Rapid effective dose calculation for raster-scanning 4He ion therapy with the modified microdosimetric kinetic model (mMKM)

Purpose: To develop and verify effective dose (D-RBE) calculation in 4 He ion beam therapy based on the modified microdosimetric kinetic model (mMKM) and evaluate the bio-sensitivity of mMKM-based plans to clinical parameters using a fast analytical dose engine. Methods: Mixed radiation field particle spectra (MRFS) databases have been generated with Monte-Carlo (MC) simulations for He-4-ion beams. Relative biological effectiveness (RBE) and DRBE calculation using MRFS were established within a fast analytical engine. Spread-out Bragg-Peaks (SOBPs) in water were optimized for two dose levels and two tissue types with photon linear-quadratic model parameters alpha(ph), beta(ph), and (alpha/beta)(ph) to verify MRFS-derived database implementation against computations with MC-generated mixed-field alpha and beta databases. Biosensitivity of the SOBPs was investigated by varying absolute values of beta(ph), while keeping (alpha/beta)(ph) constant. Additionally, dose, dose-averaged linear energy transfer, and bio-sensitivity were investigated for two patient cases. Results: Using MRFS-derived databases, dose differences less than or similar to 2% in the plateau and SOBP are observed compared to computations with MC-generated databases. Bio-sensitivity studies show larger deviations when altering the absolute beta(ph) value, with maximum D-50% changes of similar to 5%, with similar results for patient cases. Bio-sensitivity analysis indicates a greater impact on D-RBE varying (alpha/beta)(ph) than beta(ph) in mMKM. Conclusions: The MRSF approach yielded negligible differences in the target and small differences in the plateau compared to MC-generated databases. The presented analyses provide guidance for proper implementation of RBE-weighted He-4 ion dose prescription and planning with mMKM. The MRFS-D-RBE calculation approach using mMKM will be implemented in a clinical treatment planning system.

Automated summary

This study developed and verified the effective dose calculation in helium ion beam therapy based on the modified microdosimetric kinetic model, and evaluated the bio-sensitivity of the plans to clinical parameters. The research utilized fast analytical engine to optimize SOBPs in water and investigate the impact on dose and bio-sensitivity for patient cases. The results suggest that the MRFS-D-RBE calculation approach can be effectively implemented and bio-sensitivity analysis plays a significant role in helium ion therapy planning.