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Ann Thorac Surg 1998;66:1876-1883
© 1998 The Society of Thoracic Surgeons
a Department of Surgery, Creighton University, Omaha, Nebraska, USA
b The Crump Institute for Biological Imaging and Department of Molecular and Medical Pharmacology, Division of Nuclear Medicine, and Department of Biomathematics, University of California Los Angeles School of Medicine, Los Angeles, California, USA
Address reprint requests to Dr Gambhir, Crump Institute for Biological Imaging, UCLA School of Medicine, A-222B JLNRC, 700 Westwood Plaza, Box 951770, Los Angeles, CA 90095-1770
e-mail: (sgambhir{at}mednet.ucla.edu, wscott@creighton.edu)
Presented at the Thirty-fourth Annual Meeting of The Society of Thoracic Surgeons, New Orleans, LA, Jan 2628, 1998.
| Abstract |
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Methods. Five decision strategies for selection of potential surgical candidates were compared; thoracic CT alone or four different strategies that use thoracic CT plus thoracic PET. The various paths of each strategy are dependent on numerous variables that were determined from a review of the medical literature. Life expectancy was calculated using the declining exponential approximation of life expectancy and reduced on the basis of procedural morbidity and mortality. Costs were based on national Medicare reimbursed costs. For all possible outcomes of each strategy, the expected cost and projected life expectancy were determined. The effects of changing one or more variables on the expected cost and life expectancy were studied using sensitivity analysis.
Results. A strategy that uses PET only after a negative CT study is shown to be a cost-effective alternative to the CT-alone strategy ($25,286 per life-year saved).
Conclusions. These results show through rigorous decision tree analysis the potential cost-effectiveness of using thoracic PET in the management of nonsmall cell lung carcinoma. Greater use of thoracic PET for nonsmall cell lung carcinoma staging is warranted, and further clinical trials should help to validate the analytic results predicted from this study.
| Introduction |
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Rational decisions regarding the use of new technology, such as the use of FDG-PET in lung cancer staging, depend on an assessment of its effects under actual or expected conditions of use. The technique of decision analysis offers useful ways to organize information and evaluate strategies involved in staging the patient with lung cancer [6]. By including information on cost and life expectancy, decision analysis can relate costs and benefits of a lung cancer staging strategy. A previously published analysis of PET in the staging of NSCLC by Gambhir and colleagues [6] indicated that PET has a cost-effective role. The current study builds on and enhances the analysis of Gambhir and coworkers by investigating additional management strategies, precisely modeling the dependence between CT and PET scans, as well as updating the relative costs of procedures and changing to the more universal Medicare reimbursement values. The goals of the present study were to quantitatively model under what conditions PET could play a cost-effective role in the staging of NSCLC by more accurately determining the presence or absence of metastases to mediastinal (stage N2 or N3) lymph nodes.
| Material and methods |
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Calculations of expected cost and life expectancy of competing strategies were calculated by summing the products of the probabilities and values (in terms of national Medicare reimbursed dollar cost and patient life expectancy) of the outcomes for each strategy.
To compare each PET-based strategy with the CT-alone strategy (strategy A), an incremental cost-effectiveness ratio (ICER) was formed
, where LE represents life expectancy [8]. Finally, because the precise value of the various variables are not known, a sensitivity analysis was performed for each decision tree. This involved evaluating each tree over a particular variables range and determining the effect on the ICER. In addition, multiple variables that favored the winning strategy (strategy B) were shifted by 10% to understand the effects of simultaneously varying multiple variables. New software developed at the University of California Los Angeles [9] was used to construct and analyze each decision tree.
Structure of decision trees
Five strategies labeled A to E were modeled in this analysis. Simplified versions of strategies A to D are depicted in Figure 1. Strategy A is a baseline strategy that uses only thoracic CT for noninvasive preoperative staging, whereas strategies B to E include the use of a thoracic PET scan in different approaches. Strategy A and strategies similar to D and E were previously analyzed by Gambhir and coworkers [6].
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The cost of subsequent therapies such as chemotherapy and radiation therapy were not included in this analysis. A patient diverted from surgical intervention incurs subsequent treatment costs similar to those of the patient found to have advanced stage disease at thoracotomy (terminal costs). Therefore, our model primarily accounts for the difference in treatment cost that is due to thoracotomy. We also assumed that based on the relatively high positive predictive value of biopsy, there will be negligibly few patients who will be falsely positive after biopsy [10].
