Proton dose distribution measurements using a MOSFET detector with a simple dose-weighted correction method for LET...

Area of Science:

• Medical Physics
• Radiation Oncology
• Detector Physics

Background:

• Accurate dosimetry is crucial for proton therapy.
• Metal Oxide Semiconductor Field Effect Transistor (MOSFET) detectors offer potential for precise dose measurements.
• Proton beams present unique dosimetry challenges due to their depth-dependent energy deposition and linear energy transfer (LET) characteristics.

Purpose of the Study:

• To experimentally evaluate the performance of a new Metal Oxide Semiconductor Field Effect Transistor (MOSFET) detector for proton beam dosimetry.
• To assess the detector's reproducibility, sensitivity, angular dependence, and depth-dose relationships.
• To develop and validate a practical method for correcting MOSFET detector response to proton beams, accounting for LET effects.

Main Methods:

• Fabrication of a new MOSFET detector with a thinner oxide layer and operation at high-bias voltages.
• Evaluation of dose reproducibility, angular dependence, and depth-dose response using a 190 MeV proton beam.
• Development of a dose-weighted correction method for LET dependence, with correction factors determined as a function of residual proton range calculated using the pencil beam algorithm.
• Comparison of MOSFET detector measurements with ionization chamber (IC) results for lateral dose profiles and depth-output curves.

Main Results:

• The MOSFET detector demonstrated excellent dose reproducibility (within 2%) and acceptable angular dependence (less than 9%).
• The detector showed a good response at the Bragg peak, comparable to ionization chamber measurements (0.74 relative to IC).
• Corrected MOSFET dose measurements for complex dose distributions (e.g., through an L-shaped bolus) agreed well with ionization chamber results, achieving absolute proton dosimetry with a precision of approximately 3% (1 sigma).

Conclusions:

• The new MOSFET detector, particularly with its thinner oxide layer, is suitable for proton beam dosimetry.
• Employing a dose-weighted correction method effectively addresses LET dependence, enabling accurate absolute proton dose measurements.
• MOSFET detectors, when properly corrected, can be a valuable tool for precise dose monitoring in proton therapy.