A new detection system for microdosimetry has been developed and successfully tested at the Orsay Proton Therapy Center (CPO, France). It is based on novel silicon 3D-cylindrical microdetectors designed and manufactured at the Centro Nacional de Microelectrónica (IMB-CNM, CSIC) in Barcelona, Spain. The microdetectors have a cylindrical shape with a size comparable to that of the nuclei of human cells (20 µm-thick, 25 µm-diameter) and have been specifically customized for being used in particle therapy, overcoming some of the technological challenges in this domain, namely the low noise capability, well-defined sensitive volume, high spatial resolution and pile-up robustness. Likewise, the 3D-cylindrical architectures reduce loss of charge carriers due to trapping effects, charge collection time, and voltage for full depletion when compared to planar silicon detectors.
The new detection system includes two 2D-arrays of 121 independent microdosimeters, two multichannel readout chips, and a customized data acquisition system. The real-time data analysis during the irradiations is possible by means of an in-house developed software. This detection system and the new software allow us to register the information of each individual dosimeter and obtain, in situ, all microdosimetric quantities relevant for proton therapy, such as the lineal energy (y), and the associated probability density functions, such as f(y) or d(y).
During the first tests, an 11 $\times$ 11 array has been irradiated at the CPO under clinical-like conditions. We present here the results of the performed microdosimetric measurements and the first 2D lineal-energy maps ever obtained. Hence, this microdosimetry system can have a positive impact in clinical treatments by allowing for further relative biological effectiveness (RBE) calculations under clinical conditions and, therefore, reducing the radiobiological uncertainties in healthy tissue surrounding the target.