David Israel

CT and PET: Early Prognostic Indicators of Response to Imatinib Mesylate in Patients with Gastrointestinal Stromal Tumor

OBJECTIVE We report results from a pilot study aimed at optimizing the use of CT bidimensional measurements and 18F-FDG PET maximum standardized uptake values (SUVs-(max)) for determining response to prolonged imatinib mesylate treatment in patients with advanced gastrointestinal stromal tumors (GISTs). SUBJECTS AND METHODS Sixty-three patients enrolled in a multicenter trial evaluating imatinib mesylate therapy for advanced GIST underwent FDG PET at baseline and 1 month after initiation of treatment. Of these 63 patients, 58 underwent concomitant CT. Time-to-treatment failure (TTF) was used as the outcome measure. Patients were followed up over a range of 23.7 to 37 months (median, 31.7 months). The predictive power of change in CT bidimensional measurements, change in PET SUVmax, and PET SUVmax at 1 month after initiation of treatment were determined, optimized, and compared. The effectiveness of combining metrics was also evaluated. RESULTS Both a threshold PET SUVmax value of 2.5 at 1 month (p = 0.04) and the European Organization for Research and Treatment of Cancer (EORTC) criteria for partial response on FDG PET (25% reduction in PET SUVmax) at 1 month (p = 0.004) were predictive of prolonged treatment success. The Southwest Oncology Group (SWOG) criteria for partial response ((3) 50% reduction in CT bidimensional measurements) at 1 month were not predictive (p = 0.55) of TTF. Optimizing metrics improved results performance. An optimized PET SUVmax threshold of 3.4 (p = 0.00002), a reduction in the SUVmax of 40% (p = 0.002), and an optimized CT bidimensional measurement threshold--that is, no growth from baseline to 1 month (p = 0.00005)--outperformed the existing standards (i.e., EORTC and SWOG criteria). Combinations of metrics did not improve performance. CONCLUSION The two best metrics were the optimized PET SUVmax threshold of 3.4 at 1 month (p = 0.00002) and the optimized CT bidimensional measurement threshold (no growth from baseline to 1 month, p = 0.00005) in this patient group.

End-of-treatment but not interim PET scan predicts outcome in nonbulky limited-stage Hodgkin’s lymphoma

BACKGROUND Early interim positron emission tomography (PET) scans appear powerfully predictive of outcome in Hodgkins lymphoma (HL), particularly in advanced-stage disease where it has been predominantly studied. The prognostic value of interim PET in limited-stage patients with nonbulky disease has not been well established. PATIENTS AND METHODS Ninety-six patients with nonbulky limited-stage HL were identified who had interim and end-of-treatment PET scans. Response rate, overall survival (OS), and progression-free survival (PFS) were calculated. RESULTS Four-year PFS and OS for the entire cohort were 88% and 97%, respectively. Interim PET did not predict outcome, with PFS in positive and negative patients 87% versus 91% (P=0.57), respectively. End-of-treatment PET result was predictive of outcome, with PFS of 94% in end PET-negative patients versus 54% in end PET-positive patients (P<0.0001). Four-year OS was 100% in end PET-negative patients and 84% in end PET-positive patients (P<0.0001). CONCLUSIONS Interim PET scans were not predictive of outcome, compared with scans carried out at completion of therapy. End-of-treatment PET was highly predictive of PFS and OS, regardless of interim PET result. In this low-risk patient population, even patients with interim positive PET scans show a favorable prognosis.

PET/CT and Renal Pathology: A Blind Spot for Radiologists? Part 1, Primary Pathology

OBJECTIVE PET/CT with (18)F-FDG shows metabolically active disease and is widely used for the diagnosis and follow-up of patients with cancer. Nonmetabolically active renal pathology may be missed without close attention to the CT portion of the study, whereas metabolically active pathology may be missed on PET because of physiologic tracer excretion in the kidneys. This article illustrates primary lesions of the kidney on FDG PET/CT with emphasis on key anatomic features and the appearance of tracer uptake. CONCLUSION Close attention to both the FDG PET and CT portions of the study is essential to interpret renal pathology correctly on FDG PET/CT examinations.

