Computed tomography, or CT scanning, is currently a popular and productive
way of examining virtually any part of the body in order to detect a tumor
or other abnormality. Using a beam of x-rays that rotates around the stationary
patient, along with sophisticated computer analysis, CT produces cross-sectional
images, or "slices," of the body area of interest. Most CT exams are done
to find the cause of a patient's symptoms or to rule out suspected disease.
But CT also may be used as a screening test, to detect disease at an early
stage before it produces any symptoms and while it remains limited enough
to be effectively treated. The best screening tests find disease in people
even if no symptoms have developed. As with other tests, however, disease
may be detected by CT in some who have it, but many other patients will
have changes that resemble disease when none is actually present (false
positive). In such cases there is a chance that further tests, or even
a surgical procedure, will be done when there is nothing wrong, increasing
the risk and overall cost.
It is not enough just to have a productive screening test. It is also necessary
to choose the right people to be screened, meaning those who, because of
age, blood test results, high blood pressure, or some other reason are more
likely than others to have a particular condition. Many screening tests
are not worth doing if no such "risk factors" are present because the chance
of finding something wrong is very small.
For some time targeted CT exams of specific body areas have been done to
detect particular conditions. Grading the amount of calcium in the coronary
arteries is an example; this test may identify people who are especially
likely to have a heart attack. Other CT exams are intended to identify early
tumors in the lung in current or former smokers; or polyps in the colon,
which, if removed, may prevent colon cancer from developing. There is reason
to believe that these "targeted" CT scans may have clinical value and be
cost-effective. Recently the idea of using CT to screen the entire body
(generally the chest, abdomen and pelvis) has gained increasing popularity
among the public and some radiologists as well. Such "targeted" CT scans
when done at the same sitting effectively constitute a "whole body" scan.
Whole-body CT screening (WBCT) as often advertised is a non-targeted exam
that usually is done without the intravenous contrast material injection
used in targeted CT scans.
Why Whole-Body CT Screening?
The public first became widely aware of whole-body CT as a health screening
measure not from reports in medical journals, but from a Wall Street
Journal article appearing in early 2000. The article reported on the efforts of
several radiologists who were seeking to make CT part of preventive medicine
programs. Whole-body CT can be viewed as a combination of targeted studies
covering the chest, abdomen, and pelvis. New facilities for whole-body
CT screening have been the subject of media reports mentioning the life-saving
potential of a "painless 15-minute test" (Chicago Tribune, Jan 15, 2003).
While hard numbers are not available, industry reports claim that whole-body
scans have doubled or possibly even tripled over the past two to three
years. People who are concerned about possibly harboring a threat to their
health and who can afford the cost have enthusiastically accepted the
idea of having a whole-body CT scan, which if normal is thought to provide
the comforting assurance that all is well. They are not especially concerned
that a high benefit-to-risk ratio has not been established for whole-body
CT or that it may not be a cost-effective approach, claiming that the
same criticism applies to accepted screening tests such as Prostate Specific
Antigen blood testing for presence of prostate cancer (which may lead
to many unnecessary biopsies and has not been proven to save lives).
Among many reasons for the impressive growth of CT as a diagnostic method
in recent years is that it does provide very high-quality and detailed pictures
of body organs and tissues. It is not scientifically proven that a patient's
likelihood of surviving goes up if cancer is found at a very early stage,
but present-day medical practice generally assumes that early detection
of cancer (or other types of disease for that matter) offers the best chance
for a good outcome. Whole-body CT appeals to many in the "baby-boomer" generation,
who tend to be health-conscious and willing to spend discretionary income
on seemingly promising medical strategies. Those who opt to have whole-body
CT certainly will be reassured if the findings are normal, but at the same
time they must not use a normal test as an excuse to continue dangerous
practices such as smoking or overeating. Moreover, a normal finding may
miss existing conditions (false negative), giving the patient a false sense
of well-being.
Performing and Interpreting Whole-body CT
For a whole-body CT screen the patient is positioned on an examining
table with the arms above the head. Brief periods of breath-holding are
necessary as the images are recorded. The scanner may cover the body for
a short time but the patient is able to see out. It is possible that a
person who feels uncomfortable in small closed areas will have trouble
with whole-body CT, but the procedure takes only about 15 minutes, and
the patient and technologist can communicate throughout. The results will
be read and interpreted by a radiologist, a physician who will send a
report to the patient's attending or referring physician. This physician
will, in turn, go over the results with the patient and, if necessary,
propose a treatment plan.
