PURPOSE: An economic option appraisal to determine whether early investment in capital is an efficient means of expanding radiation therapy services. METHODS AND MATERIALS: Costs were based on 1991 data from a center in western Sydney. Two options were costed: Option 1 based on an increase in overtime performed by existing staff, using capital more intensively and possible use of shifts; Option 2 based on an investment in new capital and associated increases in levels of staffing. The health sector costs of both options were determined in one center at workloads of between 70,940 and 98,525 fields per year to assess relative efficiency. RESULTS: There was very little difference in cost between both options, with Option 1 slightly cheaper at workloads up to 98,525 fields per year. CONCLUSIONS: The results suggest that capital investment may be introduced at a fairly early stage without efficiency loss. Sensitivity analysis reinforces these conclusions and the generalizability of the results.