Investigating volumetric repainting technique in pencil beam scanning proton therapy

The fundamental goal of radiotherapy is to maximize the radiation dose to enhance the tumor control while minimizing dose to the normal tissues. Proton radiotherapy for clinical use has increased in the last decade. Currently, the use of pencil beam scanning (PBS) proton therapy technology for the treatment of various cancers is gaining popularity. The potential challenge of clinical utilization of PBS proton therapy occurs in the case of mobile tumors such as lung. The mitigation of interplay effect in PBS proton therapy is critical to maintain a higher local control. Volumetric repainting is considered as one of the tumor motion management techniques in PBS proton treatment. Volumetric repainting is accomplished by scanning the entire target volume repeatedly. This thesis examines the application of volumetric repainting in PBS proton therapy, with a particular emphasis on the alternating order repainting technique. The experiments were carried out on an IBA ProteusPLUS PBS proton system operating in a magnetic field regulation mode. The “magnetic field regulation” mode on an IBA ProteusPLUS PBS proton system is capable of delivering a proton beam from the distal end to proximal end and vice-versa, with a faster energy layer switching. There is a lack of published scientific guidelines on the implementation of such commercially available advanced technology in a clinical setting. This thesis work is primarily focused on investigating the feasibility of clinical implementation of volumetric repainting technique in an alternating order to treat lung tumors in PBS proton therapy. Specifically, this thesis work provides the experimental results for a PBS proton beam model as well as addresses the interplay effect, proton dose calculation algorithms, spot size and position errors, treatment plan robustness, radiobiological analysis, and dose-averaged linear energy transfer (LETd) distributions in PBS proton lung cancer patients