Several conditions associated with aging can make it difficult to interpret
whole-body CT findings in an elderly person. Many primary care physicians
are getting reports that specify possible lesions in the chest, abdomen
or pelvis, with suggestions that further exams be done to confirm or rule
out a disease condition. Some of the more common findings are:
-
A cyst or hemangioma—a benign collection of small blood vessels—in
the liver. Without injecting contrast material it may be very difficult
to distinguish between a hemangioma (which may be found in 10 percent
of
the population) from a tumor.
-
Adrenal adenoma, another "leave alone" lesion that occurs in seven percent
to 10 percent of the population and calls for no further work-up.
-
A cyst or hemangioma in the spleen, an organ where tumors are rarely
found.
-
Ovarian cyst, which typically is benign but may have to be followed up
by an ultrasound exam. Up to five percent of women may have ovarian cysts.
-
Small areas of scarring or local tissue thickening in the lung, which
may be left over from past infection. More than 90 percent of suspected
lung abnormalities seen on whole-body CT turn out not to be cancer.
It should be noted that all of these findings are occasionally encountered
in targeted CT studies and are managed by accepted follow-up protocols,
as they would be in self-referred patients who request whole-body screening
CT.
What's at Issue?
Part of the controversy about whole-body CT centers around the question
of whether patients should refer themselves for testing (self-referral)
without risk factors or symptoms of disease. Yet, whole-body CT fits in
well with the current healthcare scene in which individuals self-refer
themselves for a wide range of examinations including mammography, the
"heart test" for calcium in the coronary arteries, and even genetic testing.
Another issue revolves around "informed consent" notifications describing
the CT screening procedure and potential test results. At present there
is no requirement that examiners obtain informed consent, yet it may be
prudent for all test centers to obtain signed informed consent forms from
patients. By so doing, patients would realize that a potentially serious
condition may go undetected by whole-body CT, and also that there is a chance
that finding an abnormality that proves to be unimportant will still require
further evaluation. A compromise would be to make CT screening part of a
trial protocol. This would ensure that patients understand both the potential
benefits and possible risks of the procedure.
Radiation Risk
Like all x-ray examinations, WBCT carries a risk that cumulative radiation
doses will induce cancer later in life. Radiation doses from a typical
CT study are in general larger than for most conventional x-ray imaging
procedures. The risk of a single individual developing cancer from a single
exposure may be negligible, but exposure of large populations to radiation
from periodic CT screening exams may exceed recommended upper limits and
increase the overall risk. The actual radiation dose from any form of
CT varies from one patient to another depending on the area of the body
that is examined, the type of CT equipment that is used, and how it is
operated. Improvements in detector design have permitted lower doses but
possibly at the cost of poorer image quality.
The FDA cites a lack of scientific data showing that any clinical benefit
from WBCT screening of persons lacking symptoms or signs of disease will
outweigh the potential risks, including exposure to ionizing radiation.
The organization has never approved, cleared, or certified any form of CT
screening for asymptomatic individuals. Similarly, the Health Physics Society,
which monitors the radiation risk associated with various radiographic procedures,
asserts in a recent position statement that no medical use of radiation
should be adopted unless it yields clear medical benefit and that, at present,
WBCT does not meet this criterion. These concerns should not preclude CT
scanning when a physician has recommended a diagnostic examination for a
patient with symptoms of disease.
Cost Issues
When an abnormality is detected, the follow-up tests and treatment
can be costly. Insurance companies are more likely to cover the cost
of further testing if the screening study is positive, but there is
no assurance that they will cover the entire cost. Self-referred whole-body
CT itself is not covered. Regardless of whether it remains a consumer-driven
procedure or eventually is accepted and its cost reimbursed, screening
CT—like any preventive health care measure that may prolong life—undoubtedly
will increase overall healthcare expenditures. The important question
is whether the benefit from whole-body CT makes it worthwhile,
and this question cannot be answered until there is persuasive evidence
that detecting cancer at an early stage does in fact lengthen survival
or prevent deaths. If it does, overall health care costs certainly
would increase.
