Use of PET/CT (combined positron emission tomography and computed tomography) after CT (computed tomography) for initial staging of lymphoma changed treatment decisions in roughly one-quarter of patients with non-Hodgkin’s lymphoma (NHL) and roughly one-third of patients with Hodgkin’s disease (HD). Changes in staging and treatment were most likely for patients with stage I or stage II disease based on CT. These results were published in the Annals of Oncology.
Computed tomography (CT) has been a principal staging tool for patients with lymphoma. A CTscan uses computer-controlled x-rays to create a three-dimensional image that helps the physician estimate the extent of the disease. Although use of CT has improved the diagnosis and care of patients with lymphoma, it does have limitations: It may miss lymph nodes that have early disease involvement; it may falsely classify benignly enlarged lymph nodes as cancer; and it may not provide good information about lymphoma that has spread to the liver, skin, or skeleton.
Positron emission tomography (PET) is another imaging technique. Prior to a PET scan, a substance containing a type of sugar attached to a radioactive isotope (a molecule that spontaneously emits radiation) is injected into the patient’s vein. The cancer cells “take up” the sugar and attached isotope. The low energy radiation emitted by these cells helps physicians locate cancer. Used alone, however, this technique also has limitations.
To overcome the limitations of CT and PET used individually, an integrated (combined) PET/CT system has been developed. In order to determine whether use of PET/CT results in different staging information and treatment decisions than use of CT alone, researchers in Israel conducted a study among 103 patients with newly diagnosed lymphoma. Sixty-eight patients had NHL and 35 had HD.
PET/CT often suggested a higher stage of disease than CT, particularly for subjects with stage I or stage II disease based on CT. Among patients with NHL, PET/CT suggested a higher stage of disease than CT in 31% of patients and a lower stage of disease in 1% of patients. Among patients with HD, PET/CT suggested a higher stage of disease than CT for 32% of patients and a lower stage of disease than CT in 15% of patients.
Use of PET/CT also changed treatment decisions. Among NHL patients, use of PET/CT after CT alone changed treatment decisions for roughly one quarter of patients. Among HD patients, use of PET/CT after CT alone changed treatment decisions for 32%–45% of patients. In contrast, compared to treatment decisions based on PET/CT alone, the addition of CT changed treatment decisions for only a small number of subjects.
The researchers note that PET/CT may become the standard approach for initial staging of lymphoma. In the meantime, following an initial diagnostic CT by PET/CT appears to be most appropriate for patients with early-stage disease.
Reference: Raanani P, Shasha Y, Perry C et al. Is CT Scan Still Necessary for Staging in Hodgkin and non-Hodgkin Lymphoma Patients in the PET/CT Era? Annals of Oncology. 2006;17:117-122.