Energy dependence corrections to MOSFET dosimetric sensitivity

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Semiconductor Devices

Background:

• Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) are widely used as dosimeters in radiotherapy.
• Clinical Semiconductor Dosimetry Systems (CSDS) utilize improved MOSFET packaging for enhanced performance.

Purpose of the Study:

• To investigate the energy dependence of MOSFET sensitivity to X-ray radiation.
• To evaluate the impact of integrated dose history on MOSFET detector sensitivity.
• To assess the feasibility of correcting for sensitivity variations for accurate dose assessment.

Main Methods:

• Studied MOSFET sensitivity to X-ray radiation across a range of energies (50 kVp to 10 MV).
• Analyzed detector lifespan in relation to radiation energy.
• Investigated sensitivity changes with accumulated radiation dose.
• Developed a polynomial function to model and correct for sensitivity reduction.

Main Results:

• MOSFET sensitivity varied up to a factor of 3.2 across the studied energy range, with 75 kVp showing the highest sensitivity.
• Detector lifespan ranged from approximately 100 Gy (75 kVp) to 300 Gy (6 MV).
• MOSFETs exhibited reduced sensitivity with increasing integrated dose, an effect more pronounced at lower energies.
• Sensitivity reduction was found to be reproducibly approximated by a second-order polynomial function.

Conclusions:

• The energy dependence and dose history effects of MOSFET dosimeters necessitate correction for accurate radiotherapy dose measurements.
• The developed polynomial correction function allows for more precise in-phantom and in-vivo dose assessments.
• Improved CSDS show promise for reliable dosimetry in clinical radiation applications.