Radiotherapy planning for the lymphomas: expanding roles for biologic imaging

Radiotherapy planning now uses advanced technologies to accurately image and assess the extent of disease for treatment. PET scanning has become established as perhaps the most important imaging study for patients with Hodgkin's disease. With respect to initial staging, FDG-PET is more sensitive overall than CT scanning. PET can detect disease at sites that do not meet size criteria by CT. Also, PET is more specific than CT alone because of the functional information that it provides. However, some disease may still escape PET imaging, and false negative results can occur. With respect to treatment response, PET has now become accepted as the most important response measure for the lymphomas. Current protocols are investigating the benefit of this information for radiotherapy planning, and even the possible elimination of radiotherapy in patients completely responding to chemotherapy. For radiotherapy planning, PET/CT should be obtained prior to and after chemotherapy; both scans give important information for the design of the radiation treatment. This chapter will review specific guidelines for planning radiotherapy based on these new imaging capabilities.