(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: This is a pilot planning study for TBI irradiation at short distance. Sweep beams were used as a base, together with attachment free compensation beams, including dynamic wedges and/or partial static arcs, to deliver a uniform dose in the total body irradiation (TBI) treatment to a phantom or test patient lying underneath the gantry, making TBI deliverable in most of the standard-size clinics.
Methods: A rectangular cuboid human size phantom (40cm x 25cm x 170cm) was created in treatment planning system. Additionally, a CT from an anonymized patient with upper and lower body scans was concatenated to form a full body scan from head to toe. Test plans using multiple sweep beams and/or dynamic wedges were generated on the phantom and test patient from AP and PA directions. The field sizes and relative weighting were adjusted so that the dose to the central axis of the phantom or test patient along the SI direction was within 10% of the prescription. The plan sums were created and the dose was evaluated. Physical blocks will be used for lung shielding and are not considered in this study.
Results: the dose calculated by the treatment planning system was within acceptable range for both phantom and test patient. The mean, max, min, and stand deviation of the relative dose delivered to the central axis of the cuboid phantom in the plan sum were 102.1%, 106.5%, 94.4%, and 1.8%, respectively. And for the test patient, they were 100.2%, 107.8%, 91.8%, and 4.0%, respectively.
Conclusion: The planning technique of using sweeping beams and/or dynamic wedges to deliver TBI treatment at short distance is promising. The dose calculated to the phantom and test patient is within a reasonable range.
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