Limited PET-CT May Be Adequate for Interim and End of Therapy Response Assessment in Patients with Early Stage Hodgkin and Aggressive Non-Hodgkin Lymphoma - A Retrospective Single Center Study
Authors: Wolach Ofir , Berenstine Hana , Edel Yonatan , Bairey Osnat , Shpilberg Ofer , Groshar David , Lahav Meir 
Published: October 2019

Abstract
Abstract 1562

Background:
PET-CT is of central importance in the staging of patients with Hodgkin (HL) and non-Hodgkin aggressive lymphoma and in the assessment of their response to therapy. Repeated imaging of patients is associated with cumulative exposure to substantial doses of radiation that have been linked to an increased life attributed risk of cancer. Reduction of the PET CT imaging region will decrease significantly the cumulative radiation dose.

Objectives:
This study aims to evaluate whether a limited PET-CT focused to the initially involved field of view (FOV) at diagnosis, above or below the diaphragm, is sufficient for effective follow up and decision making in patients with early stage curable lymphoma.

Methods:
We retrospectively reviewed all patients treated in our center for HD and non-Hodgkin aggressive lymphoma that were diagnosed with stage I or II disease according to the Ann-Arbor staging system during September 2006 to December 2010. Included were patients that had a PET-CT preformed as part of their initial staging and that were followed by interim PET-CT and/or a PET CT at the completion of therapy. Clinical and epidemiologic data were extracted from the patients' medical charts. All PET-CT were reviewed by a nuclear medicine specialist. We then analyzed whether limiting the PET-CT imaging to the initially involved FOV at diagnosis, above or below the diaphragm, would miss findings obtained by standard PET CT.

Results:
Out of 668 patients 44 were eligible for full analysis. Patient median age at diagnosis was 37.5 years (range 19–84) and 59% of patients were females. Twenty seven patients had HD and 17 had diffuse large B cell lymphoma (DLBCL). Two cases of primary mediastinal DLBCL were included in the DLBCL group. Forty two patients had stage II disease while 2 patients were diagnosed at stage I. Thirty five patients (79%) had their lymphoma located above the diaphragm while 9 patients (21%) had disease involvement below the diaphragm.
One hundred twenty seven PET-CT examinations were analyzed. Of these, 44 were preformed at diagnosis. Of the 43 interim exams preformed 32 were compatible with complete response (CR) and 11 were compatible with partial response (PR). Of the 40 PET-CT preformed at the end of treatment 34 were compatible with CR, 4 were compatible with PR and 2 showed a stable or progressive disease. There was no single case in which disease progressed outside the initially involved FOV. Thus, elements of response to therapy were contained and available for analysis within the preliminary filed of involvement in all cases.

Conclusion:
Our findings suggest that limiting PET-CT analysis of the initially involved FOV, above or below the diaphragm, in patients with early stage curable lymphoma may be satisfactory for response assessment and the associated clinical decision making. The use of limited PET-CT will significantly reduce patient exposure to cumulative radiation. The time required to complete limited PET-CT is reduced by 50% and the cost by more than 15%. To our best of knowledge this is the first analysis demonstrating the potential utility of reduction of PET CT FOV in curable lymphoma in adults.

Disclosures:
No relevant conflicts of interest to declare.