Whole-Body versus Routine Skull Base to Mid-thigh 18F-Fluorodeoxyglucose Positron Emission Tomography/ Computed Tomography in Patients with Malignant Melanoma.

OBJECTIVES: The objectives of this study are to assess the utility of whole-body 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) (skull vertex to toes) imaging relative to the standard field of view (skull base to mid-thigh) in patients with primary melanoma site that is not located in the lower extremities. MATERIAL AND METHODS: The primary site of the melanoma and metastatic disease was determined based on 18F-FDG PET/CT findings in 26 patients. The FDG avid sites were tabulated as the primary site, lower extremity, brain, and other sites. The hypothesis is that routine skull base to mid-thigh versus whole-body 18F-FDG PET/CT in patients with malignant melanoma will not change management. RESULTS: Patients (26) were divided into those with primary melanoma site in either the lower extremities (six patients) or other site (20 patients). Four of the six patients with the primary site in the lower extremities also had positive findings in the ipsilateral inguinal lymph nodes. One of the patients with a positive inguinal lymph node had metastatic sites in the external iliac region and lungs on the initial study. On follow-up imaging, this patient also exhibited diffuse metastatic disease, including a lower extremity. None of the remaining patients in this group had positive findings other than the primary site in the lower extremity. Of the remaining 20 patients with the primary site not in the lower extremity, one had diffuse metastatic disease that included a lower extremity. However, lower extremity involvement would not change patient management in this case. A second patient in this group had diffuse metastatic disease that also involved the brain. However, no metastatic disease was present in the lower extremities in this patient. None of the remaining 18 patients in this group had metastatic disease in a lower extremity. Two patients in the entire study group of 26 had brain metastasis on contrast-enhanced head CT, with one having multiple brain metastasis. PET failed to demonstrate some of the brain lesions. In the other patient with solitary brain metastasis detected on contrast-enhanced head CT, PET was negative. CONCLUSION: 18F-FDG PET/CT imaging of the lower extremity may not be justified if the primary neoplasm is not located in the lower extremities. Elimination of lower extremity imaging will reduce scanning time and additional radiation exposure. Similarly, PET/CT imaging of the brain may not be justified if contrast-enhanced CT or magnetic resonance imaging of the head is already obtained since these are more sensitive.

18F-FDG PET/CT in patients with suspected recurrent or metastatic well-differentiated thyroid cancer.

UNLABELLED: PET using 18F-FDG has been shown to effectively detect various types of cancer by their increased glucose metabolism. The aim of this study was to evaluate the use of coregistered PET and CT (PET/CT) in patients with suspected thyroid cancer recurrence. METHODS: After total thyroidectomy followed by radioiodine ablation, 61 consecutive patients with elevated thyroglobulin levels or a clinical suspicion of recurrent disease underwent 18F-FDG PET/CT. Of these, 59 patients had negative findings on radioiodine (131I) whole-body scintigraphy (WBS). Fifty-three of the 61 patients had both negative 131I WBS findings and elevated thyroglobulin levels. PET/CT images were acquired 60 min after intravenous injection of 400-610 MBq of 18F-FDG using a combined PET/CT scanner. Any increased 18F-FDG uptake was compared with the coregistered CT image to differentiate physiologic from pathologic tracer uptake. 18F-FDG PET/CT findings were correlated with the findings of histology, postradioiodine WBS, ultrasound, or clinical follow-up serving as a reference. The diagnostic accuracy of 18F-FDG PET/CT was evaluated for the entire patient group and for those patients with serum thyroglobulin levels of less than 5, 5-10, and more than 10 ng/mL. RESULTS: Thirty patients had positive findings on 18F-FDG PET/CT; 26 were true-positive and 4 were false-positive. In 2 patients, increased 18F-FDG uptake identified a second primary malignancy. 18F-FDG PET/CT results were true-negative in 19 patients and false-negative in 12 patients. The overall sensitivity, specificity, and accuracy of 18F-FDG PET/CT were 68.4%, 82.4%, and 73.8%, respectively. The sensitivities of 18F-FDG PET/CT at serum thyroglobulin levels of less than 5, 5-10, and more than 10 ng/mL were 60%, 63%, and 72%, respectively. Clinical management changed for 27 (44%) of 61 patients, including surgery, radiation therapy, or chemotherapy. CONCLUSION: Coregistered 18F-FDG PET/CT can provide precise anatomic localization of recurrent or metastatic thyroid carcinoma, leading to improved diagnostic accuracy, and can guide therapeutic management. In addition, the findings of this study suggest that further assessment of 131I WBS-negative, thyroglobulin-positive patients by 18F-FDG PET/CT may aid in the clinical management of selected cases regardless of the thyroglobulin level.

