In this study, a reliable and robust 7-state Markov model was designed to evaluate the cost-effectiveness of IMPT versus IMRT for OPC, a fast-growing malignancy in China. On the basis of published data, the cost-effective scenarios of IMPT at the current WTP level of China were identified as the following independent conditions: ≥ 57.3% NTCP-reduction (IMPT compared with IMRT) in dysphagia and xerostomia; patient age ≤ 38-year-old; or the cost of IMPT ≤ $37,398.1. The cost-effective population in China that benefit from using PBT to treat OPC increased remarkably in the past 10 years with the growth of GDP per capita. It was estimated that such cost-effective population would be about 40.0% of the China’s total population in the year 2020.
Cost-effectiveness of PBT has been poorly evaluated worldwide, and has been referred as the proton’s “economic controversy” [18, 31]. The only documented CEA study of PBT for OPC patients was reported by Sher DJ et al., a 6-state Markov model was designed for a 65-year-old OPC patient based on a hypothesis that IMPT could make a 25% reduction of xerostomia, dysgeusia and the need for gastrostomy tube, with the model set-up reflecting the practice in American hospitals [32]. But the 6-state Markov model in that study was found not applicable for Chinese OPC patients in certain regards, such as Chinese patients’ unwillingness to undergo invasive surgery like percutaneous gastrostomy tube for treating the eating difficulty, and the extensive use of traditional Chinese medicine in dealing with xerostomia.
Markov model design is a key step of CEA modelling for PBT. In our previous CEA modelling for paranasal sinus and nasal cavity cancer, a reliable 3-state Markov model was designed to simulate the tumor development and evaluate the cost-effectiveness of IMPT in comparison to IMRT in terms of tumor control improvement [33]. Unlike paranasal sinus and nasal cavity cancer, the advantages of IMPT over IMRT for OPC patients lied in reducing late toxicities while not in improving tumor control or survival rates [34, 35]. In this CEA modelling for OPC, we also used 3 main states including “alive with cancer”, “no cancer” and “death” to simulate the tumor development of OPC, but the survival probabilities were set identical between IMPT strategy and IMRT strategy. The model-predicted OS and DFS were found correspond to the previous long-term survival outcomes [25], which demonstrated that the CEA modelling did abide with the natural disease process of OPC.
To evaluate long-term differences in effectiveness and cost between the two strategies, the state of “no cancer”, referring to OPC survivor after radiotherapy, was further divided into 4 sub-states of “dysphagia”, “xerostomia”, “dysphagia and xerostomia” and “no complication”, the initial state probabilities of the 4 sub-states were set according to the NTCPs of dysphagia and xerostomia. For each cycle, the HSUVs for states of “dysphagia”, “xerostomia”, “dysphagia and xerostomia” and “no complication” were set as 0.803, 0.846, 0.763 and 1, respectively; meanwhile, the annual costs for dealing with these toxicities were added as the accumulated incremental costs. Therefore, NTCP-reductions of dysphagia and xerostomia (IMPT compared with IMRT) became the original motivities of differences in effectiveness and cost between the two strategies. The robustness of this model design was confirmed by tornado diagram analysis, which demonstrated that only the NTCPs and the cost of IMPT had major impacts on ICER value.
In this study, the cost-effective scenarios of PBT were identified as 3 independent conditions for Chinese OPC patients: ≥ 57.3% NTCP-reduction, patient age ≤ 38-year-old, or the cost of IMPT ≤ $37,398.1. In previous PBT decision-making studies for OPC patients, the superiority of IMPT over IMRT in reducing dysphagia and xerostomia (NTCP-reductions) has been applied as the determining factor for treatment decision making between IMPT and IMRT, and NTCP models were applied to estimate NTCP-reductions using dosimetric information in IMPT and IMRT treatment plans, such as the approaches developed by Langendijk JA et al. and Brodin et al. [14, 15]. However, the threshold of NTCP-reduction, above which an OPC patient could be considered as appropriate for PBT, had not be defined in the previous studies. Here, we first defined a threshold for NTCP-reduction based on the criterion of cost-effectiveness. In our CEA modelling, we also found that younger patient who had a longer survival time could benefit more from PBT from the cost-effectiveness consideration. Thus, patient age should be another main consideration in the clinical decision making of prescribing PBT. In addition, proton treatment cost was identified as one of the major influential factors to the cost-effectiveness, and the current proton treatment cost was found high at current WTP level of China. But we estimated that such treatment cost will probably be reduced in the near future due to the market competition and technology upgrade along with more proton centers open in China [36].
Of note, at current stage without public medical insurance coverage, the level of ability-to-pay (WTP level) should also be weighed in clinical decision of using PBT. Regional difference of WTP level in China is obvious. For example, the GDP per capita in Shenzhen City of China (the second highest) are as high as $28,931 in the year 2019, corresponded a WTP of $86,793/QALY (2.8 times the current WTP of China). In order to evaluate the acceptance of using PBT to treat OPC in whole population of China, we delineated the population of a higher level of GDP level that corresponded a WTP level beyond the ICER value ($48,229.8/QALY) as an estimated cost-effective population in this study. Such cost-effective population was found increased remarkably in the 10 past years with the growth of GDP per capita, and reached to 559.7 million (about 40.0% of the China’s total population) in the year 2020. This finding indicated the great market potential and future trend of PBT in Chinese society, even though such estimation might not be accurate due to the uneven distribution of social wealth.
There are two main limitations in this study. First, our CEA modelling was hypothesis-based. We assumed that all the symptomatic dysphagia and xerostomia would occur within the first year after radiotherapy and late toxicities would be irreversible if occurred. This assumption was based on the previously observed studies, which showed that the changes of two late toxicities would be tiny and negligible after 1 year [37, 38]. The Markov models were cycled from 1 year after radiotherapy, and the potential differences in irradiation-induced adverse events within the first year after radiotherapy, including the acute toxicities and hospital admission rates, were not taken into account in CEA. Hence, these hypothesis-related problems may hamper the interpretation of the results. Second, the CEA modelling in this study was performed with the base case set-up (a 25% NTCP-reduction, 56-year-old, and the current WTP of China) to represent Chinese OPC patients of an average level. However, the clinical decision making of prescribing PBT to a specific OPC patient should base on CEA modelling with individualized set-up, which enables to take patient’s age, tumor stage and economic situation into account. So, the next step, we plan to conduct individualized CEA modelling for treatment decision making (IMPT versus IMRT).