The routine is familiar to anyone who’s broken a bone or been cursed with elaborate dental problems: the physician will give a short explanation of why an X-ray is necessary and instruct you to sit still during the procedure. They will then leave the room. The whole experience often lasts less than a minute, but the implication raised in being left alone – that the procedure carries its very own unique side effects – is obvious.
The fear that exposure of human tissue to ionising radiation (of which X-rays are just one example) can cause cancer is not a new one. The radiation that is used during an X-ray or CT scan has the potential to knock the electrons circling the atoms in human tissue out of their individual orbits; this creates ions, the constituent strands of which can be outright destroyed by coming into contact with DNA. In most cases, any damage is repaired by the body with ease, but in the few cases where that doesn’t happen, the whole strand can mutate, resulting in the growth of cancerous tumours many years down the line.
Typically, the radiation dose inflicted on the body is so small that any risk of developing cancer is negligible. However, proximity to low doses over time has been linked to an increased risk of developing the disease since at least the 1950s, when higher-than-average leukaemia mortality rates were discovered among radiologists.
Walking out of the room is essential to reducing that risk for doctors. However, the increasing popularisation of CT scans – which emit radiation 150-1,100 times the strength of a normal X-ray – has rekindled the debate over how to reach a compromise between the risk of the patient developing cancer and the reward of solving an immediate medical problem.
This discussion has posed an almost existential crisis among paediatricians, particularly those treating patients with chronic conditions that require the frequent and accurate medical imaging that only CT scans can provide. As more evidence emerges to show that the procedure does indeed increase the risk of developing cancer, the result may well be that a lower quality of life will have to be sustained at the expense of slower imaging cycles.
In small doses
The orthopaedic department at the Children’s Hospital of Los Angeles (CHLA) thinks it may have avoided that scenario altogether with the installation of a new ultra-low-dose imaging system for early-onset scoliosis: the EOS system. Used to provide 3D images of the spines of young patients with scoliosis, the device emits only 2% of the radiation of a standard X-ray.
"One of the things that a scoliosis or spinal surgeon absolutely relies upon is good imaging," says Dr David Skaggs, chief of orthopaedic surgery at CHLA. "That’s how we can tell if the patient’s condition is better or worse, or requires surgery, as well as an operation’s results. And the downside of that has always been the incurring of a decent dose of radiation on the patient."
Skaggs has specialised in paediatric orthopaedics for over two decades, although the desire to treat spinal conditions dates back to his childhood. "I wanted to be an orthopaedic surgeon since I was five years old," he recalls. "It sounded really fun to be able to fix broken people and replace worn-out parts. As I did my residency at Columbia University, I realised any time I had a baby on my lap or I was playing with kids I was happy. So for that reason, I kind of selfishly went into paediatrics, just so I’d be happy every day."
A disproportionate amount of Skaggs’ time is absorbed in caring for scoliosis patients. According to the National Scoliosis Foundation, the condition affects seven million people in the US, with onset usually occurring in young adolescents. Almost 85% of cases are idiopathic, necessitating near-constant monitoring of the patient’s spine to chart any progression in their condition.
Meanwhile, around 600,000 visits to private physicians alone by scoliosis sufferers are recorded annually in the US. Of these, 38,000 of the most serious cases will eventually undergo spinal fusion surgery. By this point, the spine is frequently curved beyond 40° and appears as a letter ‘C’ below the skin – but the after-effects of such an operation on Skaggs’ young patients have been profound.
"You take a child whose body had become deformed, and over the course of a few hours they become entirely ‘normal’ in function and appearance," he says. "They leave the hospital an inch and a half taller. But the most striking thing is watching the mental changes in these teenagers. They’re usually girls, who can’t help having scoliosis at that sensitive time in life, and they start to feel like they fit in and have a bit more self-confidence."
Reaching the point where surgery is judged to be unavoidable comprises a long sequence of X-ray or CT scans to determine the progression of spinal deformation, degree by excruciating degree. This regime can also extend beyond the operating table, to determine whether the procedure achieved permanent success, or to carry out the select advanced therapies that might require it.
