The use of ionising radiation in trauma and orthopaedic theatres.
X-rays were discovered by Rontgen in 1895 whilst experimenting with a cathode tube at Wuerzburg University in Germany (Van Tiggelen 2001). The invention of the high vacuum X-ray tube by Coolidge in 1912 allowed X-rays of sufficient penetration to be generated that allowed medicine to take advantage of the potential of radiation (Van Tiggelen 2001).
The generation of X-rays
The X-ray emitting tube where X-rays are produced is a glass vacuum tube encased in lead that consists of a cathode and an anode (Armstrong & Wastie 2001). The cathode is a filament that is heated by the passage of an electric current that allows electrons to leave the surface. A high potential of more than 50kV between the cathode and anode accelerates these electrons towards the anode. On hitting the anode the electrons produce electromagnetic radiation or X-rays. The anodes are generally made of tungsten as this has a higher atomic number and results in the production of more X-rays. The X-ray tube needs a cooling system as a large amount of heat is also produced. The X-rays are filtered as they leave the X-ray tube to remove low energy X-rays that do not contribute to image production. The X-rays then generally pass through some medium before reaching the image receptor. The image that they produce depends on the medium that they have travelled through. X-rays are high energy electromagnetic radiations that travel in straight lines at the speed of light and are not affected by electric or magnetic fields (Armstrong & Wastie 2001).
Imaging principles in clinical practice
Radiology is the use of X-rays to cross materials to see inside them. When an exposure is taken X-rays are released from the X-ray tube as a primary beam. As the radiation passes through the body some of it is absorbed by a process known as attenuation. Anatomy that has increased density has a higher rate of attenuation, so bone has a higher attenuation rate than soft tissues. When the X-rays reach the image receptor the radiation that has passed through tissues with lower attenuation will be processed as darker. This is why bone which is dense shows up as white and the lungs which are full of air show up as black. Because different materials have varying abilities to absorb the emitted radiation a two-dimensional image can be constructed from the absorption pattern on a detection film. This is known as a radiographic film.
Over the last century scientific advancement in radiology and the invention of the computer have allowed all modalities of imaging to be digitally represented. The introduction of the picture archiving and communication system (PACS) has dispensed with the need for hard copy radiographs, and allows images to be viewed in multiple locations simultaneously and on screens with all manner of enhancement tools (Kreel 1991). This includes the operating theatre where the recently introduced WHO surgical checklist has a special check-box for the availability of imaging (Haynes et al 2009).
The perioperative uses of radiation imaging
The use of radiology in theatres can be divided into two broad categories. First, radiological investigations carried out prior to an operative procedure, which aid preoperative planning and are available in theatre to assist in perioperative decision making; second, radiological investigations taken during a procedure, which again optimise and enhance surgery.
Most trauma and orthopaedic procedures require a plain film radiograph for operative planning that commonly includes templating fixation implants and prostheses. Trauma patients are managed according to Advanced Trauma Life Support (ATLS) guidelines and if appropriate undergo cervical spine, chest and pelvis X-ray after their initial assessment, as well as further imaging as indicated. Several specific fractures require more sensitive imaging modalities to fully assess the fracture configuration: computerised tomography (CT) scans are the gold standard in pelvic, tibial plateau and calcaneal fracture. Operative planning can be further enhanced by the use of three-dimensional reconstruction of the fracture pattern by a computer.
Picture archiving and communication system (PACS) is a computer server dedicated to the storage, retrieval, distribution and presentation of images. This allows electronic images to be transmitted digitally and facilitates retrieval, distribution and display that are common problems with hard copy images. PACS now also has the provision of software programmes that allow templating for fixation implants and prostheses.
The use of X-rays in theatre has increased with the realisation that more accurate surgical reduction and stabilisation of fractures with X-rays results in better healing of the fracture. This also allows procedures to be performed through smaller incisions as full visual exposure is often not required. The image intensifier is a highly complex piece of equipment that uses X-rays to produce a continuous image feed which is displayed on a monitor (Kahler 2004). This is known as fluoroscopy and there are multiple examples of its use in trauma and orthopaedic theatres. A simple application is the insertion of a dynamic hip screw for fixation of a fractured neck of femur. Fluoroscopy is used to achieve a good closed reduction of the fracture, then a guide wire followed by a screw are inserted into the hip across the fracture under imaging and through a small incision.
Fluoroscopy allows the angle and position of the screw within the bone to be checked in multiple views to confirm accurate reduction. Recent advances have seen work being done to replace the twodimensional fluoroscopic image with an intraoperative cone beam CT (Khoury et al 2007) .
