CONCEPT OF DOSE NONUNIFORMITY IN INTERSTITIAL BRACHYTHERAPY

Purpose: Evaluation of the 3-dimensional dose distributions of interst itial implants using the dose nonuniformity ratio. Methods and Materia ls: Single source, two sources, three and four sources arranged both l inearly and in the form of a triangle or a square, ribbons with differ ent seed spacings, a single-plane and double-plane implants were evalu ated. The evaluations involved the use of differential dose volume his tograms and the dose nonuniformity ratio defined as the ratio of the h igh dose volume to the reference volume. Results: For a single source, the dose nonuniformity is the same regardless which dose rate is sele cted as the Treatment dose rate. For any multi-source implant, the dos e nonuniformity is altered depending on the selection of the reference dose rate. In addition, the dose nonuniformity curve exhibited three characteristics zones. Conclusion: The dose nonuniformity ratio can be a useful tool in assessing and optimizing interstitial implants.