The kids are all right
This was the case with five-year-old Zayden Rainey. "He has a spinal rod to straighten his crooked spine," says Skaggs. "We’re doing it in a new way that is non-surgical. By placing a large rotating magnet on top of his back, it makes this rod inside his body extend. We can do this as frequently as once a month, if we want to, and straighten out his spine in an incremental fashion. By doing that, we’re not using too much force, not being too dangerous, and not doing surgery."
All of this would be possible before the EOS imaging system, but with an increased chance of developing cancer later in life, which would inevitably have meant fewer scans to lessen that risk. With the new device, Zayden can undergo a lengthening procedure every two months. What’s more, stepping into the machine – an open-plan design reminiscent of a measuring stick one might encounter in a playgroup or kindergarten – is easier to use and a far less intimidating experience for very young patients.
"On average, Zayden would have gotten six X-rays a year," says Skaggs. "Now, all of a sudden, we can do it at 50-times-lower radiation. We’re able to keep a much closer eye on his treatment and make sure that things are being done safely, and that there are no problems with using less radiation."
The EOS imaging system also provides 3D imaging of bone – vital in determining the degree to which individual vertebrae or limbs are deformed. "Again, we’re able to achieve this with much less radiation and in a three-dimensional fashion," says Skaggs. "In the past, in order to obtain that, we had to move up to a CT scan, which is lots of radiation."
Under pressure
CHLA’s embrace of the EOS imaging system is not unique. Similar ultra-low-dose scanners have been adopted at UF Health Shands Hospital in Florida and the Riley Hospital for Children in Indianapolis. Two hours away in San Diego, Rady Children’s Hospital has had a similar system to CHLA’s for the past five years.
However, Zayden’s case is symbolic of a fundamental shift in how orthopaedics specifically, and in radiology more generally, evaluates the effect of ionising radiation on the body. With the recognition that many doctors may have been overprescribing X-ray exams and CT scans, it is increasingly being thought that new technology must be adapted to break with the practice and enhance care for future generations. In the US alone, the number of such examinations increased from three million in 1980 to 72 million by 2007.
"It’s absolutely seen as a problem," explains Skaggs. "One of the difficulties is that you often don’t know it’s a problem until you see someone 50 years later having the X-ray dose. It’s something we’re slowly learning as we get more lifetime follow-up on people. And I think that many people in medicine are fearful that there may be more radiation-induced cancer than we currently realise."
Only recently has this hypothesis been tentatively confirmed, by large surveys of patients who have had CT scans in the UK and Australia. Both studies found that the procedure contributed to higher incidences of brain cancer and leukaemia, by 20-25% in the case of the latter.
"On the flipside of this, many doctors are now hesitating to get studies," says Skaggs, "because they don’t want to irradiate the person. And if a study is not done, we may be missing a treatable medical condition. It’s always about finding a balance."
More studies are set to be published in the coming years, but research into less powerful scanning methods has proceeded apace. In 2013, the American Association of Physicists in Medicine issued new guidelines for radiologists in conducting CT scans, while institutions including Massachusetts General Hospital have begun to consciously monitor the frequency with which such procedures are recommended for patients.
For all its advantages in limiting ionising radiation, the EOS imaging system is not perfect. For one thing, the quality of its 3D imaging leaves something to be desired.
"Let’s say that a patient has a truly misshapen vertebra," Skaggs explains. "It’s supposed to resemble a cylinder, almost like a tuna can. If this particular person has one that looks like a triangle, it’s called a hemi-vertebra. The EOS system could look at that well from one direction or another, but it can’t really three-dimensionally form it perfectly. If I’m going to be doing surgery on a child with such a vertebra, I would still probably request a CT scan."
The technology is also still relatively new, which naturally makes it more expensive than your average medical imaging device. However, Skaggs is confident that the new focus on dose management within radiology will lower the cost over time. "As people look at the bigger picture, I’m sure they’ll realise that cancer’s expensive," he says. "It will, I think, save society money in the long run if we use machines like this."
