Abstract
To start clinical trials with the first clinical treatment planning system supporting raster-scanned helium ion therapy, a comprehensive database of beam characteristics and parameters was required for treatment room-specific beam physics modeling at the Heidelberg Ion-Beam Therapy Center (HIT). At six different positions in the air gap along the beam axis, lateral beam profiles were systematically measured for 14 initial beam energies covering the full range of available energies at HIT. The 2D-array of liquid-filled ionization chambers OCTAVIUS from PTW was irradiated by a pencil beam focused at the central axis. With a full geometric representation of HIT’s monitoring chambers and beamline elements in FLUKA, our Monte Carlo beam model matches the measured lateral beam profiles. A second set of measurements with the detector placed in a water tank was used to validate the adjustments of the initial beam parameters assumed in the FLUKA simulation. With a deviation between simulated and measured profiles below ±0.8 mm for all investigated beam energies, the simulated profiles build part of the database for the first clinical treatment planning system for helium ions. The evolution of beamwidth was also compared to similar simulations of the clinically available proton and carbon beam. This allows a choice of treatment modality based on quantitative estimates of the physical beam properties. Finally, we investigated the influence of beamwidth variation on patient treatment plans in order to estimate the relevance and necessary precision limits for lateral beam width models.
Highlights
Lyman and Howard measured the first helium Bragg peaks to use in radiotherapy in the 1970s [1]
The standard deviation of the scaled measured full width at half maximum (FWHM) extracted from the four measured lateral profiles is approximately 0.2 mm or 2% for each position and energy
Our accurate simulation and measurement of beam profiles in air along the beam path led to a more precise TPS beam model which has been applied for the first patient irradiation with helium ions at Heidelberg Ion-Beam Therapy Center (HIT)
Summary
Lyman and Howard measured the first helium Bragg peaks to use in radiotherapy in the 1970s [1]. Between 1975 and 1992, over 2000 patients received helium ion radiotherapy at the Lawrence Berkeley National Laboratory (LBNL) [2,3,4,5,6]. At the Heidelberg Ion-Beam Therapy Center (HIT), protons, helium, carbon, and oxygen ions are accelerated and delivered with active beam scanning [7] for radiotherapeutic and research purposes since 2009. To this day, only protons and carbon ions are in regular clinical use. With the work presented in this study the first clinical application of helium ion beams was possible this year
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