Hypofractionated proton therapy appeared effective and associated with low rates of toxicity among men with prostate cancer, according to results of a prospective phase 2 study published in International Journal of Radiation Oncology Biology Physics.
These results suggest that this shorter, higher-dose delivery method may have comparable outcomes to those of standard fractionated proton therapy.
“This study provides some prospective evidence that the higher daily radiation dose delivered in hypofractionated proton therapy does not negatively impact patient quality of life,” Neha Vapiwala, MD, associate professor of radiation oncology and assistant dean of student affairs at Perelman School of Medicine at University of Pennsylvania, said in a press release. “These data can help guide clinicians and patients as they weigh treatment efficacy, tolerability and convenience.”
Vapiwala and colleagues studied 4-year clinical and patient-reported outcomes of 184 men with low-risk (n = 18; median age, 64 years), favorable intermediate-risk (n = 78; median age, 67 years) and unfavorable intermediate-risk (n = 88; median age, 68 years) prostate cancer treated with moderately hypofractionated proton therapy. The men received 70 Gy of proton therapy in 28 fractions, a dose estimated to be equivalent to that of a conventionally fractionated regimen of 79.2 Gy in 44 fractions.
Researchers assessed rates of biochemical-clinical failure (BCF), OS and toxicity.
With median follow-up of 49.2 months (interquartile range, 27.6-73.2). results showed 4-year BCF-free survival of 93.5% (95% CI, 89-98) among all patients, 94.4% (95% CI, 89-100) for men with low-risk prostate cancer, 92.5% (95% CI, 86-100) for men with favorable intermediate-risk disease, and 93.8% (95% CI, 88-100) for men with unfavorable intermediate-risk disease.
Median time to BCF was 51 months (range, 18-86).
OS at 4 years was 95.8% (range, 92-100) among all patients, with no statistically significant difference in OS among subgroups.
Cumulative 4-year incidence of late grade 2 or higher gastrointestinal toxicity was 13.6% (95% CI, 9-20). Nearly all these events, the most common of which was rectal bleeding (79%), occurred during the first 2 years of therapy.
Late urologic toxicities occurred at a cumulative 4-year rate of 7.6% (95% CI, 4-13). The most common of these was urinary frequency (57%). All urologic toxicities resolved within 6 months.
No grade 3 or grade 4 toxicities were reported.
The single-arm design of the study served as its main limitation.
“Early results from hypofractionated proton therapy for the treatment of prostate cancer show low rates of transitory urologic and GI toxicity, and low rates of patient-reported urinary, bowel, hormonal and sexual bother post-treatment, with favorable disease control,” Vapiwala and colleagues wrote. “The results from this trial are similar to series of standard fractionated proton therapy. Ongoing analyses are warranted to assess long-term toxicity and understand differences between proton and photon hypofractionated radiation therapy in the treatment of organ-confined prostate cancer.”– by John DeRosier
Disclosures: The authors report no relevant financial disclosures.