SU‐E‐T‐691: Shielding Evaluation of a Treatment Room with An Electronic Brachytherapy System

Purpose: Esteya™ (Elekta) is a brachytherapy electronic system used for treating skin cancer lesions. This unit is based on a 69.5 kV X‐ray source and a surface applicator which produces a circular beam of a specific diameter, which varies from 1 to 3 cm. This study aims to establish the radiation protection measures for the system. Methods: A characterization of the scattered and leakage radiation of the system was implemented by means of experimental measurements. The scattered radiation measurements were performed with a Berthold LB133 ionization chamber, evaluating the dose rate for different distances from the applicator surface. The patient was simulated through water equivalent solid material of 9 cm thickness. Leakage was evaluated by setting 2 cm thick lead at the output of the radiation beam.From the obtained measurements, the necessary shielding has been estimated following the Report 147 by ICRP, and particularizing those values to a hypothetical installation. The dose received by a person who exceptionally would have to eventually stay inside the room with the patient was also analyzed. Results: The scattered dose rate ranges from 17.3 mSv/h at 0.25 m distance to 0.1 mSv/h at 2.5 m. Leakage represents 0.24% of the scattered dose rate. With these measurements and some assumptions on the workload and dimensions of a hypothetical treatment room it was estimated that the overall lead shielding for primary and secondary barriers was well below 1 mm, although it depends on each particular case. The overall absorbed dose to an eventual companion placed 0.5 m away from the patient is below 2 mSv after the complete treatment. Conclusion: Esteya shielding requirements are minimal, which facilitate its integration into conventional rooms. Furthermore, the presence of a companion during treatment is possible if absolutely necessary, recommending the use of a leaded apron and thyroid shielding.