Characteristics of electrotubular applicator for linear accelerator

This paper reports on characteristics of the electron tubular applicator for the Philips SL25 linear acceleration measured for circular fields 2, 3, 4, and 5 cm in diameter and for energies of 4 to 22 MeV. These characteristics were compared with those for the same fields produced with a 6 x 6-cm applicator and appropriate lead mask insert. Agreement between the two sets of measurements is within 5% for conditions of clinical interest. One drawback of the tubular applicator is the strong dependence of the dose rate on the energy: for the 2- cm-diameter field, the dose rate at 4 MeV is five times smaller than that at 22 MeV. We can optimize this characteristic by a change of primary jaws setup. Ionization measurements were made with a Markus chamber in water and acrylic for dose rate calibration, water and air for leakage measurements, and acrylic for surface dose determination. Isodose collection and depth dose measurements were realized with film in a solid water phantom and with a Wellhofer data acquisition system in a water phantom