SU-E-T-12: Radiation Detector Responses to Applied Homogeneous Transverse and Parallel Magnetic Fields

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Integrated magnetic resonance (MR)-linear accelerator (linac) systems offer advanced cancer treatment capabilities.
• Accurate dosimetry is critical for effective radiotherapy, but magnetic fields in MR-linacs can affect detector performance.
• Existing dosimetry protocols need evaluation and refinement for these novel clinical environments.

Purpose of the Study:

• To assess the relative dose response of a diamond detector and an ion chamber in a clinical photon beam under uniform magnetic fields.
• To evaluate and refine reference dosimetry techniques for integrated MR-linac systems.
• To determine the impact of magnetic field strength and orientation on detector readings.

Main Methods:

• Monte Carlo simulations using PENELOPE modeled a diamond detector (PTW60003) and an ion chamber (PR06) in a 6MV photon beam.
• Simulations covered magnetic field strengths from 0 to 1.5T, with parallel and transverse orientations relative to the beam central axis.
• Detector orientations (perpendicular and parallel to the beam) were simulated, and experimental validation was performed up to 0.2T transverse fields.

Main Results:

• Simulated and experimental results for both detectors showed good agreement.
• In transverse magnetic fields, detector response varied up to ±8.5% for the ion chamber and >9% for the diamond detector.
• In parallel magnetic fields, detector response was largely insensitive, with a maximum change of 2% for the ion chamber at 1.5T.

Conclusions:

• Magnetic field-dependent correction factors are necessary for dosimetry in MR-linac systems, particularly for transverse field orientations.
• Detector response changes in parallel magnetic fields < 1T are minimal and can likely be disregarded for dosimetry protocols.
• This research is vital for establishing reliable dosimetry in advanced MR-linac radiotherapy.