Geant4 simulation of a particle range telescope used as calorimeter at MedAustron

Abstract

Ion beam therapy with its advantageous property to selectively irradiate tu-mours, while sparing healthy tissue, has become an increasingly used method forcancer treatment in many facilities around the globe. For accurate dose delivery,the computer-assisted treatment planning process is an essential part requiringappropriate imaging of the tumour region and the surrounding structures.The current standard in radiation therapy is the use of computed tomography(CT) images with photons by means of Hounsfield units (HUs), which is essen-tially a normalisation of linear attenuation coefficients to the one of water. Inconventional radiation therapy with photons, the acquired HUs have to be trans-lated into electron densities, which can be done with high accuracy. In ion beamtherapy, however, stopping power values (energy deposition per unit length) ofprotons and heavier ions are required and currently have to be determined fromHUs obtained from photon based CT imaging. Due to the different interactionmechanisms for photons and protons, this procedure entails range uncertainties,resulting in unwanted dose deposition outside of the tumour region, since largermargins around the tumour are necessary to account for this uncertainty.Imaging with protons can overcome these uncertainties. It is based on thedetermination of the particle’s entry and exit points using a tracking telescopeand its residual energy with a calorimeter. From these data, and an estimateof the most likely proton path in the object, the required stopping power forthe treatment planning can be obtained. By directly measuring the stoppingpower with the same particle as used in therapy, safety margins resulting fromrange uncertainties can be reduced, thus leading to less deposited dose in healthytissue.The objective of this master thesis will be to establish a Geant4 model of anavailable range telescope, which is planned to be used as calorimeter in upcomingbeam times for the ongoing effort to establish proton computed tomography1(pCT) at MedAustron. This range telescope consists of one part for stoppingthe ions with 48 individually read out plastic scintillator plates with ≈ 3 mmthickness. Additionally, a gas electron multiplier (GEM) part is used to obtainspatial and angular information of ions entering the range telescope.The simulated data will be analysed using the ROOT framework and theobtained results will be used for planning first measurements with the rangetelescope in the MedAustron proton beam later this year. If the planned testmeasurements can be performed during the course of this work, then the simu-lated data will be compared to measured data.