Three-Step Image Guidance Strategy for Rectal Anterior Wall Margin Reduction in Hypofractionated Prostate Radiation
Gao Yan1, Huang Lei1, Zhao Bo2
1Department of Radiotherapy, Peking University First Hospital, Beijing, China.
Practical Radiation Oncology
|February 4, 2026
Summary
A novel three-step image guidance strategy significantly reduces rectal toxicity in prostate radiotherapy by aligning bone, prostate, and rectal anterior wall. This approach maintains target coverage while minimizing rectal dose, offering a safer treatment option.
Area of Science:
- Radiation Oncology
- Medical Imaging
- Image-Guided Therapy
Background:
- Hypo-fractionated prostate radiotherapy requires precise image guidance to balance target coverage and organ-at-risk toxicity.
- Reducing planning target volume (PTV) margins, especially posteriorly, is desirable but challenging due to soft-tissue motion and anatomical variability.
Purpose of the Study:
- To evaluate a three-step image guidance strategy (bone-prostate-rectal anterior wall alignment) for reducing posterior CTV-PTV margins in prostate radiotherapy.
- To assess the impact on target coverage, rectal toxicity, and dose distribution using deformable image registration (DIR).
Main Methods:
- A three-step alignment protocol (bony, prostate soft-tissue, rectal anterior wall) was applied to 23 patients undergoing 70 Gy/25 fractions radiotherapy.
- A hybrid DIR workflow was used for deformable dose accumulation, with DIR uncertainty thoroughly evaluated.
- Normal Tissue Complication Probability (NTCP) for Grade≥2 GI/GU toxicity was calculated using the Lyman-Kutcher-Burman model.
Main Results:
- The three-step strategy significantly reduced rectal NTCP (7.95% vs. 13.61%) compared to prostate-only alignment, with comparable CTV coverage.
- Deformable dose accumulation confirmed adequate internal target volume (DIL) coverage, except for DILs close to the rectal wall or with significant rectal overlap.
- Image registration quality was high, with Dice Similarity Coefficients (DSC) exceeding 0.8 and minimal non-physical deformations.
Conclusions:
- The three-step image guidance protocol effectively enhances rectal protection while maintaining target coverage in hypo-fractionated prostate radiotherapy.
- Reducing posterior PTV margins is feasible but requires careful consideration of DIL proximity to the rectum.
- Personalized margins and adaptive radiotherapy may be necessary to ensure adequate DIL coverage in specific anatomical locations.
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