A predictive model for determining rectum and bladder dose constraints in prostate volumetric modulated arc therapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Generic dose-volume constraints are standard for rectum/bladder (R/B) sparing in prostate radiotherapy.
• Assessing the correlation between R/B overlap with the planning target volume (PTV) and organ at risk (OAR) doses is crucial for optimizing treatment.

Purpose of the Study:

• To evaluate the relationship between R/B-PTV overlap and radiation doses to these organs in prostate cancer patients.
• To identify predictive metrics for minimizing OAR doses during Volumetric Modulated Arc Therapy (VMAT) planning.

Main Methods:

• Retrospective analysis of 105 prostate cancer patients treated with VMAT.
• Collected data included R/B volume, R/B-PTV overlap volume, and R/B-PTV overlap percentage.
• Correlated these metrics with VMAT planning outcomes, specifically doses to the rectum and bladder.

Main Results:

• High correlation found between R/B-PTV percentage overlap and OAR doses (R²=0.63 for rectum, R²=0.91 for bladder).
• Identified predictive cut-off values for R/B-PTV overlap to achieve specific dose thresholds for rectum and bladder.
• A 95% prediction interval aided in establishing individualized R/B planning goals.

Conclusions:

• R/B-PTV percentage overlap is a reliable predictor of OAR sparing in prostate VMAT.
• This prediction model can enhance planning efficiency and enable customized OAR planning goals.
• Minimizing radiation doses to the rectum and bladder is achievable through individualized planning.