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In Radiology, an indication to investigate using any of its imaging armamentarium starts with:
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| Justification for the imaging test or investigation | ||||||
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| What is the best imaging test or investigation for you? | ||||||
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Just to cite an example: In
suspected gallstones, the best initial imaging test is an
ultrasound. It is preferred over an x-ray of the abdomen.
Only 10% of gallstones can be seen in plain radiographs of
the abdomen. If the reason for the test is screening, which is the best modality to investigate – if any? For example, for screening breast cancer in the appropriate age group, mammography has proven over time to be the best available for early detection. Yet one should be told, it cannot pick up 10-20% of early cancers. The ability to pick up cancer depends on the tissue composition of the breast, quality of the mammogram and ability of the interpreting radiologist reading the mammograms. ALARA refers to getting the optimum information while using the minimum amount of ionizing radiation in a particular situation, taking into account socioeconomic factors. This principle continues even though Radiology is no longer primarily radiography (x-rays). Today there are safety issues even in the use of ultrasound or magnetic resonance imaging. |
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| CT (computed tomography) scan & Radiation Dose | ||||||
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CT scans uses ionising radiation (x-rays) and because many cross sectional images are taken through the section of the body concerned, the doses of radiation can be quite high relative to the Chest X-ray. Where justified, the concern with radiation is negligible. The issue arises when apparently normal individuals are exposed to CT scans, especially whole body CT scans in a bid to screen for cancer. This increases the radiation pool to the population. Although CT scans form only about 5% of the total number of examinations, they contribute 40% of the total radiation dose received in radiological examinations (Unscear 2000 Report).
The advanced technology of
using multiple slices which can be very thin and with scan
times that are sub second per slice, makes it just too
tempting not to scan more sections of the body, scan more
phases and increase the scanning parameters to improve
signal in very thin slices (say 0.5mm sections of the body). |
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| Should you fear a CT scan then? | ||||||
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The answer is emphatically NO
if something has been discovered in preliminary tests such
as a radiograph, ultrasound or your doctor has diagnosed you
with a specific condition that is best assessed using the CT
scan. If it is going to make an impact to your treatment and
may save your life, the benefit far outweighs the risks.
Life is full of risks – such as crossing a road, smoking
cigarettes, driving a car or even just breathing the air
around you! Where justified, radiation risk is not an issue
anymore. |
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| Whole Body Screening CT – what’s the recommendation? | ||||||
CT scan has not been shown to be able to pick up diseases for which early detection and treatment will yield more benefits than harm. Not yet anyway. Therefore the risks may outweigh the benefits in the case of screening for disease in the absence of any signs or symptoms or even risk factors. This is the case even in the latest multislice CT scanners or the electron beam CT scanner. There is some basis to believe calcium scoring of the heart blood vessels will be able to help you and your doctor better manage the progress/development of the coronary artery disease, if present. The other areas where screening CT has some use is in lung cancer and colon cancer screening. However, the CT scans are just confined to specific areas of the body and not the whole body and only used in high risk individuals! In many other disease
conditions and cancers, there is no evidence yet that the CT
scan is useful for early detection. In other words, the CT
scan may prove to be normal but you may already have the
disease although you do not feel sick yet. Therefore, even
with a normal whole body CT scan, there is no 100% guarantee
that you do not have a specific disease or cancer. Not all
diseases might show up on the CT scan especially in their
early stages. |
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| Potential Harm of whole body screening CT | ||||||
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The problems start when the
modern multislice CT scan picks up many abnormalities which
may actually turn out to be harmless and may never affect
your health in anyway. However, because it has been
detected, further investigations may be needed or even a
biopsy or surgery, each of which has its own risks. The cost
incurred is not just in terms of money, but also anxiety,
worry and time entailed in seeing your doctor repeatedly and
going for many tests and even biopsy/surgery with their
