Analytical approach:
A four state Markov model, with a lifetime time horizon, was used, with a simple decision tree, to capture the progression of the disease after surgery and the data for this were obtained from various sources. The authors stated that a quasi-societal perspective was taken, where the costs of disease management were included, regardless of who incurred them, but the cost of the patient's time was excluded.
Effectiveness data:
Published studies, including a meta-analysis, were used to estimate the rate of incomplete RFA and the probabilities of local recurrence and of direct progression to metastatic disease for NSS (Gervais, et al. 2005, Manikandan, et al. 2004, see 'Other Publications of Related Interest' below for bibliographic details). Due to a lack of comparative studies, it was assumed that the probability of local recurrence for RFA was 10% higher than for NSS and the probability of direct progression to metastatic disease for RFA was the same as for NSS. These assumptions were tested in the sensitivity analysis.
Monetary benefit and utility valuations:
Due to a lack of studies providing data for the RCC utilities in the post-operative, local recurrence, and metastatic phases, published utilities for colon cancer were used. These were then scaled overtime to reflect the underlying age-specific quality of life, based on a large community-based study. The utilities for the first month after treatment were based on a published study of RFA and surgical treatments for colorectal cancer metastases in the liver.
Measure of benefit:
The measure of benefit was the quality-adjusted life-year (QALY) gained and these were discounted at an annual rate of 3%.
Cost data:
The direct costs included RFA and NSS costs, treatment and ongoing costs for local recurrence, ongoing costs for metastatic disease, and the ongoing cost of surveillance for recurrence using computed tomography (CT). RFA and NSS treatment costs, and the adjustment for complications, were based on published studies (Lotan, et al. 2005, Shekarriz. 2002, see 'Other Publications of Related Interest' below for bibliographic details). Due to a lack of studies on RCC costs in the post-operative, local recurrence and metastatic phases, published costs for colon cancer were used. All costs were converted into 2006 US dollars ($) using the medical care component of the Consumer Price Index, and were discounted at an annual rate of 3%.
Analysis of uncertainty:
One-way sensitivity analysis was used to explore the parameter uncertainty and the results were described. The probability of local recurrence after RFA was varied to determine the threshold level below which RFA would be preferred over NSS, at a societal willingness to pay of $75,000 per QALY, and this was presented in a graph.