Novel Epitaxial Silicon Array for Quality Assurance in Radiation Therapy

Purpose/Objective(s): During the last decade silicon dosimeters have found a wide application in radiation therapy due to the dose escalation in the tumor volume which demands accurate quality assurance programs. Silicon devices offer higher spatial resolution and higher performances than other commercial dosimeters like ion chambers, which suffer of limited spatial resolution, and gafchromic films, which are not real time detectors. In this article a novel epitaxial silicon array is described to demonstrate its suitability for measuring the dose properties of photon beams used in stereotactic treatments, Intensity Modulated (IMRT), and Volumetric Modulated Arc Therapy (VMAT) . Materials/Methods: The linear array prototype studied in this work is based on a 64-pixels monolithic silicon sensor made of epitaxial p-type silicon. Array length and pitch are 64mm and 1mm respectively. Sensor design is modular, and more sensors can be placed side by side without breaking pixel pitch. The prototype has four sensors mounted on a printed circuit board and connected to an electrometer based on TERA06 chips. All the pixels of the two central modules are connected to readout electronics. Due to the limited number of readout channels of this prototype (180), only 26 channels have been selected from each external module, with 2mm pitch. A full dosimetric characterization of the detector was performed and the application of the device in the dosimetric verification of clinical plans were verified. Results: Accurate measurements of the dose characteristics of beams as percentage depth doses, beam profiles, output factors and energy response, which are necessary to deliver radiation with high precision and in a trusted manner, were performed. Dose rate independence was verified irradiating the device with flattened and unflattened beams, varying dose per pulse in the range 0.03-2mGy. Results clearly indicate non-dependence of the detector sensitivity on the dose rate in all explored ranges both for flattened and unflattened beams with a variation of at most 0.5%. OFs were obtained for field with a lateral size ranging from 0.8cm to 16cm and the results are in good agreement with ion chamber A1SL (max difference < 1.5%) Field sizes and beam’s penumbra were measured and compared to those of EBT film. Eventually measured dose’s profile were compared with ones predicted by Pinnacle and Monaco TPS showing an excellent characterization of high modulated profiles. Conclusions: The device is a novel and valuable tool for QA in IMRT, VMAT, and especially for stereotactic dose delivery. In fact, all measurements demonstrated the device’s capability to measure with high spatial resolution many crucial properties of the RT beams. Moreover they show the high temporal resolution capability of the detector readout system, which allows to investigate the temporal dose pattern of IMRT and VMAT deliveries. Author Disclosure: C. Talamonti: None. M. Zani: None. D. Menichelli: None. F. Friedl: None. M. Scaringella: None. M. Bruzzi: None. M. Bucciolini: None.