The theory behind the microdosimetry variance method predicts a relation between the single event dose-mean energy imparted, the relative variance of a multi-event distribution of energy imparted, and the mean energy deposited by the multi events. The theory was published by Kellerer in 1968 and was later extended to radiation beams of varying intensity with the variance-covariance method. The first experimental results were reported in 1970. Since that time the relationship has been used in experimental microdosimetry for measurements with ionization chambers and proportional counters. Agreement between experimental and calculated values has been reported down to 20 nm.
In research for possible relationships between stochastic quantities and relative biological effectiveness (RBE) focus has recently shifted from energy imparted to number of ionizations. In this technical note, the fundamental measurement equation is rearranged to refer to an ionization mean value. The consequences of exchanging energy imparted with number of ionizations, when the radiation quality is expressed as a ratio of either of the two dose mean values, is discussed.
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Lindborg, L. & Rabus, H. (2023). Evaluation of a mean value of the number of ionizations in a single event distribution by the variance method in microdosimetry [technical note]. Medical Physics, 50(8), 5248–5251. https://doi.org/10.1002/mp.16428
