Evaluation of Performance of Metal Oxide-silicon Semiconductor Field Effect Transistor (MOSFET) Dosimeter

  • NAGASHIMA HIROYUKI
    Department of Radiology, Yamanashi Medical University Hospital
  • SANO NAOKI
    Department of Radiology, Yamanashi Medical University Hospital
  • NAKAMURA OSAMU
    Department of Clinical Radiology, Faculty of Health Sciences, Hiroshima International Universlty

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Other Title
  • MOS型電界効果トランジスタ線量計の性能評価

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Abstract

The JARP level dosimeter is the most suitable for absorbed dose determination in radiotherapy because of its high accuracy. However, in measuring the dose of an extremely small field, a dosimeter with a smaller active region is required. The active region of the MOSFET dosimeter is very small, having a volume of just 0.02mm^3. In this study, we evaluated the performance of MOSFET dosimeters with two different sensitivities and examined the usefulness of the MOSFET dosimeter in stereotactic radiosurgery. Using the high-sensitivity MOSFET dosimeter, we were able to reduce the experimental error of absorbed dose (<±1.8%), and, by correcting the sensitivity, we could use it as a field dosimeter. By turning detectors inside out, we could reduce directional dependence (<±1.8%). Correction was necessary in the TMR determination because peak depth shifts according to the material of the detector. In the determination of the dose distribution in the penumbra, the resolution of the MOSFET detectors was equal to that of the diamond detector. In the determination of OPF for the extremely small field, better results were obtained with MOSFET than with other small detectors. The high-sensitivity MOSFET dosimeter could properly evaluate the dose of an extremely small field and will be useful in dosimetry of the maximum dose of the field center in stereotactic radiosurgery.

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