Interesting Images18F-Fluorothymidine PET for Functional Response Assessment Following Radiation Therapy for Extramedullary HematopoiesisCampbell, Belinda A. MBBS, MMed, FRANZCR∗,†; Callahan, Jason BApplSc(MedRad), PhD‡,§; Cole-Sinclair, Merrole BSc(Hons), MBBS, FRACP, FRCPA, FFSc(RCPA)∥; MacManus, Michael MB BCh, BAO, MD, MRCP, FRANZCR∗,§; Hofman, Michael S. MBBS, FRACP, FAANMS‡,§Author Information From the ∗Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne †Department of Clinical Pathology, University of Melbourne, Parkville ‡Molecular Imaging and Therapeutic Nuclear Medicine, Peter MacCallum Cancer Centre, Melbourne §Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville ∥Department of Haematology, St Vincent’s Hospital Melbourne, Fitzroy, Victoria, Australia. Received for publication November 18, 2020; revision accepted January 10, 2021. Conflicts of interest and sources of funding: none declared. Correspondence to: Belinda A. Campbell, MBBS, MMed, FRANZCR, Peter MacCallum Cancer Centre, Locked Bag 5, A’Beckett St, Melbourne, Victoria 8006, Australia. E-mail: [email protected]. Clinical Nuclear Medicine: September 2021 - Volume 46 - Issue 9 - p e454-e457 doi: 10.1097/RLU.0000000000003566 Buy Metrics Abstract As a marker of cellular proliferation, 18F-fluorothymidine (FLT) PET can detect the distribution of proliferating hematopoiesis and has an emerging role in the investigation of hematopoietic disorders. These images demonstrate the novel utility of 18F-FLT PET for imaging sites of extramedullary hematopoiesis (EMH) in a patient with Chuvash-type polycythemia and suggest a role for 18F-FLT PET in response assessment following radiotherapy. Further, the discordant response observed in the irradiated marrow and sites of EMH is a unique discovery, possibly suggesting the influence of the microenvironment favoring more rapid recovery of proliferative function within EMH sites. Copyright © 2021 Wolters Kluwer Health, Inc. All rights reserved.