The Debate: The Pros and Cons
Researchers, physicians and healthcare administrators across the
globe are engaging in healthy scientific discourse about the controversies
and issues surrounding whole-body CT screening. Experts participated
in a recent panel discussion on CT screening at the 2002 scientific
assembly and annual meeting of the Radiological Society of North
America (RSNA 2002), and research studies on the topic continue to be published
in scientific and medical journals.
The Pros
Dr. Michael Brant-Zawadzki, a radiologist with wide experience in targeted
CT screening as well as whole-body CT, has found that in screening self-referred
patients older than 40 years, about one in a hundred will be found to
have a cancer. Cancers of the lung and kidney are among the most common
to be detected, but pancreatic cancer, potentially dangerous lesions of
the abdominal aorta called aneurysms, and lymphoma, a cancer of the white
blood cells, also have been found by screening CT (RadioGraphics 2002;22:1532-39).
Dr. Brant-Zawadzki cites a study carried out at the Mayo Clinic reporting
that, when CT screening for lung cancer was extended to the pelvic region,
14% of those examined were found to have clinically significant abnormalities.
The Cons
Dr. E. Stephen Amis Jr., estimates that as many as 80 percent of abnormalities
detected by whole-body CT may not be life-threatening. In a study presented
at RSNA 2002, more than one-third of nearly 1,200 patients were referred
for follow-up studies (Casola et al.). These patients may suffer considerable
anxiety, and some of the follow-up tests themselves involve an element
of risk. Surgery, for instance, carries risks of an adverse reaction to
anesthesia, bleeding, infection, and scarring. Additional radiologic exams
increase total radiation exposure, and there is a chance of an allergic
reaction if contrast material is injected. The other major concern about
whole-body CT is that a reading of "normal" may be incorrect and, as a
result, patients will be falsely reassured (false negative). The fact
that no intravenous contrast material is used in whole-body CT has been
held out as an advantage, but non-contrast scans of the abdomen and pelvis
provide only limited information. Small lesions in the liver, kidneys,
or pancreas may readily be missed. There is good reason not to screen
persons younger than 40 years, as the yield of significant disease will
be extremely low.
Current Policies on Whole-body CT
At present the American College of Radiology (ACR) believes that there
is insufficient evidence showing that whole-body CT screening prolongs
life or is cost-efficient. The College takes the position that whole-body
CT cannot be recommended for those who lack symptoms and who have no family
history of disease. Many findings that will not affect patients' health
will nevertheless cause anxiety, lead to unnecessary follow-up examinations
and treatments, and waste money. The U.S. Food and Drug Administration
(FDA) concurs that whole-body CT has not been convincingly shown to detect
disease early enough to spare patients from serious illness or premature
death. Even if such benefit is demonstrated, states the FDA, it might
not be great enough to offset potential harm from screening. The FDA has
said that a CT finding of abnormality despite the absence of significant
disease is far likelier than the discovery of actual life-threatening
disease. Even if a serious condition is found, the patient will benefit
only if there is effective treatment and if the disease is found early
enough to respond to this treatment.
The Future of Whole-body CT Scanning
New CT scanners currently under development will reduce the amount of
radiation. If screening is limited to persons older than 50 years, exposing
children or women of childbearing age will not be an issue. Future scanning
may routinely include the use of oral and intravenous contrast material.
Results could be reported to a central database so as to better determine
the effectiveness of whole-body CT.
It might be a good idea to offer whole-body CT along with other exams at
comprehensive screening centers. The same people who are likely to opt for
screening would tend to be interested in diet, fitness and other health-promoting
lifestyle changes, and screening could provide an opportunity to explore
these issues. For instance, the desirability of supplementing the diet with
vitamins, aspirin or other substances could be addressed. Even without a
formal risk reduction program, whole-body CT allows the radiologist or an
associate to talk with people about their health-related behaviors. Smoking
is an obvious behavior to target.
Further Inquiry
As happens with the invention of any new healthcare technology or the
discovery of new uses for established technologies, the issues surrounding
whole-body CT will continue to be investigated and debated by the scientific
and healthcare communities. More research will surely bring new socio-economic
and scientific findings to light prompting further professional discourse.
The debate is far from over.
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