Showing papers in "The Journal of Nuclear Medicine in 2003"

Clinical Performance of PET/CT in Evaluation of Cancer: Additional Value for Diagnostic Imaging and Patient Management

Abstract: This study assessed the clinical performance of a combined PET/CT system using 18F-FDG in oncologic patients. Methods:18F-FDG PET/CT was used to evaluate 204 patients with 586 suspicious lesions. All patients had available follow-up data, enabling assessment of the clinical significance of hybrid PET/CT findings. Differences in interpretation between PET, CT, and fused PET/CT data were prospectively documented for detection, localization, and characterization of each evaluated site. The additional value of PET/CT for data interpretation over that of separate PET and CT was classified into several criteria, including change in lesion characterization to either definitely benign or definitely malignant, precise anatomic localization of malignant 18F-FDG uptake, and retrospective lesion detection on PET and CT. The clinical impact of information provided by PET/CT on patient management was assessed on the basis of follow-up data concerning further diagnostic or therapeutic approach. Analysis of data was performed for the whole study population, for different types of cancer, and for different anatomic sites. Results: PET/CT provided additional information over the separate interpretation of PET and CT in 99 patients (49%) with 178 sites (30%). PET/CT improved characterization of equivocal lesions as definitely benign in 10% of sites and as definitely malignant in 5% of sites. It precisely defined the anatomic location of malignant 18F-FDG uptake in 6%, and it led to retrospective lesion detection on PET or CT in 8%. The results of PET/CT had an impact on the management of 28 patients (14%). Hybrid PET/CT data obviated the need for further evaluation in 5 patients, guided further diagnostic procedures in 7 patients, and assisted in planning therapy for 16 patients. Conclusion: Hybrid PET/CT improves the diagnostic interpretation of 18F-FDG PET and CT in cancer patients and has an impact on both diagnostic and therapeutic aspects of patient management.

Imaging Proliferation in Lung Tumors with PET: 18F-FLT Versus 18F-FDG

Abstract: Recently, the thymidine analog 3′-deoxy-3′-18F-fluorothymidine (FLT) was suggested for imaging tumoral proliferation. In this prospective study, we examined whether 18F-FLT better determines proliferative activity in newly diagnosed lung nodules than does 18F-FDG. Methods: Twenty-six patients with pulmonary nodules on chest CT were examined with PET and the tracers 18F-FDG and 18F-FLT. Tumoral uptake was determined by calculation of standardized uptake value (SUV). Within 2 wk, patients underwent resective surgery or had core biopsy. Proliferative activity was estimated by counting nuclei stained with the Ki-67–specific monoclonal antibody MIB-1 per total number of nuclei in representative tissue specimens. The correlation between the percentage of proliferating cells and the SUVs for 18F-FLT and 18F-FDG was determined using linear regression analysis. Results: Eighteen patients had malignant tumors (13 with non–small cell lung cancer [NSCLC], 1 with small cell lung cancer, and 4 with pulmonary metastases from extrapulmonary tumors); 8 had benign lesions. In all visible lesions, mean 18F-FDG uptake was 4.1 (median, 4.4; SD, 3.0; range, 1.0–10.6), and mean 18F-FLT uptake was 1.8 (median, 1.2; SD, 2.0; range, 0.8–6.4). Statistical analysis revealed a significantly higher uptake of 18F-FDG than of 18F-FLT (Mann–Whitney U test, P

Uptake in Supraclavicular Area Fat (“USA-Fat”): Description on 18F-FDG PET/CT

Abstract: The supraclavicular region is a common site for lymph node metastases. A commonly reported type of nonmalignant 18F-FDG uptake on PET imaging in the supraclavicular region is “muscle uptake” purportedly due to muscle contraction in tense patients during the 18F-FDG uptake phase. PET/CT offers the unique opportunity to correlate PET findings with CT anatomy in the supraclavicular region. Methods: Images from the first 359 consecutive clinical whole-body studies (in 347 patients) using 18F-FDG and a PET/CT scanner (with CT attenuation correction and ordered-subsets expectation maximization [OSEM] reconstruction) were retrospectively reviewed. The supraclavicular region was evaluated for the presence of abnormal uptake on PET images, and the corresponding CT findings were assessed. Three distinct patterns of abnormal 18F-FDG uptake were noted: pattern A (uptake localizing to supraclavicular area fat [USA-fat], i.e., without corresponding lymph node or muscle uptake on CT), pattern B (uptake localizing to muscle on CT), and pattern C (uptake localizing to lymph nodes or soft-tissue masses on CT). Results: Forty-nine patients (14.1%) (32 female, 17 male; mean age, 51.4 ± 15.6 y; age range, 12–77 y) showed abnormal 18F-FDG uptake in the supraclavicular region. Twenty patients (5.8%) had muscle uptake (group B); 15 (4.3%) had definite abnormal lymph nodes (group C). However, 14 patients (4.0%) had USA-fat (group A) and foci of very low Hounsfield units on CT. These foci were also present on 68Ge attenuation-corrected images (when obtained) and non-attenuation-corrected images. Uptake in USA-fat was typically bilateral and symmetric, intense, more often multifocal than linear, and located in fat on PET/CT. Age was not significantly different for group C versus the 2 other groups. Intensity; mean standardized uptake value, lean (SUVL MEAN); or maximum standardized uptake value, lean (SUVL MAX), did not allow differentiation between patterns A and C (P > 0.05). Standardized uptake values (SUVL MAX, 3.1; SUVL MEAN, 2.1) were significantly lower in group B than in the 2 other groups (P

89Zr Immuno-PET: Comprehensive Procedures for the Production of 89Zr-Labeled Monoclonal Antibodies

