The relative costs of proton and X-ray radiation therapy

To study the costs of intensity-modulated proton therapy and intensity-modulated X-ray therapy with the particular goal of understanding their relative differences. To analyse the ratio of the cost per fraction of proton therapy to the cost per fraction of X-ray therapy.

We have used a computer spreadsheet tool in which a large number (typically 130) of input parameters characterizing a particular therapeutic modality can be stored. From these parameters a number of derived variables are computed, and from these derived variables the costs of sub-systems, the entire facility, running costs and cost per fraction and per treatment can be computed. The sensitivity of any given variable (e.g. cost/fraction) to any given parameter (e.g. set-up time) can be explored, together with an estimate of the associated confidence interval. The costs of facility construction and facility operation are considered separately. Key data for the input variables regarding the cost of the therapy equipment (a dominant cost for proton beam therapy) were provided by four commercial vendors. Other costs, such as costs for building construction and shielding or personnel costs, are much more standard and our estimates were primarily based on practical experience. We considered two scenarios: (1) both facilities operating under current conditions; and (2) future facilities where foreseeable improvements in efficiency and a 25% reduction in the cost of the proton equipment were assumed.

The construction cost of a current two-gantry proton facility, complete with the equipment, was estimated at 62,500 kEE and of a two-linac X-ray facility at 16,800 kEE. In the case of proton therapy the cost of operation of the facility was found to be dominated, by the business cost (42%--primarily the cost of repaying the presumed loan for facility construction), personnel costs (28%) and the cost of servicing the equipment (21%). For X-ray therapy, the cost of operation was seen to be dominated by the personnel cost (51%) and the business costs (28%). The costs per fraction were estimated to be 1.025 kEE for protons and 0.425 kEE for X-rays--for a ratio of costs of 2.4 +/- 0.35 (85% confidence). In a future facility these costs could be reduced to 0.65 kEE and 0.31 kEE respectively, leading to a ratio of costs of 2.1. A number of further improvements could be imagined which could reduce the ratio of costs by some 20%. If, however, the initial capital investment were 'forgiven,' so that the operating costs need not repay the investment, both the costs and the ratio of costs would be significantly less. We estimate that, under this condition, the future costs of proton and X-ray therapies would be 0.37 kEE and 0.23 kEE, respectively, for a cost-per-fraction ratio of 1.6. This ratio could also be susceptible to a further 20% reduction.

Sophisticated (i.e., intensity-modulated) proton therapy is now, and is likely to continue to be, more expensive than sophisticated (i.e., intensity-modulated) X-ray therapy. The ratio of costs is about 2.4 at present and could readily come down to 2.1, and even, perhaps 1.7 over the next 5 to 10 years. If recovery of the initial investment is not required, the ratio of costs would be much lower, in the range of 1.6 to 1.3. The question of whether the greater cost of proton beam therapy is clinically worthwhile is a cost-effectiveness issue. The goal of this study is to contribute to the former arm of this comparison.