Evaluation of intensity-modulated radiation therapy factors by treatment site and technique for various linear accelerators

초록

Purpose: The intensity-modulated radiation therapy (IMRT) factor, which is essential for calculating leakage radiation and secondary barrier thicknesses, is represented by the ratio of average monitor units (MUs) per unit dose in IMRT compared to conventional radiotherapy. The National Council on Radiation Protection and Measurements recommends a broad range of 2–10 for this factor, which can complicate its practical use. This study aims to calculate and compare the IMRT factors of Halcyon, VitalBeam, and TrueBeam based on actual MUs, offering a more accurate foundation for effective and reasonable radiation shielding determination. Methods: Treatment data from three hospitals in Korea, collected between March 25, 2022, and December 31, 2023, was extracted using the ARIA Unified Reports Application. IMRT factors were calculated by analyzing actual MUs in fixed-gantry IMRT, volumetric modulated arc therapy (VMAT), and stereotactic ablative radiotherapy techniques across three different linear accelerators (LINACs) by treatment sites. Results: Based on the analysis of actual treatment records, the average IMRT factor for the VMAT technique was calculated as 2.82 ± 0.32 for Halcyon, 2.61 ± 0.31 for TrueBeam, and 2.22 ± 0.21 for VitalBeam, indicating that the IMRT factor for Halcyon was approximately 8% higher than TrueBeam and 27% higher than VitalBeam. Although Halcyon exhibited a tendency to use more MUs, the difference was not significant enough to warrant applying the IMRT factor of 10. The IMRT factor for fixed-gantry IMRT on Halcyon was about 1.9 times greater than that for its VMAT technique. No significant variation was observed across treatment sites. Conclusions: The presented values may assist in evaluating secondary leakage radiation and contribute to improving the practicality and efficiency of radiation shielding design by providing reference data grounded in actual clinical treatment records.

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