This Report seeks to promote the use of a common language for specifying and reporting the doses in radiation therapy, as well as the volumes in which they are prescribed. Report 50 completely supersedes and updates ICRU Report 29 (published in 1978).
The different volumes, which need to be identified prior to any radiotherapy, are first defined: the gross tumour volume, and the clinical target volume and the planning target volume (PTV). The two first ones are purely oncological concepts, the third one takes into account the movement of the patient and the inaccuracies due to patient-beam positioning, and related to the therapy equipment. Examples are given on how to identify these volumes from x-ray films and CT sections. Three classes of organs at risk are also defined. A substantial part of the report is devoted to the different ways of describing the dose variation throughout the PTV and identifying the high-dose or low-dose regions. External photon beam irradiation only is considered in Report 50. As a general rule for reporting, it is recommended to identify a Reference Point where the dose can be determined accurately and can be considered to be representative of the dose distribution throughout the PTV. The dose at the point (the ICRU Reference Point) should always be reported as well as the maximum and minimum doses in the PTV. The situation is more complex when two or more PTV’s are identified: general recommendations are given. Three important appendices are added to the Report in order to help the reader apply the ICRU recommendations. Appendix I provides a list of the minimum requirements for documentation and for reporting the irradiation techniques. An anatomical code describing the different volumes is proposed. Appendix II contains 5 examples which illustrate, in detail, how to use the ICRU recommendations in practical clinical situations (tumour of the bronchus, breast, prostate, floor of the mouth and thigh). Appendix III discusses the relative merits of the ICRU Reference Point compared to the minimum and the mean doses at the PTV for reporting a therapeutic irradiation.