INVESTIGATION OF TOMOTHERAPY BEAM DELIVERY

Experimental simulations for tomotherapy beam delivery were performed using a computer-controlled phantom positioner, a cylindrical phantom, and a 6 MV x-ray slit beam. Both continuous helical beam and sequenti al segmented tomotherapy (SST) beam deliveries were evaluated. Beam ju nctioning problem due to couch indexing error or field width errors pr esented severe dose uniformity perturbations for SST, while the proble m was minimized for helical beam delivery. Longitudinal breathing moti ons were experimentally simulated for helical and SST beam delivery. W hile motions reduced the dose uniformity perturbations for SST, small artifacts in dose uniformity can be introduced for helical beam delive ry. With typical breath frequency and magnitude, for a slit beam of 2. 0 cm width at 4 rpm, the dose uniformity perturbation was not signific ant. A running start/stop technique was implemented with helical beam delivery to sharpen the 20%-80% longitudinal dose fall-off from 1.5 to 0.5 cm. The latter was comparable to the corresponding dose penumbra of a conventional 6 MV 10x10 cm(2) field. All together, helical beam d elivery showed advantages over SST for tomotherapy beam delivery under similar delivery conditions. (C) 1997 American Association of Physici sts in Medicine.