MRI-LINAC beam profile measurements using a plastic scintillation dosimeter

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Radiation Dosimetry

Background:

• Plastic scintillation dosimeters (PSDs) offer advantageous properties for linear accelerator (LINAC) dosimetry.
• Their potential for magnetic resonance imaging-LINAC (MRI-LINAC) dosimetry requires further investigation.
• Limited research exists on PSD performance specifically within MRI-LINAC environments.

Purpose of the Study:

• To evaluate the dosimetric performance of an in-house plastic scintillation dosimeter (PSD) with an in-line MRI-LINAC.
• To compare PSD beam profiles against film measurements.
• To assess the accuracy and reliability of PSDs for relative dosimetry in MRI-LINAC applications.

Main Methods:

• An in-house PSD was utilized to acquire 8 beam profiles from an in-line MRI-LINAC.
• Film dosimetry was employed as a reference for comparison.
• One-dimensional global gamma indices (γ) and pass rates were calculated using 1%/1 mm, 2%/2 mm, and 3%/3 mm criteria.

Main Results:

• Mean global gamma pass rates reached 85.8% (1%/1 mm), 97.5% (2%/2 mm), and 99.4% (3%/3 mm).
• Gamma failures were predominantly observed in penumbral regions, with PSD penumbra widths showing agreement with film within measurement uncertainties.
• Dose differences between PSD and film remained within 2.2% globally in central regions and 1.5% in out-of-field regions.

Conclusions:

• The investigated PSD demonstrates reliable performance for relative dosimetry in MRI-LINAC setups.
• Achieved agreement levels are comparable to other established dosimeters used in MRI-LINAC relative dosimetry.
• PSDs are a viable option for dosimetry in advanced MRI-LINAC radiotherapy systems.