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Higher rates of re-irradiation following single fraction conventional radiotherapy have led to persistent views that dose-escalation might result in better quality and durability of pain control. Single centre series and an early phase trial have demonstrated high rates of complete pain response and durability following stereotactic radiotherapy (SABR). SABR is, however, markedly more expensive than conventional radiotherapy. This study aimed to assess if SABR for painful bone metastases could ever be cost-effective in the English National Health Service (NHS).

A Markov decision model was developed to model costs (in 2016 £ sterling) and benefits associated with SABR as compared to single 8Gy conventional palliative radiotherapy. Four pain response states were included, in line with the International Consensus on Palliative Radiotherapy Endpoints (ICPRE). Re-irradiation could occur where pain persisted and death was an absorbing state which could be reached from all pain response states. A life-time horizon was modelled with a cycle length of 1 week. Model parameters were informed using data from the Dutch Bone Metastases Study, literature review and NHS reference costs. Response to SABR was informed based on the outcomes of Sprave et al. One way and probabilistic sensitivity analyses were conducted to assess the impact of uncertainty in model parameters.Specific focus was placed upon the impact of plausible changes in the survival of the treated cohort and treatment costs.

SABR treatment resulted in an average QALY gain of 0.056 with associated incremental costs of £3125 for a three fraction course. At a willingness to pay threshold of £30,000/QALY the incremental cost-effectiveness ratio (ICER) for SABR was £55,592/QALY with a probability of 4% that SABR was the most cost-effective strategy. In a population with a median survival of 53 weeks, the ICER dropped to £39,200/QALY. Similarly, recognising a plausible long-term cost of treatment, beyond an initial implementation period, resulted in a fall to £28,431/QALY. Where these long-term costs were considered in a population with prolonged survival the ICER dropped markedly to £17,889/QALY with SABR having an 80.6% probability of being cost-effective.

SABR is highly unlikely to be cost-effective at currently commissioned costs and if all patients currently undergoing palliative radiotherapy for bone metastases were considered eligible. This latter limitation results from the limited survival of many patients with bone metastases. Recognition of the learning curve seen in the cost of SABR delivery and careful selection of patients could, however, allow for cost-effective treatment delivery. The efficacy of SABR, demonstrated in early phase trials, must now be replicated in larger, randomised controlled studies if these treatments are to be cost-effective.