Proposal of method dosimetry to realize in-vivo measurements in skin surface brachytherapy

Abstract Introduction Skin surface brachytherapy is a highly targeted radiation therapy used for treating superficial malignancies, offering precise dose delivery with minimal impact on surrounding healthy tissues. However, in-vivo dose verification remains a critical challenge in brachytherapy. Thermoluminescent dosimeters (TLDs) provide a promising solution for increased precision of dose delivery to cancer patients. This study proposes a TLD-based method to assess radiation exposure during skin surface brachytherapy, with a particular focus on TLDs calibration process and validation leading to the opportunity to reduce dose of radiosensitive structures such as the lens of the eye. Materials and Methods TL detectors were calibrated using both an Iridium-192 (¹⁹²Ir) source and a 6 MV photon beam , incorporating correction factors to enhance measurement accuracy. During measurements, TLDs were positioned on the skin surface of the anthropomorphic head phantom to absolute point dose measurements. The measured TLD doses were compared with treatment planning system (TPS) calculations to validate the proposed method. Additionally a specific analysis was conducted to compare the radiation exposure of the eye lens with and without the use of a protective eye shield with use of the anthropomorphic head phantom. Results TLDs response to a uniform radiation dose were within the range of ±10% of the mean. For the method of calibration used 6MV photons from medical linear accelerator, a value 3% for the energy correction factor was applied to account for the difference in sensitivity of the TLDs in 192 Ir and 6MV. For both calibration methods, with used appropriate calibration factors, obtained dose values for the anthropomorphic head phantom were within ±5% of the TPS dose values. The use of a lead shield placed in the phantom’s eye socket reduced the dose to the eye lens by up to 20%. Conclusions The developed TLD dosimetry method provides a precise and reliable approach for in-vivo dose verification in skin surface brachytherapy. By integrating calibrated TLD-based measurements, the correct implementation of radiotherapy plans can be verified. The study also confirms the protective efficacy of an eye shield in minimizing radiation exposure to the lens, reinforcing the importance of shielding strategies in clinical practice. Further validation and clinical implementation will contribute to improved patient safety and therapeutic outcomes in brachytherapy.