The dosimetric properties of an applicator system for intraoperative electron‐beam therapy utilizing a Clinac–18 accelerator

A prototype electron applicator system providing circular and rectangular fields for use in intraoperative electron beam therapy with a Varian Clinac 18 linear accelerator has been fabricated. The dosimetric properties of this system for a variety of electron‐beam energies, applicator sizes, and x‐ray collimator settings was documented. Significant findings include: (a) surface dose values are in excess of 90% for electron energies of 12 MeV and above; (b) for the 18‐MeV beam, the deepest depth where the central axis dose is 90% of its maximum value is in excess of 50 mm for circular applicators whose diameters are in excess of 5 cm; and (c) the treatment time to deliver 1000 rads “given dose” (at a given dose rate of 300 MU/min) is on the order of 3–4 min. Cross‐field behavior is acceptable for the intended application and x‐ray contamination is less than 4% for any applicator/electron energy combination. A system for irregular field blocking and TLD verification dosimetry has been developed.