An Active Matrix Flat Panel Dosimeter (AMFPD) for in-phantom dosimetric measurements

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Radiotherapy Physics

Background:

• Standard in-phantom dosimetry methods like scanning ion chambers and film have limitations.
• A need exists for high-resolution, 2-D dosimetry systems for advanced radiotherapy techniques.

Purpose of the Study:

• To modify an a-Si Active Matrix Flat Panel Imager (AMFPI) prototype into an Active Matrix Flat Panel Dosimeter (AMFPD).
• To characterize the performance of the AMFPD for in-phantom dosimetry applications.
• To evaluate the AMFPD as a potential replacement for conventional dosimetry devices.

Main Methods:

• Modification of an in-house a-Si AMFPI prototype into an AMFPD system.
• Characterization of the AMFPD's dynamic range, calibration stability, and dose rate independence.
• Comparison of AMFPD output factors with ion chamber measurements.
• Evaluation of 2-D planar dose distributions against film measurements.

Main Results:

• The AMFPD demonstrated a wide dynamic range (up to 160 cGy).
• Calibration remained stable (<1.5% variation over 1 year) with dose rate independence (<1%).
• Output factors showed excellent agreement with ion chambers (<2%) across various field sizes.
• 2-D dose distributions compared favorably with film measurements.

Conclusions:

• The developed Active Matrix Flat Panel Dosimeter (AMFPD) is a viable high-resolution, 2-D in-phantom dosimetry system.
• The AMFPD shows potential as a replacement for standard dosimetry devices in radiotherapy.
• The system is expected to be valuable for beam commissioning, algorithm verification, and IMRT quality assurance.