Defining bowel dose volume constraints for bladder radiotherapy treatment planning

Area of Science:

• Radiation oncology
• Clinical oncology
• Medical physics

Background:

• Radiotherapy dose escalation for muscle-invasive bladder cancer is limited by normal tissue toxicity.
• Understanding the relationship between radiation dose to the bowel and late toxicity is crucial for treatment planning.

Purpose of the Study:

• To assess the relationship between bowel dose-volume data and late bowel toxicity in patients with muscle-invasive bladder cancer treated with radical radiotherapy.
• To develop a model to predict the probability of late bowel toxicity based on absolute bowel volumes.

Main Methods:

• Retrospective contouring of the bowel on radiotherapy plans from 47 patients in the BC2001 trial.
• Exploration of the relationship between bowel volume at various dose levels and prospectively collected late bowel toxicity data.

Main Results:

• 15% and 6% of patients experienced grade 1 and grade 2 or higher late bowel toxicity, respectively.
• Reduced high-dose volume radiotherapy resulted in significantly smaller mean bowel volumes at doses ≥50 Gy compared to standard radiotherapy.
• Increased bowel volume correlated with a higher probability of late bowel toxicity (P ≤ 0.05 for 30-50 Gy dose levels).
• No grade 2+ toxicity was observed below proposed thresholds for 25% probability of late bowel toxicity.

Conclusions:

• A clear dose-volume effect exists for late bowel toxicity in radical bladder radiotherapy.
• A predictive model for late bowel toxicity probability based on absolute bowel volumes is presented to aid clinicians in treatment planning.
• Proposed dose-volume constraints, predicting a 25% probability of late bowel toxicity, are suggested for clinical use.