MRI-guided SBRT associated with lower GU/GI toxicity vs CT-guided SBRT in prostate cancer

Patients with prostate cancer receiving MRI–guided daily adaptive stereotactic body radiotherapy (MRg-A-SBRT) had a reduced risk of genitourinary (GU) and gastrointestinal (GI) toxicity compared with patients receiving CT-guided non-adaptive SBRT (CT-SBRT), according to a meta-analysis, recently published in Cancer.¹

The study authors also noted that in comparison to CT-SBRT, the use of MRg-A-SBRT facilitated a 44% reduction in the risk of short-term urinary side effects and a 60% reduction in the risk of short-term bowel side effects.

Specifically, those treated with MRg-A-SBRT had a 12% lower risk of GU toxicity and a 5% lower risk of GI toxicity vs those treated with CT-SBRT.

For their meta-analysis, the researchers compared toxicity rates between MRg-A-SBRT and CT-SBRT by reviewing data from a total of 2547 patients drawn from 29 prospective studies published between January 1, 2018 and August 21, 2022.

The researchers found that MRg-A-SBRT was associated with a 16% risk of acute grade 2 or higher (G2+) genitourinary (GU) toxicity in comparison to a 28% risk for CT-SBRT. The use of CT-SBRT was associated with a 9% risk for G2+ gastrointestinal (GI) toxicity in comparison to 4% for MRg-A-SBRT, according to the study.

In comparison to CT-SBRT, the study authors also noted the use of MRg-A-SBRT facilitated a 44% reduction in the risk of short-term urinary side effects and a 60% reduction in the risk of short-term bowel side effects. The researchers added that MRg-A-SBRT was the only factor in a meta-regression analysis to be associated in the study with acute toxicity outcomes.

“These findings suggest that the technical advantages of precision of radiotherapy delivery afforded by MRg-A-SBRT translate to measurable clinical benefit,” wrote lead study author Jonathan E. Leeman, MD, who is affiliated with the Department of Radiation Oncology at the Dana Farber Institute/Brigham and Women’s Hospital and Harvard Medical School in Boston, and colleagues.

The study authors noted that the meta-analysis findings do not clarify whether differences between MRI and CT guidance, or differences between adaptive and non-adaptive treatment contributed to the reduced toxicity observed in the study.

However, Leeman and colleagues pointed out that smaller treatment volume and precision of treatment delivery can be facilitated, respectively, by MRI-based contouring and tracking. They added that daily adaptive planning may “substantially limit” treatment dosing in the bladder, urethra/bladder neck and rectum.

Reference

1. Leeman JE, Shin KY, Chen YH, Mak RH, et al. Acute toxicity comparison of magnetic resonance-guided adaptive versus fiducial or computed tomography-guided non-adaptive prostate stereotactic body radiotherapy: A systematic review and meta-analysis [published online ahead of print July 24, 2023]. Cancer. doi: 10.1002/cncr.34836