Characterisation of a Synthetic Diamond Detector for Experimental Dosimetry in MRT

International audienceMicrobeam radiation therapy (MRT) is a preclinical treatment under development on the Imaging and Medical Beamline (IMBL), Australian Synchrotron. It uses spatially fractionated x-ray microbeams with a width of 50 μm and 400 μm pitch. The x-ray beam, which has a mean energy of approximately 100 keV in the treatment enclosure, is generated by a wiggler source and collimated by a tungsten multislit collimator. Preclinical studies on other synchrotron beamlines have previously demonstrated preferential tumour damage and sparing of surrounding normal tissue [1-3]. A synchrotron source is necessary to produce the high dose rates, high dose gradients and minimal beam divergence required for MRT to maintain a highly collimated, spatially fractionated array of microbeams. The ratio between the dose in the microbeams and the dose between the microbeams, known as the peak-tovalley dose ratio (PVDR) is thought to be of therapeutic importance, with the valley dose believed to be a primary factor influencing the normal tissue tolerance [3]. It is thus important to be able to perform absolute dosimetry and accurately measure the PVDR.Dosimetry for MRT is challenging due to the inherent beam properties of MRT. Small field sizes and large dose gradients can produce large uncertainties caused largely by the partial volume effect. Additionally, a number of dosimeters exhibit energy dependence for keV x-rays and ionrecombination effects at high dose rates. The PTW microDiamond detector has been identified as a potential MRT dosimeter due to its small 2.2 mm × 1 μm cylindrical sensitive volume. The purpose of the study was to characterise the microDiamond detector in broadbeam and microbeams to determine its suitability for MRT dosimetry. The energy dependence has been investigated and characterised and the dose rate dependence was found to be minimal over the dose range 1—600 Gy. Preliminary measurements of microbeam profiles and PVDR were also promising. Measurements will be repeated using the recently commissioned dedicated MRT system to optimise the procedure with a view towards developing an absolute dosimetry protocol. Results will be discussed in the presentation.References[1] – J. A. Laissue, et al., Int. J. Cancer, 78, 654—660 (1998).[2] – A. Bouchet, et al., Int, J. Radiat. Oncol.Biol. Phys.78, 1503—1512 (2010).[3] – R. Serduc, et al. Phys. Med. Biol., 53, 3609—3622 (2008)