Purpose: To conduct an end-to-end verification for VMAT based total body irradiation.
Methods: Total body irradiation (TBI) is traditionally delivered using anterior and posterior (AP/PA) beams. Recently a VMAT based hybrid planning technique was developed at our institution to improve the target coverage and patient comfort while sparing the critical organs. To validate this technique, an end-to-end test was conducted using an anthropomorphic phantom, including simulation, planning and treatment delivery following the clinical procedures of VMAT-TBI. The CT images were acquired at 5mm slice thickness and whole-body CT was generated. Planning was done in Pinnacle TPS prescribing 13.2 Gy in 8 fractions. The goals were to achieve >85% of PTV receiving the prescription dose while reducing the mean dose to lungs <80% and mean dose to kidneys <50% of the prescription dose. Hotspots were limited between 110-120% of the prescription dose. Treatment was delivered on rando phantom in HFS orientation for upper body and in FFS orientation for lower body under image guidance. Measurements were performed with MOSFET dosimeter at four locations (central and lateral thorax, abdomen and pelvis) and two transverse EBT3 films at the lung and pelvis at the junction region between the head first and feet first treatment.
Results: The 88.5% of PTV received prescription dose. Mean lung dose and mean kidney dose were 10.4Gy and 6.3Gy meeting the planning constraints. A good agreement was achieved between the measured and calculated dose. The mean dose difference for both films at lungs and pelvis were 5.1±14.9cGy and 11.8±6.6cGy respectively. The average dose difference for MOSFET dosimeters was 4.1%.
Conclusion: The hybrid VMAT based TBI planning technique was capable of delivering uniform dose to the whole body and spare critical structures such as lungs and kidneys. End-to-End test proved that the workflow of VMAT-TBI achieves accurate dose delivery.
Not Applicable / None Entered.