Effect of dose rate in hypofractionated radiotherapy

Area of Science:

• Radiation Oncology
• Radiobiology

Background:

• Hypofractionated radiotherapy aims to deliver higher doses per fraction.
• Understanding the radiobiological effects of different dose rates is essential for safe and effective treatment planning.

Purpose of the Study:

• To evaluate how radiation dose rate influences the radiobiological properties of hypofractionated radiotherapy.
• To assess the impact of dose rate on normal tissue complication probability (NTCP) under varying fractionation schedules.

Main Methods:

• Utilized the linear-quadratic (LQ) model to calculate biologically effective dose (BED).
• Analyzed changes in BED for normal tissues (BEDnt) relative to a fixed BED in the tumor target (BEDtar).
• Investigated the influence of dose rate and number of fractions (Nf) on BEDnt.

Main Results:

• Hypofractionation can increase or decrease BEDnt compared to standard fractionation, depending on the average dose rate.
• At high dose rates, BEDnt in organs at risk (OARs) like the spinal cord varies monotonically with Nf.
• At lower dose rates (e.g., 300 MU/min), BEDnt can vary non-monotonically, with an optimal Nf for minimal BEDnt.
• Increasing dose rate reduces BEDnt when target cells repair faster than OAR cells.

Conclusions:

• The radiobiological impact of hypofractionation on OARs is dose rate-dependent.
• Accurate radiobiological assessment of hypofractionation requires consideration of both dose rate and differential repair kinetics between tumor and OARs.