Combination of PET and CT to Assess Response in Non-Hodgkins Lymphoma
Combination of PET and CT to Assess Response in Non-Hodgkins Lymphoma
Abstract & Commentary
By William B. Ershler, MD, INOVA Fairfax Hospital Cancer Center, Fairfax, VA; Director, Institute for Advanced Studies in Aging, Washington, DC and is Editor of Clinical Oncology Alert. Dr. Ershler is on the speaker’s bureau for Amgen and does research for Ortho Biotech.
Synopsis: In a retrospective review of clinical outcomes in non-Hodgkin’s lymphoma patients who underwent response assessment at the end of treatment, the addition of PET to the standard International Workshop Criteria (IWC) improved staging accuracy and gave a better prediction of overall progression-free survival.
Source: Juweid ME, et al. Response assessment of aggressive non-Hodgkin’s lymphoma by integrated International Workshop Criteria and fluorine-18-fluorodeoxyglucose positron emission tomography. J Clin Oncol. 2005;23:4652-4661.
Computed tomography (CT) has played a major role in assessing treatment response in patients with non-Hodgkin’s lymphoma (NHL). Most patients being treated for NHL are evaluated using the International Workshop Criteria (IWC)1 which takes into account the clinical and biochemical features of the disease as well as bone marrow biopsy and CT findings. Of these, the CT results have a heavy impact on the assigned final response designation.
CT is capable of detecting very small-volume tumors (less than 1 cm in diameter), but cannot differentiate actively dividing tumor cells from fibrosis or necrosis in residual tumors.
Positron Emission Tomography (PET) scans have been increasingly used in pretreatment staging and in assessing response in their NHL patients. Although this technique allows for a more accurate distinction of viable tumor from benign findings, it is less capable than CT to detect small tumors (less than 1 cm).
This study was conducted to see if using both of these techniques systematically in combination would provide superior accuracy in response assessment to using either one alone. Included were 54 consecutive NHL patients treated at 4 universities with chemotherapy between 1994 and 2002. Clinical courses of patients treated at 4 centers (University of Iowa, University of Nebraska, Mayo Clinic, and University of Ulm [Germany]) were reviewed in retrospect. Each of the subjects had a posttherapy (1 to 16 weeks) PET and CT scan performed within 1 month of each other and their response was classified by the IWC criteria. When IWC was compared to IWC + PET, only the combined analysis (IWC + PET) was shown to be a statistically significant independent predictor of progression-free survival.
Commentary
This report, although retrospective in design and small in number of patients evaluated, provides a useful affirmation to a practice clinicians have begun to incorporate in practice. The coincident evaluation by CT and PET makes sense, in that the precise anatomic definition provided by CT is augmented by the estimation of metabolic activity afforded by PET. In fact, due to the rapid evolution of PET scanning technology, the equipment used in the current report has been supplanted in many centers with combined PET/CT systems. These combine both modalities into a single instrument, based upon the realization of the supplemental information to be gained. Application of this technology to lymphoma management, particularly NHL, although slow in coming, seems particularly appropriate.
In the current report, the added value of PET scanning was tested in the setting of post-therapy assessment of response. The typical IWC criteria for response, which is weighted heavily by the CT findings, was compared with those criteria when PET scanning was included (IWC+PET). The analysis demonstrated a substantially higher proportion of patients achieving CR when the method of determination included PET. Presumably this is because some of the anatomic (CT) findings in treated patients may reflect fibrotic, metabolically inactive residua and not persistent disease. Furthermore, the IWC+PET analysis resulted in a statistically significant independent predictor of progression-free survival, and this was not true of IWC alone in this cohort.
Thus, it would be reasonable to assimilate PET scanning after completion of chemotherapy for patients who have recently completed treatment for NHL with the expectation that such an approach will result in more accurate assessment of response rate and overall progression-free survival.
References
1. Cheson BD, et al. Report of an international workshop to standardize response criteria for non-Hodgkin’s lymphomas. NCI Sponsored International Working Group. J Clin Oncol. 1999;17:1244; Erratum in: J Clin Oncol. 2000;18:2351.
In a retrospective review of clinical outcomes in non-Hodgkins lymphoma patients who underwent response assessment at the end of treatment, the addition of PET to the standard International Workshop Criteria (IWC) improved staging accuracy and gave a better prediction of overall progression-free survival.Subscribe Now for Access
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