Dose Calculation Accuracy of Beam Models in RadCalc for a 1.5 T MR-Linac

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Online adaptive radiotherapy requires precise dose verification.
• Magnetic resonance linear accelerators (MR-linacs) present unique challenges for dose calculation due to magnetic field interactions.
• Independent software is crucial for patient-specific quality assurance (PSQA).

Purpose of the Study:

• To evaluate RadCalc version 7.1.4 for PSQA in 1.5 T MR-linac online adaptive planning.
• To assess the accuracy of RadCalc's beam modeling incorporating MR field characteristics.
• To validate RadCalc as a reliable tool for adaptive radiotherapy dose verification.

Main Methods:

• Established six RadCalc beam models using various percentage depth dose (PDD) data sources.
• Assessed dose-calculation accuracy using simple tests on a virtual water phantom.
• Conducted clinical tests on 575 adaptive plans (prostate, liver, breast) comparing RadCalc to PSQA measurements.

Main Results:

• Dose calculation differences ranged from -0.5% to -20.6% in virtual phantom tests.
• Clinical tests on adaptive plans showed percentage differences of -0.51% (prostate), 1.12% (liver), and 4.10% (breast).
• RadCalc calculations demonstrated similar trends to PSQA-based measurements.

Conclusions:

• RadCalc version 7.1.4 successfully models 1.5 T magnetic field characteristics for adaptive planning.
• The software's dose calculation accuracy at 1.5 T has been verified.
• RadCalc is a reliable and effective tool for PSQA in MR-linac adaptive radiotherapy.