Magnetic Resonance Imaging-Based Atlas for Prostate Bed Recurrence After Radical Prostatectomy: Consistency of...

To create a magnetic resonance image (MRI)-based atlas of prostate bed recurrence for prostate cancer patients undergoing salvage radiation therapy (sRT) after radical prostatectomy, and to evaluate the consistency of contouring guidelines for the prostatic fossa-clinical target volume.

Patients with biochemical recurrence and MRI-detected prostate bed lesions before sRT were included. Each lesion was contoured on T2-weighted (T2w) MRI using dynamic contrast-enhanced sequences for guidance. Lesions were transferred to a reference T2-w data set through deformable co-registration to generate a 3-dimensional recurrence incidence map. The volume and location of the lesions were extracted. Seven prostatic fossa-clinical target volume contouring strategies were implemented on the reference T2w data set to assess coverage: the European Organisation for Research and Treatment of Cancer, the Faculty of Radiation Oncology Genito-Urinary Group, the Francophone Group of Urological Radiotherapy, the Radiation Therapy Oncology Group, the Princess Margaret Hospital (PMH), the 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 were performed using Cochran's Q or Friedman tests. Correlations were analyzed with phi or Spearman's (rho, ρ) coefficients.

One hundred and thirty-one patients with 140 recurrences were identified. Lesions were located at the vesicourethral anastomosis (53%), bladder neck (29%), and retrovesical region (18%). Median volume of the lesion was 0.48 cm³ (range, 0.03-40.5 cm³) (vesicourethral anastomosis), 0.29 cm³ (range, 0.09-3.72 cm³) (retrovesical region), and 0.49 cm³ (range, 0.02-3.51 cm³) (bladder neck). Centroid-based coverage ranged from 65% to 93%, with ESTRO, PMH, and PERYTON achieving the highest rates (92.1%-92.9%). Volume-based coverage ranged from 63.7% to 91.2%, again favoring ESTRO (91.2%) and PERYTON (90.3%). The European Organisation for Research and Treatment of Cancer strategy showed significantly lower coverage than all other contouring strategies in most comparisons, while strong positive correlations were observed among the remaining definitions, with the highest correlation between PMH and the Radiation Therapy Oncology Group (ρ = 0.94).

According to the coverage criterion, our data support the use of ESTRO and PERYTON definitions. Here, we provide an MRI-based atlas of prostatic bed recurrence that can help optimize sRT contours.