Room: Track 3
Purpose: As our institution prepares for the first clinical trials with helium ion-beam therapy using raster-scanning technology, precise characterization of both physical and biological properties of helium ions towards development and validation of the clinical treatment planning system (TPS) is currently underway.
Methods: We measured depth dose curves and the lateral beam spread in air/water for 28 energies from 50.57 – 220.51 MeV/u. All experiments were simulated using FLUKA Monte-Carlo (MC) code, tuning and validating beam parameters against measurements. From the resulting best fit, we inferred the beam parameters for the intermittent energies. Absolute dosimetry of 2-dimensional mono-energetic fields allowed further validation of the beam model. Once the beam model matched for mono-energetic beams, we optimized more complex treatment fields and validated them against measurements in a water phantom. In preparation for LETd and biologically effective dose calculation, mixed radiation field spectra were calculated. Based on additional in vitro, in vivo and in silico biological studies, we selected an RBE model for the upcoming clinical trials using 4He.
Results: The MC model of the clinical helium beam reproduces the measured data within ~2% uncertainty for individual pencil beams. Measurements in water and behind an anthropomorphic head phantom yield physical dose values within 5% of the MC prediction for 2D fields and SOBPs. Biological studies with different cell lines and tissues advocate the selection of the modified microdosimetric model (mMKM) for RBE prediction in the clinical TPS.
Conclusion: Promising agreement between calculated and measured dose distribution was observed. Translation of the beam model into clinical practice with helium ion-beam therapy is justified with ongoing improvements.