• For most patients with early stage unfavorable prognosis Hodgkin’s lymphoma,

chemotherapy can be given until maximal tumor response, as evaluated by computed tomography scan and positron emission tomography imaging, after at least two cycles of chemotherapy. After these cicles, chemotherapy is followed by involved field radiation therapy. The progress of clinical trials to identify the best chemotherapy combination for these patients occured with early studies compared MOPP with MOPP-like combinations, later trials compared MOPP or MOPP-like combinations with ABVD in an attempt to both enhance efficacy and reduce toxicity by limiting exposure to alkylating agentes and the most recent trials compared ABVD with more intense chemotherapy combinations such as escalated BEACOPP. Currently, after all these trials ABVD combination remains as standard chemo­therapy regimen.

toxicity. There are three possible approaches to using smaller volume treatments. Since lymphatic spread involves nodes adjacent to the primary site of disease first, locoregional treatment that includes elective adjuvant irradiation of the first node stations may be given (IFRT). The CTV includes the GTV, which is the primary site, and adjacent nodes as CTV (a situation analogous to treatment of uninvolved nodes in head and neck cancer). Alternatively, only the initial macroscopic volume of disease (GTV), whether in lymph node (involved nodal INRT), or an organ (sometimes called involved site ISRT) is treated with a GTV-CTV margin. Finally, the residual GTV following chemotherapy, defined by PET-CT, could be the basis of the target volume. In published reports the target volumes used may combine aspects of these different conceptual approaches. When primary radiotherapy without chemotherapy is given (e.g. stage I follicular non-Hodgkin’s lymphoma or nodular lymphocyte predominant Hodgkin’s lymphoma), IFRT is used to include the uninvolved first node station in the CTV as well as the macroscopically involved GTV. The CTV is designed using the initial volume of involved lymph nodes, i.e. the initial GTV as shown on staging CT, MRI and FDG-PET­CT scans. These scans need to be taken in the radiotherapy treatment position, whenever possible, for accurate co-registration with subsequent CT planning scans which are taken after chemotherapy. When primary radiotherapy is given, the GTV is present both clinically and on imaging. After chemotherapy there may be a complete response (PET and CT negative) with no GTV, or a partial response with a residual GTV. The original GTV is outlined on the post­chemotherapy CT planning scan using the co-registered initial CT and PET scans. The patient’s anatomy will have altered with response to chemotherapy, and the principle is to cover the site of original disease, but to reduce toxicity by excluding wherever possible normal tissues that were displaced, but not involved by tumour. Anatomical planes act as boundaries and the volume should not extend into adjacent bone, air or viscera. For both IFRT and INRT of the mediastinum, the pre-chemotherapy volume is used for the superior– inferior extension and the post-chemotherapy volume for the axial to reduce dose to blood vessels, heart, coronary arteries and lung which may have returned to their normal position (Figure 6).