Low-cost commercial glass beads as dosimeters in radiotherapy

• We examined the dosimetric properties of a low cost commercially produced glass seed beads.
• Glass beads are available in small size of 1–3 mm, suitable for dosimetry of small radiation fields.
• The results demonstrate a mean reproducibility of 0.23% (2 SD), batch homogeneity of within 5%.
• Dose response was linear over wide dose range tested for 1 cGy to kGy.
• Improved fading effect of 10% over one month following irradiation.

Recent developments in advanced radiotherapy techniques using small field photon beams, require small detectors to determine the delivered dose in steep dose gradient fields. Commercially available glass jewellery beads exhibit thermoluminescent properties and have the potential to be used as dosimeters in radiotherapy due to their small size (<5 mm), low cost, reusability and inert nature. This study investigated the dosimetric characteristics of glass beads. The beads were irradiated by 6 MV photons using a medical linear-accelerator and 60Co gamma rays over doses ranging from 1 to 2500 cGy. A thermoluminescence (TL) system and an electron paramagnetic resonance (EPR) system were employed for read out. Both the TL and EPR studies demonstrated a radiation-induced signal, the sensitivity of which varied with bead colour. White coloured beads proved to be the most sensitive for both systems. The smallest and therefore least sensitive bead sizes allowed measurement of doses of 1 cGy using the TL system while that for the EPR system was approximately 1000 cGy. The fading rate was found to be 10% 30 days after irradiation with both readout systems. The dose response is linear with measured dose over the dose range 1 to 2500 cGy, with an R2 correlation coefficient of greater than 0.999. The batch-to-batch reproducibility of a set of dosimeters after a single irradiation was found to be 3% (1 SD). The reproducibility of individual dosimeters was found to be 1.7%. No measurable angular dependence was found (results agreed within 1%). Dose rate response was found to agree within 1% for dose rates of 100 to 600 cGy/min. These results demonstrate the potential use of glass beads as TL dosimeters over the dose range commonly applied in radiotherapy.