attendant risks. It may also mean you need follow up tests
for some time. An example for this would be screening CT for lung cancer in smokers (high risk population) which may not reduce mortality from lung cancer even though detected at an earlier stage. A report in an international journal (Radiology 2005;235:259-265) showed that although screening CT managed to detect earlier lung cancers in smokers, some of these cancers might be so slow growing they may be non-lethal. In addition, some of the early cancers detected were so aggressive it did not make a difference that they were detected early! About half of those with lung nodules detected that went for surgery actually proved to be benign nodules and not cancer! The high rate of false positives is expensive and potentially dangerous for those who undergo surgery to remove them. Do not forget - lung surgery has risks – about 3-5% of those undergoing lung surgery die. Although the CT scan is “non-invasive”, there is the issue of ionising radiation discussed earlier. This may be equivalent to undergoing hundreds to more than a 1000 chest radiographs depending on the protocol and scanning parameters use. A cost effectiveness study was published recently (Radiology 2005;234:415-422). The authors compared whole body CT screening to routine care and found out that CT provided minimal gains in life (6 days) at an average additional cost of US$ 2,513 per patient. It would therefore be inappropriate for people at average risk of disease. They concluded that whole body CT was not cost effective and would add substantially to the financial burden on the health care system. |
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| What are the situations where a CT scan may be helpful? | ||||||
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The situation is different
when there are signs and symptoms and therefore the
probability of disease is higher. In addition, your doctor
has discovered some abnormalities and a targeted CT scan is
done to better evaluate the area in question. In another situation, the CT scan is used to stage the disease, i.e. to see the extent of the disease, for example in cancers which have been diagnosed. CT scan can also guide biopsies. The CT scan is also used in conjunction with other imaging investigations to give a better evaluation of the disease in question and therefore vital for treatment planning. There are many other imaging modalities to weigh as to which is best in any specific situation such as Magnetic Resonance Imaging (MRI), Ultrasound (US), plain radiographs (x-rays), fluoroscopic tests, special procedures under imaging guidance, nuclear medicine scans, mammogram, Positron Emission Tomography (PET) and today, PET is combined with CT to give both functional and anatomical information. It does sound complicated. Is one modality better than the other? Yes and no. It depends on the body part concerned and what question we have to answer and the suspected disease to provide a useful result and conclusion. Close teamwork and good communication channels between your doctor requesting the examination, and the radiologist is ideal so that you get the most out of your radiological investigation!
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| What is the stand of the College of Radiology, Academy of Medicine of Malaysia on whole body screening CT scans? 12 April 2005 | ||||||
 The College of Radiology,
Academy of Medicine of Malaysia, after reviewing all
available current data, does not recommend whole body
screening CT scan including routine CT lung, CT colonoscopy
and CT coronary arteries in healthy asymptomatic individuals
in the absence of risk factors as the risks outweigh the
potential benefits. Some other organisations that do not recommend whole body screening CT include:
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| References: | ||||||
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US Food and Drug Administration on Whole Body CT: www.fda.gov/cdrh/ct US Food and Drug Administration on Radiation Risks: http://www.fda.gov/cdrh/ct/risks.html American College of
Radiology Position Statement on CT Screening Examinations Health Physics Society http://hps.org/documents/CTPosStm.pdf National Radiological Protection Board (UK)/Health Protection Board Radiation Division: http://www.hpa.org.uk/radiation/default.htm Royal Australian and New Zealand College of Radiologists Media Statement on Whole Body CT http://www.ranzcr.edu.au/newsandevents/mediareleases/index.cfm Radiation Health and Safety Advisory Council (Australia) www.arpansa.gov.au/pubs/rhsac/st1_aug02.pdf NSW Environment Protection Authority. Information on whole body scanning 2003. www.epa.nsw.gov.au/radiation/ctbodyscans.htm New South Wales Health:
New Penalties to Control Whole Body CT Scan
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Copyright © 2001-2008 College of Radiology, Academy of Medicine of Malaysia Last
Updated: |
adiological
investigations are an important part of the workup a person
goes through in diagnosing suspected disease, cancer
staging, monitoring progress, treatment planning, screening
for recurrence of a disease as well as guiding intervention
such as biopsies.