Dosimetric accuracy of low dose rate volumetric modulated arc therapy delivery in an Elekta Versa HD linear accelerator for pulsed low dose rate treatment of recurrent high‐grade glioma using Monaco planning system

Background and purpose Reducing the dose rate enhances efficacy in radiation therapy by allowing increased repair of sub‐lethal damage. Pulsed low‐dose radiation therapy (PLDR) is an innovative approach that is safe and effective for the reirradiation of recurrent gliomas and radioresistant tumors. In this study, the accuracy of the low dose rate volumetric modulated arc therapy (VMAT) delivery is tested in an Elekta Versa HD linear accelerator (linac) for delivering PLDR. Material and methods A retrospective study was conducted on ten patients previously treated for high‐grade glioma. The Monaco planning system was used to create two or three arc VMAT plans with a minimum monitor unit (MU) exceeding 570. The Mosaiq record and verification system (R&V) was used to select dose rates between 20 and 25 MU/min for delivering VMAT beams, achieving a beam‐on time of 30 min and an effective dose rate of 6.7 cGy/min. Measurements from IBA MatriXX resolution were used for gamma analysis. Beam characteristics at low dose rates for 8 gantry angles were investigated using the measurements from the dolphin detector. Results All the deviations of flatness and symmetry were within 1.0% in all gantry angles. MU linearity was within 1% for the lowest dose rate of 20 MU/min. The output deviations were within 1% for all dose rates. The average dose rate achieved was 6.7 ± 0.1 cGy/min. The maximum dose rate achieved in the planning target volume (PTV) was 7.28 (6.86 to 7.28) cGy/min. The gamma pass rate was above 97%, with the analysis criterion 3%3 mm, 2%2 mm, and 2%1 mm for VMAT delivered at a low dose rate. Conclusion Low‐dose rate VMAT delivery is feasible with higher accuracy in the delivered dose on the Elekta Versa HD linac. PLDR can be implemented successfully on Elekta linacs using the Monaco planning system.