Purpose: This study aims to demonstrate the planning and delivery of total marrow irradiation (TMI) and total bone marrow and lymph nodal irradiation (TMLI) using Volumetric modulated arc therapy (VMAT) ua Halcyon-E ring gantry linear accelerator.
Methods: Three patients, one female, and two male, of body weight 116 Kg, 52Kg, and 64 kg; one acute lymphoblastic leukemia (ALL) and two Chronic myeloid leukemia (CML) were simulated and planned for TMI/TMLI. Patients were immobilised with full body vacuum bag. Head first supine (HFS) and Feet First supine (FFS) CT was acquired from head to knee and Knee to toe respectively. Planning target volume (PTV) created with a uniform 5 mm margin over the total bone marrow/bone marrow + lymph nodes. A junction anterio-posterior open field plan was created for the junction contour at mid thigh for both HFS and FFS CT. Considering this junction plan as a base dose HFS and FFS multiple isocentric plans were optimised for 12 Gy in 6 fractions using 6MV unflatten beam. Further HFS , FFS, and one of the two junction plans were summed up for the combined dose distribution. The total number of isocenters were ≤10 and two to four full arcs per isocentre. A junction dose gradient technique was used for dose feathering between adjacent beams.
Results: PTV_D95% normalised to 95% volume, PTV_D107% receiving 3.3±3.1%.Total lung mean and average V12Gy were 1048.6±107.1 cGy and 19.5±12.1% respectively. Maximum lens doses were 489.5±35.5 cGy (left: L) and 497±69.2 cGy (right: R). Mean cardiac and bilateral kidney doses were 921.75±89.2 cGy, 917.9±63.2 cGy (L), and 805.9±9.7cGy (R). Average Monitor unit 7738.25±1056.6 and MU/Dose ratio 40.6±2.5. Nonetheless, due to other clinical complications and co-morbidities, none of the patients could receive the treatment.
Conclusion: Halcyon-E ring gantry linear accelerator capable of planning and delivery of TMI/TMLI.