How X-rays create a radiation hazard
X-rays are a form of ionising radiation that can in certain doses cause damage to living tissue, skin burns, radiation sickness and cancer and, in high enough doses, death. X-rays are harmful as they have the ability to ionise atoms and molecules, and potentially to damage or kill living cells. X-rays interact with other atoms and molecules in two ways. Atoms consist of neutrons and protons in the nucleus and electrons in orbit around the nucleus. If an X-ray hits an inner orbit electron, the electron leaves the orbit and the X-ray is absorbed. This is called photoelectric absorption. If an X-ray hits an outer orbit electron, the electron leaves the orbit but the X-ray is not absorbed. Instead it is deflected but has a lower residual energy. This is called Compton scattering and results in a radiation field around the X-ray tube and poses a radiation hazard for those in the vicinity (Theodorakou & Farquharson 2008) .
X-rays interact with atoms and molecules in living tissues in the same two ways described above. These interactions can have a direct and indirect effect. The direct effect on cells is by disruption of the molecular bonds of the structures within the cell including the DNA. This can result in apoptosis or cell death, or division of the cell to produce an abnormal mutated cell and carcinogenesis (Rothkamm & Lobrich 2003). The indirect effect of X-rays on cells is through the ionisation of water molecules that results in disruption of molecular bonds. The probability and the severity of the effect of radiation on living tissue increase with increasing radiation dose.
This principle is used to treat tumours with radiotherapy. Conventional radiotherapy machines create a targeted beam of ionising radiation, which penetrates tissues and causes the release of electrons which damage cells, mostly as a consequence of DNA damage. Since ionising radiation also damages normal tissue the challenge for the oncologist is to set a radiation dose that causes maximal damage to the cancer and minimal damage to the surrounding normal tissue (Vaidya et al 2005).
Radiation is the process by which energy is emitted by one body, travels through space or a material, and is absorbed by another body. It is called radiation because it radiates outwards from the source. Radiation is either non-ionising, such as thermal radiation or light, or ionising, such as alpha particles, beta particles and neutrons, which are the forms that are most dangerous but also have the most application for medical use.
Humans are constantly exposed to radiation in several different forms. Cosmic radiation comes from outside our solar system and is negligible in amount. Terrestrial radiation comes from sources like the chemical potassium found in buildings all around us. However, the biggest source of background radiation is from Radon-222 which is produced by decay from Radium-226. This is found wherever there is uranium in the world and is released as a gas. Radiation exposure is measured in Sievert (Sv) where 1Sv is equal to 1J of energy absorbed per 1kg of matter. The dose required for radiation poisoning is an acute dose of 5,000mSv. The radiation from natural sources varies geographically between 2mSv to 20mSv per year (Dewey et al 2005). Man-made sources of radiation are produced by medical procedures such as X-rays, nuclear medicine and radiation therapy. The typical radiation dose from a limb or joint X-ray is less than 0.01mSv. The radiation dose for a pelvis X-ray is 0.7mSv and increases to 10mSv for a CT of the abdomen and pelvis. Man-made sources represent around 15% of the total average background radiation (Clark 1997).
All radiological procedures carry a risk. The International Commission on Radiological Protection (ICRP) has developed three important principles in radiological protections (ICRP 60 1991). These are: justification, optimisation and limitation.
Exposure to radiation should only be performed if it provides a net benefit. The risk incurred from undertaking the procedure must be balanced against the benefit for the patient from the information the imaging provides. All exposures should be kept as low as reasonably achievable. Individual exposure should be dose limited. The limits set for members of the public is 1mSv and for occupationally exposed staff including theatre staff, 20mSv. These limits do not include background radiation or radiation exposure for personal medical treatment.
Some human organs are more sensitive than others to the effects of radiation. The gonads are particularly vulnerable and are exposed in imaging of the lumbar spine and pelvis as well as in barium enemas. Precautions should therefore be taken to protect sensitive areas in patients with lead gowns. Finally, it should also be noted that irradiating the foetus in utero is especially hazardous because the rapidly dividing cells are very radiosensitive; the main risk being induction of childhood cancers. A risk benefit assessment should be made in any such cases and exposure to radiation in the first trimester should be avoided. This has implications not only for the patient but also for staff working in radiation-prone areas and local guidelines should be followed.
Risk to theatre staff and necessary precautions
All staff in theatres or wards where radiological imaging techniques are used are at risk from radiation exposure. For staff working regularly with radiation, the potential for harm comes from the cumulative effect of exposure over a length of time. There are many steps that can be taken to reduce this cumulative effect and these are summarised in Table 1. In operating theatres, the patient and the image intensifier should be placed at the optimum position. Radiation exposure is greater at the image intensifier end with the X-ray tube and lower behind the image receptor. The image receptor should be placed as close as possible to the patient (Kahler 2004). Screening time should be kept to a minimum by reducing the number and duration of exposures. The field size should be kept to a minimum to reduce radiation. Most modern image intensifier machines have an image memory facility that should be used. Other methods and devices that reduce exposure include proper beam focusing and filtering as well safe housing of the radiation source (Herscovici & Sanders 2000).
