Interaction of therapeutic ¹²C ions with bone-like targets: physical characterization and dosimetric effect at material interfaces

Abstract

Carbon therapy is a promising treatment option for cancer. The physical and biological properties of carbon ions can theoretically allow for the delivery of curative doses to the tumor, while simultaneously limiting risks of toxicity to adjacent healthy structures. The treatment effectiveness can be further improved by decreasing the uncertainties stemming from several sources, including the modeling of tissue heterogeneity. Current treatment plans employ density-based conversion methods to translate patient-specific anatomy into a water system, where dose distribution is calculated. This approach neglects differences in nuclear interactions stemming from the elemental composition of each tissue. In this work, we investigated the interaction of therapeutic carbon ions with bone-like materials. The study concentrated on nuclear interactions and included attenuation curves of 200 and 400 AMeV beams in different types of bones, as well as kinetic energy spectra of all charged fragments produced up to 29 degrees from the beam direction. The comparison between measurements and calculations of the treatment planning system TRiP98 indicated that bone tissue causes less fragmentation of carbon ions than water. Overall, hydrogen and helium particles were found to be the most abundant species, while heavier fragments were mostly detected within 5 degrees from the beam direction. We also investigated how the presence of a soft tissue-bone interface could affect the depth-dose profile. The results revealed a dose spike in the transition region, that extended from the entry channel to the target volume. The findings of this work indicated that the tissue-to-water conversion method based only on density considerations can result in dose inaccuracies. Tissue heterogeneity regions containing bones can potentially produce dose spikes, whose magnitude will depend on the patient anatomy. Dose uncertainties can be decreased by modeling nuclear interactions directly in bones, without applying the tissue-to-water conversion.

Extension of matRad with a modified microdosimetric kinetic model for carbon ion treatment planning: Comparison with Monte Carlo calculation

“…To illustrate the difference in the trajectory of the ions, other options can be considered, such as the trichromic beam model, which uses different beam models for light and heavy ions; triple Gaussian parameterization; and the Gaussian-logistic beam model, which adds a logistic component to the double Gaussian. 29,53,56 Using the MKM-implemented matRad, the RBEweighted doses were calculated for a water phantom with various target sizes, which agreed within 2.0% when compared with MC recalculation. The agreement between TPS and MC dose calculation results was comparable to another published study, with an average difference of 2.5% observed across various depth targets.…”

“…In this study, the TOPAS MC simulation with double‐Gaussian fitting was used to generate beam data, as shown in Figures 4 and 5. To illustrate the difference in the trajectory of the ions, other options can be considered, such as the trichromic beam model, which uses different beam models for light and heavy ions; triple Gaussian parameterization; and the Gaussian‐logistic beam model, which adds a logistic component to the double Gaussian 29,53,56 …”