DIFFERENTIAL DOSE DELIVERY USING A NONDOCKING APPLICATOR FOR INTRAOPERATIVE RADIATION-THERAPY

Purpose: Although treatment of a field within a field to deliver a boo st dose is quite common with external photon beam radiation therapy, t he same is not always true with electron beam radiation or in intraope rative radiation therapy (IORT), The purpose of this work is to report the results and details of a new technique developed to treat a field within a field in intraoperative radiation therapy, Methods and Mater ials: This technique makes use of the nondocking IORT system currently used at our institution, Treatment is given in two segments: the larg e field is first treated by using standard circular lucite cones; the second dose segment is delivered using a new circular brass cone desig ned to fit concentrically within the large lucite cone, Results: Centr al axis depth dose, surface dose, output factors, and two-dimensional beam profiles have been measured for a 7 cm inner diameter (i.d.) flat lucite cone and 3.8 and 5 cm i.d. flat brass cones for electron beam energies ranging from 4-22 MeV. For different clinical target volumes, summed dose distributions differentially weighted in both energy and dose are presented, Conclusions: A simple technique for delivering dif ferential dose in intraoperative radiation therapy is presented, The t echnique provides a method for escalating dose to higher values for a defined target volume. (C) 1997 Elsevier Science Inc.