ESTRO 2024 - Abstract Book

S3374

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

2965

Digital Poster

Characterisation of micro silica glass bead TLDs in electron radiotherapy

Shakardokht M Jafari 1,2,3 , Kai H Ng 2 , Antony L Palmer 1,2

1 Portsmouth Hospitals University NHS Trust, Radiotherapy Physics, Portsmouth, United Kingdom. 2 University of Surrey, Centre for Nuclear & Radiation Physics, Guildford, United Kingdom. 3 Trueinvivo Ltd, Surrey Technology Centre, Guildford, United Kingdom

Purpose/Objective:

Verification of electron radiotherapy dosimetry is critical to accurately treat cancer patients. Silica bead TLDs have been used in photon beams, including for in-vivo measurement, but not previously applied for electron treatments. The dosimeters have favorable properties due to their small size, inert nature, high sensitivity, linear dose response, dose rate & angular independence[i],[ii],[iii]. This study characterises and evaluates micro silica bead TLDs for use in electron radiation treatment.

Material/Methods:

A radiotherapy linac (Varian Truebeam) was used to irradiate TLDs in various electron treatment conditions: dose range 1-30 Gy, dose rates 100-1000 mu/min, and 0°,45°,90° angles, at 6, 12 and 18 MeV. Percentage Depth Dose (PDD) curves compared at entrance dose, R90, and R50 ranges to the reference data that was obtained using a parallel plate ionization chamber. A TLD reader (Harshaw 4500) was used. Each measurement point used 3 or5 beads for reduced uncertainty. Shadowing effect also assessed using EBT-3 Gafchromic film.

Results:

A dose response linearity with an R2 correlation coefficient of >0.999 was obtained for investigated range (fig1(a)). Dose rate response agreed within experimental uncertainty. Response of beads with angles of irradiation was within ±1%. Maximum PDD shift to reference data (ion chamber) was 0.5 mm. Entrance dose measured -5.2%, -6.3% and - 5.2% at 6, 12 and 18 MeV respectively. PDDs showed up to 2.0 mm differences in proximal and distal ranges of R90 at 6, 12 and 18 MeV. R50 range differed 0.0, 0.5, and 0.5 mm at 6, 12 and 18 MeV respectively (fig1(c)). An edge enhancement of 12.8%, 7.5%, and 4.7% at either side of the bead and shadowing effect of 45%, 33%, and 21% at the centre of the beads were observed which were varied with depth as shown in fig1(b) for 6, 12, and 18 MeV respectively.