Brain tumors and synchrotron radiation: new methods for mini-beams radiation therapy and treatment follow-up by functional imaging

An innovative method of synchrotron radiation therapy, called mini-beams, was proposed by A. Dilmanian et al. in 2006. Mini-beams consists in tumor irradiation with monochromatic sub-millimetric x-ray beams spatially fractionated produced by a synchrotron source. To obtain a homogeneous dose in the target volume, an interleaving is realized using two orthogonal incidences. Adjacent healthy tissue is only partially irradiated by mini-beams, the areas between the beams only receive scattered radiation and therefore the energy deposited is 10 to 15 times lower than on one mini-beam axis, leading to a sparing effect of healthy tissue even when a high dose is deposited in the target volume. The thesis project is the development of this experimental method of monochromatic mini-beams, which involves the control of the irradiation geometry, the control of dosimetry and its modeling by Monte Carlo simulations. To evaluate the method, preclinical experiments on models of brain tumors implanted in rats (F98) are performed. Follow-up by anatomical and functional imaging is carried out to evaluate the effectiveness of the treatment. Functional imaging of cerebral perfusion (volume and cerebral blood flow, mean transit time of heavy elements) appears to be associated in the literature as a relevant method for monitoring prognostic. The key parameters of the cerebral vasculature are mainly studied in magnetic resonance imaging (MRI), because of the harmlessness of this imaging modality. The relation between MRI signal and contrast agent concentration is very complex and no quantitative relationship is well known. Synchrotron Radiation Computed Tomography (SRCT) is an imaging modality with performances to measure absolute contrast agent concentration very close to the theoretical limits and can be used as gold-standard. The used pharmacokinetic models need as input parameters a contrast agent concentration versus time. A comparison of perfusion measurements between MRI and SRCT has been done in order to calibrate MRI measurements. (author)