Rationale and Objectives
18-Fluoro-2-deoxyglucose (18F-FDG) positron emission tomography (PET) is effective but costly in the early detection of recurrence for nasopharyngeal carcinoma (NPC) in patients after treatment. In this study, we developed a decision tree model to analyze the cost utility of 18F-FDG PET in detecting loco-regional recurrences for NPC patients after therapy.
Materials and Methods
The analysis for cost utility is based on the decision-tree model for three different strategies: 1) magnetic resonance imaging (MRI)-only, 2) PET-only, and 3) MRI-PET (performing PET if MRI result is uncertain). Sensitivity analyses have been performed to examine changes in the cost ratio of PET/MRI and the probability of uncertain MRI.
Results
After inputting the data for utilities and life expectancies into the decision tree model, the quality-adjusted life expectancies turn out to be 16.16 quality-adjusted life-years (QALYs) for strategy 1, 16.70 QALYs for strategy 2, and 17.35 QALYs for strategy 3. The additional cost per additional QALYs for strategy 3 relative to strategy 1 is calculated to be US $462. Strategy 3 dominates over strategy 2 because strategy 3 costs less and yields more QALYs than strategy 2. If the cost ratio of PET/MRI is less than 1.85 or the probability of uncertain MRI is greater than 73%, then the PET-only strategy becomes more cost-effective than the MRI-PET strategy.
Conclusion
Our analysis shows that the MRI-PET strategy is the most cost-effective for now. It is likely the PET-only strategy will become the most cost-effective for recurrent NPC in patients in the near future as the cost of PET has decreased in a faster rate than the cost of MRI.
In Southern China and Southeast Asia, nasopharyngeal carcinoma (NPC) is one of the more common malignant tumors ( ), with an incidence rate of 10–30 persons per 100,000 people per year. The loco-regional recurrence is one of the crucial prognostic factors for NPC patients who have undergone radiotherapy (RT) or RT with adjuvant chemotherapy ( ). The conventional structure based diagnostic tools, such as magnetic resonance imaging (MRI) and computed tomography (CT), have been proved ineffective in the early detection of residual or recurrent foci for NPC patients ( ).
In contrast, it has been demonstrated in previous studies that 18-fluoro-2-deoxyglucose (18F-FDG) positron emission tomography (PET) is an effective tool for distinguishing recurrent tumors from post-treatment changes, such as tissue necrosis or fibrosis in the nasopharynx ( ). However, 18F-FDG PET scan is not routinely scheduled for the follow-up of NPC patients in our center due to its prohibitive cost. It is performed only when suspicious recurrences have been revealed in the results of other conventional radiologic findings during follow-up.
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Materials and methods
Decision Analysis Model
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The Baseline Case
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Probabilities
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Table 1
Probabilities Used in the Decision Tree
Variables Value (%) Range Reference For MRI-only MRI Sensitivity 60 50–70 MRI Specificity 60 50–70 For PET-only PET Sensitivity (low pretest probability) 70 60–80 PET Specificity (low pretest probability) 70 60–80 For MRI-PET Probability of an indeterminate MRI 50 20–80 MRI Sensitivity 75 65–85 MRI Specificity 75 65–85 PET Sensitivity (high pretest probability) 90 75–95 PET Specificity (high pretest probability) 90 75–95
MRI, magnetic resonance imaging; PET, positron emission tomography.
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Outcome Measures
Utility
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Table 2
Utilities Estimated from Visual Analog Scale
Status Utility Standard Deviation Post-initial treatment disease free 0.76 0.14 During treatment for recurrence 0.35 0.15 Recurrence after treatment 0.57 0.18 Recurrence delayed treatment 0.32 0.11
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Life expectancy
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Table 3
Life Expectancies for NPC Patients After Initial Chemoradiation without Recurrence, Recurrence with Immediate Treatment, and Recurrence but Delayed Treatment
Status 5-y Disease-specific Mortality Life Expectancy Reference Recurrence free 0% 32 Recurrence with immediate treatment 50% 7.7 Recurrence but delayed treatment 80% 3.5
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Costs
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Table 4
Costs of Magnetic Resonance Imaging (MRI) and Positron Emission Tomographic (PET) Scans
Study Cost (US$) MRI scan 350 PET scan 1,100
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Diagnostic accuracy
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Cost-utility analysis
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ICUR=[cost(strategyX)−cost(strategyY)]/[utility(strategyX)−utility(strategyY)]. ICUR
=
[
cost
(
strategy
X
)
−
cost
(
strategy
Y
)
]
/
[
utility
(
strategy
X
)
−
utility
(
strategy
Y
)
]
.
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Statistical Analysis
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Results
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Table 5
Baseline Results from Cost-utility Analysis
Strategy Cost ($) Diagnostic Accuracy QALY Incremental Cost Per QALY ($) MRI-only 350 0.60 16.16 — PET-only 1100 0.70 16.70 1389 MRI-PET only 900 0.82 17.35 462
MRI, magnetic resonance imaging; PET, positron emission tomography; QALY, quality-adjusted life years.
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Diagnostic Accuracy
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QALYs
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Sensitivity Analysis
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Discussion
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Conclusion
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Acknowledgment
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