Abstract: The use of immuno-PET, the combination of PET with monoclonal antibodies (mAbs), is an attractive option to improve tumor detection and mAb quantification. The long-lived positron emitter 89Zr has ideal physical characteristics for immuno-PET, such as a half-life of 3.27 d, which is compatible with the time needed for intact mAbs to achieve optimal tumor-to-nontumor ratios. Thus far, a major limitation in the use of 89Zr has been the lack of suitable methods for its stable coupling to mAbs. In this article, practical protocols for reproducible isolation of highly pure 89Zr and the production of optimal-quality mAb-89Zr conjugates are provided. Methods:89Zr was produced by a (p,n) reaction on natural yttrium (89Y), isolated with a hydroxamate column, and used for labeling of premodified mAbs. mAbs were premodified with a novel bifunctional derivative of the chelate desferrioxamine B (Df) via a new linker chemistry. To this end, Df was initially succinylated (N-sucDf), temporarily filled with Fe(III), esterified by use of tetrafluorophenol, and then directly coupled to mAbs. Chimeric mAb (cmAb) U36, directed against head and neck cancer, was used for in vitro and in vivo evaluation. The in vitro stability of cmAb U36-N-sucDf-89Zr was assessed in human serum, and its in vivo behavior was evaluated by biodistribution and PET imaging studies in tumor-bearing nude mice. A cmAb U36-Df-89Zr conjugate containing a previously described succinimide ring–thioether unit in the linker was used as a reference. Results:89Zr was produced in large batches (6.5–13.5 GBq) and isolated with improved radionuclidic purity (>99.99%) and high yield (>94%). The Df-premodified mAbs gave 89Zr-labeling efficiencies of 80% within 30 min, resulting in conjugates with preserved integrity and immunoreactivity. With respect to stability, the novel cmAb U36-N-sucDf-89Zr conjugate appeared to be superior to the reference conjugate. In vivo, the novel conjugate demonstrated selective tumor targeting, and on PET images obtained at 24, 48, and 72 h after injection of this conjugate, small tumors in the range of 19–154 mg were readily visualized. Conclusion: Methods were developed for improved purification of the long-lived positron emitter 89Zr. Moreover, a novel bifunctional Df chelate was synthesized for the reproducible coupling of 89Zr to mAbs. The suitability of such conjugates to detect millimeter-sized tumors in xenograft-bearing nude mice was demonstrated.

Determination of the Attenuation Map in Emission Tomography

Abstract: Reliable attenuation correction methods for quantitative emission CT (ECT) require accurate delineation of the body contour and often necessitate knowledge of internal anatomic structure. Two broad classes of methods have been used to calculate the attenuation map: transmission-less and transmission-based attenuation correction techniques. Whereas calculated attenuation correction belonging to the first class of methods is appropriate for brain studies, more adequate methods must be performed in clinical applications, where the attenuation coefficient distribution is not known a priori, and for areas of inhomogeneous attenuation such as the chest. Measured attenuation correction overcomes this problem and uses different approaches to determine this map, including transmission scanning, segmented magnetic resonance images, or appropriately scaled CT scans acquired either independently on separate or simultaneously on multimodality imaging systems. Combination of data acquired from different imagers suffers from the usual problems of working with multimodality images--namely, accurate co-registration from the different modalities and assignment of attenuation coefficients. A current trend in ECT is to use transmission scanning to reconstruct the attenuation map. Combined ECT/CT imaging is an interesting approach; however, it considerably complicates both the scanner design and the data acquisition and processing protocols. Moreover, the cost of such systems may be prohibitive for small nuclear medicine departments. A dramatic simplification could be made if the attenuation map could be obtained directly from the emission projections, without the use of a transmission scan. This is being investigated either using a statistical model of emission data or applying the consistency conditions that allow one to identify the operator of the problem and, thus, to reconstruct the attenuation map. This article presents the physical and methodologic basis of attenuation correction and summarizes recent developments in algorithms used to compute the attenuation map in ECT. Other potential applications are also discussed.

Patterns of (18)F-FDG uptake in adipose tissue and muscle: a potential source of false-positives for PET.

Abstract: The routine use of PET/CT fusion imaging in a large oncology practice has led to the realization that 18F-FDG uptake into normal fat and muscle can be a common source of potentially misleading false-positive PET imaging in the neck, thorax, and abdomen. The goal of this study was to characterize this normal variant of 18F-FDG uptake in terms of incidence and characteristic extent. Methods: All body scans done on our PET/CT scanners in July and August 2002 were retrospectively reviewed. All cases in which increased 18F-FDG uptake in the neck was not localized to lymph nodes or other obvious anatomic sites on the CT scans were included in this study. Sites of any unexplained 18F-FDG uptake in the rest of the body were also recorded. Results: A total of 863 PET scans (476 males, 387 females; age, 2–88 y; mean age, 57 y) were reviewed. The following distinctive patterns of nonpathologic 18F-FDG activity were observed: (a) neck fat, 20 patients (2.3%); (b) paravertebral uptake, 12 patients (1.4%); (c) perinephric fat, 7 patients (0.8%); (d) mediastinal fat, 8 patients (0.9%); (e) normal musculature, 12 patients (1.4%). Patients showing paravertebral uptake, perinephric fat, and mediastinal fat were all associated with the neck fat pattern, singly or in combination. On the other hand, patients showing the normal musculature pattern did not show any of the other uptake. In this analysis, the incidence of 18F-FDG uptake in sites other than the neck is restricted to the patient population with neck fat uptake and may be an underestimation of the true incidence. Neck fat is found predominantly in females, whereas normal musculature is usually seen in males (P

11C-Acetate PET Imaging in Hepatocellular Carcinoma and Other Liver Masses

Abstract: It is well known that 18F-FDG PET has a high average false-negative rate of 40%–50% in the detection of hepatocellular carcinoma (HCC). This is not an acceptable accuracy, particularly in countries where this tumor is prevalent. In this study, we evaluated prospectively the characteristics of 11C-acetate and 18F-FDG metabolism in HCC and other liver masses. Methods: Fifty-seven patients were recruited into this study, with masses consisting of 39 HCC; 3 cholangiocarcinomas; 10 hepatic metastases from lung, breast, colon, and carcinoid primary malignancies; and 5 benign pathologies, including focal nodular hyperplasia (FNH), adenoma, and hemangioma. All patients, except 2 with typical findings of hemangioma and 3 clinically obvious metastases, were confirmed histopathologically by liver biopsy or resection. All patients fasted for at least 6 h and blood glucose concentration was measured before they underwent dual PET radiopharmaceutical evaluation of the upper abdomen with 11C-acetate and 18F-FDG. Results: In the subgroup of HCC patients with the number of lesions ≤ 3 (32 patients; 55 lesions; mean size ± SD, 3.5 ± 1.9 cm), the sensitivity of detection by 11C-acetate is 87.3% (11C-acetate maximum SUV [SUVmax] = 7.32 ± 2.02, with a lesion-to-normal liver ratio of 1.96 ± 0.63), whereas the sensitivity of detection by 18F-FDG is only 47.3%, and 34% lesions show uptake of both tracers. None of the lesions was negative for both tracers (100% sensitivity using both tracers). In some lesions and in the subgroup of HCC patients (n = 7) with multifocal or diffuse disease, dual-tracer uptake by different parts of the tumor is demonstrated. Histopathologic correlation suggests that the well-differentiated HCC tumors are detected by 11C-acetate and the poorly differentiated types are detected by 18F-FDG. All 16 non-HCC malignant (cholangiocarcinoma and metastatic) liver lesions do not show abnormal 11C-acetate metabolism. Of the benign liver lesions, only FNH shows mildly increased 11C-acetate activities (11C-acetate SUVmax = 3.59, with a lesion-to-normal liver ratio of 1.25). Conclusion:11C-Acetate has a high sensitivity and specificity as a radiotracer complementary to 18F-FDG in PET imaging of HCC and evaluation of other liver masses.

