Monte Carlo simulations of Linear Energy Transfer distributions in radiation therapy

Sammanfattning: In radiotherapy, a quantity asked for by clinics when calculating a treatment plan, along withdose, is linear energy transfer. Linear energy transfer is defined as the absorbed energy intissue per particle track length and has been shown to increase with relative biologicaleffectiveness untill the overkilling effect. In this master thesis the dose averaged linear energytransfer from proton and carbon ion beams was simulated using the FLUKA multi purposeMonte Carlo code. The simulated distributions have been compared to algorithms fromRaySearch Laboratories AB in order to investigate the agreement between the computationmethods. For the proton computation algorithm improvements to the current scoring algorithmwere also implemented. A first version of the linear energy transfer validation code was alsoconstructed. Scoring of linear energy transfer in the RaySearch algorithm was done with theproton Monte Carlo dose engine and the carbon pencil beam dose engine. The results indicatedthat the dose averaged linear energy transfer from RaySearch Laboratories agreed well for lowenergies for both proton and carbon beams. For higher energies shape differences were notedwhen using both a small and large field size. The protons, the RaySearch algorithm initiallyoverestimates the linear energy transfer which could result from fluence differences in FLUKAcompared to the RaySearch algorithm. For carbon ions, the difference could stem from someloss of information in the tables used to calculate the linear energy transfer in the RaySearchalgorithm. From validation γ-tests the proton linear energy transfer passed for (3%/3mm) and(1%/1mm) with no voxels out of tolerance. γ-tests for the carbon linear energy transfer passedwith no voxels out of tolerance for (5%/5mm) and a fail rate of 2.92% for (3%/3mm).