The effectiveness of CT scans is not in doubt: quick, accurate and diagnostically precise, CT changed the face of medical imaging when it was introduced in the 1970s. Since that time, its use has continued to soar, climbing from three million scans in 1980 to 85 million in 2011, with many lives saved as a result.

However, in recent years, we have seen something of a backlash towards CT, with doubts emerging as to whether these scans are always necessary. While estimates vary, research suggests that as many as a third of CT scans serve little medical purpose, ordered when a different imaging modality would be sufficient or when no exam is needed at all.

Although cost is a factor against CT here, it is far from the most important one. A CT scan exposes the patient to a powerful dose of radiation – in some cases up to 200 times what they would experience from an X-ray. It is thought this may increase the patient’s lifetime risk of cancer, causing fear that the supposed remedy is becoming worse than the disease itself.

Legalised morality

In the US, an upcoming legislative change is expected to weed out many unnecessary exams. The Protecting Access to Medicare Act, signed into law in 2014, will require physicians to consult ‘appropriateness criteria’ before ordering a CT exam. In essence, this will mean ignorance is no longer a factor: while doctors will still be free to follow their judgment, they will have the best available medical information at hand.

Unfortunately, there have been delays in the law’s implementation, and it now seems unlikely that the correct mechanisms will be in place by the original deadline of 2017. In the meantime, it falls to individual hospitals to determine their own course of action.

At Massachusetts General Hospital, radiation exposure from CT exams has long been flagged up as a concern. Intent on reducing radiation wherever possible, the hospital has taken steps to curtail the number of unnecessary tests and to bring down radiation dosage. Its proportion of inappropriate CT exams has fallen from 6.0% in 2006 to less than 1.5% today.

According to Dr Dushyant Sahani, head of CT at Massachusetts General, the hospital considers limiting radiation to be a ‘moral obligation’.

“The safety of our patients has always been our number one priority,” he says. “We have been investing in radiation dose reduction efforts and research since the proliferation of CT scans in the mid-90s. It’s a cultural issue for us – people pride themselves on ensuring they are providing the safest environment – and all our staff members, including radiologists, technologists, researchers, physicists and equipment engineers, are engaged in these efforts of lowering radiation dose.”

In their most basic form, these efforts involve a commitment to safety checks – checking and double-checking patient information, and the type of exam to be performed. After the exam is ordered, the radiologist assesses its applicability, and after it has been signed off, the technologist follows suit. This layered safety approach helps reduce human error, ensuring the patient receives the correct exam and that the right procedure is being pursued.

Here, the hospital relies on ‘smart protocols’ – detailed descriptions of how each exam should be conducted and how much radiation to use. Each protocol is created based on clinical indication, the patient’s age and body type, and any further information that has been provided.

“They’re the collective effort of a specialty radiologist and technologist,” explains Sahani. “Once they have been approved, they are pre-programmed on the scanner, meaning the technologist has to just pull the protocol and run it for that patient. That reduces the opportunity for error and simplifies the technologists’ workflow, as they don’t have to make any adjustments on their own.”

While these smart protocols are helpful across the board, they are particularly useful in the case of paediatric patients, for whom the radiation dose needs to be kept very low. In part, this is simply a matter of body size – a smaller patient will require less exposure overall – but it also has to do with children’s radiosensitivity. As a general rule, the younger the child, the more hazardous the scan may be to their DNA.

This is well supported by data, though the accuracy of such information is debatable. In general, the true risks of medical radiation are tricky to determine, with data extrapolated from incidents such as the atomic bomb blasts of World War II. And while estimates abound – the National Cancer Institute (NCI) has suggested around 2% of future cancer diagnoses may be directly attributed to CT scans – their accuracy is a matter of some debate.

Balancing act

Only recently have researchers started to track population data for patients who have received CT scans, a task problematised by the length of time it can take for a cancer to develop. But so far, the evidence suggests that young patients are far more vulnerable in the long term. To cite just one example, a 2012 study found that children who had received multiple brain CT scans were three times more likely than their peers to develop brain cancer or leukaemia further down the line.

“I don’t know if I have a clear answer regarding the risk associated with diagnostic imaging, but we believe it is still prudent to lower radiation dose as much as we can, and that explains some of the investments we have made,” explains Sahani. “Often, perception is reality – patients feel vulnerable and there is a lot of anxiety. So there is no dose that we feel is fine. It is desirable that we make the radiation dose so low that the risk from any of these exams becomes negligible.”

While this is a laudable mission, the difficulty lies in preserving image quality. Radiologists must walk a fine line between reducing exposure and reducing image noise. Lower the dose too much, and the exam may be difficult to interpret, necessitating follow-up scans and a higher dose of radiation overall. Mass General therefore uses specialised software that tracks the individual dose and the cumulative dose the patient has received over time.

“That gives us an opportunity to compare our dose with benchmarks published by the American College of Radiology, allowing us to assess our success or failure,” says Sahani. “We have managed to lower our dose for a head exam by 25%, for a chest exam by 28%, for an abdominal and pelvic exam by 39%, for kidney stones by 55%, and for cardiac CT by 75%. For follow-up CT with kidney stones, we have reduced radiation by 87%.”

Make the cut

Of course, the most foolproof means of reduction is simply to avoid administering any radiation at all. With that in mind, the hospital uses an intelligent IT solution called ‘decision support’, helping to identify situations where an MRI or ultrasound may prove as effective as CT. For example, women’s pelvic issues may be best addressed with pelvic ultrasonography, and follow-up exams for Crohn’s disease can be performed with MRI. In both of these instances, CT was routine procedure in the past.

“Decision support requires doctors to answer certain questions regarding their patients; based on their answers, it looks to see if the ordered exam is indeed appropriate,” says Sahani. “It gives a colour-coded signal: when it’s green, that means it’s an appropriate test; orange means it’s OK, but not the most attractive test; and red is clearly an inappropriate test. So that eliminates unnecessary scans.”

Particularly in a large hospital, where a patient may be shuttled from one team to the next, computerised systems of this kind are critical. They ensure each team is on the same page – aware of which exams have been ordered and where the justification lies – as well as fending against the scheduling of duplicate exams.

This kind of foresight is liable to pay off in the long run. Since January, certain outpatient departments have fallen foul of the new NEMA Standard XR-29 (otherwise known as the MITA SmartDose Standard).

All imaging equipment must now include DICOM-compliant radiation dose structured reporting, dose check features, automatic exposure control, and reference adult and paediatric protocols. The penalty for noncompliance is a 5% reduction in reimbursement, set to rise to 15% by January next year.

“Fortunately, we took care of these issues a while back, so that all our scanners are in compliance with the requirements for the law,” says Sahani. “We take advantage of new technology and exploit any new software that is available for lowering radiation dose or improving image quality – we keep a very aggressive schedule for replacing outdated equipment.”

While Mass General is undoubtedly ahead of the curve in terms of its dose reduction efforts, the hospital is not resting on its laurels. With the ACR’s guidelines perennially changing and new laws set to bite, it’s safe to say an imaging department’s work is never done.

As Sahani puts it: “We haven’t yet reached where we ultimately want to be. The benefits of CT scans in  the medical community are pretty well established, and so to reap those benefits, it is critical that we undertake clinical research efforts. We also need to keep looking at new technologies and innovations to ensure that our radiation doses from CT scans are extremely low.”