Direct Comparison of 18F-FDG PET and PET/CT in Patients with Colorectal Carcinoma

Abstract: The purpose of this study was to compare 18F-FDG PET and PET/CT in a population of patients with colorectal cancer. Methods: PET and PET/CT images from 45 patients (17 women, 28 men; mean age ± SD, 60.8 ± 11.1 y) with known colorectal cancer referred for PET from June to November 2001 were retrospectively reviewed. Images were acquired with a PET/CT scanner, and 68Ge attenuation correction was applied. PET images and fused 68Ge attenuation–corrected PET and CT images were independently and separately interpreted by a moderately experienced reader unaware of the clinical information. Certainty of lesion characterization was scored on a 5-point scale (0 = definitely benign, 1 = probably benign, 2 = equivocal, 3 = probably malignant, 4 = definitely malignant). Lesion location was scored on a 3-point scale (0 = uncertain, 1 = probable, 2 = definite). The presence or absence of tumor was subsequently assessed using all available clinical, pathologic, and follow-up information. Analysis was provided for lesions detected by both PET and PET/CT. Results: The frequency of equivocal and probable lesion characterization was reduced by 50% (50 to 25) with PET/CT, in comparison with PET. The frequency of definite lesion characterization was increased by 30% (84 to 109) with PET/CT. The number of definite locations was increased by 25% (92 to 115) with PET/CT. Overall correct staging increased from 78% to 89% with PET/CT on a patient-by-patient analysis. Conclusion: PET/CT imaging increases the accuracy and certainty of locating lesions in colorectal cancer. More definitely normal and definitely abnormal lesions (and fewer probable and equivocal lesions) were identified with PET/CT than with PET alone. Staging and restaging accuracy improved from 78% to 89%.

11C-Acetate PET Imaging of Prostate Cancer: Detection of Recurrent Disease at PSA Relapse

Abstract: Patients with rising prostate-specific antigen (PSA) levels after definitive local therapy of prostate carcinoma present a diagnostic dilemma. A local recurrence would be amenable to additional local therapy with curative intent, whereas metastatic disease would require palliative androgen ablation therapy. In this study, we evaluated the effectiveness of PET with 11C-acetate (AC PET) for evaluation of patients with rising PSA after radical prostatectomy or radiation therapy. We also compared the reliability of AC PET in detecting recurrent prostate cancer with that of PET with 18F-FDG. Methods: Two groups of patients with PSA recurrence were enrolled in this study: group A, 30 patients after prostatectomy, and group B, 16 patients after radiation therapy. After administration of 1,110 MBq (30 mCi) of 11C-acetate, whole-body PET images were obtained. After allowing for 11C decay, 555 MBq (15 mCi) of 18F-FDG were administered and repeated whole-body imaging was performed. The PET findings were scored as positive or negative in each of the following regions: prostatic bed, pelvic nodes, paraaortic nodes, and other sites (bone or soft tissue). PET findings were correlated with those of CT, bone scintigraphy, and biopsy. Results: Twenty-seven of 46 AC PET studies (59%) had positive findings, whereas only 8 18F-FDG PET studies had positive findings (17%). Limiting the analysis to patients with findings confirmed by CT, bone scintigraphy, or biopsy or considered highly likely to represent tumor, 14 (30%) had disease identified by AC PET, whereas only 4 (9%) had disease identified by 18F-FDG PET. CT was performed on 22 patients and had positive findings in 3 (14%). Thirteen of 22 patients (59%) with serum PSA > 3 ng/mL had positive AC PET findings, whereas only 1 of 24 patients (4%) with serum PSA levels ≤ 3 ng/mL had positive findings. Conclusion: AC PET demonstrates marked uptake in prostate cancer and has higher sensitivity than 18F-FDG PET. These preliminary data show that 11C-acetate is a promising tracer for detection of recurrent prostate cancer.

"USA-Fat": prevalence is related to ambient outdoor temperature-evaluation with 18F-FDG PET/CT.

Abstract: Increased 18F-FDG activity in fatty tissue has previously been reported with PET/CT. We previously named this activity uptake in supraclavicular area fat (“USA-Fat”). We and others have speculated that this uptake exists in metabolically active brown adipose tissue (BAT). Such tissue might be expected to have varying metabolic activity depending on the ambient temperature. The purpose of this study was to evaluate the frequency of USA-Fat and its relationship to the outdoor temperature. Methods: Between July 2001 and June 2002, 1,017 consecutive whole-body scans were obtained with a PET/CT scanner and 18F-FDG for clinical patients. PET images were reviewed for the presence of USA-Fat. Results: USA-Fat was observed in 68 scans obtained from 62 patients (51 female and 11 male). The incidence of USA-Fat was highest, at 13.7%, in January through March, while outside temperatures were low, and was significantly lower, at 4.1%, during the rest of the year. Conclusion: The incidence of USA-Fat is clearly increased during the cooler period of the year. This finding suggests that stimulation by cold temperatures increases the frequency with which USA-Fat occurs, supporting underlying BAT as the etiology for this activity.

Preoperative Staging of Pelvic Lymph Nodes in Prostate Cancer by 11C-Choline PET

Abstract: Prostate cancer is known for its difficulties in preoperative staging of pelvic lymph nodes by conventional imaging techniques. Thus, a histopathologic examination of the pelvic lymphadenectomy specimen is mandatory for patients at risk for metastatic disease. The aim of this study was to evaluate the strength and accuracy of 11C-choline PET in preoperative noninvasive staging of pelvic lymph nodes in prostate cancer. Methods: In a prospective study we examined 67 consecutive patients with histologically proven prostate cancer with 11C-choline PET. The results of PET were compared with the results of histology of the pelvic lymph nodes and with the follow-up data. Conventional axial imaging was routinely performed using MRI or CT. The sensitivity, specificity, and accuracy of 11C-choline PET were calculated. Results: Fifteen patients had histologically proven lymph node metastases. 11C-Choline PET was true-positive in 12 of 15 patients and false-negative in 3 patients. Fifty-two patients had no lymph node metastases. 11C-Choline PET was true-negative in 50 of 52 patients and false-positive in 2 patients. We calculated a sensitivity of 11C-choline PET for staging metastatic lymph node disease of 80%, a specificity of 96%, and an accuracy of 93%. Next, 11C-choline PET detected solitary extraregional lymph node metastases in 5 of 12 patients with nodal metastases. Conclusion: This study showed that 11C-choline PET is sensitive and accurate in preoperative staging of pelvic lymph nodes in prostate cancer.