In strategies A through D all patients have a biopsy to confirm lymph node involvement before being diverted from operation. Therefore, in these strategies no patients who can benefit from a thoracotomy are denied this intervention, whereas in strategy E some patients who are surgical candidates are mistakenly diverted from operation. For this reason strategy E is only treated in brief in this analysis.
In strategy A those patients who are CT positive for contralateral or mediastinal lymph node involvement, or both, have a biopsy to confirm that the patient is not a surgical candidate. If the biopsy results are negative, the patient proceeds to thoracotomy. Patients who are CT negative proceed directly to thoracotomy.
In strategy B those patients who are CT positive undergo a confirming biopsy, and if the biopsy results are negative, they proceed to the necessary operation. The CT-negative patients undergo thoracic PET. If the PET results are positive, the patient has a confirming biopsy. If the PET results are negative, the patient proceeds to operation. This strategy potentially reduces the number of thoracotomies performed in patients who have N2 or N3 lymph node metastasis and a false-negative CT compared with strategy A.
In strategy C all patients undergo thoracic PET regardless of the CT result. The PET-positive patients proceed to biopsy, and the PET-negative patients proceed to thoracotomy. This strategy uses PET for the staging decisions and uses CT only for anatomic information.
In strategy D all patients undergo thoracic PET regardless of the CT result. All CT-positive patients also undergo a confirming biopsy regardless of the PET result. The CT-negative patients with PET positivity undergo a confirming biopsy; those with PET negativity proceed directly to thoracotomy. This strategy uses the combined CT and PET information for staging.
Strategy E (not shown in Fig 1) is similar to strategy D, except that patients who are positive on both CT and PET do not have a confirming biopsy but are treated without thoracotomy. Some of these patients will have false-positive results on both CT and PET and will therefore be incorrectly diverted from a beneficial operation.
Survey of medical literature
The prevalence of contralateral or mediastinal involvement, or both, in patients with NSCLC was estimated at 31% (range, 28% to 38%) on the basis of our review of the literature [1115]. This value is not the prevalence of NSCLC, but the prevalence of N2 or N3 lymph node metastases in those patients with a histologic diagnosis of NSCLC who are being considered for thoracotomy. The prevalence baseline value and range are given in Table 1, along with values for all other variables used in this analysis.
We used pooled sensitivity (67%) and specificity (73%) for thoracic CT based on five published studies [1115] that used a patient-based analysis (Table 2), as has been previously done [6]. Using receiver operating characteristic (ROC) analysis and the mean threshold criteria [16], the sensitivity and specificity were estimated as 66% and 76%, respectively. Because of the small difference in the estimates, we used the pooled estimates, in keeping with the previous analysis [6]. A CT criterion of greater than or equal to 1 cm lymph node size in the short-axis diameter to represent lymph node metastasis was used in these studies.
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The risk associated with CT is primarily attributable to administration of intravenous contrast material. We previously chose a baseline mortality of 0.0025% (range, 0% to 1%) [6]. The risk associated with PET is assumed to be negligible because there have been no reports to date of reactions or complications from the injection of FDG.
Baseline life expectancy was calculated using the declining exponential approximation of life expectancy method developed by Beck et al. [21]:
, where ASR is the age-, sex-, and race-specific annual mortality rate of the general population, and DSR is the additional average mortality rate attributable to the patients disease. The age-, sex-, and race-specific mortality rate for a healthy 64-year-old white man is 0.067 (range, 1 to 15 years). The disease-specific mortality rate for a 2.3-cm cancer (average diameter of T1N0M0 tumors) has been estimated to be 0.075 [21]. The combined annual mortality rate for our baseline patient is equal to 0.142, and his life expectancy would be the reciprocal of this sum, 7.0 years. We used a baseline of 7.0 years (range, 1 to 15 years).
The life expectancy for unresectable lung cancer for patients with highly advanced disease (evident on chest radiography) has been shown to be 0.47 years according to surgical data and the declining exponential approximation of life expectancy method [19]. Although there are few data concerning the life expectancy of patients with mediastinal metastasis not evident on the chest radiograph, these patients are expected to live longer than those with metastasis evident on the chest radiograph. Therefore, we chose a slightly greater baseline value of 1.0 years (range, 0.1 to 2 years). For patients with false-positive results on both CT and PET and are not operated on, we chose a mean life expectancy of 2 years, as previously reported [6]. We assigned a value of 0.0 year for all death outcomes, as is usually done [19, 20].
