Predicting acute and late toxicity in prostate cancer stereotactic ablative radiotherapy: the role of dosimetric parameters and prostate volume.

Purpose: Our objective was to identify the dosimetric parameters and prostate volume that most accurately predict the incidence of acute and late gastrointestinal (GI) and genitourinary (GU) toxicity in prostate cancer stereotactic ablative radiotherapy (SABR) treatments.

Methods: We conducted a retrospective analysis of 122 patients who received SABR for prostate cancer at our clinic between March 2018 and September 2022 using a five-fraction SABR regimen. The existing plans of these patients were re-evaluated according to our institutional protocols (Hacettepe University [HU-1] and HU-2) as well as PACE‑B, RTOG 0938, and NRG GU005 dose-volume constraints. Univariate and multivariate logistic regression analyses were performed using SPSS version 23.0 (IBM, Armonk, NY, USA).

Results: The median follow-up was 24.7 months (0.8-94.4 months). For acute GU toxicity, moderate-dose regions were predictive for grade 1-2 toxicity, while high-dose regions were more associated with grade 3-4 toxicity. For late GU toxicity, moderate-high-dose regions were predictive. For GI toxicity, moderate-dose regions were important for both acute and late toxicity. The HU protocol encompassed all significant dosimetric factors influencing toxicity outcomes. A prostate volume threshold of 60 cc was predictive of acute grade 3-4 GU toxicity.

Conclusion: Our study highlighted the critical role of moderate-dose regions for acute and late GI and GU toxicity. Prostate treatment plans should be rigorously evaluated, and moderate doses should be minimized. The HU protocol is an eligible choice for five-fraction SABR plans.