Assessment of a new p-MOSFET usable as a doserate insensitive gamma dose sensor

In this work, a low-power commercial MOS transistor was tested as a gamma radiation dosimeter. Due to the small size of its detector, low cost, reproducibility, minimal power requirements, signal conditioning and data processing, it offers excellent possibilities as a dose monitor in radiotherapy. Sensor irradiation in the unbiased mode was aimed at improving patient comfort and facilitating use. Uncertainties in the results were obtained from an exhaustive dosimetric study, following a full statistical study using Monte Carlo analysis techniques. A procedure to compensate for temperature effects was introduced in order to correct the dosimetric parameter extracted. Excellent linearity and good reproducibility were found in the accumulated threshold voltage shift as a function of the accumulated dose, up to 58 Gy (air equivalent). The uncertainty regarding sensor sensitivity was found to be less than 1% for individual device calibration. When collective calibration was carried out, the uncertainty was around 5%, accounting for a set of 31 devices. In this case, a mean value of 29.2 mV/Gy was obtained. In addition, the angular and dose rate dependencies showed good behaviour. These results suggest that the transistor studied would be an excellent candidate for use as the sensing device of a low-cost measurement system capable of in vivo dosimetry.

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“…A standard deviation of 1.0 mV/Gy was obtained for this dose rate range. This value is similar to that of previous studies [26].…”

Section: Dose Rate Dependencesupporting

confidence: 83%

Evaluation of a low-cost commercial mosfet as radiation dosimeter

Asensio¹,

Carvajal²,

López‐Villanueva³

et al. 2006

Sensors and Actuators A: Physical

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“…Another compensation method involves setting the drain current at the point where the effect of temperature fluctuations is expected to be minimal, that is, where the temperature coefficient is zero. This point is called the ZTC point and the current is denoted as I ZTC (O'Sullivan et al 1990, Buehler et al 1993, Vettese et al 1996, Tsividis 1999, Kimoto et al 2003. Another thermal compensation method is based on differential measurements of the source-drain voltage of two identical MOSFETs.…”

Section: Introductionmentioning

confidence: 99%

Thermal drift reduction with multiple bias current for MOSFET dosimeters

et al. 2011

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New thermal compensation methods suitable for p-channel MOSFET (pMOS) dosimeters with the usual dose readout procedure based on a constant drain current are presented. Measuring the source-drain voltage shifts for two or three different drain currents and knowing the value of the zero-temperature coefficient drain current, I(ZTC), the thermal drift of source-drain or threshold voltages can be significantly reduced. Analytical expressions for the thermal compensation have been theoretically deduced on the basis of a linear dependence on temperature of the parameters involved. The proposed thermal modelling has been experimentally proven. These methods have been applied to a group of ten commercial pMOS transistors (3N163). The thermal coefficients of the source-drain voltage and the threshold voltage were reduced from -3.0 mV °C(-1), in the worst case, down to -70 µV °C(-1). This means a thermal drift of -2.4 mGy °C(-1) for the dosimeter. When analysing the thermal drifts of all the studied transistors, in the temperature range from 19 to 36 °C, uncertainty was obtained in the threshold voltage due to a thermal drift of ±9 mGy (2 SD), a commonly acceptable value in most radiotherapy treatments. The procedures described herein provide thermal drift reduction comparable to that of other technological or numerical strategies, but can be used in a very simple and low-cost dosimetry sensor.

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“…The MOSFET itself is not significantly influenced by neutrons (Vettesse et al, 1996) and the response if any is mainly due to the interaction of neutrons with the packaging (Rosenfeld et al, 1995;Ravotti et al, 2005). However when covered with a converter it can be used as a neutron dosemeter (Kronenberg and Bruker, 1995;Lee et al, 2004;Price et al, 2004).…”

Section: Introductionmentioning

confidence: 98%