PET/CT for Lymphoma Post-therapy Response Assessment in Hodgkin Lymphoma and Diffuse Large B-cell Lymphoma

Over the course of many decades, combined chemotherapy and radiotherapy adapted to the stage of disease have become the optimal and standard treatment for Hodgkin lymphoma (HL) and diffuse large B-cell lymphoma. Besides achieving optimized cure rates of the underlying disease, reduction of toxicity has become a major goal. Since the introduction of FDG-PET for the staging and restaging of patients with lymphoma, a high predictive value of F-18-FDG-PET in response assessment has been observed. Several PET-response-guided therapy regimens have already been established, and even more PET-adapted study designs are being tested in large study groups. PET has a very high negative predictive value following chemotherapy, and radiotherapy can be safely omitted in PET-negative patients with HL after effective chemotherapy with regimens such as bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine, and prednisone in advanced stages. As "state-of-the-art" PET-guided therapy is based on the results of large clinical trials, the reliability of end-of-treatment PET as a basis for abandoning radiotherapy in early and intermediate HL stages remains to be shown. As in HL, the predictive value of FDG-PET after induction therapy of diffuse large B-cell lymphoma is higher than that of CT alone so that we obtain relevant prognostic information unavailable through anatomical imaging. Recent results from trials in aggressive non-HL with a de-escalating strategy suggest that radiotherapy may be safely omitted if FDG-PET is negative after standard chemoimmunotherapy. Since 2007, FDG-PET at end of treatment is integrated into the International Working Group criteria and became the imaging tool of choice for response assessment in aggressive lymphoma. Robust and reproducible interpretation criteria are being used both in the ongoing clinical trials and in daily routine. The recommended five-point scale has become the standard in PET response assessment, with the caveat that the consequence of a PET scan may be influenced by foregoing and following treatments.