Alternative effective modality of Leipzig applicator with an electron beam for the treatment of superficial malignancies

Abstract

Object: The project was designed to study the effect of the same aperture high-energy electron beams from a dual photon-energy linear accelerator with the Leipzig applicator being a successful method of treating superficial malignancy in achieving a maximum relative surface dose. Methods: Leipzig applicator with its protective cap beams and small field electron beams from a Varian Clinac 2100CD linear accelerator were used. Circular fields at 100 cm SSD were obtained from cadmium-free cerrobend shields attached to the bottom face of a 6×6 cm 2 open wall electron cone. The central axis depth–dose curves, profiles and isodose curves measurement were carried out in a water phantom (NWP, Nucletron, The Netherlands) with a pair of silicon p-type diode electron detectors (Scanditronix, Sweden) with cross-section facing the source. The output factors, central-axis depth–dose curves, 90% isodose curve depth and area, flatness at depth of maximum dose were compared and the sagittal plane leakage of the Leipzig applicator were examined. Results: The data show that the maximum dose of Leipzig applicator and all 1 cm diameters electron beam are all located at the surface. The central-axis depth–dose curve of the Ir-192 beam is attenuated in an inverse square law manner. The surface to maximum dose ratio of the electron field decreases when the aperture size increases. The specified dose depths of Leipzig applicators are at least 3–6-fold less, and the area are at least 2–5-fold less than those of same aperture electron beams. The hot spot of a Leipzig applicator is located at the top and surrounding the source for both types of applicator with a leakage dose of up to 30% of D max. Conclusions: The Leipzig applicator with 192Ir high-dose-rate brachytherapy source can be used as an alternative method to electron beam irradiation in the treatment of superficial malignancies when the bulky electron applicator is difficult to set-up and approach.