An interim analysis of an ongoing phase III study indicated that using magnetic resonance imaging (MRI) to guide stereotactic body radiotherapy for patients with prostate cancer reduced side effects associated with the treatment. The findings were presented at the 2022 ASCO Genitourinary Cancers Symposium by Amar U. Kishan, MD, and colleagues (Abstract 255).
Advanced radiation techniques like high-dose stereotactic body radiotherapy (SBRT) offer the opportunity to deliver high radiation doses to tumors while sparing surrounding tissues. Clinicians often use computed tomography (CT) to help make sure the dose is delivered with precision. MRI offers several theoretical advantages over CT to guide SBRT for prostate cancer, including the ability to aggressively reduce planning margins needed for radiation due to enhanced imaging capabilities.
Amar U. Kishan, MD
In the single-center phase III MIRAGE trial, men undergoing SBRT for localized prostate cancer were randomly assigned to receive treatment guidance with either CT or MRI. Investigators planned to compare the groups to see how often men experienced genitourinary toxicities during the 90 days after treatment. The investigators believed they would need to enroll 300 patients to be able to detect a benefit to MRI guidance but had planned to analyze the data after 100 patients were treated in order to see if this hypothesis were true or if fewer patients might need to be enrolled.
In this analysis of the first 100 patients treated, the investigators found that men undergoing MRI guidance were less than half as likely to experience grade 2 genitourinary toxicities (22% vs 47%), like frequent urination, a burning sensation while urinating, bloody urine, or urinary incontinence. Notably, a significant proportion of men who had CT guidance suffered gastrointestinal toxicities, such as diarrhea, discharge, or rectal/abdominal pain to abdominal distention or obstruction, but none of the men undergoing MRI guidance experienced any gastrointestinal toxicity (14% vs 0%).
“MRI guidance offers a statistically significant reduction in acute genitourinary as well as gastrointestinal toxicity for prostate SBRT,” said Dr. Kishan, Vice Chair of Clinical and Translational Research in the Departments of Radiation Oncology and Urology at the University of California, Los Angeles Jonsson Comprehensive Cancer Center. “Because of the significant effect size we saw, we were able to cut our projected sample size in half. Thus, we finished enrolling on our trial in October 2021. Our final results are expected later this year, but we are extremely optimistic by what we’re seeing, and hope this technology will soon begin to offer men undergoing radiotherapy for prostate cancer better outcomes.”
Disclosure: For full disclosures of the study authors, visit coi.asco.org.The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.