Ultra-hypofractionated SBRT has low acute toxicity in localized prostate cancer
medwireNews: Ultra-hypofractionated stereotactic body radiotherapy (SBRT) does not increase the risk for acute toxicity over standard of care radiotherapy in men with localized prostate cancer, according to a phase III trial.
“This pre-planned analysis of acute toxicity in the PACE-B trial, occurring up to 12 weeks after radiotherapy delivery completion, does not suggest that patients have greater acute RTOG [Radiation Therapy Oncology Group] toxic effects with [SBRT] compared with conventionally fractionated or moderately hypofractionated radiotherapy,” say Nicholas van As (The Royal Marsden NHS Foundation Trust, London, UK) and co-researchers.
A total of 415 men received ultra-hypofractionated SBRT, in which 36.25 Gy was delivered in an accelerated schedule of five fractions over 1–2 weeks, while 432 men received conventionally or moderately hypofractionated radiotherapy, comprising 78 Gy in 39 fractions over 7.8 weeks or 62 Gy in 20 fractions over 4.0 weeks, respectively.
Participants were followed up for a median of 12 weeks, at which point RTOG gastrointestinal toxic events of grade 2 or more were seen in 10% of those receiving ultra-hypofractionated SBRT and 12% of those given conventionally or moderately hypofractionated radiotherapy, while RTOG grade 2 or worse genitourinary toxicity occurred in 23% and 27% of patients, respectively – both nonsignificant differences.
The incidence of RTOG gastrointestinal toxicities of grade 3 or higher was similarly comparable across the ultra-fractionated radiotherapy and control groups, at rates of less than 1% and 1%, respectively, while genitourinary toxic effects of this severity were observed in 2% of participants in each group.
Patient-reported outcomes, measured using four different tools, were also comparable between the two groups.
And although significantly more patients in the SBRT arm had more CTCAE grade 2 or worse toxic effects at early timepoints, these differences had resolved by 12 weeks after the end of radiotherapy, note van As and colleagues.
“The absence of increased toxicity in the stereotactic body radiotherapy group is reassuring given the higher acute toxicity suggested in the only previously published phase 3 ultra-hypofractionation trial [HYPO-RT-PC], especially given the more abbreviated (five-fraction) investigational radiotherapy protocol used in PACE-B,” say the researchers in The Lancet Oncology.
“Results regarding late toxicity and biochemical control from PACE-B will be reported in the next 3-4 years,” they conclude.
By Catherine Booth
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