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Description
There are numerous applicators available for HDR brachytherapy. This thesis compares treatment plans, catheter usage, and dwell position variance for the CAPRI applicator for HDREBT over a range of conformities and homogeneities for differing CTV geometries for rectal cancer. The optimization process is not a straightforward one, with several potential pitfalls. This experiment attempts to create guidelines to aid in the treatment planning process. Treatment plans were constructed using Brachyvision software. CTVs of various geometries were contoured as well as an avoid structure to simulate organs at risk. Treatment plans were then constructed using different techniques to explore the effects on dwell positions and dwell times as well as the effects on healthy tissue sparing. Treatment plans were constructed with a Vrx of 100%, 95%, 90%, and 80% for each of the geometries. Conformity and homogeneity indices were calculated for each trial and compared to the dwell times. Relative dwell times were found for each plan and compared. To deliver a more homogeneous dose to the CTV, applicator channels further from the tumor were used for higher relative dwell times. For best rectal tissue sparing, applicators closest to the tumor are used in higher relative dwell times. It was found that each channel applicator used should be extended at least 1 cm beyond the CTV in both the inferior and superior directions during optimization for high tissue sparing technique and 1.5cm for higher homogeneity techniques. Depending on the dose allowance to healthy tissue, proximity to radiosensitive organs, and the desired treatment coverage of the tumor, parameters for which channels and dwell positions in the Capri applicator to use in the optimization are given
