Mahadevappa Mahesh
Professor of Radiology, Cardiology and Chief physicist, Johns Hopkins Hospital in Baltimore
There’s a new focus on radiation dose monitoring. Here’s how new technology can help clinicians, and how patients can help themselves.
Radiation dose tracking might sound esoteric, but it is increasingly important to everyone involved in imaging – including patients.
Mahadevappa Mahesh, Professor of Radiology, Cardiology and Chief physicist at Johns Hopkins Hospital in Baltimore, USA, says: “Dose tracking helps us ensure that the doses of ionising radiation delivered to patients when they have X-rays, CT scans, fluoroscopy and nuclear medicine are within specified ranges. “It is growing in importance around the world as the use of radiation-based imaging increases.”
Why dose tracking matters
The levels of radiation used in imaging are thought to increase the risk of developing cancer only by a very marginal degree. However, when results showed that in 2006, Americans were exposed to more than seven times as much ionizing radiation from medical procedures as was the case in the early 1980s, and that the increase was largely a result of the growth in CT scans and nuclear medicine, it triggered action internationally to limit exposures.
However, simply reducing the dosage of radiation used in imaging could lead to grainier and ‘nosier’ images, which increase the chances of missed or inaccurate diagnosis.
“The key is optimising the dose, so that we get the most useful image possible at the lowest dosage level,” says Dr Mahesh.
Monitoring dosages of radiation for therapy
In the USA, these considerations led the American College of Radiology (ACR) to establish diagnostic reference levels (DRLs) that specify optimal, size-specific dosages required to produce the most diagnostically-useful images of patients.
The ACR has developed a Dose Image Registry (DIR), in which data from 42 million exams (82 million scans) as of 2017, forms the basis of a radiation dosage tracking system. “It means that clinics can collect their own data, send it to the ACR, and receive reports on how their dosages compare with the averages locally, regionally and nationally,” says Mahesh.
Clinics are not required to take part in the dose tracking initiative, but the government provides incentives for them to do so, while insurance companies and regulators are starting to demand it.
The UK has had DRLs since 1989, which local imaging departments use to set and measure acceptable dosing, depending on what kind of equipment they use. National DRLs are in place to guide hospital trusts and imaging centres.
How technology helps alongside dose limitation
Manufacturers have responded to the pressure for dose limitation by producing technology that uses lower radiation doses to achieve optimum images.
Dr Mahesh says: “Automatic tube current modulation allows CT scanners to automatically vary the dosage according to the thickness of the body part being scanned.
“Iterative reconstruction technology allows for CT scan images that have been acquired at lower dosages, normally associated with higher levels of image ‘noise’, to be reconstructed to produce levels of quality normally only achievable with the use of higher dosages.”
Manufacturers have also improved detector technology, enabling better image results at lower dosage levels.
Meanwhile, computerised clinical decision support systems have been developed to help clinicians select the most appropriate image modality for a particular patient’s condition.
Patients can help clinicians optimise dosage
“All of these factors help ensure the use of appropriate doses, but even the best dose tracking systems will fail if clinicians do not use the resulting reports to review their practices,” says Dr Mahesh.
Patients can help themselves and clinicians here. Dr Mahesh says: “There is a thirst among patients for more information on imaging risks and, as clinicians, we are beholden to them to reduce their anxieties. Asking clinicians about the level of dosage used in any CT scan you are prescribed, tends to mean that the clinician will be more careful about optimising the image.”