Acute intramural hematoma of the aorta as a cause of positive FDG PET/CT.

Type A acute intramural hematoma (IMH) of the ascending aorta is defined as hemorrhage in the aortic wall in the absence of intimal disruption. Proximity to the adventitia may explain the higher incidence of rupture in IMH. We present a case of IMH, diagnosed by the presence of linear intense uptake of FDG on PET/CT, in a 70-year-old woman undergoing staging for colorectal cancer. There is no current role for FDG-PET in the diagnosis of IMH. This case demonstrates that incidental focal FDG activity in the wall of the aorta may indicate the life-threatening diagnosis of IMH.

Importance of baseline PET/CT imaging on radiation field design and relapse rates in patients with Hodgkin lymphoma.

PURPOSE: This study analyzed the impact of pretreatment positron emission tomography/computed tomography (PET/CT) scans on involved site radiation therapy (ISRT) field design and pattern of relapse among patients with Hodgkin lymphoma (HL). METHODS AND MATERIALS: Thirty-seven patients with stage I or II HL who received first-line chemotherapy followed by consolidative ISRT to all initial sites of disease were enrolled in an institutional review board-approved outcomes-tracking protocol between January 2009 and December 2014. Patients underwent standard-of-care follow-up. Relapse-free survival (RFS) was evaluated using a Kaplan-Meier analysis and cohort comparisons using a χ2 test. RESULTS: Thirty-one patients underwent (PET/CT) scans before chemotherapy and 6 did not because of a lack of insurance (n = 2), inpatient chemotherapy administration (n = 2), scheduling conflicts (n = 1), and unknown reasons (n = 1). The median follow-up was 46 months, and the 4-year RFS rate was 92%. Patients without pretreatment PET imaging were more likely to experience disease relapse (4-year RFS, 97% vs. 67%; P = .001). Among the 6 patients who did not receive a baseline PET/CT scan, all 3 recurrences occurred in lymph node regions outside of, but immediately adjacent to, the radiation field. CONCLUSIONS: Patients with stage I/II HL who receive ISRT without pretreatment PET/CT scans appear to have an increased risk for relapse in adjacent nodal stations just outside the radiation field. A larger cohort with a longer follow-up is needed to confirm these findings.

Positron emission tomography/computed tomography: protocol issues and options.

Combined positron emission tomography/computed tomography (PET/CT) became FDA-approved for clinical use in late 2001. There are several design advantages of combined PET/CT over PET and CT acquired on separate devices, including more accurate CT and PET data co-registration, improved lesion localization, consolidation of imaging studies, and reduced scan times compared to dedicated PET. There are several protocols that can used to scan patients on combined PET/CT devices. Although there is no single "correct" protocol for performing a PET/CT scan, the use of oral and intravenous contrast media may improve the diagnostic value of the CT component. Whether to utilize contrast media depends on important clinical variables, including the specific type of tumor and the likelihood of encountering viable abdominal and pelvic malignancy. This article discusses various protocols pertinent to PET/CT imaging, including how the CT portion of a PET/CT scan can be performed and optimized, as well as PET/CT interpretation and reporting issues.

Full-dose 90Y ibritumomab tiuxetan therapy is safe in patients with prior myeloablative chemotherapy.

