Adding a chest CT scan to screening virtual colonoscopy (also known as CT colonography or CTC) isn't cost-effective in a cohort of average-risk patients, a new model-based analysis concluded. Although the additional anatomic coverage increased the clinical efficiency of CT-based screening, the combined test would not detect enough serious pathology to cover the costs of detection and follow-up of disease.
A previous study found that virtual colonoscopy was cost-effective compared to both optical colonoscopy and no screening, but it is unknown whether performing chest CT would increase or decrease the cost-effectiveness of screening, wrote Dr. Cesare Hassan from Rome's Nuovo Regina Margherita Hospital and colleagues.
"To assess coronary artery disease (CAD) and to screen asymptomatic people for early treatable lung cancers could, in theory, reduce the mortality related to cardiovascular attacks (the highest rated cause of death) and lung cancer (the highest-rated cancer-related cause of death) in the U.S. population," they wrote. "The aim of our simulation was to analyze the impact of performing chest CT on the clinical effectiveness and cost-effectiveness of CT colonography when screening average-risk subjects" (Radiology, April 2009, Vol. 251:1, pp. 156-165).
Hassan and his team, which included Dr. Perry Pickhardt and Dr. David Kim from the University of Wisconsin in Madison and Dr. Andrea Laghi and Dr. Franco Iafrate from the University of Rome "La Sapienza," used a Markov model to simulate the occurrence of serious diseases and death in a cohort of 100,000 U.S. subjects ages 50 to 100 years.
The model was based on screening once every 10 years between ages 50 and 80 years, with mortality rates and population data derived from the National Vital Statistics Report for the U.S.
"We simulated the natural history of both the adenoma-carcinoma sequence and the most serious diseases, which may be detected by performing unenhanced CT of the chest, abdomen, and pelvis, including ovarian cancer, pancreatic cancer, hepatocellular carcinoma, renal cell carcinoma, and bronchogenic carcinoma, as well as [abdominal aortic aneurysm (AAA)] and CAD," they wrote.
Screening efficacy was simulated differently for the various diseases based on available evidence. The presence of each disease was considered independently of the presence of the other diseases, and, key to the results, the cohort was assumed to be at average risk, which excluded current smokers, for example.
In their average-risk cohort, the authors assumed that the cancer-specific distribution of stages and associated costs and mortality would downshift 50% from regional to local disease. Adjustments for lead-time bias were accomplished by reducing the overall gain in life expectancy by 50% as the result of downstaging. No detectable precursor lesion was assumed for any extracolonic cancer.
According to the results, performing CTC and whole-body (chest) CT was both more effective and costlier than CTC alone, increasing costs by 48% per person from $9,223 to $13,605.
"Both strategies were cost-effective as compared with no screening, with an incremental cost-effectiveness ratio (ICER) of $17,672 (CT colonography alone) and $44,337 (CT colonography and whole-body CT), respectively, but performing CT colonography and whole-body CT was not a cost-effective option when compared with CT colonography alone (ICER, $164,020)," Hassan and colleagues wrote. The expected value of perfect information resulting from the tests was $520 per patient. An ICER of $50,000 to $100,000 is generally considered a reasonable cost for the use of a procedure.
VC's efficacy was found mainly in the saving of 9,767 (81.5%) life-years in the cohort due to prevention of 3,705 (prevention rate, 62.4%) cases of colorectal cancer and, to a lesser extent, to the early detection of abdominal aortic aneurysm (2,024 life-years; prevention rate, 16.9%). However, the impact of screening on abdominal-pelvic extracolonic cancers was marginal (199 life-years; prevention rate, 1.6%).
Sixty-five percent of the costs of CTC screening ($6,038 per person) was spent on the procedure, 25% ($2,278 per person) was spent on the treatment of the aforementioned six serious diseases, and 10% ($907 per person) was spent on following up false-positive results.
Adding chest CT to CTC added 2,672 life-years due to the prevention of myocardial infarction (2,390 life-years) and early detection of lung cancer (282 life-years), for an overall gain of 14,662 life-years compared to no screening, corresponding to a 22% increase in efficiency compared with CTC alone, they wrote.
"However, the higher efficacy was set off by a 48% increase in the program cost, leading to an overall expenditure of $13,605 per person," they wrote. "Although performing CT colonography and whole-body CT was still cost-effective as compared with no screening (ICER, $44,337), it was not a cost-effective alternative to CT colonography alone (ICER, $164,020)."
The simulation showed that adding chest CT to CTC is not cost-effective for the screening of average-risk subjects, due mainly to the poor efficacy of lung cancer screening in a low-risk population and the high cost related to the workup of false-positive results with CAD. The ICER for lung cancer screening of more than $400,000 per life-year gained was similar to that of a previous model of low-risk subjects.
"We also showed that when simulating a very high risk of lung cancer, as with active smokers, the cost-effectiveness of CT colonography and whole-body CT substantially improves," they added. "However, when simulating CT colonography and whole-body CT in a population with a sevenfold increase in lung cancer risk -- similar to the incidence rate assessed for heavy smokers -- the ICER of CT colonography and whole-body CT was still close to the accepted $100,000 threshold level, raising doubts about its cost-effectiveness in clinical practice."
The prevention of coronary artery disease was only moderately effective, and only a threefold increase in disease prevalence or a 73% cost reduction were associated with an ICER below $100,000, suggesting a potential cost-effectiveness for the combined scan only in selected scenarios, they added.
The authors cited a lack of knowledge of the natural history of extracolonic malignancies as a principal limitation. This prevented the simulation of their prevalence and may have underestimated the cost-effectiveness of the combined screening exam.
"In conclusion, our simulation shows that performing chest CT and CT colonography is not a cost-effective alternative to CT colonography alone, and further research is needed before it can be recommended in clinical practice," the authors concluded.
By Eric Barnes
AuntMinnie.com staff writer
April 7, 2009
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