Investigation of mixed ion fields in the forward direction for 220.5 MeV/u helium ion beams: comparison between water and PMMA targets

Abstract

Currently there is a rising interest in helium ion beams for radiotherapy. For benchmarking of the physical beam models used in treatment planning, there is a need for experimental data on the composition and spatial distribution of mixed ion fields. Of particular interest are the attenuation of the primary helium ion fluence and the build-up of secondary hydrogen ions due to nuclear interactions. The aim of this work was to provide such data with an enhanced precision. Moreover, the validity and limits of the mixed ion field equivalence between water and PMMA targets were investigated. Experiments with a 220.5 MeV/u helium ion pencil beam were performed at the Heidelberg Ion-Beam Therapy Center in Germany. The compact detection system used for ion tracking and identification was solely based on Timepix position-sensitive semiconductor detectors. In comparison to standard techniques, this system is two orders of magnitude smaller, and provides higher precision and flexibility. The numbers of outgoing helium and hydrogen ions per primary helium ion as well as the lateral particle distributions were quantitatively investigated in the forward direction behind water and PMMA targets with 5.2-18 cm water equivalent thickness (WET). Comparing water and PMMA targets with the same WET, we found that significant differences in the amount of outgoing helium and hydrogen ions and in the lateral particle distributions arise for target thicknesses above 10 cm WET. The experimental results concerning hydrogen ions emerging from the targets were reproduced reasonably well by Monte Carlo simulations using the FLUKA code. Concerning the amount of outgoing helium ions, significant differences of 3-15% were found between experiments and simulations. We conclude that if PMMA is used in place of water in dosimetry, differences in the dose distributions could arise close to the edges of the field, in particular for deep seated targets.

Measurement of He4 charge- and mass-changing cross sections on H, C, O, and Si targets in the energy range 70–220 MeV/u for radiation transport calculations in ion-beam therapy

“…We therefore decided to complement previous 4 He fragmentation studies related to radiotherapy [22][23][24][25] and to further support the nuclear reaction modeling for 4 He ions in FLUKA by extending our previous experiment to a broader set of target materials. Thin C, CH 2 , Si, SiO 2 , and H 2 O targets were irradiated with 4 He ions in the intermediate energy range during this new measurement campaign at HIT.…”

Extension of RBE-weighted 4D particle dose calculation for non-periodic motion

“…The physical dose distribution was calculated and compared to the measurement of the IC array detector in a water equivalent depth of 13.3 mm. This is the sum of the water equivalent thicknesses of the PMMA holder (WEPL = 1.15 [43]) and the reference point of the PTW Octavius 1500XDR.…”

Challenges in Monte Carlo Simulations as Clinical and Research Tool in Particle Therapy: A Review

“…Of these measurements, the cross section measurements by Schall [111], Heattner [112,113], and Golvschenko [114,115] are most suitable for benchmarking MC codes at particle therapy energies, and these data were used for benchmarking FLUKA [63], GEANT4 [63], PHITS [116], and SHIELD-HIT [55,56]. Examples of studies aimed at studying emission angles and fragment yields were performed for PHITS [117], FLUKA [118], and GEANT4 [119], allowing for additional improvements in these codes. A recent experimental work of Aricò et al [120] points out that there are differences in secondary fragment production between water and PMMA targets.…”