| dc.description.abstract | Background and aim: Proton therapy has the potential to deliver dose in a more precise way than traditional photon therapy, which allows for increased sparing of organs at risk (OAR). The aim of this thesis is to determine the potential to increase the biological dose to the biologic target volume (BTV) through biological optimization using proton therapy in the most precise and effective way and simultaneously spare the OARs, as well as to explore the use of imaging to adapt target dose and to ensure tumor control, through testing and exploring an optimization tool developed at the University of Bergen.
Material and methods: Intensity modulated proton therapy treatment plans for a water phantom and head and neck cancer (HNC) patients were created in Eclipse Treatment Planning System. The plans were optimized in a FLUKA based optimization tool developed at the University of Bergen. The water phantom was linear energy transfer (LET) optimized, and the BTV was subject to a 1.1 relative biological effectiveness (RBE) weighted dose escalation as well as LET escalation, while the dose and LET of the OAR was minimized. Furthermore, a method for RBE and oxygen enhancement ratio (OER) weighted dose optimization was implemented in the optimization tool. Subsequently, the water phantom was RBE and OER weighted dose (ROWD) optimized to achieve a homogeneous ROWD over the clinical target volume and the BTV. The ROWD optimization was performed with different values of oxygen pressure level of the BTV to investigate the effect of hypoxia with the optimization tool. Various optimization strategies were investigated, and the most promising ROWD optimization strategies were applied on 5 HNC patient plans.
Results: The dose-averaged LET (LETd) of the BTV increased and the LETd of the OAR decreased simultaneously, without significant changes in the dose of the structures when considering LETd optimization of the water phantom. A homogeneous ROWD of the BTVs was achieved successfully for both the water phantom and the patient plans, and the level of oxygen in the BTVs did not have a noteworthy effect on the dose or LETd of the OARs.
Conclusion: The optimization of biological dose with the optimization tool was successful for both LETd and ROWD optimization. The OARs were successfully spared in the optimizations. The results contribute to the idea of biological optimization being a promising technique in proton therapy which could significantly improve treatment as more precise techniques to quantify pO2 emerge. | |
