General purpose MOSFETs for the dosimetry of electron beams used in intra-operative radiotherapy

The experimental response of different commercial metal-oxide-semiconductor transistors to electron beams in order to check their capabilities as radiation sensors for intra-operative radiotherapy treatments is studied. The main characteristics of the radiation response, such as sensitivity and reproducibility, have been determined using measuring algorithms previously developed by our research group for photon beams and which allow, among other advantages, the thermal compensation of the devices. Reproducing typical intra-operative radiotherapy treatment sessions, several vertical and lateral p-channel transistors in different configurations (single and two stacked transistors, unbiased and biased during irradiation) have been studied. Non zero temperature coefficients are presented in the analyzed vertical transistors (BS250F, ZVP3306 and ZVP4525) and their responses show a linear behaviour with a low dispersion in the results obtained for all the studied devices. Though all of them appear to be reliable for electron dosimetry, the best candidates are the transistors included in the well known integrated circuit CD4007, due to its higher sensitivity and better thermal compensation. In this case, a sensitivity of 13 ± 1 mV/Gy to 6 MeV electron beams has been measured with two stacked devices in biased mode. Linearity and uncertainty are comparable to that of commercial dosimetry sensors, while sensitivity is smaller.