Clinically Significant Inaccurate Localization of Lesions with PET/CT: Frequency in 300 Patients

Abstract: This study evaluated lesion mislocalization between PET and CT on PET/CT studies when CT instead of germanium is used for attenuation correction (AC). Methods: PET/CT scans were obtained for 300 clinical patients. Both CT and germanium scans were used to correct PET emission data. Cases were noted of suspected inaccurate localization of lesions on any of the 5 sets of images (PET using germanium AC [GeAC] fused and not fused with CT, PET using CT AC fused and not fused with CT, and PET with no AC [NAC]). Independent CT or MRI was used to determine true lesion locations. Results: Six of 300 patients (2%) had lesion mislocalization when CT was used for AC or fusion. True liver dome lesions were mislocalized to the right lung base on PET/CT, likely because of a respiratory motion difference between PET and CT. No mislocalization was present on NAC PET or non-CT-fused GeAC PET images. Conclusion: Serious lesion mislocalization on PET/CT studies may occur, albeit very infrequently, when CT is used for either AC or fusion.

Preoperative Localization and Radioguided Parathyroid Surgery

Abstract: Clinical or subclinical hyperparathyroidism is one of the most common endocrine disorders. Excessive secretion of parathyroid hormone is most frequently caused by an adenoma of >or=1 parathyroid gland. Unsuccessful surgery with persistent hyperparathyroidism, due to inadequate preoperative or intraoperative localization, may be observed in about 10% of patients. The conventional surgical approach is bilateral neck exploration, whereas minimally invasive parathyroidectomy (MIP) has been made possible by the introduction of (99m)Tc-sestamibi scintigraphy for preoperative localization of parathyroid adenomas. In MIP, the incision is small, dissection is minimal, postoperative pain is less, and hospital stay is shorter. Localization imaging techniques include ultrasonography, CT, MRI, and scintigraphy. Parathyroid scintigraphy with (99m)Tc-sestamibi is based on longer retention of the tracer in parathyroid than in thyroid tissue. Because of the frequent association of parathyroid adenomas with nodular goiter, the optimal imaging combination is (99m)Tc-sestamibi scintigraphy and ultrasonography. Different protocols are used for (99m)Tc-sestamibi parathyroid scintigraphy, depending on the institutional logistics and experience (classical dual-phase scintigraphy, various subtraction techniques in combination with radioiodine or (99m)Tc-pertechnetate). MIP is greatly aided by intraoperative guidance with a gamma-probe, based on in vivo radioactivity counting after injection of (99m)Tc-sestamibi. Different protocols used for gamma-probe-guided MIP are based on different timing and doses of tracer injected. Gamma-probe-guided MIP is a very attractive surgical approach to treat patients with primary hyperparathyroidism due to a solitary parathyroid adenoma. The procedure is technically easy, safe, with a low morbidity rate, and has better cosmetic results and lower overall cost than conventional bilateral neck exploration. Specific guidelines should be followed when selecting patients for gamma-probe-guided MIP.

124I-Labeled Engineered Anti-CEA Minibodies and Diabodies Allow High-Contrast, Antigen-Specific Small-Animal PET Imaging of Xenografts in Athymic Mice

Abstract: Prolonged clearance kinetics have hampered the development of intact antibodies as imaging agents, despite their ability to effectively deliver radionuclides to tumor targets in vivo. Genetically engineered antibody fragments display rapid, high-level tumor uptake coupled with rapid clearance from the circulation in the athymic mouse/LS174T xenograft model. The anticarcinoembryonic antigen (CEA) T84.66 minibody (single-chain Fv fragment [scFv]-CH3 dimer, 80 kDa) and T84.66 diabody (noncovalent dimer of scFv, 55 kDa) exhibit pharmacokinetics favorable for radioimmunoimaging. The present work evaluated the minibody or diabody labeled with 124I, for imaging tumor-bearing mice using a high-resolution small-animal PET system. Methods: Labeling was conducted with 0.2–0.3 mg of protein and 65–98 MBq (1.7–2.6 mCi) of 124I using an iodination reagent. Radiolabeling efficiencies ranged from 33% to 88%, and immunoreactivity was 42% (diabody) or >90% (minibody). In vivo distribution was evaluated in athymic mice bearing paired LS174T human colon carcinoma (CEA-positive) and C6 rat glioma (CEA-negative) xenografts. Mice were injected via the tail vein with 1.9–3.1 MBq (53–85 μCi) of 124I-minibody or with 3.1 MBq (85 μCi) of 124I-diabody and imaged at 4 and 18 h by PET. Some mice were also imaged using 18F-FDG 2 d before imaging with 124I-minibody. Results: PET images using 124I-labeled minibody or diabody showed specific localization to the CEA-positive xenografts and relatively low activity elsewhere in the mice, particularly by 18 h. Target-to-background ratios for the LS174T tumors versus soft tissues using 124I-minibody were 3.05 at 4 h and 11.03 at 18 h. Similar values were obtained for the 124I-diabody (3.95 at 4 h and 10.93 at 18 h). These results were confirmed by direct counting of tissues after the final imaging. Marked reduction of normal tissue activity, especially in the abdominal region, resulted in high-contrast images at 18 h for the 124I-anti-CEA diabody. CEA-positive tumors as small as 11 mg (

Targeting of osseous sites with alpha-emitting 223Ra: comparison with the beta-emitter 89Sr in mice.

Abstract: The bone-seeking property and the potential exposure of red marrow by the α-particle emitter 223Ra (half-life, 11.43 d) were compared with those of the β-emitter 89Sr (half-life, 50.53 d). Methods: The biodistributions of 223Ra and 89Sr were studied in mice. Tissue uptake was determined at 1 h, 6 h, 1 d, 3 d, and 14 d after intravenous administration. Radiation absorbed doses were calculated for soft tissues and for bone. Multicellular-level doses were estimated for bone marrow cavities. Results: Both 89Sr and 223Ra selectively concentrated on bone surfaces relative to soft tissues. The measured bone uptake of 223Ra was slightly higher than that of 89Sr. At 24 h, the femur uptake of 223Ra was 40.1% ± 7.7% of the administered activity per gram of tissue. The uptake in spleen and most other soft tissues was higher for 223Ra than for 89Sr. Although predominant clearance of 223Ra was observed from the soft tissues within the first 24 h, the bone uptake of 223Ra, which was not significantly different from maximum after only 1 h, was not significantly reduced during the 14 d. Furthermore, little redistribution of 223Ra daughter products away from bone was found (2% at 6 h and less than 1% at 3 d). Estimates of dose to marrow cavities showed that the 223Ra α-emitter might have a marrow-sparing advantage compared with β-emitters for targeting osteoid surfaces because the short-range α-particles irradiate a significantly lower fraction of the marrow volumes. At the same time, the bone surfaces will receive a therapeutically effective radiation dose. Conclusion: The results of this study indicate that 223Ra is a promising candidate for high-linear-energy transfer α-particle irradiation of cancer cells on bone surfaces. 223Ra can, together with its daughter radionuclides, deliver an intense and highly localized radiation dose to the bone surfaces with substantially less irradiation of healthy bone marrow compared with standard bone-seeking β-emitters.

