Toxicity After Post Prostatectomy Image-Guided Intensity-Modulated Radiation Therapy Using Australian Guidelines

Abstract

Australian post prostatectomy radiotherapy (PPRT) contouring and treatment guidelines are in use in clinical practice, but late toxicity outcomes have not been published and concern over toxicity may contribute to underutilization. In addition, there are no reports of late toxicity for patients treated with image-guidance using implanted fiducial markers. This study reports single institution toxicity outcomes after post prostatectomy radiotherapy (PPRT) via image guided intensity modulated radiation therapy (IG-IMRT) using the national eviQ guidelines. Baseline, acute and late toxicity data are reported both using incidence and prevalence which will help to inform radiation oncologists, patients and referring clinicians regarding the expected patterns of genitourinary, gastrointestinal and sexual toxicity before, during and after post prostatectomy radiotherapy. Prospectively collected toxicity data using Common Terminology Criteria for Adverse Events version 4 was reviewed for 293 men who underwent 64-66Gy IG-IMRT to the prostate bed between 2007 and 2015. Image-guidance was achieved via implanted fiducial markers. Median follow up after PPRT was 39 months. Baseline grade ≥ 2 genitourinary (GU), gastrointestinal (GI) and sexual toxicity was 20.5%, 2.7% and 43.7% respectively, reflecting ongoing toxicity after radical prostatectomy. Incidence of new (compared to baseline) acute grade ≥ 2 GU and GI toxicity was 5.8% and 10.6% respectively. New late grade ≥ 2 GU, GI and sexual toxicity occurred in 19.1%, 4.7% and 20.2% respectively, however many patients also experienced improvements in toxicities. For this reason, prevalence of grade ≥ 2 GU, GI and sexual toxicities four years after PPRT was similar to or lower than baseline (21.7%, 2.6% and 17.4% respectively). Baseline and acute grade ≥ 2 GU and sexual toxicity predicted respective late toxicities, while salvage intent predicted late grade ≥ 2 GU toxicity. There were no grade ≥ 4 toxicities. Post prostatectomy IG-IMRT using Australian contouring guidelines appears to have tolerable acute and late toxicity. The four year prevalence of grade ≥ 2 GU and GI toxicity was virtually unchanged compared to baseline, and sexual toxicity improved over baseline. This should reassure radiation oncologists following these guidelines. Late toxicity rates of surgery and PPRT are higher than following definitive IG-IMRT, and this should be taken into account if patients are considering surgery and likely to require PPRT.