A novel conformal superficial high-dose-rate brachytherapy device for the treatment of nonmelanoma skin cancer and keloids

Purpose To develop a novel conformal superficial brachytherapy (CSBT) device as a treatment option for the patient-specific radiation therapy of conditions including superficial lesions, postsurgical positive margins, Dupuytren's contractures, keloid scars, and complex anatomic sites (eyelids, nose, ears, etc.). Methods and Materials A preliminary CSBT device prototype was designed, built, and tested using readily available radioactive seeds. Iodine-125 (¹²⁵I) seeds were independently guided to the treatment surface to conform to the target. Treatment planning was performed via BrachyVision Planning System (BPS) and dose distributions measured with Gafchromic EBT3 film. Percent depth dose curves and profiles for Praseodymium-142 (¹⁴²Pr), and Strontium-90/Yttrium-90 (⁹⁰Sr–⁹⁰Y) were also investigated as potential sources. Results achieved with ⁹⁰Sr–⁹⁰Y and electron external beam radiation therapy were compared and Monte Carlo N-Particle eXtended 2.6 simulations of ¹⁴²Pr seeds were validated. Results BPS was able to predict clinical dose distributions for a multiple seeds matrix. Calculated and measured doses for the ¹²⁵I seed matrix were 500 cGy and 473.5 cGy at 5 mm depth, and 171.0 cGy and 201.0 cGy at 10 mm depth, respectively. Results of ⁹⁰Sr–⁹⁰Y tests demonstrate a more conformal dose than electron EBRT (1.6 mm compared to 4.3 mm penumbra). Measured ¹⁴²Pr doses were 500 cGy at surface and 17.4 cGy at 5 mm depth. Conclusions The CSBT device provides a highly conformal dose to small surface areas. Commercially available BPS can be used for treatment planning, and Monte Carlo simulation can be used for plans using beta-emitting sources and complex anatomies. Various radionuclides may be used in this device to suit prescription depths and treatment areas.