Optimising on-treatment review schedules: A narrative review of acute toxicities in ultra-hypofractionated stereotactic ablative body radiotherapy (SABR) for localised prostate cancer

INTRODUCTION: Ultra-hypofractionated stereotactic ablative body radiotherapy (SABR) delivers high radiation doses to a planned target volume. Compared to conventional radiotherapy (CRT), SABR offers radiobiological advantages and improved tumour control for localised prostate cancer but may present a different acute toxicity profile. This review synthesises existing literature regarding acute toxicities associated with ultra-hypofractionated SABR to identify the timing, incidence, and severity of side effects and inform optimal treatment review schedules. METHODS: A narrative review was conducted using SCOPUS and Ovid MEDLINE databases. Eligible publications included randomised controlled trials and quasi-experimental studies, published in English between 2017 and 2024, reporting acute toxicities during or after ultra-hypofractionated SABR. Data were extracted to identify patterns in the incidence, severity, and timing of acute side effects. RESULTS: Evidence from 20 studies showed broadly comparable toxicity between ultra-hypofractionated SABR and CRT, although patient-reported outcomes suggest earlier onset and greater severity with SABR. Genitourinary toxicities are more common than gastrointestinal effects and tend to peak earlier compared to CRT. Higher radiation doses, shorter schedules, and baseline urinary symptoms increase acute toxicity risk, while alternate-day or weekly regimens and rectal spacers may reduce gastrointestinal but not necessarily genitourinary toxicity. However, inconsistent reporting across studies limits direct comparison. CONCLUSION: For alternate-day ultra-hypofractionated SABR, post-radiotherapy reviews should occur near treatment completion and again at four weeks after radiotherapy to capture peak gastrointestinal and genitourinary toxicities, with continued follow-up over subsequent months. Weekly SABR schedules may delay toxicity peaks and require adjusted review timing. IMPLICATIONS FOR PRACTICE: Understanding the timing and pattern of acute toxicities can support radiotherapy teams in designing evidence-based review schedules, improving early detection of side effects, guiding patient education, and ensuring timely symptom management during SABR pathways.