PURPOSE: Targeted radioimmunotherapy with yttrium-90 (90Y)-labeled ibritumomab tiuxetan (Zevalin, IDEC-Biogen, San Diego, CA) has shown significant activity in the treatment of relapsed or refractory CD20+ non-Hodgkin's lymphoma. Eligibility criteria used in phase I trials, and adopted in phase II and III trials, excluded patients with prior myeloablative therapy. We treated eight patients with 90Y ibritumomab tiuxetan who had prior autologous stem cell transplant, but met all other treatment criteria. EXPERIMENTAL DESIGN: Eight patients with CD20+ non-Hodgkin's lymphoma had extensive prior therapy including myeloablative chemotherapy but did not receive total body irradiation. Each had bone marrow cellularity of >15%, platelet count of >100,000/mm3, and one had documented lymphomatous bone marrow involvement of <25%. The standard course of 0.3 to 0.4 mCi/kg of 90Y ibritumomab tiuxetan was administered to patients at full dose. 18-Flouro-deoxyglucose positron emission tomography/computed tomography scans were done at pretreatment and approximately 12 weeks after treatment to assess patient response. Maximum toxicities were monitored and classified according to the Common Terminology Criteria for Adverse Events (ver. 3.0). RESULTS: Toxicities observed included grade 4 thrombocytopenia in three of eight evaluable patients and grade 4 neutropenia in one of eight evaluable patients. One patient had a neutropenic fever; all patients were off blood product support 12 weeks post-zevalin. Complete response by 18-flouro-deoxyglucose positron emission tomography/computed tomography imaging occurred in one of seven evaluable patients and one patient treated as consolidation had no evidence of disease. CONCLUSION: Our experience suggests that 90Y ibritumomab tiuxetan treatment is safe for use in patients with prior myeloablative therapy when the general inclusion criteria are fulfilled. In this small series, the response rates, however, are limited. Nevertheless, 90Y ibritumomab tiuxetan treatment may provide clinical benefit in carefully selected extensively pretreated patients.

A Phase 2 Trial of Concurrent Chemotherapy and Proton Therapy for Stage III Non-Small Cell Lung Cancer: Results and Reflections Following Early Closure of a Single-Institution Study.

PURPOSE: Proton therapy has been shown to reduce radiation dose to organs at risk (OAR) and could be used to safely escalate the radiation dose. We analyzed outcomes in a group of phase 2 study patients treated with dose-escalated proton therapy with concurrent chemotherapy for stage 3 non-small cell lung cancer (NSCLC). METHODS AND MATERIALS: From 2009 through 2013, LU02, a phase 2 trial of proton therapy delivering 74 to 80 Gy at 2 Gy/fraction with concurrent chemotherapy for stage 3 NSCLC, was opened to accrual at our institution. Due to slow accrual and competing trials, the study was closed after just 14 patients (stage IIIA, 9 patients; stage IIIB, 5 patients) were accrued over 4 years. During that same time period, 55 additional stage III patients were treated with high-dose proton therapy, including 7 in multi-institutional proton clinical trials, 4 not enrolled due to physician preference, and 44 who were ineligible based on strict entry criteria. An unknown number of patients were ineligible for enrollment due to insurance coverage issues and thus were treated with photon radiation. Median follow-up of surviving patients was 52 months. RESULTS: Two-year overall survival and progression-free survival rates were 57% and 25%, respectively. Median lengths of overall survival and progression-free survival were 33 months and 14 months, respectively. There were no acute grade 3 toxicities related to proton therapy. Late grade 3 gastrointestinal toxicity and pulmonary toxicity each occurred in 1 patient. CONCLUSIONS: Dose-escalated proton therapy with concurrent chemotherapy was well tolerated with encouraging results among a small cohort of patients. Unfortunately, single-institution proton studies may be difficult to accrue and consideration for pragmatic and/or multicenter trial design should be considered when developing future proton clinical trials.

Controversial ectopic thyroid: a case report of thyroid tissue in the axilla and benign total thyroidectomy.

A 43-year-old woman presented with a mass in her left axilla, which was surgically excised. Histologically, the tissue was a reactive lymph node with adjacent thyroid follicular tissue. The differential diagnosis included benign ectopic thyroid versus metastatic well-differentiated follicular-derived thyroid carcinoma. Because of the possibility of carcinoma, the patient underwent a diagnostic total thyroidectomy. The thyroid was grossly normal with no histologic evidence of malignancy. Post-operatively, the patient underwent a whole body 131I scan. Aside from an expected residual uptake in the thyroid bed region, there was no extrathyroidal uptake to suggest additional ectopic thyroid tissue or metastatic disease. At the time of this scan, her thyrotropin (TSH) was 92.8 microU/mL, thyroglobulin was less than 0.3 ng/mL, and thyroglobulin antibody was less than 3 IU/mL. Abnormalities in the embryologic development and migration of the thyroid gland can result in ectopic thyroid tissue. The most frequent locations are along the midline from the base of the tongue to the mediastinum. Only rare case reports exist of ectopic thyroid in other locations, including the chest (heart, trachea), abdomen (liver, gallbladder, pancreas), and pelvis (vagina). This case represents the first description of thyroid tissue in the axilla with a histologically benign thyroid gland.

Combined PET-CT in the head and neck: part 1. Physiologic, altered physiologic, and artifactual FDG uptake.