Lymphoscintigraphy for Sentinel Node Mapping Using a Hybrid SPECT/CT System

Abstract: Lymphoscintigraphy is performed before sentinel node (SN) biopsy for SN mapping. It is of clinical importance mainly if the tumor is located in body parts with ambiguous lymph node drainage. The purpose of this study was to assess the clinical benefit of fused SPECT/CT images to planar images for SN mapping. Methods: Thirty-four consecutive patients with cutaneous malignant melanoma (n = 28) and squamous cell carcinoma (n = 6) and scheduled for SN biopsy were enrolled. Primary tumors were located in the trunk (n = 12), in the extremities (n = 12), in the head and neck (n = 9), and in the penis (n = 1). Scintigraphy was performed using a hybrid gamma-camera/low-dose CT system. Planar images and fused SPECT/CT images were interpreted separately. Results: SPECT/CT identified multiple draining basins in 6 of 12 patients (50%) with trunk melanoma and in 3 of 9 patients (33%) with head and neck melanoma or mucosal tumor. In 9 of 21 patients (43%) with a primary tumor located in the head and neck or trunk region, SPECT/CT-fused images identified SNs that were missed on planar images, 2 of which were involved with tumor. Three of the 9 nodes were located close to the injection site and were hidden by its scattered radiation, and 2 were in-transit nodes. Another 4 nodes, identified on fused images only, were located in an additional basin to those identified on planar images. Fused images were of no added value either in patients with limb melanoma or in a patient with a penile melanoma. Conclusion: SPECT/CT SN mapping provides additional data that are of clinical relevance to SN biopsy in patients with trunk or head and neck melanoma and in patients with mucosal head and neck tumor.

Identification of cardiac sarcoidosis with (13)N-NH(3)/(18)F-FDG PET.

Abstract: To our knowledge, no study investigating the usefulness of cardiac PET for detection of myocardial involvement of sarcoidosis is available. We investigated whether 13N-NH3/18F-FDG PET could identify cardiac involvement in patients with sarcoidosis. Methods: Seventeen patients with cardiac sarcoidosis underwent cardiac 13N-NH3/18F-FDG PET under fasting condition. Systemic sarcoidosis was diagnosed by histologically proven noncaseating epithelioid granuloma, and cardiac sarcoidosis was diagnosed according to the Japanese Ministry of Health and Welfare guidelines for diagnosing cardiac sarcoidosis. Results: Only 6 patients exhibited myocardial 201Tl defects and only 3 patients exhibited abnormal 67Ga accumulation in the heart. Thirteen patients exhibited 13N-NH3 defects, and 14 patients exhibited increased 18F-FDG uptake in the heart; 12 patients exhibited both 13N-NH3 defects and increased 18F-FDG uptake, 2 patients exhibited increased 18F-FDG uptake but no 13N-NH3 defect, and 1 patient exhibited 13N-NH3 defects but no increased 18F-FDG uptake. 13N-NH3 defects were observed frequently in the basal anteroseptal wall of the left ventricle, and increased 18F-FDG uptake was observed frequently in the basal and midanteroseptal-lateral wall of the left ventricle. Involvement of the apex was rare. Seven patients were treated with steroid hormone and underwent follow-up cardiac PET 1 mo after steroid therapy. 13N-NH3 defects exhibited no significant change after steroid therapy, whereas increased 18F-FDG uptake was markedly diminished in size and intensity in 5 patients and disappeared completely in 2 patients. Conclusion: Our findings suggest that cardiac 13N-NH3/18F-FDG PET is the most useful method both for the identification of cardiac involvement of sarcoidosis and for the assessment of cardiac sarcoidosis disease activity.

Pretargeted Radioimmunotherapy of Cancer: Progress Step by Step

Abstract: To enhance the therapeutic efficacy of radioimmunotherapy of cancer, several pretargeting strategies have been developed. In pretargeted radioimmunotherapy, the tumor is pretargeted with an antibody construct that has affinity for the tumor-associated antigen on the one hand and for a radiolabeled hapten on the other. The radiolabeled hapten is administered in a later phase, preferably after the antibody construct has cleared from the circulation. In pretargeted radioimmunotherapy, 2 main approaches can be distinguished: pretargeting strategies based on the avid interaction between streptavidin (SA) or avidin and biotin, and pretargeting strategies based on the use of bispecific antibodies. In pretargeting strategies based on biotin and SA or avidin, the use of a clearing agent that could remove the pretargeting construct from the circulation markedly improved the targeting of the radiolabeled biotin to the tumor. Thus, multistep injection schemes in which 3-5 different agents are subsequently injected were developed. In bispecific antibody-based pretargeting strategies, the use of bivalent haptens improved the efficacy of the tumor targeting, and a 2-step pretargeted radioimmunotherapy strategy is now being tested in cancer patients. Preclinical studies as well as studies on cancer patients have shown that these pretargeting strategies can result in higher radiation doses to the tumor than can directly radiolabeled antitumor antibodies. Here, the development and state of the art of the most effective approaches for pretargeted radioimmunotherapy are reviewed.

Radiation Dosimetry Results and Safety Correlations from 90Y-Ibritumomab Tiuxetan Radioimmunotherapy for Relapsed or Refractory Non-Hodgkin’s Lymphoma: Combined Data from 4 Clinical Trials

Abstract: Ibritumomab tiuxetan is an anti-CD20 murine IgG1 κ monoclonal antibody (ibritumomab) conjugated to the linker-chelator tiuxetan, which securely chelates 111In for imaging or dosimetry and 90Y for radioimmunotherapy (RIT). Dosimetry and pharmacokinetic data from 4 clinical trials of 90Y-ibritumomab tiuxetan RIT for relapsed or refractory B-cell non-Hodgkin’s lymphoma (NHL) were combined and assessed for correlations with toxicity data. Methods: Data from 179 patients were available for analysis. Common eligibility criteria included

Routine (18)F-FDG PET preoperative staging of colorectal cancer: comparison with conventional staging and its impact on treatment decision making.

