A very-low-cost dosimeter based on the off-the-shelf CD4007 MOSFET array for in vivo radiotherapy applications

• We present a low-cost, cable/battery-free MOSFET sensor for radiotherapy.
• We analyze methods to extract the key MOSFET dosimetric parameter (VT).
• We discuss fundamental aspects of building blocks of a MOSFET dosimeter.
• Reproducibility (2.6%) comparable to commercial MOSFET dosimeters (1.7%).
• Similar responses to radiation with commercial TLDs (S.D. around 2%).

PurposeThis paper presents a low-cost MOSFET dosimeter suitable for in vivo radiotherapy applications. We analyze different methods to extract the threshold voltage and how this extraction is affected by the dose dependence of slope factor and carrier mobility. Also, we discuss fundamental aspects of the basic building blocks of a MOSFET dosimeter, namely, the radiation sensor, the reader circuit and temperature desensitization.MethodsExperiments with ionizing radiation (6 MV X-ray beams) were carried out at the Centro de Pesquisas Oncológicas (CEPON) using linear accelerators to test the MOSFET dosimeter.ResultsThe main performance parameters of the dosimeter prototype are radiation sensitivity about 100 mV/Gy (sensor's sensitivity is around 6.7 mV/Gy), thermal dependence of 0.5 cGy/°C, reproducibility is about 2.6%, and radiation beam attenuation of 0.14%.ConclusionsThe MOSFET dosimeter described in this article, which combines a simple and accurate readout procedure with a small size, low-cost, cable/battery-free sensor and very little attenuation of the radiation beam is a very appealing option for in vivo dosimetry.