Arc technique for total-body irradiation by a 42-MV betatron

An arc technique for total-body irradiation (TBI) has been developed using a Siemens 42-MV betatron. Dose is administered with the isocenter approximately one-third the distance from source to patient. A modified inverse-square function for a beam arcing isocentrically was derived and confirmed experimentally. Relationships between stationary and arcing beam equilibrium and depth doses have been established theoretically and experimentally. Depth doses for TBI by 42-MV beams are compared with those for 60Co and 4-MV beams. The simplicity of setup and short treatment times are comparable to setup and treatment times of 60Co and linear accelerator TBI techniques.