Radiology debate

Discussion: the Pros and Cons of contact shielding

Contact shielding is one of the most divisive areas in the field of radiography today. Some practitioners believe it remains an essential part of protecting patients from radiation, while others believe the risk has reduced significantly in recent years. The matter was debated at a session at the online ISRRT (International Society of Radiographers and Radiological Technologists) congress in Dublin (August 20-22), with arguments presented for, and against, shielding in radiography.

Ahead of the session, “The Big Debate: Shielding in radiography - an outdated practice?”, an on-the-spot poll of online delegates was taken on the question, “do you believe contact shielding should be routinely used for optimisation?” Just over 37% of online delegates said ‘yes’, 42.9% ‘no’, and 20% said they were unsure.

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In introducing the speakers, debate chair Louise Rainford said guidance documents on the subject remained vague, while other advice said shielding should be discontinued for routine use. “So, where does that leave us as radiographers?” she asked. “It leaves us very confused but it is time we have this debate. The subject is very important for our profession.” With that, Dr Shane Foley, Head of Subject for Radiography at University College Dublin, stepped forward to argue for an end to shielding, while Mark McEntee, Professor of Diagnostic Radiography at University College Cork, stated the case for retaining shielding. Both participants drew on their own research and studies on the subject, interpreting findings to back the case for and against.

portrait of Shane Foley
Dr Shane Foley

In opening his case, Dr Foley said the poll result underlined “exactly why we are having this debate.” He said that in the decades since the benefits of organ dose reduction were introduced in the 1950s, the typical radiation dose delivered in radiography had dropped significantly. “We now have really good equipment, much better education and technology, and the risk has come down, as have the doses we typically deliver,” he said.

He said there are risks with shielding, such as inappropriate location of shielding. That can obscure the anatomy and lead to increased dose with the need for re-takes, or interfere with automatic exposure control. Using shielding in CT scans can also cause artefacts and noise. “In terms of the dose we deliver, and where is it coming from, the vast majority of radiation dose is in the primary x-ray beam and dose from scatter radiation is less than one per cent. Most of the scanner dose is coming from internal scatter within patient, which we cannot protect against.”

Stating that the majority of scatter dose is less than 0.1 mSv, he said there is a need for that to be put into perspective for patients and in the context of radiation that people are exposed to in everyday environments such as from air travel or radon gas.

There are benefits and risks with shielding, but he suggests radiographers should focus on alternatives, such as collimating the primary beam. He pointed to evidence that by collimating the beam on a radiography lumbar spine, saves the dose patients receive by 48%. Doing nothing on the topic is not an option, he warned. With the profession already split, that only sends a message to patients that radiographers cannot agree on the evidence. He also referred to a European consensus document that in general recommends against use of routine shielding for most exams.

portrait of Mark McEntee
Prof Mark McEntee

Professor McEntee said placing of a lead shield takes “very little effort” but as the risk is the patient’s and not the radiographer’s, patients should have a choice in this risk – something that is still “absent from the guidelines.” He said: “While doses may have decreased for clinical examination, the number of examinations that people are having has increased. In 1996, 149 out of 1000 patients entering hospital had a CT scan, but by 2012 that had tripled and tripled again by 2020. Now, about a third of patients that enter hospital have a CT exam. These examinations are also getting more complex, and common examinations now exceed 50 mSv.” He also pointed out that even low doses are dangerous and not all patients are the same.

In addition, there are patients that are at increased risk of diagnostic radiology, such as carriers of BRCA1/2 mutations, where radiation can be harmful, and children. He said that during CTA (computed tomography angiography), the breast may receive up to 24.3 milligrays (mGys) of radiation, compared to 4mGys with a mammogram. “If we displaced the breast and add lead on top of that, we can reduce dose to the breast by 10 mGys. If I was a patient with that mutation, I would want that protection but we just don’t know who those patients are. Lead shielding, correctly placed outside the field of view and away from the AEC, can help reduce these harms.” He pointed to ‘hundreds of papers’ that demonstrate that lead shielding can reduce dose to patient. “The evidence against using lead shielding is very weak,” he added. “As a profession, we need to carry out our own randomized controlled trials and do our own systematic reviews. Shielding in radiography is not outdated. If it is used outside of the field, it reduces dose and it protects patients.”

At the end of the debate, the poll was repeated and indicated a shift in position on contact shielding among online delegates with 47.2% believing “shielding should be routinely used for optimisation”, while 34.8% said not, and 18% remained unsure But what clearly emerged was the value of debating the subject, the need for further detailed research, and the importance of involving patients in the process of whether contact shielding should continue or be phased out. (MN)


Profiles:

Mark McEntee is Professor of Diagnostic Radiography at University College Cork and a recognized leader in clinical translation of medical imaging optimization and radiological perception. With more than 200 original papers in radiological journals, his publications explore novel technologies and techniques that enhance the detection of clinical indicators of disease, whilst minimising risk to the patient.

Shane Foley is Associate Professor and Head of Subject for Radiography at University College Dublin, a past-President of the Irish Institute of Radiography and Radiation Therapy, and a current Executive Board member of the European Federation of Radiographer Societies (EFRS). He is currently on the EuroSafe Imaging Paediatric working group and was the EFRS representative on the European consensus statement on contact shielding.

02.09.2021

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