Feasibility of using dental putty-based custom molds for high-dose-rate brachytherapy of oral mucosal melanoma

Abstract

Purpose: To investigate the feasibility of using dental putty to fabricate custom molds for high-dose-rate (HDR) brachytherapy of oral mucosal melanoma. Practical guidelines of using dental putty for the custom mold fabrication are presented. Methods: Dose measurements were performed using radiochromic films to understand the dosimetric charac-teristics of dental putty. The percentage depth dose (PDD) and profile curves were obtained using a single Co-60 source located on top of a cubic volume of the dental putty. Two custom molds were fabricated for a patient with mucosal melanoma lesions, which were spread throughout the right mandibular gingiva and soft palate regions. Furthermore, pretreatment dosimetry for both lesions was performed to evaluate the delivery quality of the resulting HDR brachytherapy plans and adjust the overall dose level. Results: Prescribed doses for the two oral cavity regions were successfully delivered with a reasonable dose uniformity. Based on the measured single-source PDD curve, the maximum dose was observed at a depth of approximately 1 mm, which indicated steep dose gradients at depths ranging from 0 to 2 mm. Furthermore, a simulation with the measured single-source two-dimensional profile revealed that a source-to-source distance of 10 mm was appropriate to generate a uniform dose distribution at a source-to-surface distance of 5 mm. Conclusions: The use of a custom mold was found to be feasible for HDR brachytherapy while carefully considering the source-to-surface and source-to-source distances. Pretreatment delivery verification would be necessary when a uniform dose distribution is required.