This study assesses the influence of new techniques and technologies in radiotherapy on the derivation and applicability of the margins currently used for treatment planning. The validity of the continued use of the recommendations of International Commission on Radiation Units and Measurements (ICRU) and other recommendations as a result of the additional information derived from these emerging techniques is also reviewed. The ICRU formulations still remain fundamental in the derivation of target volumes in radiotherapy; however, revisions to these have been recommended through various experimental and modelling techniques leading to the publication of various margin recipes. These recipes are used for margin definitions in new radiotherapy techniques including intensity-modulated radiotherapy (IMRT). The use of image-guided radiotherapy (IGRT) techniques leads to the reduction in organ motion uncertainties and setup errors, allowing for the adjustment of margins and treatment plans as well as dose escalation. Clinical trials are still needed to validate most of the new techniques in radiotherapy, particularly in IGRT techniques leading to adaptive radiotherapy. It is recommended that well devised clinical trials should be conducted to investigate fully the efficacy of these new techniques, particularly in radiotherapy image guidance and adaptive radiotherapy. Such trials would validate any recommendations regarding the current clinical margins and impact on their continued clinical use.