Monte Carlo simulations, in vitro and in vivo experimental verifications for preclinical studies

Cancer is a leading cause of death worldwide. Nowadays, various methods are employed to treat this disease, such as surgery, chemotherapy, brachytherapy and/or external beam radiotherapy, either separately but in most cases different modalities are combined. Glioblastoma Multiforme (GBM) is the most common primary brain tumor in adults with a patient’s mean survival rate ranging from 15 to 17 months. The standard therapy for GBM is maximal surgical resection followed by radiotherapy with concurrent and adjuvant temozolomide (TMZ) but, in spite of extensive treatment, clinical outcome remains unsatisfying. To improve the outcome of patients with GBM, alternative treatment modalities are still needed. For translational cancer research, pre-clinical in vivo studies using small animals have become indispensable in bridging the gap between in vitro cell experiments and clinical implementation. When setting up such small animal experiments, various biological, technical and methodical aspects have to be considered. Development and standardization of in vitro and in vivo models can increase the predictability of the antitumoral drug or radiation response and be used as a good tool for preclinical assessment of treatment modalities. The present thesis is focused on three aspects concerning preclinical research: - Pre-treatment evaluation of the dose distribution and LET within the target: phantom or small animals. This purpose has been fulfilled by developing a Monte Carlo GEANT4-based application reproducing the experimental setup used in preclinical in vivo experiment and implementing the target within the simulation framework through its DICOM micro-CT images. - The role of an innovative radiosensitizing molecule in Glioblastoma tumor protontherapy quantifying the variation in survival response and the dose modifying factor investigating also the gene expression modification induced during in vitro studies. In addition, the role of hypoxia in primary GBM cancer stem-like cells was investigated using two radiation qualities (X-ray and alpha particle beams). - Biological effectiveness along SOBP by means of in vivo experiments using skin deterministic damage as endpoint in mice. Nevertheless, further studies are necessary to assess and quantify the RBE variations along the Bragg peak. A complete long-term observational analysis placing the target at the end-part of a clinical SOBP has been accomplished. The structure of the thesis is divided as follows into 5 chapters: - Chapter 1 contains the description of radiation used in the medical physics field and the quantities, the methods and the tools used to quantify and measure it. A description of the main radiobiological quantities is also given, such as LET, RBE and oxygen enhancement ratio (OER). - Chapter 2 includes a survey on the state of the art in preclinical studies concerning radiation research applied to radiotherapy. A description of the preclinical collaboration in Catania and of the foreign research institute involved in this thesis is also provided. - Chapter 3 describes the development of the GEANT4-based application, the final aim of which is to simulate small animals pre-clinical protontherapy treatment. Simulations were performed importing the DICOM micro-CT images of phantoms in the GEANT4 framework and the dose results were validated by comparing them to experimental ones. - Chapter 4 describes in vitro studies about a new radiosensitizing molecule used in combination with proton beam in GBM tumor cases and about the characterization of primary GBM cancer stem-like cells response to radiations when they undergo hypoxia and normoxia conditions. - Chapter 5 describes the preclinical in vivo experiment performed at LNS-INFN. Specifically will be discussed: the treatment planning phase, using the GEANT4-based application described in Chapter 3, the experimental setup used for irradiations, the problems encountered and the results analysis about deterministic damage induced by proton beam irradiation in mice.