Glass beads and Ge-doped optical fibres as thermoluminescence dosimeters for small field photon dosimetry

Abstract

An investigation has been made of glass beads and optical fibres as novel dosimeters for small-field photon radiation therapy dosimetry. Commercially available glass beads of largest dimension 1.5 mm and GeO2-doped SiO2 optical fibres of 5 mm length and 120 µm diameter were characterized as thermoluminescence dosimeters. Results were compared against Monte-Carlo simulations with BEAMnrc/DOSXYZnrc, EBT3 Gafchromic film, and a high-resolution 2D-array of liquid-filled ionization chambers. Measurements included relative output factors and dose profiles for square-field sizes of 1, 2, 3, 4, and 10 cm. A customized Solid-Water® phantom was employed, and the beads and fibres were placed at defined positions along the longitudinal axis to allow accurate beam profile measurement. Output factors and the beam profile parameters were compared against those calculated by BEAMnrc/DOSXYZnrc. The output factors and field width measurements were found to be in agreement with reference measurements to within better than 3.5% for all field sizes down to 2 cm2 for both dosimetric systems, with the beads showing a discrepancy of no more than 2.8% for all field sizes. The results confirm the potential of the beads and fibres as thermoluminescent dosimeters for use in small photon radiation field sizes.

Feasibility study of silica bead thermoluminescence detectors (TLDs) in an external radiotherapy dosimetry audit programme

“…3, the positive value of mean percentage differences may suggest that, like other silicon based detectors [27,28] the silica beads slightly over respond (0.6% on average compared to alanine in this study). This was also noticed in previous work, [16,17]. However, all the values are within measurement uncertainty and so it is not possible to form a firm conclusion.…”

“…Silica beads have previously been characterised as novel high spatial resolution micro TLDs [14,15,16,17,18]. The particular silica beads employed have several potentially favourable physical characteristics as dosimeters in postal dosimetry audit of advanced radiotherapy.…”

Feasibility of using glass-bead thermoluminescent dosimeters for radiotherapy treatment plan verification

“…[9][10][11] The glass beads employed were found to have several potentially favourable physical characteristics as dosemeters in complex, radiation fields. They are small in size (2-mm diameter and 1-mm thickness), chemically inert, inexpensive, readily available and reusable.…”

“…9 Their performance in small field dosimetry applications has also been shown to agree within measurement uncertainty with other detectors; a high-resolution twodimensional array of liquid-filled ionization chambers and EBT3 Gafchromic film (Ashland) and was also confirmed by DOSXYZnrc Monte Carlo simulations (NRC, Ottawa, ON), for relative output factors and beam profiles for a range of small field sizes of a 6-MV photon beam. 11 Although glass beads are silicon-based TLDs and not soft-tissue equivalent, they have shown a close-to-uniform response over the megavoltage (MV) photon energy range which is commonly used in advanced radiotherapy techniques. 10 The maximum percentage difference compared with that obtained at 6-MV photons was shown to be 23.8% and 24.7% for 15-MV photons and 20-MeV electrons, respectively.…”

Evaluation of effective field size characteristics for small megavoltage photon beam dosimetry

“…Modern techniques in radiation therapy such as image guided radiotherapy (IGRT), intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and stereotactic radiosurgery (SRS), and stereotactic radiotherapy (SRT), lead to the use of small therapeutic photon beams for the treatment of cancer patients (1) . The absence of lateral electronic equilibrium (2,3) , source occlusion by the collimating devices, and energy spectrum changes as a function of field size (1,4) makes challenging in the dosimetry of small photon beams. Additionally, detector properties play a crucial role in the dosimetry accuracy (1) .…”