The OER of Mixed High- and Low-LET Radiation

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 percent 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. (auth)