Broad Beam Attenuation in Concrete for 50 to 300-Kvp X-Rays and in Lead for 300-Kvp X-Rays

Trout, E. Dale; Kelley, John P.; Lucas, A.C.

doi:10.1148/72.1.62

Cited by 17 publications

(4 citation statements)

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“…The x-ray attenuation data in narrow and broad beam geometry measured in the context of shielding and room design is available for various materials in kilovoltage beams. [6][7][8] However, the broad beam data reported in the literature cannot provide information on the interface effects.…”

Section: Introductionmentioning

confidence: 99%

Forward dose perturbation at high atomic number interfaces in kilovoltage x‐ray beams

Das

1997

Medical Physics

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High atomic number (Z) materials such as lead, used for field shaping and shielding normal tissues in kilovoltage beams could produce significant dose enhancement in the forward direction contrary to our normal belief with respect to the attenuation of photon beams. Such a dose enhancement has not been studied in kilovoltage beams, which is investigated in this study. Using a Siemens ortho-voltage unit (60-240 kVp) and a thin window (5 microns) parallel plate ion chamber, forward dose perturbation factor (FDPF) was measured at interfaces created by high- and low-Z materials. The FDPF is defined as the ratio of doses with and without an interface (FDPF = Di/Dh; where Di is the dose at an interface and Dh is the dose in a homogeneous medium). Results indicate that dose enhancement (FDPF > 1) as high as 20-fold can be observed for a thin (> or = 0.02 mm) Pb sheet in contact with soft tissue. The magnitude of FDPF is relatively independent of field size and falls off exponentially with Pb thickness. The typical photon beam attenuation takes at a thickness > 1 mm. This intense dose enhancement is localized within 250 microns of the interface. The FDPF is energy dependent but saturates above 140 kVp, unlike the backscatter dose perturbation that peaks around 200 kVp. The FDPF varies inversely with the thickness of high Z and distance between the surface and high-Z medium. The FDPF falls off rapidly to a level of photon transmission usually predicted by exponential attenuation when distance is increased. In conclusion, with kilovoltage beam, a high-Z medium placed in contact with soft tissue may not attenuate radiation dose unless adequate thickness and proper distance between the surface and high-Z medium is used. The localized intense dose enhancement (approximately 20-fold) created by the high-Z interface could be exploited for clinical use.

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Section: Introductionmentioning

confidence: 99%

Forward dose perturbation at high atomic number interfaces in kilovoltage x‐ray beams

Das

1997

Medical Physics

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“…(238) Figures 21 and 22, and Table 6, indicate the absorbed dose rate (kerma rate) measured in air due to scatter in typical situations. Figure 21 shows the variation with accelerating potential of x rays scattered at 90" from various thick scatterers (Wachsmann et al, 1964). The beam is filtered so that its effective energy is about half the maximum photon energy; thus the figure may be used for gamma rays by reading from the curves the percentage scatter at the point corresponding to twice the gamma-ray energy.…”

Section: Scattering Of X Rays and Gamma Raysmentioning

confidence: 99%

Appendix

1982

Ann ICRP

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Introduction (224) The design of shields against x rays and gamma rays, and the estimation of radiation doses to staff and to patients undergoing radiological procedures is a common radiation protection task. This Appendix contains a substantial amount of output data, data on scattered radiation and of transmission data in graphical and tabulated form. It also contains some guidelines on design procedures in order to fulfil the criteria based on optimization considerations including cost-effectiveness analysis. Some new material, particularly from NCRP Publications 49 and 51 is included, which was not available at the time of the publication of ICRP Publication 15. Outputs of x-ray generators (229) The outputs of x-ray generators, at a certain distance from the target, can be predicted with reasonable accuracy for a given potential, tube current, and beam filtration. The output is, however, a function of the type of generator and of the target material and configuration. When possible, therefore, the output of the generator of interest should be measured. (225) Typical outputs on the axes of the x-ray beams are shown in Figs. 14. When calculating outputs for distances other than the ones shown, one may find it necessary to take air attenuation into account, especially at low potentials. (226) The reference for Figs. l-4 are as follows: Fig. 1 O'Riordan and Catt (1968); Fig. 2 Glasser et al. (1959); Fig. 3 upper curve Kaye and Binks (1940); lower curve Miller and Kennedy (1955). More recent measurements have confirmed the accuracy of Figs. 1 and 2; Birch, Marshall and Ardran (1979), HPA report series No. 7. Figure 4is also taken from Birch, Marshall and Ardran (1979). Outputs of gamma-ray sources (227) The outputs of gamma-ray sources, for which transmission data are provided in this appendix, are given in Table 1. Narrow beam Goldie et al. (1954) Unidirectional broad beam ICRP Publication 21 Diverging broad beam Greene and Massey (1961) Diverging broad beam Kirn and Kennedy (1954) Diverging broad beam Miller and Kennedy (1956) Diverging broad beam Maruyama et al. (1971) Unidirectional broad beam NCRP Report No. 49 Steel, concrete 15, 18 Diverging broad beam

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“…showing that the characteristics of the radiation generators were different [5,7,8]. Therefore, these differences in radiation generators and radiation quality may limit the use of data in NCRP Report No.…”

Section: Introductionmentioning

confidence: 99%