Patient-specific MU rate optimization to reduce lung dose rate in Volumetric Modulated Arc Therapy-based Total Body
Surendran Jagadeesan1, S P Vijaya Chamundeeswari2
1Department of Physics, School of advanced sciences, Vellore Institute of Technology, Vellore, Tamilnadu, India; Department of Radiation Oncology, Burjeel Cancer Institute, Burjeel Medical City, Abu Dhabi, United Arab Emirates.
Purpose:
Reducing the lung dose rate significantly decreases the risk of toxicity in high-dose total-body irradiation (TBI). This study investigated the feasibility of delivering Volumetric Modulated Arc Therapy (VMAT) TBI with a reduced monitor unit (MU) rate on a Versa HD linear accelerator.
Materials And Methods:
Treatment data for nine patients who underwent VMAT TBI were retrospectively analyzed. The mean lung dose per fraction and thorax VMAT field MU were used to calculate a patient-specific MU rate required to achieve a lung dose rate below 10 cGy/min. The patient-specific MU rate was implemented for thorax VMAT fields using the Mosaiq record-and-verification system and delivered in continuous variable dose-rate (CVDR) mode. Dosimetric consistency was evaluated using MatriXX Resolution detector-based planar dose verification with 3%/2 mm gamma analysis, and treatment log files were reviewed to assess MU rates and beam-on times.
Results:
The mean lung dose was 782.3 ± 12.8 cGy. With a MU rate of 600 MU/min, the average lung dose rate was 16.1 ± 1.8 cGy/min. Application of patient-specific MU rates (95-196 MU/min) reduced the average lung dose rate to 8.8 ± 0.2 cGy/min in all patients (p < 0.001). Gamma pass rates exceeded 95% for all plans, confirming dosimetric consistency.
Conclusion:
Patient-specific MU-rate optimization is a feasible and reproducible strategy for reducing lung dose rate in VMAT-TBI on Elekta linacs. Further prospective studies with clinical outcome assessments are necessary to validate the impact of patient-specific lung dose rate reduction.