Abstract: UNLABELLED The preoperative staging of colorectal cancer (CRC) with (18)F-FDG PET is not as yet generally considered to be evidence based. We have found only 1 study that evaluated (18)F-FDG PET in a nonselected population with proven CRC. Several other studies have concentrated on more advanced disease. The aim of this study was to assess the potential clinical benefit of (18)F-FDG PET in the routine staging of CRC. METHODS Thirty-eight consecutive patients who had had CRC histologically proven by colonoscopy underwent prospective preoperative staging by plain chest radiography, sonography, CT, and (18)F-FDG PET. Sensitivity, specificity, and accuracy were retrospectively assessed by comparison with the histologic results after surgery (36 patients) or clinical follow-up (2 inoperable cases-both patients died within 1 y of the PET examination). The impact of (18)F-FDG PET on therapeutic decision making was evaluated by comparing medical records before and after (18)F-FDG PET. RESULTS (18)F-FDG PET correctly detected 95% of primary tumors, whereas CT and sonography correctly detected only 49% and 14%, respectively. Lymph nodes were involved in 7 patients. The sensitivity, specificity, and accuracy of (18)F-FDG PET were 29%, 88%, and 75%, respectively. CT and sonography did not reveal any lymph node involvement. Liver metastases were present in 9 patients. (18)F-FDG PET, CT, and sonography had a sensitivity of 78%, 67%, and 25%, respectively; a specificity of 96%, 100%, and 100%, respectively; and an accuracy of 91%, 91%, and 81%, respectively. (18)F-FDG PET revealed further lesions in 11 patients. Levels of carcinoembryonic antigen and carbohydrate antigen 19-9 tumor markers were elevated in, respectively, only 33% and 8% of cases of proven CRC. (18)F-FDG PET changed the treatment modality for 8% and the range of surgery for 13% of patients. In total, (18)F-FDG PET changed the method of treatment for 16% of patients. CONCLUSION Plain chest radiography and sonography did not bring any clinical benefits. No correlation was found between the level of tumor markers and the stage of disease. CT is necessary for confirmation of PET findings at extraabdominal sites (PET-guided CT) and for their morphologic specification at abdominal and pelvic sites before an operation. (18)F-FDG PET is the best method for the staging of CRC in all localities, despite the high rate of false-negative PET findings in patients with lymph node involvement. PET should be performed as a first examination after verification of CRC. We propose a PET/CT hybrid system as optimal in the staging of CRC.

Patterns of Lymphatic Drainage from the Skin in Patients with Melanoma

Abstract: An essential prerequisite for a successful sentinel lymph node biopsy (SLNB) procedure is an accurate map of the pattern of lymphatic drainage from the primary tumor site in each patient. In melanoma patients, mapping requires high-quality lymphoscintigraphy, which can identify the actual lymphatic collecting vessels as they drain into the sentinel lymph nodes. Small-particle radiocolloids are needed to achieve this goal, and imaging protocols must be adapted to ensure that all true sentinel nodes, including those in unexpected locations, are found in every patient. Clinical prediction of lymphatic drainage from the skin is not possible. The old clinical guidelines based on Sappey's lines therefore should be abandoned. Patterns of lymphatic drainage from the skin are highly variable from patient to patient, even from the same area of the skin. Unexpected lymphatic drainage from the skin of the back to sentinel nodes in the triangular intermuscular space and, in some patients, through the posterior body wall to sentinel nodes in the para-aortic, paravertebral, and retroperitoneal areas has been found. Lymphatic drainage from the head and neck frequently involves sentinel nodes in multiple node fields and can occur from the base of the neck up to nodes in the occipital or upper cervical areas or from the scalp down to nodes at the neck base, bypassing many node groups. The sentinel node is not always found in the nearest node field and is best defined as "any lymph node receiving direct lymphatic drainage from a primary tumor site." Lymphatic drainage can occur from the upper limb to sentinel nodes above the axilla. Drainage to the epitrochlear region from the hand and arm as well as to the popliteal region from the foot and leg is more common than was previously thought. Interval nodes, which lie along the course of a lymphatic vessel between a lesion site and a recognized node field, are not uncommon, especially in the trunk. Drainage across the midline of the body is quite common in the trunk and in the head and neck. Micrometastatic disease can be present in any sentinel node regardless of its location, and for the SLNB technique to be accurate, all true sentinel nodes must be biopsied in every patient.

Changes in blood flow and metabolism in locally advanced breast cancer treated with neoadjuvant chemotherapy

Abstract: Locally advanced breast cancer (LABC) is commonly treated with neoadjuvant chemotherapy followed by definitive surgery. The factors influencing the response of LABC to presurgical chemotherapy are incompletely understood. To characterize in vivo tumor biology in patients with LABC, we performed serial measurements of blood flow and glucose metabolism in LABC patients over the course of neoadjuvant chemotherapy and compared measurements with response. Methods: Thirty-five patients with newly diagnosed LABC underwent 18F-FDG and 15O-water PET imaging before therapy and after 2 mo of chemotherapy. Tumor metabolism was estimated from graphical analysis of dynamic 18F-FDG studies and was expressed as the metabolic rate of 18F-FDG (MRFDG). Blood flow was estimated from dynamic images after bolus 15O-water injection using a 1-compartment model. Metabolism and blood flow data were analyzed with and without partial-volume corrections to account for changes in tumor size over the course of therapy. Changes in tumor blood flow and metabolism were compared with response to chemotherapy and with patient survival. Results: For all patients, the mean MRFDG after 2 mo of chemotherapy decreased by 54% and the mean blood flow by 21%. Responders showed a greater decline in MRFDG than did nonresponders; however, the difference was of borderline significance (P = 0.05) after correction for partial-volume effects. Patients who responded had a decline in tumor blood flow, whereas nonresponders had an average increase (−32% vs. +48%, P

18F-FDG Accumulation with PET for Differentiation Between Benign and Malignant Lesions in the Thorax

Abstract: Recent reports have indicated the value and limitations of 18F-FDG PET and 201Tl SPECT for determination of malignancy. We prospectively assessed and compared the usefulness of these scintigraphic examinations as well as 18F-FDG PET delayed imaging for the evaluation of thoracic abnormalities. Methods: Eighty patients with thoracic nodular lesions seen on chest CT images were examined using early and delayed 18F-FDG PET and 201Tl-SPECT imaging within 1 wk of each study. The results of 18F-FDG PET and 201Tl SPECT were evaluated and compared with the histopathologic diagnosis. Results: Fifty of the lesions were histologically confirmed to be malignant, whereas 30 were benign. On 18F-FDG PET, all malignant lesions showed higher standardized uptake value (SUV) levels at 3 than at 1 h, and benign lesions revealed the opposite results. Correlations were seen between 18F-FDG PET imaging and the degree of cell differentiation in malignant tumors. No significant difference in accuracy was found between 18F-FDG PET single-time-point imaging and 201Tl SPECT for the differentiation of malignant and benign thoracic lesions. However, the retention index (RI) of 18F-FDG PET (RI-SUV) significantly improved the accuracy of thoracic lesion diagnosis. Furthermore, 18F-FDG PET delayed imaging measuring RI-SUV metastasis was useful for diagnosing nodal involvement and it improved the specificity of mediastinal staging. Conclusion: No significant difference was found between 18F-FDG PET single-time-point imaging and 201Tl SPECT for the differentiation of malignant and benign thoracic lesions. The RI calculated by 18F-FDG PET delayed imaging provided more accurate diagnoses of lung cancer.

