Response of a Commercial MOSFET to Clinical Photon and Electron Beams Used in Radiotherapy

Luiz Flavio Kalil Telles; L. M. Maria; Divanízia N. Souza; Luiz Antonio Pereira dos; Clayton Augusto Benevides

doi:10.15392/2319-0612.2026.2995

Authors

Luiz Flavio Kalil Telles National Nuclear Energy Commission
L. M. Maria Hospital Chama
Divanízia N. Souza Federal University of Sergipe
Luiz Antonio Pereira dos Santos National Nuclear Energy Commission
Clayton Augusto Benevides National Nuclear Energy Commission

DOI:

https://doi.org/10.15392/2319-0612.2026.2995

Keywords:

Dosimetry, beam-on drain current, calibration beam, linear accelerator

Abstract

One type of dosimeter used in radiotherapy is the metal-oxide-semiconductor field-effect transistor (MOSFET), which is widely employed in in vivo dosimetry. This study investigated the response of a commercial MOSFET (STQ2HNK60ZR-AP) to photon and electron beams from a clinical linear accelerator. Radiation damage is typically associated with the dose received by the device and is reflected in shifts in the transistor’s characteristic curve. In this work, however, a different approach was taken: the evaluated response was the beam-on drain current (I_D), integrated during beam exposure. The I_D under irradiation (I_DX) was obtained by subtracting the I_D measured without radiation, making the MOSFET functionally similar to an ionization chamber or diode detector. The transistor was placed between solid water plates in a 10 × 10 cm² radiation field, with a source-to-surface distance of 100 cm. I_DX was found to be directly proportional to the beam dose rate, and the collected charge showed minimal dependence on the dose rate (<3%). A Farmer ionization chamber was used as the reference detector. The MOSFET’s response was linear with dose, and the energy dependence for photon beams was approximately 7% between 15 MV and 6 MV. The calibration factor varied by around 6% across different energies and beam types. These results highlight the need for correction factors when using a beam other than the calibration beam to meet the uncertainty threshold recommended by the International Commission on Radiation Units and Measurements for radiotherapy (±5%). The findings are consistent with previously published results and support the suitability of the MOSFET for dosimetry of photon beams from clinical linear accelerators. Future work will focus on evaluating clinical dosimetry parameters, including percentage depth dose, output factor, and beam profile.

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Author Biography

Luiz Flavio Kalil Telles, National Nuclear Energy Commission

Física médico.

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