We estimated the mean national Medicare reimbursed dollar costs (combined technical and professional charges) of thoracic CT, biopsy, and curative thoracotomy, as shown in Table 1. The Medicare reimbursement for diagnosis related group 75 (major thoracotomy) is based on several characteristics, such as the presence of the hospital in a large urban area or other area, the number of indigent patients cared for by that hospital, whether the hospital is a teaching hospital (including the ratio of residents and trainees to the number of hospital beds), regional wages, capital costs, and other important factors. Therefore, an average, national figure that is relevant to all possible practices is difficult to derive. We used a baseline reimbursement value of $18,500 derived from estimates of the highest and lowest Medicare reimbursement values ($14,000 to $21,000) for the relevant diagnosis related group, combined with estimates of Medicare reimbursement for the relevant professional services (Current Procedural Terminology codes).
The biopsy costs can vary considerably depending on the exact type of biopsy performed. We assume that two of three of all biopsies are mediastinoscopies and the rest are mediastinotomies. Thoracic PET reimbursement for NSCLC was approved by the Health Care Financing Administration at the end of 1997, and the amount of reimbursement was set at $2,080 (global fee, including technical, professional, and tracer components) in June 1998. This value will vary according to many factors, including those mentioned previously regarding thoracotomy reimbursement. We used a mean PET national Medicare reimbursed cost of $2,000 (range, $1,200 to $2,200).
| Results |
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Strategy B is preferred to strategy A because strategy B yields higher life expectancy at an additional expense that generates an ICER of $25,286 per life-year saved. Table 5 (row 1) shows that strategy B is the most cost-effective strategy if one is trying to maximize life expectancy while incurring the least additional cost. Strategy C would be the best strategy if increasing life expectancy were the sole consideration; however, the higher expected cost of strategy C gives an ICER of $70,889, greater than the acceptable limit of $50,000 per life-year saved.
Table 5 also includes results for changing several of the variable values. Rows 2, 3, 5, and 6 show results for changing a single value. Rows 4 and 7 show results for simultaneously altering the sensitivity and specificity of PET and CT, respectively. Row 4 shows the results for using the same estimated values of PET sensitivity and specificity regardless of the CT results. This illustrates that modeling CT and PET as statistically independent tests leads to higher expected costs and lower life expectancy.
Rows 8 and 9 of Table 5 are the analytic results for altering several values by 10% that penalize the alternative strategies. Row 8 decreases all PET sensitivity and specificity values by 10% of their baseline values (sensitivity and specificity of 80% and 73%, respectively, when CT results are positive and 69% and 87%, respectively, when CT results are negative). This analysis shows that strategy B remains the cost-effective alternative when PET accuracy is penalized. Row 9 of Table 5 penalizes PET sensitivity and specificity and increases the cost of PET by 10%. For this change none of the alternative strategies are more cost-effective than strategy A.
Performing a sensitivity analysis of other variables in Table 1 did not have a significant impact on the baseline results. The most critical variable in this analysis is the ratio of the cost of thoracotomy to the cost of PET. Shown in Figure 2 is a plot of the effect of varying the cost of PET versus the ICER for strategies B to D compared with strategy A. This plot shows that strategy B remains cost-effective over the entire range of PET costs analyzed and that strategy C becomes cost-effective for PET costs below $1,800. Strategies B to D all have a higher life expectancy than strategy A, and life expectancy is not affected by changing PET costs. Therefore, the negative ICER for strategies B and C indicates that those strategies have a lower expected cost than strategy A and dominate strategy A. Figure 2 shows that strategy B dominates strategy A if PET were to cost less than $1,700.
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| Comment |
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Some of the limitations of this decision analysis imposed by our assumptions and tree structure deserve mention. These analyses assume that PET is readily available and that extra days in the hospital are not required while patients are waiting for this study. Furthermore, this analysis supports the fact that technologies such as PET, which may be more expensive, can be more cost-effective because of their improved accuracy and they are negligible to no risk.
