Abstract
Modern facilities for actively scanned ion beam radiotherapy allow in principle the use of helium beams, which could present specific advantages, especially for pediatric tumors. In order to assess the potential use of these beams for radiotherapy, i.e., to create realistic treatment plans, the authors set up a dedicated (4)He beam model, providing base data for their treatment planning system TRiP98, and they have reported that in this work together with its physical and biological validations. A semiempirical beam model for the physical depth dose deposition and the production of nuclear fragments was developed and introduced in TRiP98. For the biological effect calculations the last version of the local effect model was used. The model predictions were experimentally verified at the HIT facility. The primary beam attenuation and the characteristics of secondary charged particles at various depth in water were investigated using (4)He ion beams of 200 MeV/u. The nuclear charge of secondary fragments was identified using a ΔE/E telescope. 3D absorbed dose distributions were measured with pin point ionization chambers and the biological dosimetry experiments were realized irradiating a Chinese hamster ovary cells stack arranged in an extended target. The few experimental data available on basic physical processes are reproduced by their beam model. The experimental verification of absorbed dose distributions in extended target volumes yields an overall agreement, with a slight underestimation of the lateral spread. Cell survival along a 4 cm extended target is reproduced with remarkable accuracy. The authors presented a simple simulation model for therapeutical (4)He beams which they introduced in TRiP98, and which is validated experimentally by means of physical and biological dosimetries. Thus, it is now possible to perform detailed treatment planning studies with (4)He beams, either exclusively or in combination with other ion modalities.
Highlights
Radiotherapy with heavy charged particles is an established option for the treatment of certain kinds of tumors
A beam model for a Treatment Planning System (TPS) has to be created and verified, which is the intention of this paper. It is outlined as follow: in material and methods we shortly introduce our treatment planning system, TRiP98, we describe the experimental equipment used for verification and report on the newly developed pragmatic beam model for therapeutic 4He ions
The natural choice is the well established TRiP98,6–8 developed in-house for clinical use during the carbon ion pilot project at GSI.[9]. It served as a prototype for the commercial Siemens SynGo PT planning system, which is currently in use at various ion beam radiotherapy sites [Heidelberger Ionenstrahl-Therapiezentrum (HIT), CNAO, Shanghai, MIT (Marburg, Germany)]
Summary
Radiotherapy with heavy charged particles is an established option for the treatment of certain kinds of tumors. Most heavy charged particle treatments are nowadays performed with protons and carbon ions (Table I). Whereas the usage of pions certainly is history, there is growing interest, for example, in fast helium ion beams. To some extent, they fill the gap between protons and carbon ions. From the radiobiological point of view, their Relative Biological Effectiveness (RBE) is closer to protons, though not negligible, but certainly lower than that of carbon ions. This might be beneficial in certain treatment situations, for example, for pediatric patients
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