On the revised concept of linear energy transfer.

The quantities linear energy transfer or restricted linear energy transfer are utilized in calculations that link absorbed dose to the fluence distribution of a radiation field. The computations provide approximations to absorbed dose in terms of the intermediate quantity cema or reduced cema. With the definition of the restricted linear energy transfer, L delta, given in ICRU Report 33, the approximation remains imperfect. This study deals with the resulting need for a modified definition of L delta, as proposed in a draft report of ICRU. Essential differences between the old and the new definitions are demonstrated. The changed definition permits a rigorous formulation of the dependence between fluence and absorbed dose.