A Cell Risk Meters. Microdosimetry “Microdosimetry”, altnough originally apolied only techniques devised by Rosst et al. Dec cell and thelr caynitude, Aas anscrumental and calculativnai _ re the Guanticties.* [f is geriau3 (2-5) aow vost to measure Deen extended iwersaches in to the context ot t be number of include Fits both 1 tlia.inactiaz to veserice tne instrument approach. A mferocosineter equivalent sas. is sitcly a nrovortionil cvuunter contaiiing ALtnough partial evacuation toe countec may be centimeters ind suitable sealing pernits subcellular volumes af several microns fapinges om or traverses the ready ia diameter. Tacr instrument, a siagle “hit” the resulting “event", measured in terns of cascade, taken as Thus instrurent can be t ragisters re that the the magnituce of the size of the dosimetry of rt ia several quite siznaificant _ The rapid, tissue volumes. the in the Hoeever, sense ic tacro-phantons The recovery Thus, ome obtains not oaly tne stochastic: ly delivered hit sizes, but aiss idea of discrete, sizz of time so thac, with low-to-tocdest exposure SC aach hit is registered separately. Steetrcun of tne respects from the usual organs or other the instrument is’extremely tates, ts rez che “hie size" the “cell dose” delivered. used c* line a particle regarcet as a “cell omanton”, diffe $ in the hic, ilameter, situlation of the size of is in Che the tutal stucnastic hizh-density energy cepusiticas + from radiation exposure crobably originated early with Dessacer’s “soln: heat” tneory and was certainly weil appreciated by Lea (5). ieeas were not formaliy cevelopec until by Rossi (2-4). the quantity LET, Its use ras been more the “aicrodusimeter” «435 these invented in the context of a substitute foc to descrive energy definition within a non-anatomically defined “gross sensitive volume” within dose” was probably applied developed however, the cell. The idea of a “cell firse by Bond and Fetnendezen (10), and in NCR? Report No. 63 (11). The idea of a microdosimeter bein; conceptually a cell shanton with whicn cell dose could Se determined with stochastic douse delivery relatively cecent (Bond et al., sefs. 6 and 12}. co al., is soos i Felnendegen et