Advanced brain imaging in radiation-induced changes after novel radiotherapy techniques

 Radiotherapy is pivotal in treating primary and metastatic brain tumors. While new techniques like PBT decrease radiation to surrounding healthy brain tissue, they introduce challenges in interpreting post-treatment imaging. The overarching goal is to optimize clinical outcomes and reduce potential harms from these therapies, which, although advanced, present new challenges. Proton therapy provides some physical advantages over photon therapy, this leads to a high conformal dose distribution to target volume and a reduced dose to adjacent healthy tissue. These physical advantages have resulted in an increased use of proton therapy in brain tumors to improve clinical outcomes. Some studies show increased incidence radiation induced imaging changes after proton therapy for primary brain tumors. Imaging changes after proton therapy can lead to diagnostic uncertainty and misdiagnosis of progression. The first aim is to identify the incidence, clinical relevance and risk factors associated with the occurence of radiation induced injury. The second goal is to improve the diagnostic accuracy of radiation induced brain injury. Currently, the standard post-radiotherapy evaluation hinges on routine MRI techniques. However, the advent of advanced imaging modalities might hold the key to more accurately distinguishing between treatment-related effects and genuine tumor progression. The third main objective is to investigate the link between imaging changes and variable RBE. There is increasing in vitro and in vivo evidence of a radiobiological effectiveness of protons beyond the currently used factor of 1.1, particularly in the distal part of the Bragg peak, a region that may fall in healthy brain tissue. When the area of higher RBE is within the healthy tissue, unexpected toxicity might occur.