Dosimetry of microbeam radiotherapy by flexible hydrogenated amorphous silicon detectors.

Detectors that can provide accurate dosimetry for microbeam radiation therapy (MRT) must possess intrinsic radiation hardness, a high dynamic range, and a micron-scale spatial resolution. In this work we characterize hydrogenated amorphous silicon detectors for MRT dosimetry, presenting a novel combination of flexible, ultra-thin and radiation-hard features. Two detectors are explored: an n-i-p planar diode (NIP) and an NIP with an additional charge selective layer (NIP+CSC). The sensitivity of the NIP+CSC detector was greater than the NIP detector for all measurement conditions. At 1 V and 0 kGy under the 3T Cu-Cu synchrotron broadbeam, the NIP+CSC detector sensitivity of (7.76 ± 0.01) pC/cGy outperformed the NIP detector sensitivity of (3.55 ± 0.23) pC/cGy by 219 %. The energy dependence of both detectors matches closely to the attenuation coefficient ratio of Silicon against Water. Radiation damage measurements of both detectors out to 40 kGy revealed a higher radiation tolerance in the NIP detector compared to the NIP+CSC (17.2 % and 33.5 % degradations, respectively). Percentage depth dose profiles matched the PTW microDiamond detector's performance to within ± 6 % for all beam filtrations except in 3T Al-Al due to energy dependence. The microbeam field profile was reconstructed with a high spatial resolution, returning microbeam widths and peak-to-peak distances of (51 ± 1) µm and (405 ± 5) µm, respectively. The peak-to-valley dose ratio was measured as a function of depth and agrees within error to the values obtained with the PTW microDiamond. X-ray beam induced charge mapping of the detector revealed minimal dose perturbations from extra-cameral materials. The detectors are comparable to commercially available dosimeters for quality assurance in MRT. With added benefits of being micron-sized and possessing a flexible water-equivalent substrate, these detectors are attractive candidates for quality assurance, in-vivo dosimetry and in-line beam monitoring for MRT and FLASH therapy. &#xD.

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