PET/CT and Renal Pathology: A Blind Spot for Radiologists? Part 2???Lymphoma, Leukemia, and Metastatic Disease

OBJECTIVE PET/CT with (18)F-FDG is a powerful tool to evaluate patients with hematologic malignancy or to assess the burden of metastatic disease from solid tumors. Metabolically active renal pathology associated with lymphoma, leukemia, or metastatic disease can be missed without close attention to both the PET and CT portions of the study because of physiologic FDG excretion in the kidneys. This article illustrates the appearance of tracer uptake and the key anatomic features of lymphoma, leukemia, and metastatic disease involving the kidney on FDG PET/CT. CONCLUSION Close attention to both the FDG PET and CT portions of an FDG PET/CT study is essential to evaluate the kidneys in oncology patients.

Evaluation of low-density neutral oral contrast material in PET/CT for tumor imaging: results of a randomized clinical trial.

OBJECTIVE The objective of this study was to determine the impact on image quality and risks in terms of artifacts and side effects of a low-density barium-based suspension as oral contrast material for CT during PET/CT examinations of an oncologic patient population. SUBJECTS AND METHODS Eighty-five patients (51 men and 34 women; mean age, 53 years; age range, 21-87 years) were prospectively randomized to receive either 0.1% barium sulfate oral suspension or no oral contrast material during PET/CT. Patients in the oral contrast group were given 1,350 mL over 60-75 minutes. The (18)F-FDG PET component of each examination was reviewed for the presence of artifacts by two nuclear medicine physicians and was classified as adequate (no presence of artifactual focal FDG uptake attributed to attenuation-correction errors) or inadequate (focal uptake in attenuation-correction PET images with no corresponding uptake in non-attenuation-corrected PET images). Two radiologists reviewed the CT studies and scored the degree of bowel opacification using a 5-point scale, ranging from 0 for no opacification (i.e., not possible to delineate the bowel structures from the surrounding tissues) to 4 for excellent opacification (i.e., bowel structure identifiable and bowel wall clearly visible). The attenuation values (in Hounsfield units) were recorded in the stomach, duodenum, mid jejunum, and terminal ileum for quantitative analysis. Interobserver variability was assessed using kappa coefficients. RESULTS None of the patients who received oral contrast material experienced side effects. All 85 PET examinations were considered adequate with no observable artifacts. The mean bowel opacification scores of the oral contrast group (2.59 and 2.93) as evaluated by radiologists 1 and 2, respectively, were significantly higher (p < 0.01) than those of the control group (1.55 and 1.59). The level of attenuation achieved in the contrast group was significantly higher than in the control group. The interobserver variability was moderate (kappa = 0.32). CONCLUSION The use of low-density neutral oral contrast material for CT during combined FDG PET/CT studies significantly improves visualization of the bowel structures compared with no contrast material without causing side effects or clinically detectable errors in the attenuation correction of the FDG PET study.

FDG uptake in lipomatous hypertrophy of the interatrial septum is not likely related to brown adipose tissue.

Lipomatous hypertrophy of the interatrial septum (LHIS) may be associated with arrhythmias or sudden death. Increased fluorine-18 fluorodeoxyglucose (FDG) uptake in LHIS is occasionally found on positron emission tomography, and has been attributed to metabolically active brown adipose tissue (BAT) contained within LHIS. We report a case of a patient suggesting that neither of the 2 currently known mechanisms of glucose uptake by BAT is responsible for FDG uptake in LHIS, unless a mechanism of BAT activation exists that has not been previously described. This study also suggests that FDG uptake is unlikely to be due to cardiomyocytes contained within LHIS. Inflammation is a potential mechanism, although further investigation is needed.

Positron Emission Tomography Imaging for Tumor Ablation

Nuclear medicine imaging involves the injection or ingestion of radioactive Pharmaceuticals known as radiotracers, each designed to track a particular physiologic or pathophysiologic process. In contrast to conventional radiologic imaging such as x-ray computed tomography (CT) and magnetic resonance imaging (MRI), which map out anatomic structure and depend on changes in morphology or size for determination of pathology, nuclear medicine imaging provides information on the metabolic function of the investigated organ or tissue.