One Minute Poster Pitches Archive

UK & Ireland Prostate Brachytherapy Conference 2024

Abstract number 3 

Development of a commissioning protocol for micro silica bead thermo-luminescent dosimeters (TLDs) for use in high dose rate brachytherapy.

William Hamblyn, Amani Chowdhury, Gerry Lowe, Peter Hoskin Mount Vernon Cancer Centre, Northwood, UK
Shakardokht Jafari,Nigel Biggs TrueInvivo, Surrey, UK 

Purpose: To develop a commissioning protocol for micro silica bead thermo-luminescent dosimeters (TLDs) for use in high dose rate brachytherapy using an Iridum-192 radioactive source. 

Methods: TrueInvivo provided the micro-silica TLDs and read-out services. Calibration involved two templates: 1) 20 TLDs placed 20mm from the central point in a circle and 2) 48 TLDs arranged in 4 spiral arms placed between 10 to 100mm from the centre. A spiral design was selected to prevent shielding from the inner beads. Each template underwent irradiation to 7Gy at 20mm from an Ir-192 source, with a reference calibration performed using a 6MV LINAC. 

Results: The results indicate an energy response factor (ERF) of 1.085 ± 0.004 at 20mm from the circular template. For reproducibility, an ERF from the four beads at 20mm on the spiral template was calculated to be 1.07 ± 0.2, demonstrating reasonable agreement between the two template irradiations. The ERFs from the spiral template normalised at 20mm displayed a linear relationship with distance from the source with an even spread of residuals and an R-squared value of 0.97. Beyond 40mm there is good agreement and no noticeable systematic difference between the arms. Below 40mm, on average arms 1 and 2 read 6% higher than arms 3 and 4 at 15mm, 20mm, 25mm, and 30mm. This is potentially attributed to the asymmetry in where the source comes to rest in the inner lumen of the needle. An anomaly at 10mm where arm 4 is 10% higher than arm 2 is likely attributed to the increased sensitivity to bead placement close to the source where the dose gradient is high. 

Conclusion: These promising results demonstrate the silica bead’s potential for in-vivo use in HDR brachytherapy. Further testing and validation are warranted to develop confidence, particularly in the high gradient region close to the source (<40mm).