A Review of Radiation Exposure from Musculoskeletal Computerised Tomography
Abstract
Computerised tomography (CT) is a remarkably useful clinical tool for physicians, and orthopaedists in particular. While CT accounts for only 5–10% of all diagnostic radiology procedures, it is responsible for up to two-thirds of the effective dose of radiation exposure that the public receives from medical interventions. For musculoskeletal CTs, the effect dose varies depending on what anatomical region is imaged. In general, imaging the spine and regions in close proximity to the axial skeleton such as the shoulders, hips orpelvis subject the patient to significant quantities of ionising radiation. This radiation exposure can be substantial and can theoretically increase the risk of cancer or heritable defects for later life. Recognition of these theoretical risks should play a role in the clinical decision-making process of any physician who regularly acquires these scans for the purpose of evaluating musculoskeletal conditions. Citation: European Musculoskeletal Review, 2010;5(2):69–72Tomography, X-ray computed, radiation dosage, neoplasms, radiation-induced, orthopaedics, diagnostic imaging
Over the past two decades, the increasing need for high-resolution, rapid acquisition imaging studies has led to significant advances in computerised tomography (CT) technology. For example, the development of helical and multidetector CT devices has drastically reduced scanning times and increased the efficiency of imaging processing. CT scans can now be performed in under one second for many body parts and give excellent 3D information in terms of the anatomy and pathology of interest. These innovations have undoubtedly contributed to the current popularity of CT, which is reflected by the over 62 million scans that are obtained each year in the US alone, up 20-fold from 1980.1
However, while CT is clearly one of the most expedient 3D imaging modalities available, as opposed to magnetic resonance imaging (MRI), these studies are not without risks. It is estimated that, while CT accounts for only 5–10% of all diagnostic radiology procedures, it is responsible for up to two-thirds of the effective dose of radiation that the general public receives from medical interventions.2,3 Within orthopaedics, musculoskeletal CT scans are frequently used for diagnosis, pre-operative planning and post-operative monitoring and assessment. As such, patients may receive repeated CT imaging when seeking orthopaedic treatment.
This article will discuss the radiation exposure associated with musculoskeletal CT imaging in three sections. The first will provide a brief overview of the concept of the effective dose and how it is used clinically. The second will review recent studies that have attempted to calculate the effective dose for musculoskeletal CT scans. Finally, the third section will discuss the risk of cancer and other illnesses associated with diagnostic radiation.
Effective Dose
The amount of ionising radiation to which a patient is exposed during medical imaging can be measured in different ways. The most basic is the physical quantity of radiation that is emitted from the source when the CT scan or plain radiograph is obtained. While this is a useful measure, it ignores patient factors. For example, larger patients require higher amounts of radiation to obtain adequate imaging. Similarly, the tissue type and even shape of the anatomy can affect how much radiation is actually absorbed. Additionally, some tissues are more radiosensitive than others. Therefore, because of this tissue variability and that most CT scans expose the patient to non-uniform, partial-body radiation, the most useful measure of overall risk from radiation exposure is calculated based on the specific dose absorbed by each organ.
To account for the above limitations, the effective dose represents a weighted, whole-body calculation of an individual’s estimated radiation exposure that considers the specific radiosensitivities of radiated organs.2,4–6 Thus, radiosensitive organs are given a higher weight when calculating the effective dose than non-radiosensitive tissue types. For example, the gonads receive higher weighting than bone due to their greater radiosensitivity and potential for malignant degeneration. As such, the effective dose represents one of the more common methods used to define radiation exposures from medical imaging and is particularly useful for direct comparisons of exposure between different imaging modalities (i.e. CT versus plain radiography).
For the purposes of this article, all dosage exposure estimates are given as aneffective dose to the patient. In addition to reporting the actual effective dosages in radiological units (i.e. miliSieverts [mSv]) we have also converted the dose estimates into the equivalent number of chest radiographs for ease of comparison across various studies.
The effective dose of a posteroanterior chest radiograph is known to be approximately 0.08mSv,3 which is roughly equivalent to the background radiation absorbed during a round-trip aeroplane flight from New York to London.7 Since chest radiographs are one of the most frequently obtained imaging studies, this quantity serves as a useful benchmark for evaluating the radiation risks inherent to other radiographic procedures.
