Microdosimetric studies of Cf-252

The authors have analyzed the microdosimetric distribution of specific energy f(y) around a Cf-252 implant in order to determine the probability of producing a microdosimetric high LET miss in clonogenic cell nuclei. The high LET miss probability depends on the choice of critical specific energy (yc) as well as the absorbed dose in the tissues in question. It is found that in most bulky tumors there is a high probability that cell nuclei near the periphery will contain no events of specific energy above 20 keV/μ. It is postulated that the lower LET components of Cf-252 and external beam photon dose are important elements in local control of solid tumors implanted with Cf-252. Certain implications for scheduling these components are discussed. (Auth.)