Three-Step Image Guidance Strategy for Rectal Anterior Wall Margin Reduction in Hypofractionated Prostate Radiation Therapy

A 3-step image guidance protocol enhanced rectal protection while maintaining target coverage compared to prostate-only alignment. Reducing the posterior PTV margin preserved CTV coverage, but DIL coverage varied by location. If the DIL is less than 0.7 mm from the rectum or overlaps more than 1.5 cm³ within 2 mm of the rectum, the reduced margin may not be suitable, potentially compromising DIL coverage, suggesting the need for personalized margins and adaptive radiation therapy to prevent underdosage.