Theatre staff should stand as far away as is practical from the radiation source. X-rays obey the inverse square rule and the intensity of X-rays decreases as the square of the distance from the source increases. Moving away from one meter to two meters, reduces radiation exposure to a quarter; moving to three metres reduces exposure to a ninth. A study looking at the radiation dose operating staff receive during hip fracture surgery concluded that at a within a two-metre radius of the patient, gowns and thyroid neck protectors should be worn They also stated that at a distance of greater than two metres, theatre staff would not need to wear a lead gown because the very low dose of scattered radiation (Alonso et al 2001). The authors however disagree with this and in a high-stress environment where the image intensifier may be changing positions it is difficult to fully adhere to the two-metre rule, and all theatre staff wearing lead gowns and thyroid neck protectors eliminates an additional potential hazard.
Lead gowns of 0.5-1.0mm should be worn to absorb the radiation and provide protection. These are available as one- and two-piece gowns. The gowns should be handled carefully to avoid cracking of the protective material. All staff exposed to radiation should wear a personal radiation dosimeter under their protective apron to record personal exposure. Additional protective garments include thyroid shields and lead acrylic glasses, or head shields with lead acrylic visors. Lead screens reduce exposure to X-ray radiation but are not commonly used in the UK trauma and orthopaedic theatre setting. They can be mounted on the operating table or the ceiling. All equipment ranging from the image intensifier to the protective garments should be regularly inspected by the radiology department (Herscovici & Sanders 2000). It is also important that all staff regularly exposed to radiation receive training and updates to make working with radiation as safe as possible for them and other members of the team.
The role of team work and good communication could not be overemphasised. The radiographer has primary responsibility for screening and the operator has primary responsibility for the patient. Good communication between the radiographer and the operator is crucial to produce a satisfactory image and to reduce radiation exposure to patient and theatre staff. A lack of consistent names for various movements of the image intensifier and ambiguity in commands often leads to confusion between the radiographer and the operator. Knowledge of the movements of the image intensifier and consistent names for these various movements can improve the efficacy of communication between radiographers and operators, avoid confusion and improve theatre time utilisation (Chaganti et al 2009).
X-rays have revolutionised the delivery of medicine and nowhere is this more evident than in the trauma and orthopaedic operating theatre. Despite the obvious integral role for X-rays it is important to bear in mind the risks it can pose to patients and theatre staff. This highlights the need for a thorough understanding and awareness of radiation, as well as a sound knowledge of the precautions required for using this technology.
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Mr Matthew S Prime
MBBS, BSc, MRCS
Orthopaedic Registrar, Department of Trauma and Orthopaedics, Charing Cross Hospital, London
Mr Wasim S Khan
MBChB, MSc, MRCS, PhD
Academic Clinical Fellow, University College London Institute of Orthopaedic and Musculoskeletal Sciences, Royal National Orthopaedic Hospital, Stanmore
Mr Sujay Dheerendra
Research Fellow, Department of Trauma & Orthopaedics, Royal Free Hospital, London
Mr Nimlan Maruthainar
Consultant Orthopaedic Surgeon, Department of Trauma and Orthopaedics, Royal Free Hospital, London
No competing interests declared
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by Matthew Prime, Wasim Khan, Sujay Dheerendra and Nimlan Maruthainar
Correspondence address: Mr W Khan, UCL Institute of Orthopaedics, Royal Orthopaedic Hospital, Stanmore, HA7 4LP. Email: firstname.lastname@example.org
Table 1 Necessary precautions for theatre staff exposed to radiation Necessary precautions for theatre staff exposed to radiation * The patient and the image intensifier should be placed at the optimum position. * Image intensifier screening time and field size should be kept to a minimum. * Theatre staff should stand as far away as is practical from the radiation source. * All theatre staff should wear lead gowns, thyroid neck protectors and a personal radiation dosimeter under their protective gown. * Lead gowns should be handled carefully to avoid cracking of the protective material. * All equipment, ranging from the image intensifier to the protective garments, should be regularly inspected by the radiology department. * All staff should receive training and updates to make working with radiation as safe as possible for them and other members of the team. * Team work and good communication.
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|Title Annotation:||CLINICAL FEATURE|
|Author:||Prime, Matthew; Khan, Wasim; Dheerendra, Sujay; Maruthainar, Nimlan|
|Publication:||Journal of Perioperative Practice|
|Date:||May 1, 2010|
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