Search

Highlights: [•] Experimental response of commercial metal-oxide-semiconductor transistors to electron beams for IORT is studied. [•] Sensitivity, linearity and reproducibility have been determined. [•] Vertical and lateral p-channel transistors in different configurations have been studied. [•] CD4007 with two stacked devices in biased mode is the best candidate as dosimeter. [Copyright &y& Elsevier]

This work presents a dosimetry system based on MOSFET sensors for real-time dose monitoring. MOS transistors were biased during irradiation, and the response of lateral, general-purpose 3N163 and CD4007 transistors were characterized with a 15-MV photon beam provided by a linear accelerator. The electronic circuitry to condition the sensor output and the measurement algorithm are described in depth. Due to the real-time measurement mode, the dosimetric parameter (the source voltage) showed drift. This drift depends on the bias voltage applied between the gate and the bulk terminals alternately during irradiation and readout. It can be minimized by applying a 1-V bias voltage for the 3N163 transistor and 0.85 V for the CD4007 during readout. The CD4007 transistor showed an average sensitivity of (7.8 ± 0.4) mV/Gy and the 3N163 an average of (26.4 ± 0.8) mV/Gy. The low uncertainty and acceptable sensitivity yields a resolution of 0.8 and 1.5 cGy for the CD4007 and 3N163 transistors respectively for unirradiated devices, which increases to 3 cGy and 2 cGy after 16 Gy of cumulative dose, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A study of the degradation of the subthreshold swing in a general-purpose pMOSFET is carried out to evaluate its use as a dosimetric parameter. Its reliability in terms of sensitivity, linearity, and reproducibility is experimentally tested and compared with the threshold voltage shift under gamma rays from a 60Co source up to 56Gy, typical in radiotherapy treatments. The dependence of the subthreshold swing as a function of temperature is characterized and modelled as a mean for thermal compensation when used for dose measurement. Very promising results have been obtained for the subthreshold swing as a complementary dosimetric parameter to the threshold voltage for enhancing the confidence of dose verification systems based on MOSFETs. [Copyright &y& Elsevier]

Abstract: A compact and low-cost dosimetry system based on MOSFET for in vivo radiotherapy has been developed and characterized. This electronic system consists of a wireless sensor module containing a general-purpose MOSFET and a microcontrolled reader unit. Various methods, developed in previous works, to extend the linear range and reduce noise and thermal drift have been implemented and tested in the present system. A complete dose response characterization of the system has been carried out, including thermal drift, fading effect, linear range, sensitivity, and angular dependence for a 60Co source and for 6MV and 18MV photon beams provided by a linear accelerator. As a result, a procedure to use the system has been built, including the recalibration conditions to enhance the dosimeter life. The system provides suitable values for monitoring in vivo radiotherapy treatments in a reliable way. Although the present system has specifications that are comparable to those of some available commercial dosimetry systems, also based on MOSFET, the sensors here considered have a larger range of use. [Copyright &y& Elsevier]