Derivation of factors for estimating the scatter of diagnostic x-rays from walls and ceiling slabs

Abstract

Computed tomography (CT) scanning rooms and interventional x-ray facilities with heavy workloads may require the installation of shielding to protect against radiation scattered from walls or ceiling slabs. This is particularly important for the protection of those operating x-ray equipment from within control cubicles who may be exposed to radiation scattered from the ceiling over the top of the protective barrier and round the side if a cubicle door is not included. Data available on the magnitude of this tertiary scatter from concrete slabs are limited. Moreover, there is no way in which tertiary scatter levels can be estimated easily for specific facilities. There is a need for a suitable method for quantification of tertiary scatter because of the increases in workloads of complex x-ray facilities. In this study diagnostic x-ray air kerma levels scattered from concrete and brick walls have been measured to verify scatter factors. The results have been used in a simulation of tertiary scatter for x-ray facilities involving summation of scatter contributions from elements across concrete ceiling slabs. The majority of the ceiling scatter air kerma to which staff behind a barrier will be exposed arises from the area between the patient/x-ray tube and the staff. The level depends primarily on the heights of the ceiling and protective barrier. A method has been developed to allow tertiary scatter levels to be calculated using a simple equation based on a standard arrangement for rooms with different ceiling and barrier heights. Coefficients have been derived for a CT facility and an interventional suite to predict tertiary scatter levels from the workload, so that consideration can be given to the protection options available.

Monte Carlo Modeling of Computed Tomography Ceiling Scatter for Shielding Calculations

“…Fog and Cormack (2010) concluded that, "For CT emissions, scatter over the shielding barrier can be considerable." Martin et al (2012) similarly state that, "The level of radiation scattered downwards from a ceiling slab into the control cubicle or into the adjacent room, is likely to exceed the protection dose criterion for virtually all CT scanning facilities." Calculations using the present model further support the premise that contributions to personal dose for individuals adjacent to CT scanner suites cannot be regarded as negligible or inconsequential.…”

“…The difference in beam quality will invariably affect the scatter ratios. Moreover, Martin et al (2012) simplified the overall equation for calculating ceiling scatter by importing coefficients that were only variable with kV, ceiling height, and barrier height, while other room geometry parameters remained fixed. Although it is acknowledged that these applied constants were based on considered estimations of typical CT room configurations, the model inherently dropped a degree of accuracy and adaptability to widely varying facility designs, particularly with respect to source and exposure locations relative to the barrier.…”

Both sides now: diagnostic imaging medical physics in two hemispheres

“…I have witnessed the work of such "experts", who have demonstrated little or no understanding of e.g., modern diagnostic imaging technology, or of modern healthcare delivery. Experts who deny the very real, and published phenomenon of "tertiary scatter" [10][11][12][13], using outdated paradigms for shielding design, resulting in unnecessary doses to staff and the public potentially in excess of legal limits. This is a real and serious issue, from Work Health and Safety, public health, regulatory and possible litigation perspectives.…”

COMP Report: A survey of radiation safety regulations for medical imaging x‐ray equipment in Canada

“…One paper that compared shielding design using NCRP 49 and NCRP 147 showed that NCRP 49 methodology overestimated the required thickness of Pb by up to 50% 10. NCRP 147 is not without criticism, however, including concerns about tertiary radiation scattered from the ceilings of CT and angiography rooms into control areas 11. For high workload rooms the dose to staff in adjacent rooms can exceed several mSv/yr 11.…”

“…NCRP 147 is not without criticism, however, including concerns about tertiary radiation scattered from the ceilings of CT and angiography rooms into control areas 11. For high workload rooms the dose to staff in adjacent rooms can exceed several mSv/yr 11. The British Institute of Radiology's (BIR) Radiation Shielding for Diagnostic x-rays published in 200012 and updated in 2012 6 uses a different approach to shielding calculation compared to the NCRP.…”