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Ann Thorac Surg 1998;66:1884-1885
© 1998 The Society of Thoracic Surgeons
a Division of Pulmonary and Critical Care, Medical University of South Carolina, Room #812-CSB, 171 Ashley Ave, Charleston, SC 29425, USA
Invited commentary
The use of decision analysis is increasing in the surgical literature [1]. Because this method of research may be unfamiliar to clinicians, it is worthwhile to review the technique of decision analysis before commenting on this study. Decision analysis is useful when it is desirable to quantitatively compare alternative treatment strategies. As pointed out by Berkmeyer and Welch in their article, "A Reader’s Guide to Surgical Decision Analysis" [2], there are four basic components to a decision analysis. The first is the decision model, which specifies the alternative strategies and the outcomes associated with each strategy. Second, probabilities for each of these outcomes are estimated from the best available literature and assigned to each decision point in the model. Third, a value such as cost, patient preference, life expectancy, or quality adjusted life expectancy is assigned to each possible outcome. These values are labeled utilities. Fourth, an analysis is performed to calculate the expected value of each strategy. This is accomplished by multiplying the outcome utilities by the probabilities of each occurrence. By calculating the expected value, a favored strategy is identified. A well-performed decision analysis includes a sensitivity analysis, which varies each of the baseline probabilities over a plausible range.
In this issue of The Annals of Thoracic Surgery, Scott et al performed a decision analysis of the cost-effectiveness of FDG-PET for staging non–small cell lung cancer. The model asks whether the addition of the FDG-PET scan to the current preoperative evaluation of the mediastinum in patients with lung cancer is cost-effective. The authors identify all relevent treatment strategies in Figure 1. Do the strategies make sense to the surgeon who may wish to order this extra test? The answer is clearly yes. The researchers use all the possible combinations of CT with or without PET scan to delineate benign from malignant lymphadenopathy before surgery. It is also apparent that Scott and coworkers included the important outcomes possible for each strategy. Next we turn to the probabilities for each of the outcomes. The authors of this study painstakingly reviewed the best available literature on the subject, and the baseline probabilities for each of these outcomes are shown in Table 1. The same table shows the range over which those baseline estimates were analyzed in the model. They seem reasonable, with the possible exception of the specificity of CT scan, which may be higher in patients with T1N0M0 lesions [3]. A higher specificity for CT could make PET scans less cost-efficacious. Satisfied with both the decision model and the baseline probabilities, we turn to the results. In this study, the favored strategy is one that uses PET only after a negative CT of the mediastinum, as compared to a strategy that uses CT scan alone. If the PET scan is positive, biopsy by mediastinoscopy is performed. If that is positive, the patient is not referred to surgery. The cost savings in this study are gained because less patients are referred for unnecessary thoracotomy by having a positive PET scan after a false negative CT scan. It should be noted that all of the decision strategies are equally efficacious. The life expectancy does not differ between any of the strategies. Thus, the cost benefit analysis depends completely on true differences in cost and not efficacy. It would appear from the study that the additional cost of PET scan in patients with a negative CT of the mediastinum is worth the benefit.
This study does not obviate the need for further evaluation of the role of PET scan in the staging of bronchogenic carcinoma. Although there is much excitement over the utility of FDG-PET for evaluation of the solitary pulmonary nodule and possibly for evaluation of metastatic disease, its current role in staging lung cancer is yet to be defined. A study in which patients undergo CT of the chest followed by FDG-PET scan and definitive mediastinal lymphnode sampling is warranted. The importance of the decision analysis performed here is that it defines a reasonable, cost-efficacious approach for evaluation of the mediastinum in preoperative patients with newly diagnosed lung cancer that is worthy of further study.
References
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