SU-E-T-615: Quantifying the Benefit of Adaptive Fractionation

Area of Science:

• Radiation oncology
• Medical physics
• Radiotherapy planning

Background:

• Adaptive radiotherapy aims to improve treatment accuracy by adjusting plans based on anatomical changes.
• Fraction size variation is a key parameter in adaptive treatment strategies.
• Organs-at-risk (OARs) often experience dose accumulation due to inter-fractional motion.

Purpose of the Study:

• To quantify the dosimetric benefits of adaptive fractionation.
• To evaluate adaptive fractionation using theoretical models and patient data.
• To assess the impact of varying fraction sizes on OAR dose reduction.

Main Methods:

• Simulated adaptive fractionation by adjusting radiation fraction sizes based on anatomical changes.
• Developed a one-dimensional theoretical model to simulate OAR dose reduction with varying tumor-OAR distances.
• Applied the adaptive fractionation methodology to CT images from five prostate cancer patients.

Main Results:

• Theoretical models showed 5-85% dose reduction to OARs, with a 10% decrease for a 20% daily fraction size deviation.
• Prostate patient data indicated average rectal dose reductions of 1.4%, 3.5%, and 7.0% for 20%, 50%, and 100% daily fraction size deviations, respectively.
• Dose reduction varied based on anatomical motion, number of fractions, and allowed fraction size deviations.

Conclusions:

• Adaptive fractionation is beneficial for treating cancers with significant inter-fractional motion.
• Greater benefits are observed with more fractions and larger daily fraction size deviations.
• Adaptive fractionation shows promise for sites like rectal and cervical cancers, warranting further investigation.