Reduction of Respiratory Motion Artifacts in PET Imaging of Lung Cancer by Respiratory Correlated Dynamic PET: Methodology and Comparison with Respiratory Gated PET

Abstract: This study proposes a new method to reduce respiratory motion artifacts in PET images of lung cancer. The method is referred to as respiratory-correlated dynamic PET (RCDPET). RCDPET enables the acquisition of 4-dimensional PET data without the need for a respiratory tracking device. In this article, we compare this method with respiratory-gated PET (RGPET). Both methods provide the ability to correct for motion artifacts and more accurately quantitate radiotracer uptake within lung lesions. Both methods were evaluated in phantom studies and 1 patient. Methods: With RCDPET, data are acquired in consecutive 1-s time frames. A point source attached to a rigid foam block is set on the patient’s abdomen and is extended into the camera field of view at the level of the lesion by means of a low-density rod. The position of this source is used to track respiratory motion through the consecutive dynamic frames. Image frames corresponding to a user-selected lesion position within the breathing cycle, in correlation with the point source position, are then identified after scanning. The sinograms of the selected image frames are summed and then reconstructed using iterative reconstruction with segmented attenuation correction. Results: The results from phantom studies with both RGPET and RCDPET were within 10% agreement, for both activity quantitation and image noise levels. In a clinical application, the quantitation of the SUVmax and the lesion’s size showed a 6% and 2% difference, respectively, between RCDPET and RGPET measurements. Conclusion: RCDPET can be considered as a comparable, or alternative, method to RGPET in reducing the smearing effects due to respiration and improving quantitation of PET in the thorax. One advantage of RCDPET over RGPET is the ability to retrospectively reconstruct the PET data at any phase or amplitude in the breathing cycle.

18F-FDG PET for the Diagnosis and Grading of Soft-Tissue Sarcoma: A Meta-Analysis

Abstract: PET using 18F-FDG is increasingly used for the diagnosis and grading of tumors. Several studies have been performed that evaluate the diagnostic and grading performance of 18F-FDG PET for soft-tissue sarcoma, but each study has had a limited sample size. Therefore, we undertook a comprehensive meta-analysis of the evidence. Methods: Relevant studies were identified from MEDLINE and EMBASE. Diagnostic and grading performance were evaluated for qualitative visualization; standard uptake value (SUV, cutoffs of 2.0 and 3.0); and metabolic rate of glucose (MRG, cutoff of 6.0 μmol/100 g/min). Quantitative data synthesis included independent weighting of sensitivity and specificity, construction of summary receiver operating characteristic curves, and pooled analyses. Results: The meta-analysis included 15 studies with 441 soft-tissue lesions (227 malignant, 214 benign). For diagnosis of malignant versus benign lesions, typical pairs of sensitivity and specificity estimates from the summary receiver operating characteristic curves were 92% and 73% for qualitative visualization; 87% and 79% for SUV 2.0; 70% and 87% for SUV 3.0; and 74% and 73% for MRG 6.0. Diagnostic performance was similar for primary and recurrent lesions. By qualitative interpretation, 18F-FDG was positive in all intermediate/high-grade tumors (95% confidence interval [CI], 97.3%–100%), 74.4% (95% CI, 58.6%–85.9%) of low-grade tumors, and 39.3% (95% CI, 29.1%–50.3%) of benign lesions (including 11 of 12 inflammatory lesions). Using an SUV cutoff of 2.0, respective rates were 89.4% (95% CI, 79.4%–95.6%), 33.1% (95% CI, 15.6%–55.3%), and 19.1% (95% CI, 10.6%–30.5%). Limited data on comparisons with MRI and CT showed no differences against 18F-FDG PET in diagnosing recurrent and metastatic disease. Conclusion:18F-FDG PET has very good discriminating ability in the evaluation of both primary and recurrent soft-tissue lesions. 18F-FDG PET may be helpful in tumor grading but offers inadequate discrimination between low-grade tumors and benign lesions.

Evaluation of 18F-FDG PET in patients with advanced, metastatic, or recurrent gastric cancer.

Abstract: PET with 18F-FDG has been widely used in oncology, but its application for stomach neoplasms has been limited. The aim of this study was to evaluate the visual diagnostic accuracy of 18F-FDG PET for advanced, metastatic, or recurrent gastric cancer and to generate semiquantitative values for lesions. Methods:18F-FDG PET scans were obtained on 42 patients (29 men, 13 women; age, 27–78 y; median age, 63 y): 20 patients with a PT931/04 scanner and 22 patients with a SET2400W scanner. The PT931/04 has a spatial resolution of 6.0 mm at full width at half maximum (FWHM) and covers 15 cm above and below the targeted lesion, and the SET2400W has a spatial resolution of 3.9 mm at FWHM and images the entire body. All PET images were interpreted visually, and tracer uptakes were quantitated as standardized uptake values (SUVs) on SET2400W images. Results: The sensitivity, specificity, and accuracy as a whole were as follows: 71%, 74%, and 73%, respectively, with the SET2400W scanner and 47%, 79%, and 62%, respectively, with the PT931/04 scanner. Values were high for primary lesions, liver, lymph node, and lung metastases, but were low for bone metastases, ascites, peritonitis, and pleuritis carcinomatoses. SUVs were 8.9 ± 4.2 (primary lesions, 19 patients/19 lesions), 6.5 ± 2.2 (liver, 9/55), 6.1 ± 2.5 (lymph nodes, 14/38), 6.5 ± 1.8 (abdominal wall, 4/7), 3.9 ± 2.0 (bone, 3/27), and 4.7 ± 2.6 (lung, 2/3). Comparing SUVs and histologic findings for 17 untreated patients, values for well-differentiated and moderately differentiated adenocarcinomas versus poorly differentiated adenocarcinomas and signet ring cell carcinomas were 13.2 ± 6.3 (4/4) versus 7.7 ± 2.6 (13/13) (P

Radiolabeled monoclonal antibodies specific to the extracellular domain of prostate-specific membrane antigen: preclinical studies in nude mice bearing LNCaP human prostate tumor.

