To measure the out-of -field mean photon energy and dose imparted by the secondary radiation field generated by 6 MV and 6 MV FFF beams using TLD-300 and TLD-100 dosimeters and to use the technique to quantify the contributions from the different sources that generate out-of -field radiation. Methods: The mean photon energy and the dose were measured using the TLD-300 glow curve properties and the TLD-100 response, respectively. The TLD-300 glow curve shape was energy-calibrated with gamma rays from 99m Tc, 18 F, 137 Cs, and 60 Co sources, and its energy dependence was quantified by a parameter obtained from the curve deconvolution. The TLD-100 signal was calibrated in absorbed dose-to-water inside the primary field. Dosimeters were placed on the linac head, and on the surface and at 4.5 cm depth in PMMA at 1-15 cm lateral distances from a 10 × 10 cm 2 field edge at the isocenter plane. Three configurations of dosimeters around the linac were defined to identify and quantify the contributions from the different sources of out-of -field radiation. Results: Typical energies of head leakage were about 500 keV for both beams. The mean energy of collimator-scattered radiation was equal to or larger than 1250 keV and, for phantom-scattered radiation, mean photon energies were 400 keV for the 6 MV and 300 keV for the 6 MV FFF beam. Relative uncertainties to determine mean photon energy were better than 15% for energies below 700 keV, and 40% above 1000 keV. The technique lost its sensitivity to the incident photon energy above 1250 keV. On the phantom surface and at 1-15 cm from the field edge, 80%-90% of out-of -field dose came from scattering in the secondary collimator. At 4.5 cm deep in the phantom and 1-5 cm from the field edge, 50%-60% of the out-of -field dose originated in the phantom. At the points of measurement, the head leakage imparted less than 0.1% of the dose at the isocenter. The 6 MV FFF beam imparted 8-36% less out-of -field dose than the 6 MV beam. These energy results are consistent with general Monte Carlo simulation predictions and show excellent agreement with simulations for a similar linac. The measured out-of -field doses showed good agreement with independent evaluations. Conclusions: The out-of -field mean photon energy and dose imparted by the secondary radiation field were quantified by the applied TLD-300/TLD-100 method. The main sources of out-of -field dose were identified and quantified using three configurations of dosimeters around the linac. This technique could be of value to validate Monte Carlo simulations where the linac head design, configuration, or material composition are unavailable.
In microCT imaging, there is a close relationship between the dose of radiation absorbed by animals and the image quality, or spatial resolution. Although the radiation levels used in these systems are generally non-lethal, they can induce cellular or molecular alterations that affect the experimental results. Here, we describe a dosimetric characterization of the different image acquisition modalities used by the microCT unit of the Albira microPET/SPECT/CT scanner, which is a widely used multimodal imaging system in preclinical research. The imparted dose at the animal surface (IDS) was estimated based on Boone’s polynomial interpolation method and experimental measurements using an ionization chamber and thermoluminescent dosimeters. The results indicated that the imparted dose at surface level delivered to the mice was in the 30 to 300 mGy range. For any combination of current (0.2 or 0.4 mA) and voltage (35 or 45 kV), in the Standard, Good, and Best image acquisition modalities, the dose imparted at surface level in rodents was below its threshold of deterministic effects (250 mGy); however, the High Res modality was above that threshold.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.