You read that right.
A recent study says that in America alone, hundreds of thousands are getting prone to cancer every year due to CT scans, most of the scans being unnecessary.
In fact, the study estimates that as many as 5 out of 100 new cancer cases might be arising due to CT scans!
What is CT scan, and why is it so harmful?
A CT scan is 'computed tomography', which means, a body part is scanned and pictured in a way that it looks like a slice of the body.
For making these slices of human body, they flash a series of X-rays on the body from an X-ray machine rotating around it. Individual pictures created by each burst of X-rays are then woven together by a computer into a whole picture - a slice.
In CT scan machine, there is donut type round structure with a hole (called gantry), through which the patient is passed. The X-ray machine is hidden inside the donut and it makes a circle around the person in a second or so. Once a series of X-rays are passed, the person is pushed by a few millimetres, and the X-ray machine again rotates around him, resulting in another slice-picture.
When the patient has been moved enough to cover the organ being pictured, all the slice-pictures are put together to make a 3-D picture of that organ. So, the physician has pictures of slices of the organ as well as the whole organ.
You mean X-rays pass through the patient hundreds of times in one CT scan?
That is right. For making one slice, 16 or 32 or more bursts of X-rays are flashed upon the patient and if a patient is thus moved 50 times, many hundred X-ray bursts would pass through him.
The number of X-ray bursts being used in a single CT scan depends on many factors, including the size and shape of the organ or the process being scanned. When a whole-body scan is made, the number of such bursts runs into thousands.
Why are X-rays so harmful? Is it these X-rays that are responsible for cancer from CT scans?
X-rays are a type of rays known as ionizing radiation. As the term indicates, such rays can ionize atoms into charged particles, called ions. This process breaks down molecules, which are nothing but atoms bound together with charges.
The DNA is a typed of complex biological molecule that has the capacity to make proteins. These proteins are part of all biological processes, either directly or as controlling proteins such as enzymes, hormones, etc. So ,when X-rays fall on the DNA molecule, they break it down or corrupt (= mutate) it, that leads to some cells misbehaving. A type of misbehaving cells lead to tumours and cancers.
The DNA also stores biological information that can be inherited. Therefore, when a living being's DNA mutates due to X-rays, it affects the types of traits parents pass on to the progeny. That might manifest in inherited deformities or diseases in the child.
When does imaging with CT scan become dangerous?
Though CT scans use X-rays, care is taken that X-rays fall only on the intended organ, leaving other body parts unexposed. The quantity and intensity of X-rays is also kept much within human body's tolerance limits.
However, problem arises in the following cases:
1. When CT scans are done while other, safer, ways of diagnosis are available. It is a well-known fact that a large number of such scans are mandated either due to commercial considerations or the physician playing safe. In a recent study in the US, it was found that up to 74% of CT scans being administered were unnecessary.
2. When CT scans are done excessively. The human body can tolerate the immediate impact of a CT scan and repair internal damages. However, the damage becomes too much for the body to repair when the scan is repeated within a short time, say, a few weeks.
3. When young patients are made to undergo such scans. The proneness to develop tumour and cancers in the lifetime due to CT scans is much higher among children as compared to grown ups. Yet, doctors do not hesitate in prescribing CT scans to child patients even when alternative imaging modes are available.
4. When pregnant women undergo CT scans. Though CT scan of the foetal area is strictly prohibited, it is reported that non-disclosure on the part of women and carelessness on the part of doctors sometimes exposes the foetus.
What should one do when advised a CT scan?
1. Check with the doctor if an alternative imaging or other test would do.
2. If the doctor insists, take a second opinion.
3. If the doctor wants a repeat CT scan, analyse - with another expert's opinion if required - if the likely benefits from the repeated CT scan far outweigh the likely harms.
4. In case of a child or a young adult, and a pregnant woman, be extra careful with imaging that uses ionizing radiation (X-ray scan, CT scan, CT with nuclear medicine).