Commissioning total body irradiation using a computerised treatment planning system

Abstract

Total body irradiation (TBI) is frequently used as a component of hematopoietic stem cell transplant (HSCT). TBI in conjunction with chemotherapy has proven useful for eradicating residual malignant cells and for immunosuppression prior to HSCT. Treatment planning for TBI has traditionally been performed using a manual point dose calculation approach, with treatment delivered in a single fraction through multiple fields. Although this approach has given a good clinical outcome there are drawbacks: manual calculation of a homogenous dose distribution is an arduous, time-consuming task, treatment setup can be complex and the use of fractionated TBI would reduce toxicity without compromising clinical outcome. We are in the process of commissioning a new fractionated TBI process, this will utilise a CT-based computer treatment planning system to create TBI plans with two patient irradiations using a field-in-field approach. We have opted to validate our existing Eclipse AAA beam model for use at an extended SSD of 450cm. Validation of the algorithm involved measurements of percentage depth doses, beam profiles and also investigation of dose calculations beyond inhomogeneities at extended SSD. The project involved design and construction of a suitable combination of treatment couch, Perspex headbox and spoiler for TBI. Furthermore, a TBI treatment planning study has been carried out and an independent MU check program has been created. The presentation is a description of our validation measurements, treatment planning study and also an introduction of our independent TBI MU check program.