CONCEPT OF DOSE NONUNIFORMITY IN INTERSTITIAL BRACHYTHERAPY

Purpose: Evaluation of the 3-dimensional dose distributions of interstitial implants using the dose nonuniformity ratio. Methods and Materials: Single source, two sources, three and four sources arranged both linearly and in the form of a triangle or a square, ribbons with different seed spacings, a single-plane and double-plane implants were evaluated. The evaluations involved the use of differential dose volume histograms and the dose nonuniformity ratio defined as the ratio of the high dose volume to the reference volume. Results: For a single source, the dose nonuniformity is the same regardless which dose rate is selected as the Treatment dose rate. For any multi-source implant, the dose 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.