OBJECTIVES: Particle therapy (PT) with protons or carbon-ions is a promising treatment modality for non-small cell lung cancer (NSCLC). However, its initial investment is high, and it is unclear whether the potential extra effects are worth the extra costs. The cost-effectiveness of PT as opposed to stereotactic body radiotherapy (SBRT) for inoperable stage I NSCLC was examined to inform the adoption decision for PT. METHODS: A Markov model was constructed with four health states regarding survival and irreversible adverse events. Health care costs and effects of SBRT, proton therapy and carbon-ion therapy were compared over a five-year time horizon. Transition probabilities were derived from single-armed observational studies, as no comparative studies were available. Utilities were collected in a cross-sectional survey. Probabilistic sensitivity analysis was performed to reflect parameter uncertainty. RESULTS: Preliminary results showed that the expected total health care costs per patient for SBRT were €18,366, for protons €24,267 and for carbon-ions €26,720. The expected quality adjusted life-years (QALYs) were 2.24, 2.40 and 2.45 respectively. This resulted in an incremental cost-effectiveness ratio (ICER) of €36,651 per QALY for protons as opposed to SBRT, and an ICER of €44,668 per QALY for carbon-ions as opposed to protons. For a ceiling ratio of €40,000 protons had the highest probability of being cost-effective (41%), followed by carbon-ions (35%) and SBRT (24%). For a ceiling ratio of €80,000 these probabilities were 42%, 52% and 6% respectively.CONCLUSIONS: These preliminary results indicate that PT is a potentially cost-effective treatment modality for inoperable stage I NSCLC. However, caution is warranted, as the differences are small and surrounded by considerable uncertainty. More analyses will be performed of which the results are presented at the conference. First, more advanced statistical techniques are applied to synthesize the available evidence. Second, for operable patients PT is compared to surgery. Third, the cost-effectiveness of PT is assessed for stage III NSCLC. Finally, expected value of perfect information analyses are presented to support research decisions.