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An empirical model of proton RBE based on the linear correlation between x-ray and proton radiosensitivity
David B Flint1, Chase E Ruff1, Scott J Bright1
1Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
Medical Physics
|July 13, 2022
Summary
A new proton relative biological effectiveness (RBE) model predicts higher RBE values in clinical proton beams, improving accuracy over fixed RBE=1.1. This model uses intrinsic cell radiosensitivity and linear energy transfer (LET) to predict proton survival curves more effectively.
Area of Science:
- Medical physics
- Radiation oncology
- Radiobiology
Background:
- Proton relative biological effectiveness (RBE) is currently fixed at 1.1 in clinics, despite known dependencies on linear energy transfer (LET) and cell-specific DNA repair.
- Existing empirical models for variable proton RBE are limited by noisy biological data, hindering clinical adoption.
Purpose of the Study:
- Introduce a novel proton RBE model based on intrinsic cell radiosensitivity variation with LET, moving beyond linear-quadratic model (LQM) parameters.
- Develop a more accurate and clinically feasible method for predicting proton RBE.
Main Methods:
- Performed clonogenic cell survival assays across eight cell lines with varying proton LETs (1.2, 2.6, 9.9 keV/µm) and X-rays.
- Combined experimental data with published survival data (n=397) to characterize DSF% variation with LET.
- Constructed a six-parameter model predicting proton survival curves based on LET-dependent radiosensitivity, validated against existing models and in a clinical workflow.
Main Results:
- Found a linear correlation between X-ray and proton DSF% across survival levels, with slopes varying by proton LET.
- The novel model predicts proton RBE within 15%-30% (68.3% confidence), outperforming previous empirical models.
- In clinical scenarios, the model predicted higher RBE-weighted doses, particularly up to 50.7% higher in the distal beam edge compared to RBE=1.1.
Conclusions:
- Established a new empirical proton RBE model offering superior accuracy compared to existing models.
- The model predicts significantly higher RBE values at the distal edge of clinical proton beams.
- Demonstrated the model's feasibility for clinical treatment plan evaluation, suggesting potential for improved dose delivery.
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