CLINICAL INVESTIGATION Lymphoma [ 18 F]FDG-POSITRON EMISSION TOMOGRAPHY COREGISTRATION WITH COMPUTED TOMOGRAPHY SCANS FOR RADIATION TREATMENT PLANNING OF LYMPHOMA AND HEMATOLOGIC MALIGNANCIES STEPHANIE A. TEREZAKIS, M.D.,* MARGIE A. HUNT, M.S., y ALEXANDER KOWALSKI, B.A., y PATRICK MCCANN, B.A., y C. ROSS SCHMIDTLEIN,PH.D., z ANNE REINER, B.S., x MITHAT GO ¨ NEN,PH.D., x ASSEN S. KIROV,PH.D., y ANNE MARIE GONZALES, B.A.,* HEIKO SCHO ¨ DER, M.D., z AND JOACHIM YAHALOM, M.D.* *Department of Radiation Oncology Medical Physics, y Radiology, Nuclear Medicine Service, and z Epidemiology and Biostatistics, x Memorial Sloan-Kettering Cancer Center, New York, New York Purpose: Positron emission-tomography (PET) using 2-[ 18 F]fluoro-2-deoxyglucose (FDG-PET) increases sensitiv- ity and specificity of disease detection in lymphoma and thus is standard in lymphoma management. This study examines the effects of coregistering FDG-PET and computed tomography (CT) (PET/CT) scans on treatment planning for lymphoma patients. Methods and Materials: Twenty-nine patients (30 positive PET scans) underwent PET/CT treatment planning from July 2004 to February 2007 and were retrospectively studied. For each patient, gross tumor volume was blindly contoured on the CT-only and PET/CT studies by a radiation oncologist. Treatment plans were generated for both the CT-only and PET/CT planning target volumes (PTVs) for all patients. Normal tissue doses and PTV coverage were evaluated using dose–volume histograms for all sites. Results: Thirty-two treatment sites were evaluated. Twenty-one patients had non-Hodgkin lymphoma, 5 patients had Hodgkin lymphoma, and 3 patients had plasma cell neoplasms. Previously undetected FDG-avid sites were identified in 3 patients during PET/CT simulation, resulting in one additional treatment field. Due to unexpected PET/CT simulation findings, 2 patients did not proceed with radiation treatment. The addition of PET changed the volume of 23 sites (72%). The PTV was increased in 15 sites (47%) by a median of 11% (range, 6-40%) and reduced in 8 sites (25%) by a median of 20% (range, 6%-75%). In six (19%) replanned sites, the CT-based treatment plan would not have adequately covered the PTV defined by PET/CT. Conclusions: Incorporation of FDG-PET into CT-based treatment planning for lymphoma patients resulted in considerable changes in management, volume definition, and normal tissue dosimetry for a significant number of patients. Ó 2011 Elsevier Inc. Lymphoma, PET/CT radiation planning, [ 18 F]FDG-PET, Involved field radiation, Target volume definition. INTRODUCTION Positron emission-tomography (PET) using 2- [ 18 F]fluoro-2- deoxyglucose (FDG-PET) scanning provides functional imaging due to the increased glucose uptake of tumor cells relative to that of normal cells. FDG-PET images can com- plement CT scans’ anatomic information by localizing meta- bolically active cells within the tumor volume. PET scanning is now widely accepted as a diagnostic tool in lymphoma management due to its improved sensitivity in the staging of Hodgkin and non-Hodgkin lymphoma (1–6). As a result, the active incorporation of FDG-PET in radiation treatment planning for lymphoma patients is now occurring Radiation treatment is integral to the management of lym- phoma. Historically, radiation was delivered to an extended field, which resulted in significant exposure of normal tissue to radiation. The majority of patients with early-stage lym- phoma are now treated with combined modality therapy us- ing chemotherapy followed by involved field radiation therapy (IFRT), which includes the involved site and imme- diately adjacent lymph node region(s) in the treatment field (7). Combined modality therapy has allowed a decrease in Reprint requests to: Joachim Yahalom, M.D., Department of Ra- diation Oncology, Memorial Sloan-Kettering Cancer Center, 1275 York Ave., New York, NY 10021. Tel: (212) 639-5999; Fax: (212) 639-2417; E-mail: yahalomj@mskcc.org This work was supported by the Lymphoma Foundation and the Sports Foundation Against Cancer. Dr. Terezakis was supported by the Dr. Mortimer J. Lacher Fellowship Fund. Dr. Terezakis is now a faculty member in the Department of Ra- diation Oncology and Molecular Radiation Sciences at Johns Hop- kins. Conflict of interest: none. Received Nov 20, 2009, and in revised form June 18, 2010. Accepted for publication June 25, 2010. 615 Int. J. Radiation Oncology Biol. Phys., Vol. 81, No. 3, pp. 615–622, 2011 Copyright Ó 2011 Elsevier Inc. Printed in the USA. All rights reserved 0360-3016/$–see front matter doi:10.1016/j.ijrobp.2010.06.044