Verification of dynamic intensity-modulated beam deliveries in canine subjects

Our objective in this work was to assess the precision and degree of accura cy with which intensity modulated radiation therapy (IMRT) can deliver high ly localized dose distributions to tumors near critical structures using th e dynamic sliding window technique. Measurements of dose distribution were performed both in vivo and in vitro using a combination of dosimeters [ther moluminescent dosimeters (TLD's), films, and diodes]. In vivo measurements were performed in two groups of purpose-bred dogs: one receiving four-field three-dimensional (3D) conformal treatment and the other receiving IMRT. T he algorithms used in the inverse planning process included the Macro Penci l Beam (MPB) model and Projections onto Convex Sets (POCS). Single beam mea surements were performed in phantoms to verify the accuracy of monitor unit settings required for delivering the desired doses. The composite doses fr om the delivery of the seven beam intensity modulated plans were measured i n phantoms and cadavers. Biological end points (spinal cord toxicity and ne urolgic deficits due to irradiation) were evaluated at the end of one year to determine the spatial accuracy of the IMRT treatments over a fractionate d course in live subjects. Results in single beam measurements were used at first to improve the dose calculation and translation algorithms. Results of the measurements for the delivery of all seven beams in phantoms confirm ed that the system was capable of accurate spatial and dosimetric IMRT deli very. The in vivo results showed dramatic differences between control and I MRT-treated dogs, with the IMRT group showing no adverse effects and the co ntrol animals showing severe spinal cord injuries due to irradiation. The m easurements presented in this paper have helped to verify the successful an d accurate delivery of IMRT in a clinically related model using the Univers ity of Washington Medical Center (UWMC) system. (C) 2001 American Associati on of Physicists in Medicine.