A feasibility study of applying thermal imaging to assist quality assurance of high-dose rate brachytherapy

Aim: High-dose rate (HDR) brachytherapy poses a special challenge to radiation safety and quality assurance (QA) due to its high radioactivity, and it is thus critical to verify the HDR source location and its radioactive strength. This study explores a new application for thermal imaging, to visualize/locate the HDR source and measure radioactivity using temperature information. A potential application would relate to HDR QA and safety improvement. Methods: Heating effects by an HDR source were studied using finite element analysis (FEA). Thermal cameras were used to visualize an HDR source inside a plastic catheter made of polyvinylidene difluoride (PVDF). Using different source dwell times, relationships between the HDR source strength and heating effects were studied, thus establishing potential daily QA criteria using thermal imaging. Results: For an Ir-192 source with a source radioactivity of 10 Ci, the decay-induced heating power inside the source was about 13.3 mW. After the HDR source was extended into the PVDF applicator and reached thermal equilibrium, thermal imaging visualized the temperature gradient of 10 K/cm along the PVDF catheter surface, which agreed with FEA modeling. For the Ir-192 source strengths ranging from 16.9 to 41.1 kU, thermal imaging could verify source activity with a relative error of 6.3% with a dwell time of 10 s, and a relative error of 2.5% with 100 s. Conclusion: Thermal imaging could be a feasible tool to visualize HDR source dwell positions and verify source integrity. Potentially, patient safety and treatment quality may be improved by integrating thermal measurements into HDR QA procedures.