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MRI-Guided SBRT Cuts Radiation Toxicity in Prostate Cancer


The use of magnetic resonance–guided daily adaptive stereotactic body radiotherapy (SBRT) for patients with prostate cancer reduces the risk of acute urinary side effects of grade 2 or higher by 44% and the risk of acute bowel side effects of grade 2 or higher by 60% compared with standard CT-guided SBRT (CT‐SBRT).


  • With the use of magnetic resonance–guided daily adaptive SBRT, clinicians can customize radiation dosing to accommodate changes in prostate anatomy during treatment, which may also make SBRT safer and less toxic for patients.

  • To determine whether this approach does reduce patient side effects, investigators ran a meta-analysis that included 29 studies with 2547 patients comparing the incidence of short-term, physician-assessed bowel and genitourinary side effects between the MRI-guided approach and standard CT-SBRT.

  • The investigators reported no statistically significant differences in age, prescribed radiation doses, planning target volumes, or International Prostatism Symptom Scores between the two groups; the use of rectal spacers and the number of patients who received pelvic lymph node radiation were low in both.

  • The average window for collecting acute toxicity data was 70 days in the MRI-guided investigations and 94 days in CT-SBRT investigations.


  • The pooled estimate for acute grade 2 or higher genitourinary toxicity was 16% with MRI-guided SBRT vs 28% with CT-SBRT (odds ratio [OR], 0.56; P = .04).

  • The pooled estimate for grade 2 or higher gastrointestinal toxicity was 4% with the MRI approach vs 9% with CT-SBRT (OR, 0.40; P = .04).

  • There were no differences in grade 3 or higher events, which were rare, between the groups.

  • There was also no difference in toxicity among CT‐SBRT studies that used fiducial markers and those that did not.


  • “These findings suggest that the technical advantages in precision of radiotherapy delivery afforded by [MRI-guided] SBRT translate to measurable clinical benefit,” the authors concluded. Potential reasons for the reduced risk of acute toxicity with the MRI-guided approach include “daily online adaptive planning, MRI‐based contouring that results in smaller treatment volumes, and MRI tracking, all of which may facilitate the precision and accuracy of treatment delivery.”


  • The study was led by Jonathan Leeman, MD, of the Dana-Farber Cancer Institute, Boston, and was published July 24 in Cancer.


  • The analysis did not account for differences in dosimetry, radiation planning, and toxicity management and assessment between the studies.

  • Late toxicity and cancer control rates were not tracked and may have differed between the two approaches.


  • No external funding was reported.

  • Investigators reported grants and consulting, personal, and other payments from Novartis, AstraZeneca, Janssen, and other companies.

M. Alexander Otto is a physician assistant with a master’s degree in medical science. He is an award-winning medical journalist who worked for several major news outlets before joining Medscape and is an MIT Knight Science Journalism fellow. Email: [email protected].

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