Feasibility of a robust and homogeneous volumetric modulated arc therapy based total body irradiation technique and analysis of dose rate using Elekta solutions.

Volumetric Modulated Arc Therapy (VMAT) for Total Body Irradiation (TBI) provides superior coverage, homogeneity, and organ sparing, leading to reduced toxicity. In this study, we present a VMAT-TBI technique delivered using Elekta solutions and report the average beam and lung dose rates. Nine patients were treated by VMAT-TBI technique. Treatment planning included VMAT for the upper body and VMAT or inverse optimized dynamic multileaf collimator (dMLC) plan using anteroposterior-posteroanterior (AP/PA) fields for the lower body. Plan robustness was evaluated for the 9 patients. Treatment log data was recorded with a sampling rate of 250 ms in the linear accelerator (linac) computer used for assessing the beam dose rates and delivery time. The average volume of all PTV receiving 95% of the prescription dose was 95.7 ± 1.3%. The mean heterogeneity index was 0.16 ± 0.03. The lung, kidney, and heart mean doses were 7.8 ± 0.2 Gy, 6.8 ± 0.3 Gy, and 6.8 ± 0.2 Gy, respectively, and the oral avoidance mean dose was 4.8 ± 0.6 Gy for myeloablative regimens. Robustness evaluation revealed the deviation of lung mean dose and the PTV maximum dose within 5% and 12.5%, respectively, with a 5 mm longitudinal isocenter shift. The mean instantaneous dose rate (IDR) for the thorax VMAT beam was 217 ± 26 MU/min. The average lung volume receiving above 20 cGy/min was 24.7 ± 8.2%. VMAT-TBI provides a homogeneous, robust, and selective organ-sparing treatment. Lung average dose rates can be reduced without any control applied to the IDR.