We have shown under a wide range of assumptions varying efficacy, utility, and cost that SBRT for patients with low- or intermediate-risk prostate cancer would potentially be an attractive alternative to IMRT from the cost-effectiveness perspective of the payer. One- and two-way sensitivity analyses showed that the model was most sensitive to QoL outcomes or PROs. As such, evaluating QoL is critical to assessing the cost-effectiveness of SBRT. PFS is also important but has a lesser impact on cost-effectiveness. The reason for this discrepancy is the fact that QoL outcomes affect all patients who receive treatment, yet differences in recurrence rates still affect only a small fraction. For example, a 5% decrease in QoL for one treatment results in an absolute decrease in QoL of 5%. On the other hand, a 50% increase in recurrence only affects an additional 1% of patients from 2% to 3%.
Although this decision analysis took the perspective of the payer, from a societal standpoint, the costs associated with treating prostate cancer are significant, with more than $12 billion per year being spent to treat patients with prostate cancer.1
More than 100,000 patients per year are diagnosed with organ-confined prostate cancer, and 35% to 46% elect to undergo radiation therapy. At a savings of $13,000 per patient, if 50% of these patients were eligible for SBRT and treated with SBRT instead of IMRT, then a conservative societal-level savings would approach $250 million per year.1
In addition, from the patient perspective, the indirect cost savings of this hypofractionated treatment option, such as time lost from work and the treatment-related costs of transportation and housing, are substantial. Thus, the use of SBRT as an initial treatment option could potentially have a profound economic impact from both societal and individual patient perspectives as well.
This model builds on several studies that have evaluated the cost-effectiveness of radiation treatment options for patients with low- and intermediate-risk prostate cancer. These analyses have all been based on the decision analysis first modeled by Fleming et al.44
In a prior analysis, three-dimensional conformational radiation therapy was compared with IMRT, with the conclusion that IMRT is a cost-effective treatment option given a societal WTP threshold of $50,000 per QALY, especially given the ability for improved dose escalation and sparing of normal structures.24
In a recently published robust analysis of initial treatment options for low-risk prostate cancer, Hayes et al7
examined several initial treatment options for low-risk prostate cancer including brachytherapy, IMRT, and prostatectomy as compared with active surveillance. This comparative effectiveness analysis concluded that active surveillance would be more effective than initial treatment based on a quality-adjusted life expectancy end point. Despite its emergence as a well-tolerated, noninvasive, efficacious treatment option, SBRT was not included in the model reported by Hayes et al. Given the impressive recent 5-year bPFS data reported by Freeman et al22
and King et al,26
with an accumulation of early toxicity data from several phase I and II SBRT trials showing highly comparable toxicity data, it is clear that SBRT warrants consideration as a cost-effective initial treatment option for patients with organ-confined prostate cancer.
There are several potential limitations to our model. First, the data on bPFS and long-term toxicity from SBRT for prostate cancer are still maturing; however, recent reports are promising, as shown in . The results of this study highlight the importance of utility outcomes or PROs, because late effects and toxicities to nearby normal tissues such as the rectum, bladder, and urethra could potentially affect patient-reported QoL as well as increase treatment-related costs in the model. Should late effects for SBRT prove to be higher, the actual impact of these toxicities as measured by PROs would be valuable in determining the cost-effectiveness of SBRT as compared with IMRT. Thus, a major limitation to the study is the lack of long-term utility data available on SBRT for prostate cancer. It is encouraging that a currently enrolling Radiation Therapy Oncology Group study is comparing a five-fraction SBRT treatment course with a 12-fraction IMRT treatment course, with the primary end point of patient-reported QoL at 1 year. Additionally, Markov decision analyses implicitly require assumptions regarding cost, efficacy, and utility outcomes. Thus, these assumptions raise concerns regarding the accuracy of costs and transition rates given the variability of different practice patterns, local costs, and differences in reported prostate cancer outcomes in clinical trials. To account for these variances, Markov decision models typically employ Monte Carlo simulation, which uses a range of values with characteristic distributions for imputed variables to simulate a large cohort of patients. However, by assuming equal efficacy based on several published reports of 5-year bPFS for IMRT in dose-escalation trials, the model actually conservatively underestimated bPFS compared with the recent SBRT bPFS 5-year report by King et al.25
In conclusion, the recent 5-year bPFS data on SBRT for organ-confined prostate cancer are promising, and as such, the cost-effectiveness of SBRT has great potential in improving the treatment of organ-confined prostate cancer from the payer perspective in addition to patient and societal perspectives. Our study using the Markov decision tree with Monte Carlo simulation found that SBRT is more cost-effective than IMRT, assuming similar outcome measures. SBRT loses its cost-effectiveness with small decreases in QoL or effectiveness. Future studies evaluating SBRT need to focus on both acute and long-term QoL outcomes as well as efficacy.