTRO (91.2%) and PERYTON (90.3%). EORTC showed significantly lower coverage than all other contouring strategies in most comparisons, while strong positive correlations were found among the remaining definitions, with the highest between PMH and RTOG (rho = 0.94). According to the criterium of coverage, our data support the use of ESTRO and PERYTON definition. Here we provide an MRI-based atlas of prostatic bed recurrence that can help optimize sRT contours.