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

Phys Med. 2021 Jan:81:273-284. doi: 10.1016/j.ejmp.2020.11.028. Epub 2021 Jan 19.

Abstract

Purpose: To develop and verify effective dose (DRBE) calculation in 4He 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 4He-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 αph, βph, and (α/β)ph to verify MRFS-derived database implementation against computations with MC-generated mixed-field α and β databases. Bio-sensitivity of the SOBPs was investigated by varying absolute values of βph, while keeping (α/β)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 ≲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 βph value, with maximum D50% changes of ~5%, with similar results for patient cases. Bio-sensitivity analysis indicates a greater impact on DRBE varying (α/β)ph than βph 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 4He ion dose prescription and planning with mMKM. The MRFS-DRBE calculation approach using mMKM will be implemented in a clinical treatment planning system.

Keywords: Biological model; FRoG/PRECISE; Heidelberg Ion-Beam Therapy Center; Helium ion therapy.

MeSH terms

  • Heavy Ion Radiotherapy*
  • Humans
  • Linear Energy Transfer
  • Monte Carlo Method
  • Proton Therapy*
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted
  • Relative Biological Effectiveness