Positron emission tomography (PET) with 2-[fluorine-18] fluoro-2-deoxy-D-glucose (FDG) has been effective for the diagnosis, staging, and restaging of malignancies of the head and neck region. However, lack of anatomic landmarks, variable physiologic uptake, and asymmetric FDG distribution in several altered physiologic states can confound image interpretation. In addition, many benign causes and several artifacts can simulate physiologic or pathologic FDG uptake in the head and neck. Combined PET-computed tomography (CT) is a unique imaging modality that permits anatomic and functional imaging on a single scanner with nearly perfect coregistration. Combined PET-CT provides information that cannot be obtained with PET or CT alone. In particular, PET-CT facilitates the interpretation of FDG uptake in the head and neck, an area that is characterized by dense and complex anatomic structures. An atlas of FDG uptake in this anatomic region was compiled on the basis of combined PET-CT findings in 11,000 patients. In general, patterns of FDG uptake were variable and often reflected patient activity during or immediately preceding the uptake phase. With the growing interest in PET-CT, interpreting radiologists and nuclear medicine physicians must be familiar with the patterns of FDG uptake in the head and neck to avoid misinterpretation or mis-diagnosis.

Indium-111 pentetreotide imaging of carcinoid tumor of the thymus.

INTRODUCTION: Carcinoid tumors are relatively rare and can occur in the thorax, abdomen, or pelvis. Indium-111 pentetreotide scanning is useful for the identification of these tumors. In this report, we present imaging findings and discussion pertaining to a 43-year-old man who presented with Cushing's syndrome resulting from a thymic carcinoid tumor. The imaging is of interest because there is not only marked uptake of In-111 pentetreotide in the thymic carcinoid tumor, but also within the adrenal glands attributable to elevated tumor-derived ACTH. METHOD: Planar and single-photon emission computed tomography (SPECT) images of the chest and abdomen were obtained 15 minutes after the injection of 6.6 mCi of In-111 pentetreotide. Further planar and SPECT images were obtained approximately 4 and 24 hours after injection of the radiopharmaceutical. Correlation of In-111 pentetreotide SPECT was made with laboratory results and CT evaluation of the chest and abdomen. RESULTS: Initial clinical workup for Cushing's syndrome included a contrast-enhanced brain magnetic resonance image that showed a small pituitary lesion thought to represent a microadenoma. Normal inferior petrosal venous sinus sampling for ACTH suggested there was an ectopic ACTH source. Subsequent CT of the chest identified a 3 x 3-cm enhancing mediastinal mass. Avid uptake within the mass on In-111 pentetreotide images suggested that the underlying cause of Cushing's syndrome was ACTH production from a thymic carcinoid. Increased uptake of In-111 pentetreotide was also noted within hyperplastic adrenal glands. Surgical resection and histologic evaluation established the diagnosis of a moderately differentiated thymic carcinoid tumor. CONCLUSION: This case illustrates the complementary ability of In-111 pentetreotide planar and SPECT imaging and CT to diagnose an ACTH-producing thymic carcinoid tumor leading to adrenal hyperplasia and Cushing's syndrome.

FDG PET CT assessment of treatment response after yttrium-90 ibritumomab tiuxetan radioimmunotherapy.

Yttrium-90 ibritumomab tiuxetan (Zevalin; IDEC Pharmaceuticals Corp., San Diego, CA) is the first radioimmunotherapy agent approved by the U.S. Food and Drug Administration (FDA) for treatment of non-Hodgkin lymphoma. In a randomized clinical trial comparing Zevalin with rituximab, the overall response rate was 80% and 56%, respectively. Response was determined by assessing the size of lymph nodes on CT scans. FDG PET has been well accepted as an accurate imaging study for staging non-Hodgkin lymphoma and evaluating response to treatment. Simultaneous FDG PET and CT imaging (PET CT) provides coregistered functional PET images with anatomic CT images. We describe 2 cases of non-Hodgkin lymphoma treated in which response was followed using PET CT.

The use of combined PET/CT for localizing recurrent head and neck cancer: the Pittsburgh experience.

