Poster - Thur Eve - 31: RapidArc total body photon irradiation: A feasibility study

Total body photon irradiation (TBI) may be delivered with a number of standard techniques, typically using extended SSD geometries to obtain large field sizes. Since 1982 we have treated over 620 patients (adult and pediatric) mostly in the floor-located prone/supine treatment position with AP/PA beams using a column mounted 4 MV linac, and more recently with a fixed field, extended SSD, Cobalt teletherapy unit. This treatment position has many advantages for TBI including ease of delivery (especially for pediatric or compromised patients), improved dose uniformity, simplicity for partial or complete organ shielding, and imaging capabilities to name a few. In an effort to transfer this technique to a conventional isocentric linac, we have undertaken a feasibility study for RapidArc based extended SSD total body irradiation. Proof of principle was first explored using the DBD (Dynamic Beam Delivery) toolbox to configure a 6 MV beam with an 80 degree arc, centered on the 12 o'clock gantry angle with a sliding-window beam. This was followed by the development of an ECLIPSE generated 80 degree RapidArc plan. Initial measurements were conducted with a Varian 21EX using the 6 MV DBD beam to explore characteristics such as PDD, surface dose, off-axis ratios, output, dose per MU, and linearity. Subsequently ECLIPSE generated RapidArc TBI plans using similar partial arcs were also evaluated. Encouraged by our results, we believe this technique shows potential for making floor-located AP/PA total body photon irradiation possible for any standard RapidArc enabled isocentric linac.