[Dosage specification at the ICRU reference point: the consequences for clinical practice. International Commission on Radiation Units and Measurements].

Abstract

In the Department of Radiotherapy, University of Tübingen, dose specification is performed according to the new ICRU recommendations since June, 1991. The purpose was to prescribe, record and report photon beam therapy in a consistent way applicable to most clinical situations and to provide uniform criteria for a comparison of treatment results from different radiotherapy centers. For "level 2" plans (including CT planning), the concept of dose specification has been changed to the "ICRU reference point" instead of to form the isodose encompassing the target volume as we did previously. A total of 24 representative treatment plans have been analyzed to assess the consequences of this change on dose prescription, treatment technique, and the size of the irradiated volume. Our results revealed that the prescription of single and total doses have to be individually adjusted according to the specific treatment plans. ICRU recommendations on dose homogeneity may significantly affect treatment technique and field sizes. Small deviations in dose prescription may be of particular influence on late responding normal tissues ("double trouble" due to simultaneous adjustment of single and total doses). Detailed comparisons of individual treatment plans with respect to physical, biological, and clinical data are obviously necessary in order to make sure that the outcome of a radiation treatment is not deviating too much from the clinical experience based on the former dose specification concept.