Nanodosimetry, a tool to measure radiation effectiveness!?

The biological effect of ionizing radiation in tissue and matter in general does not only depend on the absorbed dose but crucially also on the radiation quality, i. e. type of radiation and its energy distribution. The large span of relative biological effectiveness (RBE) over more than an order of magnitude is related to the biological end point and, on the physical side, on the pattern of energy deposition on the microscopic scale, the so-called track structure. Clusters of lesions in the DNA molecule within site sizes of a few nanometers play a particular important role in this context. Metrology of radiation effects in tissue therefore have not only to provide means for precise measurement of absorbed dose but also needs to answer the question of RBE and develop tools for experimental quantification of this parameter. The talk will present experimental and theoretical approaches to deal with the question of RBE from a metrological approach, using simulation and nanodosimetry as a tool to measure the microscopic ionization pattern in matter. Actual developments at PTB in his field will be presented and also fundamental limitations of the method will be discussed.