Study Of A Linac-based Intensity Modulated Method For Total Body Irradiation

Background and Objectives: Total body irradiation (TBI) is commonly used as a preconditioning regimen in the treatment of hematological malignancies that require bone marrow transplantation (BMT) or hemopoietic stem cell transplantation (HSCT). Conventional TBI is primarily limited by the toxicity to organs at risk because of impossibility of sparing critical organs. The purpose of this study is to develop a novel "rotation-translation" intensity-modulated radiation therapy (IMRT) method that is able to conform the radiation dose to target volumes and to reduce dose to critical organs for TBI using linac. The method is expected to has widespread operability with low expenditure, comparing against two currently available IMRT methods, tomotherapy and three-isocenter IMRT.Materials and Methods:For the "rotation-translation" method, the treatment couch was set to 90°or 270°, and then the gantry would rotate and the couch would move longitudinally when the radiation beam is on. The main advantage of this method was that the treatment field would penetrate longer in human body since the radiation beam was in the coronal plane rather than the transverse plane. The performance of the proposed method was evaluated with two clinical situations of TBI, total marrow irradiation (TMI) and total marrow irradiation plus lymphatic irradiation (TMLI). The dose distribution and DVH of the treatment plans were evaluated and compared to other TBI techniques. Then the entire treatment planning and delivery process for a simulated case was completed using an anthropomorphic Rando phantom, and the treatment delivery efficiency and the panning dose accuracy were determined.Results: The method conformed the high dose region to the target volume while minimizing the dose to critical organs compared to conventional TBI. The 100% isodose surface (12.00 Gy) covered 90% of the PTV. The mean doses of lungs were 7.24 Gy and 7.30 Gy for TMI and TMLI respectively. TLD measurements on Rando showed an accurate dose delivery (mean dose error of 4.5% and 4.0%, respectively) to the target and critical organs. Compared to three-isocenter technique for TBI, the "rotation-translation" technique simplified the planning process and increased the irradiation area of a treatment beam. The planning time was reduced by 33%. The delivery efficiency is almost the same.Conclusions: This study developed a new linac-based intensity modulated method for total body irradiation. Simulation experiment in planning and delivery of this method was performed and compared with an IMRT method in the literature. The method is promising and current work has laid down a solid theoretical basis for the method to be put into clinic implementation.