Radiation field and dose inhomogeneities using an X‐ray cabinet in radiation biology research

Abstract

Purpose: X-ray cabinets are replacing 137 Cs/ 60 Co sources in radiation biology research due to advantages in size, handling, and radiation protection. However, because of their different physical properties, X-ray cabinets are more susceptible to experimental influences than conventional sources. The aim of this study was to examine the variations related to the experimental setups typically used to investigate biological radiation effects with X-ray cabinets. Materials and methods: A combined approach of physical dose measurements by thermoluminescence dosimetry and detection of biological effects by quantification of γH2AX and 53BP1 foci was used to analyze field inhomogeneity and evaluate the influence of the components of the experimental setup. Results: Irradiation was performed using an X-ray tube (195 kV,10 mA,0.5-mmthick copper filter, dose rate of 0.59 Gy/min). Thermoluminescence dosimetry revealed inhomogeneity and a dose decrease of up to 42.3% within the beam area (diameter 31.1 cm) compared to the dose at the center. This dose decrease was consistent with the observed decline in the number of radiation-induced foci by up to 55.9 %. Uniform dose distribution was measured after reducing the size of the radiation field (diameter 12.5 cm). However, when using 15-ml test tubes placed at different positions within this field, the dose decreased by up to 17% in comparison to the central position. Analysis of foci number revealed significant differences between the tubes for γH2AX (1 h) and 53BP1 (4 h) at different time points after irradiation. Neither removal of some tubes nor of the caps improved the dose decrease significantly. By contrast, when using 1.5-ml tubes, dose differences were less than 4%, and no significant differences in foci number were detected. Conclusion: X-ray cabinets are user-friendly irradiation units for investigating biological radiation effects. However, field inhomogeneities and experimental setup components considerably affect the delivered irradiation doses. For this reason, strict dosimetric monitoring of experimental irradiation setups is mandatory for reliable studies.

Dose Variations Using an X-Ray Cabinet to Establish in vitro Dose-Response Curves for Biological Dosimetry Assays

“…Due to the horizontal orientation of the tube and a lower height of the liquid level (5 cm vs. 1.2 cm), less shielding and absorption effects occur. In this study, it was irrelevant in most cases whether one or two tubes were irradiated in the center of the radiation field, and is thus an indication of a homogeneous radiation field together with the results of an earlier study ( 31 ). At least for the horizontal tubes it is possible to correct the dose deviation, e.g., by adjusting the irradiation time or by specifying the true radiation dose, since in these cases the dose gradient has no significant influence.…”

“…The following recommendations for the irradiation setup of blood samples are the result of the present and other studies ( 2 , 28 , 30 , 31 , 44 , 46 ):…”

“…In this study, all irradiations were performed in the center of the radiation field and only single sample vessels were irradiated. Previous studies have shown that many other factors, such as the field inhomogeneity, the energy spectrum of the X-rays, the dose rate and the shape, material, position and number of sample vessels or the volume of the cell suspension may have a significant effect on the absorbed dose ( 2 , 28 – 31 ). In this study, the reduction in tube size and blood volume (e.g., 2– or 5 mL tubes) would contribute to a lower dose gradient and thus a more uniform radiation of the blood samples.…”

“…The common use of additional filtering to produce X-ray spectra of a desired quality or to remove unwanted energy ranges from the spectrum leads to additional inhomogeneities ( 28 ). In addition, several radiobiological studies have shown that the experimental setup itself affects the irradiation ( 28 – 31 ), as X-rays have usually lower photon energies than sealed sources and are thus easier attenuated ( 32 ). The resulting dose variation could have a significant impact on the yield of aberrations induced and thus on the dose estimation in biological dosimetry.…”

Commissioning and Assessment of Radiation Field and Dose Inhomogeneity for a Dual X-ray Tube Cabinet Irradiator: To Ensure Accurate Dosimetry in Radiation Biology Experiments

“… 12 , 13 The lack of reproducibility in radiobiological experiments could potentially be exacerbated by the introduction of x-ray sources, with several groups reporting their dosimetry work for single x-ray tube equipment, which can be highly variable owing to the x-ray energy spectrum, dose rate, and other dosimetric variables. 14 , 15 , 16 , 17 , 18 …”