Radiobiological Modeling for Acute Proctitis After Conventional and Hypofractionated Radiation Therapy for Prostate...

Area of Science:

• Radiation Oncology
• Medical Physics
• Clinical Oncology

Background:

• Acute proctitis (AP) is a frequent side effect of pelvic radiation therapy.
• Moderate hypofractionated radiation therapy with shorter treatment times (TTs) is associated with increased AP risks.
• Accurate prediction of AP is crucial for optimizing radiation therapy protocols.

Purpose of the Study:

• To develop normal tissue complication probability (NTCP) models for acute proctitis (AP).
• To evaluate the impact of dose-fractionation and treatment time on AP development.
• To incorporate clinical factors like androgen deprivation therapy (ADT) into AP prediction models.

Main Methods:

• Analysis of patient data (n=321) from two prospective studies receiving various hypofractionated radiotherapy schedules.
• Development of three logistic regression models based on equivalent uniform dose (EUD) and biologically effective dose (BED).
• Inclusion of clinical predictors such as diabetes and ADT; estimation of model parameters using maximum likelihood estimation (MLE) and bootstrapping for validation.

Main Results:

• AP incidence varied significantly with fractionation: 66% for 20 × 3.0/3.1 Gy, 25% for 20 × 2 Gy, and 24% for 12 × 3.4 Gy.
• The developed NTCP models demonstrated good predictive performance (AUC=0.77) with EUD and ADT as significant predictors.
• Model analysis supported an alpha/beta ratio of 10 Gy and indicated potential AP risk reduction with extended treatment times.

Conclusions:

• Well-performing NTCP models for AP were successfully developed, incorporating EUD and ADT.
• The models provide a good fit for both conventional and moderate hypofractionated schemes, supporting an alpha/beta of 10 Gy.
• Findings suggest that optimizing treatment time is a viable strategy to mitigate AP risk in radiation therapy.