Description
Background: Proton beam therapy is a treatment used against cancer. Compared to conventional photon beam treatment it has a superior dose distribution, resulting in the potential to reduce the damage to surrounding healthy tissue while achieving tumor control. While proton beams have steep distal dose falloffs, the lateral dose fall-off broadens at the end of the proton range, due to multiple Coulomb scattering (MCS). Moreover, protons have a higher biological effectiveness on tissue compared to photons. A constant relative biological effectiveness (RBE) factor of 1.1 is commonly assumed for clinical use, despite it being known that the RBE varies throughout the track of the proton beam.
Methods: In the first part, Monte Carlo simulations of proton beams were performed on a virtual water phantom with the FLUKA simulation package. We investigated the effects on the proton dose distribution when applying magnetic fields to reduce the diverging effect of MCS. The conventional pencil beam scanning technique that is clinically used was implemented as a reference. Different conditions in the water phantom were perturbed to also allow evaluation of potential effects on the RBE-weighted dose when the beam is modified by magnetic fields. The last part of the project will evaluate both beam delivery techniques on clinical cases of head and neck cancer patiens.
Results: The FLUKA setups for both the pencil beam scanning technique and the modified approach with magnetic fields have been successfully implemented, allowing investigations in the virtual water phantom. Preliminary results from the water phantom show that the proton beams in the magnetic fields have steeper lateral dose falloffs, and a higher peak dose delivered at the center of the longitudinal beam axis. This indicates that the modified approach with magnetic fields can reduce the diverging effect of MCS and further optimize the proton dose distribution as intended. This is an ongoing master project, where more results will be generated during the spring and presented at the meeting.
Conclusions: Although proton beam therapy is a very promising high-precision treatment modality of cancer patients, more detailed knowledge of the physical properties of proton delivery, may lead to further optimization of the treatment in the future. We demonstrate a new method of shaping the beam with magnetic fields to achieve steeper lateral dose penumbra resulting in more precise delivery of the proton dose. The initial results in this project are interesting and has generated ideas for further investigations.