The current work assumes that biopsy has 100% accuracy. Although biopsy is very accurate, it will produce some false-negative results in some patients. Such patients would be sent for operation when in fact they are not surgical candidates. This error will increase costs for both the CT and CT plus PET strategies. Therefore the results are not expected to be sensitive to small deviations in accuracy of 100% for biopsy. Studies to explore the effects of inaccuracies of biopsy are currently underway.
We also assume for the purposes of the present analysis that the benefit of surgical intervention has not been proved for most patients with N2 or N3 metastases from NSCLC and that these patients will not be referred for operation. Most clinicians would agree that surgical resection and adjuvant therapy are not optimal therapy for patients with preoperatively documented N2 disease (although patients with lymph node metastases to levels 5 and 6 [aortopulmonary window] from a left upper lobe lung cancer were shown by Patterson and colleagues [23] to have up to a 45% 5-year survival rate after lobectomy and lymph node resection alone). The benefit, if any, of surgical intervention in the multimodality treatment of patients with stage III NSCLC is currently being investigated in Thoracic Intergroup Trial 1039. That study randomizes patients with biopsy-proved T1 to T3 N2 NSCLC to receive induction radiation therapy and concurrent induction chemotherapy followed by operation or to the same induction therapy with uninterrupted radiation therapy and with two additional cycles of chemotherapy.
Also, some patients will be operable even though they have a distant metastasis (eg, single brain metastasis). This category of patients is not explicitly accounted for in the current analysis. These patients are very small in number and are therefore not expected to alter the results of this study significantly. Also the current analysis assumes that all patients are candidates for surgical procedure. There will be a small number of patients who will not be surgical candidates for various medical reasons.
The present analysis used estimated national Medicare reimbursed costs to compare the costs of various procedures. An optimal approach would look at the true costs of each procedure and model those costs explicitly. Indirect costs such as patient income loss would also be directly modeled. Such cost analyses are beyond the scope of the current work, but many cost-effectiveness analyses have used national Medicare reimbursed costs as an attempt to standardize costs across various procedures. In actuality, it is the relative ratio of surgical costs to PET costs that control the cost-savings component. If surgical procedures can be performed at overall lower costs, then PET would also have to decrease in costs to continue to have a cost-effective role.
The present work did not directly account for costs associated with bone scans, whole-body screening, or plain films. These studies will vary significantly on an individual by individual basis. This is not expected to alter the outcome of the present work because most patients would not require this workup, and both the CT and CT plus PET strategies would be affected equally.
Additionally, the use of whole-body FDG-PET (which was not modeled in this work) would potentially identify more patients with advanced disease than are currently being identified by a comprehensive clinical evaluation including chest CT and other appropriate studies (bone scan or head or abdominal CT). The cost of whole-body FDG-PET would be somewhat more than thoracic PET, but it may also prove to be cost-effective in the long term.
The current study has also used life expectancy as an outcome measure to model effectiveness. Future studies that use quality-adjusted life-years may prove to be a more useful outcome measure to model effectiveness. It is assumed that including quality of life will favor the alternative strategies because surgical procedures have at least a short term negative impact on quality of life.
The previous analysis of NSCLC staging by Gambhir and colleagues [6] indicated that a strategy similar to strategy D in the current analysis was dominant over strategy A. Strategy D differs from the previous analysis in several aspects previously mentioned. Modeling the dependence of CT and PET resulted in a more cost-effective strategy D; however, using the current Medicare reimbursement values for costs has substantially reduced the ratio of surgical costs to PET costs, with the result that strategy D now has higher expected costs than strategy A. A related analysis has shown that thoracic PET has a cost-effective role in diagnosing solitary pulmonary nodules [24]; future analysis will merge the solitary primary nodule and NSCLC analysis to develop a single cohesive understanding of overall treatment strategies for lung cancer.
In conclusion, the present study quantitatively showed the cost-effectiveness of using a PET-based strategy in the management of patients with NSCLC. It was shown that several different CT plus PET strategies result in a greater life expectancy than a CT-only strategy. A strategy in which a thoracic PET is only performed after negative CT results was found to have the lowest costs of all the PET-based strategies. Furthermore, even with the uncertainty in various variables, the cost-effectiveness of the CT plus PET strategy was shown over a large range. The present study supports the wider use of PET in managing NSCLC as a significant cost-effective tool.
| Acknowledgments |
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