ESTRO 2021 Abstract Book

S1302

ESTRO 2021

PO-1577 Evaluation of a new Automated TLD Reader for silica bead radiotherapy dosimetry T. Knapton 1 , M. Masterson 1 , A. Parmer 2 , A. Nisbet 3 , S. Jafari 2 1 TRUEinvivo ltd, Medical Physics, Guildford, United Kingdom; 2 QAH Hospital, Medical Physics, Portsmouth, United Kingdom; 3 UCL, Medical Physics, London, United Kingdom Purpose or Objective To present results of the first performance testing of a new and novel automated silica-bead TLD Reader, the DOSEmapper TM Reader. This new system for radiotherapy dosimetry can read up to 400 silica bead TLDs as a single strand, without the manual handling of current TLD readers, enabling a practical approach for significant increases in TLD coverage. The DOSEmapper TM Reader has been designed to reduce the overall time it takes for each bead to be read and therefore reducing the overall time for the results to be obtained. We assess the performance and ease of use of the automated device for in vivo dosimetry. Silica Bead TLDs which have previously been shown to be linear in dose response, energy and angular independent, cheap and inert using Harshaw 4500 TLD reader [1], were now studied with the DOSEmapper TM Reader. To evaluate the capabilities of the automated DOSEmapper TM Reader for Silica Bead TLDs, the Reader was investigated for its noise level, light contamination, reproducibility, linearity and overall clinical usability. Materials and Methods The Silica bead TLDs were irradiated by 6 MV photons using a radiotherapy linear accelerator, at a depth of 5 cm and 10 cm of backscattering material for each desired dose level. Noise level and light contamination were measured using by running the Reader with no TLD beads present and with the addition of a black out cloth. Reproducibility was assessed by repeating measurements on 2 arrays made up of 100 bead TLDs. The linearity was tested over a range from 1 cGy to 40 Gy and determined using the R-Squared value. Results Glow curves were recorded using the third-party software Spectlab and were further reviewed using a bespoke inhouse software developed to view multiple Glowcurves at once (Figure 1). The noise level of the DOSEmapper reader is high, with doses of < 5 cGy indistinguishable from background. The addition of a black out cloth reduces the noise level by 0.1% indicating no light contamination. The Reader shows a reproducibility of within 3%, k=1, and linearity in the range of 5 cGy to 20 Gy showed an R-squared of 0.999 with saturation occurring at >20 Gy (Figure 2).

Conclusion The automated reader removes the tedious one-by-one handling of standard TLDs typical of other TLD readers and also reduces the time it takes to read individual TLDs by splitting the preheat and main heat cycles onto 2 separate planchets. The reader was also proven to have the capability to read up to 400 beads in one run with a good reproducibility. Further improvements are required to reduce the background noise, ensuring lower doses become distinguishable from background. Saturation was also seen at >20Gy, however, testing was run with a single sensitivity thus further investigations are required to determine the full range. References: