SU‐C‐16A‐02: A Beryllium Oxide (BeO) Fibre‐Coupled Luminescence Dosimeter for High Dose Rate Brachytherapy

Purpose: Beryllium oxide (BeO) ceramics have an effective atomic number, zeff ∼7.1, closely matched to water, zeff ∼7.4. The purpose of this study was to evaluate the use of a beryllium oxide (BeO) ceramic fibrecoupled luminescence dosimeter, named RL/OSL BeO FOD, for high dose rate (HDR) brachytherapy dosimetry. In our dosimetry system the radioluminescence (RL) of BeO ceramics is utilized for dose‐rate measurements, and the optically stimulated luminescence (OSL) can be read post exposure for accumulated dose measurements. Methods: The RL/OSL BeO FOD consists of a 1 mm diameter × 1 mm long cylinder of BeO ceramic coupled to a 15 m long silica‐silica optical fibre. The optical fibre is connected to a custom developed portable RL and OSL reader, located outside of the treatment suite. The x‐ray energy response was evaluated using superficial x‐rays, an Ir‐192 source and high energy linear accelerators. The RL/OSL BeO FOD was then characterised for an Ir‐192 source, investigating the dose response and angular dependency. A depth dose curve for the Ir‐192 source was also measured. Results: The RL/OSL BeO FOD shows an under‐response at low energy x‐rays as expected. Though at higher x‐ray energies, the OSL response continued to increase, while the RL response remained relatively constant. The dose response for the RL is found to be linear up to doses of 15 Gy, while the OSL response becomes more supralinear to doses above 15 Gy. Little angular dependency is observed and the depth dose curve measured agreed within 4% of that calculated based on TG‐43. Conclusion: This works shows that the RL/OSL BeO FOD can be useful in HDR dosimetry. With the RL/OSL BeO FODs current size, it is capable of being inserted into intraluminal catheters and interstitial needles to verify HDR treatments.