Purpose: A high-dose-rate brachytherapy surface applicator set has been commercially available for several years with sparse description in the literature. A thorough verification of the available dose distributions and dose output from all applicators as well as determining the optimal clinical settings for patient use was necessary for clinical implementation.
Methods: Measurements of dose distribution and absolute dose at depth under the applicators were made. Absolute dose was measured using a commercial diamond detector and radiochromic film. The diamond detector was calibrated for Ir-192 using a known dose in water. This calibration was used to measure the dose given in water at 1-5 mm depths for each surface applicator. Radiochromic film was used in plastic water at 3 mm depth to measure dose distributions and absolute dose of different dwell positions.
Results: All applicator/insert combinations have a pronounced dip in the center of the dose distribution due to the metal channel entering the applicator perpendicular to the patient surface. There are two logical dwell position options, and for all applicator/insert combinations the 129 cm dwell position led to a smaller dip in the center of the distribution (generally 20-25% vs. 20-44% for 128.5 cm dwell position). Using the 129 cm dwell position, dose in water was measured for each applicator/insert combination and tabulated for use in patient calculation. Absolute dose measurements from the radiochromic film agreed with the diamond detector measurements with a mean difference of 4.5%.
Conclusion: The skin applicator set is clinically useful though must be used with a specific dwell position to reduce the asymmetry of the dose distribution. Further recommendations for the use of the applicator set should be followed closely to assure optimal patient treatment, as there are multiple possibilities for asymmetric dose distribution in the center and periphery of the applicator.