Also, with the diameter of has commonly been called a "hit". specified as a nucleus of 8 microns in diameter, and often simply “cell dose" have been employed. “cell dose” will be used here the the TCV term “elementary dose” "Hit", “hit-size”, and interchangeably. Although it is also useful to distinguish between stochastically iping ing and with .t) substantive requirement. is this to avoid confusion and not a In other words, all else being equal, an organisa has no physiological means of determining whether a given agent transfer has occurred stochastically or by plan. can It is only because of the above-outlined capabilities of iguous eristic ye between microdosimetric methods that the substantial advantages of using the cell dose approach can be realized, type or energy of to the . be . to planned doses, delivered as opposed Thus energy deposition. an The instrument ts “completely blind" the radiation particle responsible the number of hits and for the given the hit sizes are “object-oriented” quantities, on which the extent and severity of etfect those the biological material is exposed. only in ity, in principle, it is unnecessary to know anything about the nature of the field in which been as In other words, resulting from radiation exposure depends. three it The large advantage of this lies not that it usually fis quite difficult practically, “pure” of radiations, to determine even for the most the field strength itn fluences and energies of the different types of particles. fields, it is often essentially impossible variables. Even if defined, the terms of In mixed to define adequately these they are too remote from the btological eftect to be satisfactory for quantitative prediction purposes. Microdosimetry in princtple obviates any requirement for their teasurement, The companion advantage of using microdosimetric methods is that, in permitting measurements to be made at the time of stochastic events, they in effect turn the abstract cisk of being dosed, and cell doses, concrete values. living cell cell, Even though it is usually not possible to desiznute whicn is hit, or to assign any particular cell dose it is possible for any given exposure. essentially all the information that one has ans an lap. to any given to state accurately the relative numbers at any given value of cell dose, toxicology, into that were hit Thus one has in pharmacology and in which the number of individuals at any given dose level is known precisely, and from which the (fractional) number of quantal responders can be determined. -215- 9012971