We performed a retrospective study of 47 patients to ascertain the ability of combined positron-emission tomography and computed tomography (PET/CT) to localize recurrent head and neck cancer. When clinically warranted, biopsies were performed in an attempt to obtain pathologic confirmation of the PET/CT findings. Of the 47 patients, 33 exhibited PET/CT findings consistent with recurrent cancer. Of the 33 patients, 25 underwent either biopsy or surgical excision of disease in an attempt to obtain a pathologic confirmation. Biopsy analysis confirmed the PET/CT findings in 22 of these patients; in the remaining 3 patients, pathologic findings were inconsistent with the PET/CT diagnosis. Based on the subset of 25 patients who underwent pathologic testing, the sensitivity of combined PET/CT was 95% and the specificity was 60%. We conclude that combined PET/CT imaging is a valuable tool for localizing tumor recurrence in patients with head and neck cancer.

Unexpected Bone Metastases from Thyroid Cancer.

Objective. To present a complicated case of differentiated thyroid carcinoma (DTC) with metastases to the skull that was evident on I-131 whole body scan (WBS) but negative on other imaging modalities in a low risk patient. Methods. We will discuss clinical course, imaging, pathological findings, and treatment of the patient with skull metastasis from DTC. Pertinent literature on imaging and pathology findings as well as radioactive iodine (RAI) treatment impact on quality of life and survival in patients with bone metastases from DTC will be reviewed. Results. The patient is a 37-year-old woman with a diagnosis of DTC who had focal areas of increased uptake in the head on WBS with no correlative findings on CT and MRI. Initially, false positive findings were suspected since patient had a low risk for developing metastases. However, the persistent findings on post-RAI treatment WBS, following two courses of treatment, were highly concerning for metastatic bone disease. WBC performed 6 months following the second RAI treatment revealed resolution of the findings. Conclusions. False positive findings in WBS are frequent and may be due to contamination, perspiration, or folliculitis of the scalp as well as benign lesions such as meningioma, hematoma, cavernous angioma, and metallic sutures. However, metastatic disease should always be considered even if the patient has low risk of distant metastatic disease and correlative images do not support the diagnosis. RAI therapy appears to improve the survival rates and quality of life of thyroid cancer patients with bone metastases based on retrospective studies.

An introduction to PET-CT imaging.

Cancer is one of the leading causes of morbidity and mortality in developed countries such as the United States. Complex clinical decisions about treatment of oncologic patients are largely guided by imaging findings, among other factors. Most radiologic procedures map the anatomy and morphology of tumors with little or no information about their metabolism. Positron emission tomography (PET) performed with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) has proved valuable in providing important tumor-related qualitative and quantitative metabolic information that is critical to diagnosis and follow-up. PET-computed tomography (CT) is a unique combination of the cross-sectional anatomic information provided by CT and the metabolic information provided by PET, which are acquired during a single examination and fused. FDG PET-CT offers several advantages over PET alone; the most important is the ability to accurately localize increased FDG activity to specific normal or abnormal anatomic locations, which may be difficult or even impossible with PET alone. Understanding the principles of FDG PET-CT and the optimal scanning techniques and recognizing the potential pitfalls and limitations are important for advantageous use of this imaging modality.

Combined positron emission tomography/computed tomography imaging of recurrent thyroid cancer.

OBJECTIVE: The study goal was to evaluate the use of combined positron emission tomography/computed tomography (PET/CT) imaging for localization of recurrent disease in thyroid cancer patients. STUDY DESIGN AND SETTING: Eight patients with suspected recurrence of thyroid cancer on the basis of elevated serum thyroglobulin or calcitonin levels underwent combined PET/CT imaging on a prototype device. All 8 patients had previously undergone total thyroidectomy and (131)I ablation for thyroid carcinoma. Patients with papillary carcinoma had negative (131)I scans. RESULTS: Eight patients underwent combined PET/CT scanning. Four (50%) of 8 patients underwent PET/CT indicating recurrence in the head and neck. A total of 11 lesions in these 4 patients were suspicious for recurrence on combined PET/CT imaging. Three patients with 8 lesions suspicious for recurrence on PET/CT underwent surgical removal of disease. All 3 patients had pathologic confirmation of recurrence, with 6 (75.0%) of 8 lesions being positive. CONCLUSION: Combined PET/CT imaging is a valuable tool for the diagnosis and anatomic localization of recurrent thyroid cancer.

Physiologic uterine uptake of FDG during menstruation demonstrated with serial combined positron emission tomography and computed tomography.

