Fractionation effects in particle radiotherapy: implications for hypo-fractionation regimes

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiobiology

Background:

• The linear quadratic (LQ) model is standard for radiotherapy dose-response calculations.
• Accurate relative biological effectiveness (RBE) values are crucial for high-energy transfer (LET) radiotherapy.
• The beta (β) radiosensitivity parameter's behavior with varying LET is not fully understood.

Purpose of the Study:

• To investigate the impact of the β parameter on clinical RBE calculations in high-LET radiotherapy.
• To evaluate the necessity of incorporating RBE(min) ≠ 1 in the LQ model for different radiation types.
• To assess the predictive accuracy of the modified LQ model for iso-effective doses.

Main Methods:

• Modified linear quadratic (LQ) model incorporating RBE(min).
• Fitting fractionated radiation data with RBE(min) = 1 and RBE(min) ≠ 1.
• Nonlinear regression and analysis of variance (ANOVA) for hypothesis testing.

Main Results:

• The RBE(min) ≠ 1 assumption improved model fit for neutron data in 89% of cases.
• For carbon ions, RBE(min) ≠ 1 improved fit only for normal tissues at the spread-out Bragg peak.
• The β parameter significantly impacts RBE calculations, particularly with hypofractionation of high-LET radiation.

Conclusions:

• Variations in the β parameter demonstrably affect clinical RBE calculations.
• The RBE(min) ≠ 1 modification offers improved accuracy for certain high-LET radiation types and tissues.
• This highlights the importance of considering β parameter changes in advanced radiotherapy planning.