PET
• False-positive: - Thymic hyperplasia - Infection - Inflammation - Sarcoidosis - Brown fat Other causes of false-positive scans should be ruled out.
• Allowing for comparisons among studies
• Facilitating the identification of more effective therapies
The widely used IWG criteria for response assessment of lymphoma are based predominantly on CT.
The Competence Network Malignant Lymphoma convened an International
Harmonization Project at which 5 subcommittees were formed:
• Response Criteria • End Points for Clinical Trials • Imaging • Clinical Features • Pathology/Biology
Use of Positron Emission Tomography for Response Assessment of Lymphoma: Consensus of the Imaging Subcommittee of International Harmonization Project in
Whole-body acquisition using a PET or PET/CT system should encompass at least the region between the base of the skull and themed thigh, and can be acquired in either two- or three-dimensional mode.
• The advantage of PET over conventional imaging techniques, such as TC or RMN, is its ability to distinguish between viable tumor and necrosis or fibrosis in residual mass(es) often present after treatment.
Response Criteria for Lymphoma
Response Category CR CRu
PR
Relapse/ progression
Physical Examination
Normal
Lymph Nodes Lymph Node Masses
Normal
Normal
Bone Marrow Normal
> 75% decrease
Normal
≥50% decrease
≥50% decrease
New or increased
Normal or indeterminate Positive Irrelevant
Irrelevant
Reappearance
Definitions of End Points for Clinical Trials
Normal
Normal
Normal
Indeterminate
Normal
Normal
Normal
Normal
Decrease in liver/spleen Enlarging liver/spleen; new sites
Normal
≥50% decrease ≥ 50% decrease
New or increased
“REVISED RESPONSE CRITERIA FOR MALIGNANT LYMPHOMA”
J Clin Oncol 25:579-586. © 2007 by American Society of Clinical Oncology
Cheson et al, J Clin Oncol 17:1244, 1999
In 1999, an International Working Group (IWG) of clinicians, radiologists, and pathologists with expertise in the evaluation and management of patients with Lymphoma published guidelines for response assessment and outcomes measurement.
Patients should have fasted for at least 4 hours before FDG injection.
Blood glucose level should not exceed 200 mg/dL at the time of FDG injection. If the blood glucose exceeds this level, the FDG-PET study should be rescheduled and an attempt made to control the blood sugar.
Lymphoma
J Clin Oncol 25:571-578. © 2007 by American Society of Clinical Oncology
PET- PET/CT
• PET using [18F]fluorodeoxyglucose (FDG, a radioactive derivative of glucose, is an advanced imaging tool, based on the increased glucose consumption of cancer cells), has emerged as a powerful functional imaging tool for staging, restaging, and response assessment of lymphomas.
It became clear that the International Working Group criteria warranted revision, because of identified limitations and the increased use of :
1. [18F] fluorodeoxyglucose-positron emission tomography (PET),
End Point Overall survival
Response Category
All patients
Event-free survival CR, CRu, PR
Progression-free survival
Disease-free survival
All patients CR, CRu
PET: 1. Increased the number of complete remission (CR)
patients, 2. Eliminated the CRu category 3. Enhanced the ability to discern the difference in
A recently developed integrated PET/CT system, which combines a PET camera and CT scanner in a single session, has overcome these drawbacks by providing both anatomical and functional imaging at the same position. PET/CT has become the new standard approach to imaging in the diagnosis and management of many cancer patients.
• False-negative: - Resolution of the equipment and technique - Variability of FDG avidity among histologic subtypes
Juweid et al. evaluated the impact of integrating PET into the IWG criteria in a retrospective study of 54 patients with diffuse large B-cell NHL who had been treated with an anthracycline-based regimen.
2. immunohistochemistry (IHC), 3. flow cytometry, 4. molecular biology
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“REVISED RESPONSE CRITERIA FOR MALIGNANT LYMPHOMA”
J Clin Oncol 25:579-586. © 2007 by American Society of Clinical Oncology
Standardization of PET and CT Imaging Parameters
Patients undergoing PET imaging should receive an FDG dose of 3.5 to 8 MBq/kg of body weight, with a minimum dose of 185 MBq in adults (5 mCi) and 18.5 MBq (0.5 mCi) in children.