Dose Distribution of Oral Cone for Electron Beam

Park, Seung Jin; Chung, Woong Ki; Ahn, Sung Ja; Nah, Byung Sik

Abstract

Purpose
This study was performed to fabricate and evaluate the dosimetric characteristics of an intra-oral cone which can be used for radiation treatment of oral cavity cancer. Method and Materials: The intra-oral cone was made of acryl with a 3-cm diameter tube. It was designed to be attached to the aluminum base plate which can be set to linear accelerator. We designed 3 types of cone of which distal end has different angles; 0o, 15o, 30o. For comparison of dose distribution 3-cm reference cone was prepared which can be attached to the ready-made 6X6 cm electron beam applicator of linear accelerator. The electron energy of 6, 9, 12, 16, 20 MeV were tested. The depth dose and beam profile were measured using ionization chamber in water phantom. Surface dose and output factor were measured in polystyrene phantom using plane-parallel ionization chamber.
Results
Difference of surface dose between reference cone and intra-oral cone was within 3.7% in all electron energy levels. Difference of practical range(Rp) was within 0.1cm in all energy levels. Mean energy(E0) revealed significant difference between reference cone and oral cone as electron energy increase; 4.57 and 4.66 in 6 MeV, 12.28 and 13.21 in 20 MeV. R50 and R80 revealed similar trends. Percent depth dose curve revealed broad shoulder in Dmax, but in case of reference cone it revealed decreased Dmax and narrowed shoulder in 16 and 20 MeV. Output factor of oral cone was more decreased than reference cone in 6 MeV, but it increased as energy increase. There was no difference in surface dose, depth dose, and output factor by different angles of distal end of oral cone. Isodose curve revealed reduced dose of about 1.5% in reference and oral cone. Difference of uniformity index between reference cone and oral cone was within 0.5. The leakage dose was within 1.5% in different energy levels.
Conclusion
The dosimetric characteristics of intra-oral cone which we designed satisfied AAPM protocol TG21, so authors think it can be safely used to the radiation treatment of oral cavity cancer.