Lung cancer is the leading cause of cancer-related death worldwide. The poor prognosis of lung cancer has barely changed in the last decades, but the prognosis is better when the disease is detected earlier.
In comparison to the chest radiography, radiograph computed tomography (CT) is not hindered by the superimposition of anatomical structures and has a better contrast resolution. As a result, small lung cancers can be detected with greater accuracy. With the advent of the low-dose computed tomography (LDCT) scan it has become feasible to detect early invasive stage 1 lung cancer in 80–90% of cases.
The NHS is now (2019) funding mobile scanners as part of a national programme to diagnose lung cancer early, improve the care for those living with lung cancer and ensure each cancer patient gets the right care for them.
Low radiation dose computed tomography (LDCT)
Chest computerized tomography, Low radiation dose computed tomography (LDCT) is faster and less expensive than standard helical CT scanning and has been shown to detect nearly three times the number of small nodules detected by chest radiograph.
Recent advances in technology, including the multi-slice technology, cine-viewing and three-dimensional (3D) reconstruction techniques have further improved the ability of LDCT to detect and accurately characterise lung nodules. By reducing the tube current (mAs value) according to the so-called “low-dose” protocol (120 kV, 50 mAs), the radiation dose can be reduced to approximately one-eighth of the dose associated with a standard dose CT.
The purpose of LDCT screening is to identify the disease at a stage when a cure is still possible. It is reasonable to conclude that the use of LDCT would allow for earlier detection.
Ideally, the screening test would identify asymptomatic patients allowing for early intervention that will change the course of the disease and result in decreased mortality. In screening trials, survival from the time of diagnosis is often reported. However, this can be misleading as this measure is prone to a number of biases, including lead-time bias, length-time bias, and over diagnosis bias.
Lead-time bias may result in increased disease incidence, seemingly better survival, but no change in mortality, as defined by the proportion of cancer deaths among the screened population. For example, if a screen-detected cancer is ultimately fatal at the same timepoint that death would have occurred had it not been detected, the diagnosis is simply made earlier in the screened group without delaying the time of death. Length-time bias allows the growth rate of the tumour to affect the probability of detecting disease with screening.
Rapidly growing and more aggressive tumour’s produce symptoms that quickly result in a shortened window for screening. If the screening test is not repeated frequently, patients are likely to present with symptoms. For those with slow growing tumour’s, the reverse is true: there is a longer potential screening period during which patients are asymptomatic, resulting in a higher proportion of indolent tumour’s detected in the screened group; this creates an apparent improvement in survival while mortality may remain unchanged.
These LDCT mobile scanners feature innovative solutions that bring an increased level of flexibility and mobility. The solutions also help to enhance patient comfort with an innovative workplace design, allowing the patient to be at the centre of the examination and for the clinician to remain in close proximity to them for longer during the scan process. It is hoped these new mobile LDCT scanners will pave the way for extraordinary progress in diagnosing and treating the highly challenging disease of lung cancer.
The advent of LDCT scanning is making it possible to detect early invasive lung cancer in a screening context. The initial results are so promising that it can be anticipated that a great demand for the testing of smokers and ex-smokers will arise. It is therefore very important that low-dose computed tomography screening is evaluated in randomised trials as soon as possible in order to permit evidence based conclusions on the value of this technique. The potential benefit is enormous if computed tomography screening truly reduces mortality and extends survival from this disease. However, it is also important to take into consideration the potential hazards and harms incurred by a screening process in the population.
Edited by John Sandham