Purpose: A diamond-based detector is being developed to solve the limitation of online monitoring in the case of Microbeam Radiation Therapy (MRT), a synchrotron-based technique using a micro-beam matrix of low energy photons (100 keV range) at very high dose rates (kGy/s range).
Methods: To demonstrate the feasibility of using diamond materials for portal online monitoring in MRT, bulk diamond-based detectors (4.5x4.5 mm2 area) have been tested under a single 50x800 µm2 micro-beam with the same characteristics as MRT photons beam). Five repetitions of 2 s measurements were performed under a 4000 Gy/s photon flux to test the stability and repeatability of our detectors under those extreme conditions, and compare the quantitative response to simulations. As our detector will be used in a portal mode, measurements has been completed using absorbers of PMMA (0 to 47 cm thickness) to study the response of our detector as a function of the dose rate between 1 and 4000 Gy/s.
Results: The study of our detector response exhibits a maximum difference within a 2 s pulse better than 0.2 % and a maximum difference on pulse mean response of 0.1 %. The reproduction of the measurement after approximately 500 kGy irradiation also shows middle term stability better than 0.3 %.
Conclusion: This study shows the suitability of the diamond-based detector for the MRT portal beam monitoring. Linearity over a wide range of dose rates, allows us to measure micro-beam-irradiated and non-irradiated zones at the same time. These results lead us to proceed to the next stage. A multi-stripped diamond detector, read out with multi-channel analog charge digitizers, is being tested to perform each micro-beam and inter-beam flux measurement simultaneously. The first results will be presented.