Evaluation of two calibration methods for MRI-based polymer gel dosimetry

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Polymer gel dosimetry (PGD) provides essential 3D dose data for evaluating treatment planning system (TPS) algorithms.
• Accurate calibration is crucial for clinical implementation of PGD, especially with MRI-based techniques.

Purpose of the Study:

• To evaluate the single-phantom electron beam (SPE) method for calibrating MRI-based polymer gel dosimetry.
• To compare the SPE method with the multi-vial x-ray (MVX) method for 3D dose validation.

Main Methods:

• Evaluated the SPE method using depth-dose data from a 9 MeV electron beam.
• Compared regression equations (third-order polynomial vs. tangent function) and dose-normalization methods (one-point vs. two-point).
• Utilized MAGAT polymer gel and a 3 cm x 3 cm open arc beam for dose distribution testing.

Main Results:

• The SPE method required less dose scaling for comparison.
• The tangent function demonstrated superior data fitting and lower coefficient uncertainty compared to the polynomial function.
• No significant advantage of SPE over MVX was found for the specific 3D dose comparison test case.

Conclusions:

• The SPE method, employing a tangent function and one-point normalization, is a recommended calibration approach for MRI-based PGD.
• This calibration strategy supports accurate 3D dose evaluation in radiotherapy.