ABSTRACT
BACKGROUND: A simple approach to calculate the effect of air gap on output factors on electron beam dose distribution is presented. METHODS: The method accounts for variations of pencil beam parameters using a model developed by Bruinvis et al. [4,5]. The evaluation of this method is based on measurements of the output factors at various distances between the final collimating device and the phantom surface. RESULTS: Comparison of calculations and measurements of output factors for various cone sizes and 0, 2 and 4 cm air gaps show agreement to within approximately 1.5% for electron energies of 6-13.5 MeV and field sizes of 5.3-10 cm in diameter. CONCLUSION: The accuracy of this semi-empirical method can be considered clinically acceptable and reduces the amount of experimental work needed.
Subject(s)
Models, Theoretical , Radiotherapy Planning, Computer-Assisted/methods , Air , Electrons , Humans , Observer Variation , Phantoms, Imaging , Radiation Dosage , Reproducibility of ResultsABSTRACT
A development of a non-docking system is described which enables collimation of an electron beam for intraoperative radiation therapy. This system, adapted to a linear accelerator (SATURNE 43-CGR MeV), has been designed to minimize the mechanical, electrical and tumor visualization problems associated with a docking system. A number of dosimetric considerations and technical innovations have been used in the design of this system. Among them are the central axis of the beam alignment with the axis of the cone via a laser system and the clamping method of the intraoperative cone to the treatment couch by a rigid system. This collimation system can be adapted for different makes of linear accelerator. The dose distribution in this new design system shows a better homogeneity in the patient's target volume and small (thus accessable) leakage radiation dose to tissues outside the intraoperative cone. The design concept and dosimetric characteristics of this novel applicator system are presented in this paper.
