Superficial doses from serial tomotherapy delivery

Serial tomotherapy patients are treated using a commercial computer-control led treatment planning and delivery system and a linear accelerator in are mode. Target volumes are irradiated using sequential 1.68-cm-thick slices w ith the patient moved between each successive slice delivery. Due to the me thod of delivery, superficial doses from a course of intensity modulated ra diation therapy may be significantly different from doses delivered with co nventional radiation therapy. An experimental investigation was conducted t o determine the superficial depth-dose distribution for geometric target vo lumes. Treatment plans were conducted for 5-cm-diam, 5-cm-long right cylind rical target volumes embedded in a 16-cm-diam, 12-cm-long water-equivalent cylindrical phantom. Three experiments were conducted with centrally locate d, off-centered, and superficial targets. Doses at superficial depths were measured using 3 X 3 X 1 mm(3) thermoluminescent dosimetry chips. For all t hree targets, the measured doses were slightly greater than the calculated doses. Doses measured in the buildup region for the superficial target indi cated that bolus would be required to provide the prescribed dose at the ph antom surface. (C) 2000 American Association of Physicists in Medicine. [S0 094-2405(00)00301-1].