OPTIMIZED DOSE DISTRIBUTION OF A HIGH-DOSE-RATE VAGINAL CYLINDER

Purpose: To present a comparison of optimized dose distributions for a set of high-dose-rate (HDR) vaginal cylinders calculated by a commerc ial treatment-planning system with benchmark calculations using Monte- Carlo-calculated dosimetry data. Methods and Materials: Optimized dose distributions using both an isotropic and an anisotropic dose calcula tion model were obtained for a set of HDR vaginal cylinders. Mathemati cal optimization techniques available in the computer treatment-planni ng system were used to calculate dwell times and positions. These dose distributions were compared with benchmark calculations with TG43 for malism and using Monte-Carlo-calculated data. The same dwell times and positions were used for a quantitative comparison of dose calculated with three dose models. Results: The isotropic dose calculation model can result in discrepancies as high as 50%. The anisotropic dose calcu lation model compared better with benchmark calculations. The differen ces were more significant at the apex of the vaginal cylinder, which i s typically used as the prescription point. Conclusion: Dose calculati on models available in a computer treatment-planning system must be ev aluated carefully to ensure their correct application. It should also be noted that when optimized dose distribution at a distance from the cylinder surface is calculated using an accurate dose calculation mode l, the vaginal mucosa dose becomes significantly higher, and therefore should be carefully monitored. (C) 1998 Elsevier Science Inc.