Abstract: Prostate-specific membrane antigen (PSMA), a transmembrane glycoprotein, is highly expressed by virtually all prostate cancers. PSMA is also expressed on the tumor vascular endothelium of virtually all solid carcinomas and sarcomas but not on normal vascular endothelium. PSMA is currently the focus of several diagnostic and therapeutic strategies. We have previously reported on the radiolabeling and in vitro binding properties of monoclonal antibodies (mAbs) (J415, J533, and J591) that recognize and bind with high affinity to the extracellular domain of PSMA (PSMAext). This article reports on the in vivo behavior and tumor uptake of 131I- and 111In-labeled antiPSMAext mAbs (J415, J533, and J591) and their potential utility for radioimmunotherapy. Methods: In nude mice bearing PSMA-positive human LNCaP tumors, the pharmacokinetics, biodistribution, and tumor uptake of these antibodies was compared with 111In-7E11 mAb, specific to the intracellular domain of PSMA (PSMAint). Autoradiographic studies were done to identify intratumoral distribution of radiolabeled mAbs. Results: With 131I-labeled antibodies, the net tumor retention of radioactivity by day 6 was significantly higher with J415 (15.4% ± 1.1%) and 7E11 (14.5% ± 1.7%) than with J591 (9.58% ± 1.1%). By contrast, the tumor uptake of 111In-1,4,7,10-tetraazacyclododecane-N,N′,N″, N‴-tetraacetic acid-labeled J415 and J591 gradually increased with time and was quite similar to that of 7E11. In addition, the blood clearance of 111In-labeled J415 and J591 antibodies was relatively faster than that of radiolabeled 7E11. As a consequence, the tumor-to-blood ratios with J415 and J591 were higher than that of 7E11. The localization of radiolabeled anti-PSMAext antibodies in PSMA-positive LNCaP tumors was highly specific because the tumor uptake of 131I-labeled J415 and J591 was more than twice that of a nonspecific antibody. Furthermore, the tumor uptake of 131I-J591 was almost 20 times higher in PSMA-positive LNCaP tumors than in PSMA-negative PC3 and DU145 tumor xenografts. Autoradiographic studies suggested that 7E11 (anti-PSMAint) distinctly favors localization to areas of necrosis whereas J415 and J591 (anti-PSMAext) demonstrated a distinct preferential accumulation in areas of viable tumor. Conclusion: These results clearly demonstrate that PSMA-specific internalizing antibodies such as J415 and J591 may be the ideal mAbs for the development of novel therapeutic methods to target the delivery of β-emitting radionuclides (131I, 90Y, and 177Lu) for the treatment of PSMA-positive tumors. In addition, because J591 and J415 mAbs are specific to PSMAext, thus targeting viable tumor, these immunoconjugates are better candidates for targeted radioimmunotherapy than are antibodies targeting PSMAint.

Prognostic value of normal exercise and adenosine (99m)Tc-tetrofosmin SPECT imaging

Abstract: UNLABELLED Event rates associated with a normal or low-risk myocardial perfusion SPECT imaging study have been shown by numerous investigators to be associated with <1%/y of follow-up. Thus, the aim of this study was to evaluate the prognostic value of a normal (99m)Tc-tetrofosmin study in a geographically diverse registry of patients undergoing stress myocardial perfusion SPECT. A total of 4,728 consecutively tested patients who underwent stress (99m)Tc-tetrofosmin SPECT at 5 U.S. hospitals were included in this series. METHODS Patients were monitored for the occurrence of major cardiac events and hospitalizations. Uniform methods of data collection and standardized epidemiologic methods for follow-up were used at all centers. We used a risk-adjusted, Cox proportional hazards model to assess time to cardiac death. RESULTS Of the 4,728 patients, one third underwent adenosine stress SPECT and two thirds underwent treadmill exercise. The observed annualized survival rate for those patients with a normal (99m)Tc-tetrofosmin study was 0.6%. Similarly, excellent survival rates were noted for the male and female subsets of this population as well as for patients who could exercise and for those undergoing pharmacologic stress testing. Compared with prior published outcomes studies on stress (201)Tl or (99m)Tc-sestamibi SPECT, the overall survival rates were similar and ranged from 99.3% to 99.7%. CONCLUSION Results from this large multicenter registry provide further supportive evidence that the excellent prognosis associated with a normal SPECT scan is independent of the radiopharmaceutical used.

Dosimetry-Guided Radioactive Iodine Treatment in Patients with Metastatic Differentiated Thyroid Cancer: Largest Safe Dose Using a Risk-Adapted Approach

Abstract: This study is a retrospective analysis of 124 differentiated thyroid cancer patients who underwent dosimetric evaluation using MIRD methodology over a period of 15 y. The objectives of the study were to demonstrate the clinical use of dosimetry-guided radioactive iodine ([RAI] 131I) treatment and the safe and effective application of a 3-Gy bone marrow (BM) dose in patients with differentiated thyroid cancer. Methods: Tumor and BM dose estimates were obtained. The administered activity that would deliver a maximum safe dose to the organ at risk (red BM or lungs) was determined as well as the resulting doses to the metastases. The clinical benefit of an individual RAI treatment was predicted on the basis of the dose estimates and the expected therapeutic response. Each patient’s response to treatment was assessed clinically and by monitoring the hematologic profile. Results: One hundred twenty-four patients underwent 187 dosimetric evaluations. One hundred four RAI treatments were performed. A complete response at metastatic deposits was attained with absorbed doses of >100 Gy. No permanent BM suppression was observed in patients who received absorbed doses of

Peritoneal Carcinomatosis: Role of 18F-FDG PET

Abstract: Peritoneal carcinomatosis can be difficult to diagnose, as CT is insensitive, with peritoneal biopsy and lavage often subject to problems of sampling error. The aim of our study was to evaluate the role of 18F-FDG PET in detecting peritoneal carcinomatosis in patients with stomach, ovarian, and adrenal cancer and mesothelioma and to compare the results with CT scans in the same patient group. Our secondary aim was to identify characteristic patterns of abdominal 18F-FDG uptake in biopsy-proven peritoneal disease and to correlate these patterns with available histologic and anatomic findings after surgery and structural imaging. Methods: The medical records of 88 patients with stomach (n = 48), ovarian (n = 13), and adrenal cancer (n = 6) and mesothelioma (n = 21) were reviewed for the presence of peritoneal tumor on 18F-FDG PET and CT scans. The results were correlated with either contemporaneous peritoneal biopsy or ascitic aspirate or with radiographic or clinical follow-up if histology was negative or unavailable. Of 24 patients with suspected peritoneal tumor, 17 had biopsy-proven findings of peritoneal disease. Results: Of the 24 patients with suspected peritoneal tumor, 18F-FDG PET was positive in 14 patients, with 1 of these scans being false-positive, CT was positive in 10 patients, and either PET or CT was positive in 18 patients. This yielded sensitivities of 57% (13/23), 42% (10/23), and 78% (18/23), with uniformly high positive predictive values of 93% (13/14), 100% (10/10), and 95% (18/19), respectively. We identified 2 distinctly abnormal scintigraphic patterns of focal and uniform 18F-FDG uptake corresponding to nodular and diffuse peritoneal disease on pathologic examination. Conclusion:18F-FDG PET adds to conventional imaging in the staging of peritoneal carcinomatosis. It is also a useful diagnostic tool when peritoneal biopsy is either unavailable or inappropriate. We have identified 2 distinct scintigraphic patterns that appear to predict the presence of either nodular or diffuse peritoneal pathology.