F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) has been used extensively to stage, restage, and follow neoplastic disease. However, focal accumulation of FDG may cause false-positive results in certain physiologic conditions. In this report, a unique PET and computed tomography (CT) combination scan helped define physiologic accumulation of FDG in the uterus during menstruation in a 40-year-old woman with a history of rectal melanoma and possible recurrent disease. An initial PET study, performed during menstruation, was followed immediately by a PET-CT scan, which showed marked accumulation of FDG in the posterior pelvis, localized to a retroverted uterus. An FDG PET-CT scan repeated 2 weeks later confirmed resolution of this "lesion." Thus, combined PET-CT correctly differentiated physiologic FDG uptake in a retroverted uterus from recurrent rectal melanoma. This case shows that physiologic FDG accumulation in the uterus should be considered when focal FDG accumulation is observed in the pelvis in women of reproductive age.

Diffuse bone marrow uptake on whole-body F-18 fluorodeoxyglucose positron emission tomography in a patient taking recombinant erythropoietin.

F-18 fluorodeoxyglucose (FDG)-positron emission tomography (PET) is used extensively in oncology to diagnose, stage, and restage patients with various malignancies. Many patients treated for malignancies develop neutropenia secondary to marrow suppressive chemotherapy and are subsequently treated with synthetic hematopoietic growth factors (HGF), both granulocyte-macrophage colony-stimulating factor (GM-CSF) and granulocyte-colony-stimulating factor (G-CSF). Patients taking HGF can present a diagnostic challenge for those interpreting PET because they can demonstrate diffuse marrow uptake on FDG-PET scans, mimicking diffuse bone marrow metastases. It has not been reported whether bone marrow uptake is affected on PET scans in patients taking erythropoietin, the erythroid-specific cell-line stimulator. We report a case of extensive diffuse bone marrow uptake in a 77-year-old man with a history of colon cancer who began taking erythropoietin 3 weeks before his PET scan. This case demonstrates the need to consider erythropoietin in the differential diagnosis of possible etiologies causing diffuse bone marrow uptake on PET scans.

PET/CT Protocols and Artifacts in the Head and Neck.

Combined PET/CT has been in existence clinically for nearly 7 years since development and initial evaluation from 1998 to 2001. Combined PET/CT offers advantages over PET and CT acquired on separate devices, including consolidation of imaging studies, more accurate data coregistration, improved lesion localization, and benefits related to radiation therapy planning. This article discusses CT and PET protocols pertinent to PET/CT imaging in patients who have head and neck cancer, including a discussion of how the CT portion of a PET/CT scan can be performed and a description of common PET/CT artifacts that may be encountered secondary to CT protocols.

90Y microsphere treatment of unresectable liver metastases: changes in 18F-FDG uptake and tumour size on PET/CT.

PURPOSE: The intra-arterial administration of 90Y microspheres is a new palliative treatment option for unresectable liver metastases. The aim of this study was to quantitatively assess changes in FDG uptake and tumour size following 90Y microsphere treatment (SIR-Spheres) using 18F-fluorodeoxyglucose (FDG) PET/CT imaging. METHODS: Five patients with unresectable liver metastases who had failed multiple prior chemotherapy regimens received seven 90Y microsphere treatments to a single liver lobe. All patients underwent a baseline PET/CT scan prior to treatment, as well as up to four follow-up PET/CT scans. The tumour area of 30 liver metastases was measured on CT and the FDG uptake was semiquantitatively assessed by calculation of standardised uptake values (SUVs). A total of 18 FDG-PET/CT scans were performed. RESULTS: The SUVs in the 30 treated liver metastases decreased from 6.5+/-2.3 at baseline to 4.2+/-1.8 after the first follow-up PET/CT scan (p=0.001). In contrast, the SUVs of untreated metastases increased slightly from 7.2+/-2.3 to 8.0+/-0.8. There was no difference in FDG uptake in treated versus untreated normal liver tissue. Using a previously defined threshold of 20% decrease in SUV from baseline to determine response, 20 out of 30 liver metastases were considered to have responded at the first follow-up PET/CT scan approximately 1 month after treatment. In these metastases, the SUV decreased by 47+/-12%, compared with a slight increase by 5.9+/-19% in ten non-responding metastases (p=0.0001). The changes in tumour size did not correlate with changes in FDG uptake. On the first follow-up PET/CT scan, the tumour area on CT increased by 3.1+/-57% in treated metastases compared with 23.3+/-32% in untreated metastases. A wide range of post-treatment changes of target lesions was observed on CT, including an increase in the size of hypodense lesions, necrotic features and complete resolution of CT abnormalities. CONCLUSION: The metabolic information obtained from FDG-PET/CT seems to provide a more accurate and earlier assessment of therapy response following 90Y microsphere treatment than does the anatomical CT information.