Dosimetric comparison of total body irradiation and total marrowirradiation using volumetric arc therapy (VMAT)

Whole body irradiation (TVI) is a specialized radiotherapy technique that is part of the conditioning of bone marrow transplantation to treat patients with leukemia, lymphoma, autoimmune diseases, multiple myeloma. It is used to suppress the immune system of the patient after transplantation, to prevent rejection of the donor bone marrow and to prepare a suitable environment for the division of healthy cells. The aim of this study is to investigate the dose distribution of whole body irradiation (TVI) and whole bone marrow irradiation (TKI) using volumetric arc therapy (VMAT). For this, the rando phantom made of materials similar to the human tissue equivalent was used. First, CT images of the rando phantom are taken in 2 mm sections and the CT images are transferred to Monaco version 5.1 for contouring and planning using the Monte Carlo dose calculation algorithm. While the plan for TVI was prepared by preserving the lungs and lenses, the plan was prepared for TKI by preserving the brain, eyes, oral cavity, lungs, heart, kidneys, liver, spleen, stomach, bladder, rectum and intestines, and the prepared plans were compared dosimetrically. Quality assurance for VMAT-TVI and VMAT-TKI plans was performed using the Octavius 4D phantom. Dosage accuracy between the planned and delivered dose was evaluated using gamma index analysis with 3 mm and 3% criteria in all 3 planes. Dose calculation and distribution between junctions of isocenters were confirmed. As a result of this study, when the measurement results for both plans and the results obtained in the treatment planning system are compared with TKI, TVI, it is observed that there is a decrease in OAR doses, and the mean right and left lung doses are approximately 20% and 28% less, respectively. As lung toxicity is the main limiting factor for TVI, this reduction may further improve quality of life and allow higher doses when clinically necessary. As a result of these studies, the mean PTV γ index was observed to be less than 4% for the 3-3% mm analysis, and very precise dose distributions were observed between the planned and administered doses.