Transformation in the use of radiation therapy of Hodgkin lymphoma: new concepts and indications lead to modern field design and are assisted by PET imaging and intensity modulated radiation therapy (IMRT).
Review
Overview
abstract
The role of radiation therapy (RT) in Hodgkin lymphoma has changed substantially; it has evolved from a first-line comprehensive single agent into a complementary adjuvant following chemotherapy. Yet, the significant contribution of adding radiotherapy has repeatedly been confirmed by recent information from several prospective randomized trials in early stage patients (CCG, Canada NCIC, and EORTC/GELA H9F). In a recent study that included patients of all stages adding radiotherapy impacted significantly on overall survival. Even in advanced-stage disease, in patients with less than CR, and/or bulky disease or in programs that use short-course chemotherapy (e.g. Stanford V) involved-field radiation therapy (IFRT) remained essential. Randomized studies and most recently the GHSG HD 10 and HD 11 documented excellent results with low-dose IFRT of only 20 Gy in both early stage and in intermediate-stage patients. It is now standard of care to use IFRT rather than the extended radiation fields of the past (mantle, inverted Y, and STLI/TLI). Even smaller volumes than IFRT, such as 'lymph-node fields' are advocated by paediatrics groups and are under consideration for future adults treatment programs. This change in RT concept has been motivated by need to reduce normal tissue exposure in order to markedly lessen the risk of late complications. The small fields of current radiotherapy allow more conformal and innovative approaches that have not been technically feasible in the past. They also mandate better targeting. Both the accuracy and the confirmality of 'min-radiation' are augmented, by using new advances in imaging, treatment planning, and new radiation delivery systems. The PET/CT/Simulator integrated hardware with innovative software allows more accurate PET and CT (or MRI) parallel volume contouring, radiation 'dose painting' (dose tailored to PET residual activity) and field 'sculpting'. Introducing intensity modulated radiotherapy technology (IMRT)--a technology that was originally designed for small tumors treated with very high doses--to the field of lymphoma provides safer and more accurate radiotherapy to selected patients with very bulky residual disease and permits re-irradiation of relapsed disease.
