Patterns and Predictors of Prostate-Specific Membrane Antigen Positron Emission Tomography/Computed Tomography-Detected Local Recurrence Following Postprostatectomy Salvage Radiotherapy for Prostate Cancer.

AIM: Salvage radiotherapy (sRT) is an effective curative option for patients with biochemical recurrence following radical prostatectomy (RP). However, a subset of patients will develop local recurrence (LR) following treatment. Predictive factors and patterns of LR after sRT remain poorly defined. This study evaluates clinicopathological predictors of LR and characterises failures anatomically relative to prior sRT fields.

MATERIALS AND

METHODS

Patients who received RP followed by sRT and subsequently underwent fluorine-18 prostate-specific membrane antigen positron emission tomography/computed tomography (18F-PSMA PET/CT) for biochemical recurrence were identified from a prospective imaging registry. Logistic regression and Fine-Gray competing risks analyses were used to evaluate clinical, pathological, and treatment-related predictors of LR. Anatomical mapping localised LR relative to prior radiotherapy fields.

RESULTS

Among 370 eligible patients, 68 (18.4%) had LR after sRT including 34 (9.2%) with isolated LR. The median prostate-specific antigen (PSA) at time of imaging was 0.77 ng/mL (interquartile range [IQR]: 0.40-2.10 ng/mL) overall, and 0.83 ng/mL (IQR: 0.41-3.33 ng/mL) for patients with LR. On univariate logistic regression analyses (UVA), Gleason grade groups 1-3 and pN0 status were significantly associated with LR (P < 0.05). No variables remained significant on multivariable analysis. Fine-Gray analysis identified younger age and longer PSA doubling time as additional predictors of LR. Of all patients with LR, 35 had sRT plans available for spatial analysis, encompassing 39 discrete lesions. When mapped to the treatment-planned clinical target volume (CTV), 29 lesions (74.4%) were in-field, 8 (20.5%) marginal, and 2 (5.1%) out-of-field. Marginal and out-of-field lesions commonly involved the posterior prostatic fossa and seminal vesicle bed.

CONCLUSION

PSMA PET/CT identified LR in nearly one-fifth of patients undergoing PSMA imaging for biochemical recurrence following sRT. Although most recurrences were within the treated volume, their distribution highlights anatomical regions that may benefit from additional attention at the time of planning.