A radiophotoluminescent (RPL) glass rod dosimeter (GRD) and a small active volume p-type silicon diode detector are used for the measurement of the output factors from Gamma-Knife fields. The GRD system consists of small rod-shaped glass chip detectors and an automatic readout device. The output factors measured with the GRD from the 14, 8 and 4 mm helmets relative to the 18 mm helmet are 0.981, 0.942 and 0.877, respectively. Similarly, the corresponding output factors measured with the p-type silicon diode detector are 0.980, 0.949 and 0.867, respectively. The output factors are corrected for the end effect for each helmet. The output factors obtained from both detectors are in good agreement with the values in a recent publication and the values recommended by Elekta, the manufacturer. The directional dependence of these detectors is also measured. For the Gamma-Knife angle ranging from 6 to 36 degrees in the y-z plane of the stereotactic space, the measured angular dependence of the GRD is approximately 1.0% at a 4 MV x-ray beam. The response of the silicon diode detector indicates approximately 3-4% directional dependence for the same angular range for a 6 MV x-ray beam. The Gamma-Knife helmet output factors measured with the silicon diode detector are corrected for angular dependence.

Transmission of visible light and ultraviolet radiation was examined for a phosphate-glass photoluminescence dosimeter irradiated with Co source gamma rays in the dose range of 1-60 Gy (H2O). The transmission for the wavelengths (lambda) less than 600 nm decreased with increasing irradiation dose beginning at 6 Gy. An approximate 20% reduction of transmission was observed for a 60 Gy exposure at the wavelength of ultraviolet radiation used for excitation (lambda = 337 nm). However, no change of transmission was seen in longer wavelength region (lambda > 600 nm), which includes the range of photoluminescence (lambda = 610-710 nm). Relative efficiencies of measured photoluminescence agreed well with estimations that were calculated from the transmission reduction of ultraviolet radiation. This fact indicates that reduction of photoluminescence efficiency induced by high-dose gamma rays is attributable mostly to attenuation of the ultraviolet radiation from an excitation source, rather than saturation of trapping or recombination centers.

The time-resolved photoluminescence from a phosphate-glass photoluminescence dosimeter (GD-300) was compared for different quality radiations: relativistic heavy ions (12C and 40Ar) and 60Co gamma rays. The intensities of photoluminescence afterglow at 2-7 micro(s) after pulsed UV excitation, i.e., in the time range used for conventional dosimetry, soon reached stable conditions for all radiations. Whereas the early photoluminescence emission at the range less than 0.4 micro(s) was notably unstable for gamma rays only; it continued decreasing even at 2 d after irradiation. In contrast, the photoluminescence afterglows for the heavy ions were stable over the whole range after excitation. These results indicate that the process of photoluminescence-center formation is different for heavy ions and gamma rays.

A radiophotoluminescence dosimetry has been proposed using a spherical silver-activated phosphate glass with a diameter of 1.5 mm. A 6 MV photon dose of 2 Sv (2 Gy) was delivered to 14 spherical glass samples placed between two solid water phantoms at a depth of 10 cm. The samples were positioned within a 20 x 20 mm(2) centred at beam axis to ensure uniform dose absorption. A normalised output from a read-out system was obtained by simultaneously measuring luminescence from a non-irradiated reference and that from an irradiated reference to eliminate background contamination and time-varying fluctuation of the readout system, leading to a normalised standard deviation of 1.8%. A dose up to 3.5 Sv (3.5 Gy) was delivered to three spherical glass samples positioned between two solid water phantoms at a depth of 10 cm. The normalised output increased linearly with the applied dose.

A two-dimensional radiophotoluminescent system for medium-sized field dosimetry has been developed using a silver-activated phosphate glass plate with a dimension of 120mm×120mm×1mm and a readout unit comprising a UV excitation lamp and a CCD imager. A dose ranging from 0 to 400 cGy, provided by a 6 MV x-ray beam, was delivered to the glass plate oriented perpendicularly to the beam and positioned in a water phantom at a depth of 10 cm, where the center of the glass plate coincided with the linac isocenter. After the dose delivery, the glass plate was placed in the readout system. The CCD output intensity increased linearly with the applied dose. The angular dependence of response on the direction of radiation incidence was measured by rotating the glass plate in the water phantom, indicating that the output remained constant up to 75° from perpendicular incident direction, followed by a steep reduction down to 85% at an angle of 90°. A lateral dose distribution resulting from a 60mm×60mm irradiation was compared between the glass plate and an x-ray film having had the same exposure, showing that the glass plate and the x-ray film led to identical dose distributions. The dose reproducibility for a glass plate and the sensitivity variation among different glass plates were also evaluated.