Low-Dose Spiral CT Scans for Early Lung Cancer Detection
Former Worker Medical Screening Program (FWP)
Low-dose spiral computed tomography (CT) scanning is a noninvasive medical
imaging test that has been used for the early detection of lung
cancer for over 16 years (Sone et al. 1998; Henschke et.al.
1999). A low-dose spiral chest CT differs from a full-dose conventional
chest CT scan primarily in the amount of radiation emitted during
CT scans. Chest CT, in general, requires less radiation exposure
than other CT procedures because the air-filled tissues of the
lungs are not as dense as the tissues of other organs (i.e.,
less x-ray radiation is needed to penetrate the lung). Radiation
dose can be further reduced with lung cancer screening due to
the naturally high contrast between low-density, normal lung
tissue and lung nodules that could be suspicious for lung cancer
(International Commission on Radiological Protection [ICRP]
2007, Naidich et.al. 1990). The amount of radiation of the low-dose
chest CT scan (an estimated average of 1.5 mSv, for the majority
of former worker participants) is over five times lower than
that absorbed during a full-dose diagnostic chest CT scan (an
estimated average of 8 mSv). As further comparison, the estimated
average annual radiation exposure from natural sources is 3.1
The low-dose spiral chest CT scan is offered only to those
workers who are determined to be at elevated risk for lung cancer.
In addition, a participant must also be medically eligible to
be enrolled in the lung cancer screening program (i.e., having
sufficient lung function to withstand chest surgery).
The low-dose spiral chest CT scanning procedure requires that
the patient lie down on an exam table as it moves through a
sophisticated x-ray machine. The x-ray equipment is housed inside
a doughnut-shaped tube. As the table moves through the "doughnut,"
the x-ray beam inside the tube rotates around the patient, taking
more than 100 pictures in sequence. Because the continuous movement
of the x-ray tube within the doughnut is combined with continuous
movement of the table throughout the scan, the x-ray beam forms
a spiral path - hence, the term "spiral" or "helical" CT. A
special computer program processes this large volume of data
and produces two-dimensional cross-sectional views of the chest,
which are then displayed on a monitor. If needed, three-dimensional
images of internal structures or abnormalities within the lung
can also be created. During the procedure, the patient is asked
to be as still as possible and to hold his or her breath for
about 11 seconds.
Any screening test may detect some abnormalities that may appear
to represent early signs of possible illness, but studies show
that most of these abnormalities turn out to be false alarms.
This is also true of screening for lung cancer. The initial
low-dose CT scan may show a white spot in the lung, called a
nodule. Most nodules detected in the Early Lung Cancer Detection
(ELCD) program are actually small areas of scar tissue or healed
infection. In most cases, this can be determined on the initial
low-dose CT scan.
However, in other cases, the nodules are indeterminate; that
is, it is not immediately clear whether the spot is benign or
something of concern. For this type of nodule, the best course
of action is to look for any changes over time. Therefore, if
an indeterminate nodule is found, the patient will be invited
back for a second low-dose CT scan three or six months after
the initial scan.
If a nodule increases in size, the patient will be advised
to follow up immediately with his/her personal doctor, because
this nodule would now be considered suspicious for lung cancer.
In this case, his/her personal doctor will arrange for the necessary
consultations and procedures to find out whether or not the
nodule is a lung cancer and, if so, to treat it appropriately.
The most common follow-up procedures are further imaging studies,
such as a positron emission tomography (PET) scan. Some people
may undergo a lung tissue biopsy, which involves removing a
piece of lung tissue from the lung and examining it under a
Most of the nodules followed as part of the ELCD program do
not increase in size and are not cancerous. Many nodules may
actually shrink on follow-up scans. If the nodule is unchanged
or smaller, it is unlikely to be malignant, and the patient
will be invited to return for an annual repeat low-dose CT scan
one year from his/her baseline CT scan.
The annual scan is offered to everyone except those diagnosed
with either lung cancer or a major illness (including other
cancers) after enrolling in the ELCD program (that is, after
completing the initial CT scan). The program offers the initial
and annual CT scan and follow-up CT scans at no cost to the
participant. The ELCD program does not provide or pay for any
diagnostic evaluation and treatment of abnormalities discovered
on CT scan, but these costs are normally covered by health insurance
Henschke CI, McCauley DI, Yankelevitz DF, et al. Early Lung
Cancer Action Project: overall design and findings from
Lancet 1999; 354(9173):99-105. ICRP, 2007. Managing Patient
Dose in Multi-Detector Computed Tomography (MDCT). ICRP
Publication 102. Ann. ICRP 37 (1).
Naidich DP, Marshall CH, Gribbin C, Arams RS, McCauley DI.
Low-dose CT of the lungs: preliminary observations. Radiology
Sone S, Takashima S, Li F, et al. Mass screening for lung cancer
with mobile spiral computed tomography scanner. Lancet 1998;