The general validity of the phenomenon of a relatively large decrease in OER below the X-ray value with only modest admixture of high-LET radiation is pointed out. For example, a 40% admixture of radiation with OER = 1.15 will decrease OER from 2.6 to 1.3. It is also pointed out that the OER is not strictly dose modifying for a mixed high- and low-LET environment, even though it may be so for the two components separately. From these considerations, it is suggested that a low-LET, high-energy photon beam could be combined with a high-LET, heavy-ion beam to take advantage both of the increased skin-sparing characteristic of the photon depth-dose curve and of decreased OER in the tumor region due to the high-LET, heavy-ion admixture.

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