Oxygen enhancement ratio

The ratio of the absorbed dose required to cause the same biological endpoint in hypoxic conditions as in normoxic conditions. Hypoxia often occurs in the middle of a rapidly growing tumour. The OER of x rays is approximately 3 while high-LET radiation tends to show smaller OERs down to 1 indicating that high-LET radiation is effective against hypoxic tumours.

(ICRP Publication 127, 2014)

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