SU-E-T-275: Dose Verification in a Small Animal Image-Guided Radiation Therapy X-Ray Machine: A Dose Comparison...

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry Technology

Background:

• Accurate radiation dosimetry is critical for effective cancer treatment.
• TG-61 provides a standard for dosimetry but may require adjustments for specific phantom geometries.
• Metal-Oxide-Semiconductor Field-Effect-Transistor (MOSFET) technology offers potential for precise dose measurements.

Purpose of the Study:

• To assess the accuracy of TG-61 dosimetry protocols when implemented with MOSFET detectors in a tissue-equivalent mouse phantom.
• To compare dose measurements obtained using MOSFETs in a mouse phantom against established TG-61 based calculations.

Main Methods:

• Commissioning of a TG-61 based look-up table using solid water and radiochromic film.
• Utilized a tissue-equivalent mouse phantom (2 cm diameter, 8 cm length) for MOSFET measurements.
• Calibrated MOSFETs in air and derived tissue dose using an f-factor; positioned phantom in CBCT mode for dose measurements with various collimators.

Main Results:

• MOSFET measurements were systematically lower than TG-61 commissioning data.
• Dose differences ranged from 2.7% to 7.7% depending on collimator size and shape.
• Specific examples include 4.3% lower dose for a 10 mm circular collimator and 7.7% lower for a 20x20 mm collimator.

Conclusions:

• The observed dose discrepancies are attributed to increased scatter in solid water blocks compared to the mouse phantom.
• MOSFET dosimetry with a tissue-equivalent mouse phantom offers a less labor-intensive, geometry-specific dosimetry method.
• This approach demonstrates improved accuracy with dose tolerances up to ±2.7%.