Room: AAPM ePoster Library
Purpose: To analyzed the linearity, dose rate dependence and percent depth dose response of an active matrix pixel, data acquisition (DAQ) and microcontroller system for radiation dose readout.
Methods: A low cost active matrix (AM) pixel, DAQ and microcontroller system were designed and constructed for dosimetric measurements. The AM pixel consisted of a BPW34S photodiode, a 1 µF storage capacitor and a NX7002AK MOSFET. The DAQ comprised an integrator, filter and amplifier while the microcontroller was a commercially available unit. A 6 MV x-ray beam irradiated the AM pixel to doses of 50, 100, 150, 200 and 250 MU for the linearity tests and, dose rates of 200, 300, 400, 500 and 600 MU/min for the dose rate tests. PDD data was collected at AM pixel depths of 1.6, 2, 10, 15 and 20 cm in water and were compared to MC simulations and linac commissioned water PDD data. Linearity and dose rate tests were performed using readout collection times of 0.25 s, 1 s and 2 s to determine the system’s dependence on this parameter.
Results: Linearity and dose rate measurements showed a percent difference of = 2% for collection times of 0.25-2 s. Response improved when the collection time was 0.25 s. Shorter collection times were prevented by the DAQ speed. Measured PDD data showed a maximum difference of 2.2% compared to the commissioned data and 2.4% compared to the MC data, both at 1.6 cm depth.
Conclusion: These results demonstrate that a radiotherapy readout system based on an active matrix design can provide accurate dosimetric data. Moreover, the dosimetric data could be further improved with a higher speed DAQ unit that can allow for a shorter (< 0.25 s) data collection time.
Funding Support, Disclosures, and Conflict of Interest: Financial support for this project was provided by HRS Oncology International and the Universidad Nacional de Ingenieria in Lima, Peru.