Dosimetric properties of radiophotoluminescent glass rod detector in high-energy photon beams from a linear accelerator and Cyber-Knife

A fully automatic radiophotoluminescent glass rod dosimeter (GRD) system has recently become commercially available. This article discusses the dosimetric properties of the GRD including uniformity and reproducibility of signal, dose linearity, and energy and directional dependence in high-energy photon beams. In addition, energy response is measured in electron beams. The uniformity and reproducibility of the signal from 50 GRDs using a 60 Co beam are both ±1.1% (one standard deviation). Good dose linearity of the GRD is maintained for doses ranging from 0.5 to 30 Gy, the lower and upper limits of this study, respectively. The GRD response is found to show little energy dependence in photon energies of a 60 Co beam, 4 MV (TPR 10 20 =0.617) and 10 MV (TPR 10 20 =0.744) x-ray beams. However, the GRD responses for 9 MeV (mean energy, Ē z =3.6 MeV ) and 16 MeV (Ē z =10.4 MeV ) electron beams are 4%–5% lower than that for a 60 Co beam in the beam quality dependence. The measured angular dependence of GRD, ranging from 0° (along the long axis of GRD) to 120° is within 1.5% for a 4 MV x-ray beam. As applications, a linear accelerator-based radiosurgery system and Cyber-Knife output factors are measured by a GRD and compared with those from various detectors including a p -type silicon diode detector, a diamond detector, and an ion chamber. It is found that the GRD is a very useful detector for small field dosimetry, in particular, below 10 mm circular fields.