Sodium fluoride (Na18F) PET Response Criteria in Solid Tumors (NAFCIST): a framework for response assessment in bone tumors.

The current Response Evaluation Criteria in Solid Tumors for measuring tumor response in osteosarcoma may be sub-optimal, as even responsive bone tumors may show limited change in tumor diameters. This limits the use of traditional imaging assessment tools. Therefore, discerning osteosarcoma response to therapy on magnetic resonance imaging before surgery is often difficult, and it is typically evaluated after surgery by assessing the amount of necrosis in resected surgical specimens. To address these challenges, sodium fluoride (Na18F) positron emission tomography/computed tomography (PET/CT) scans can be utilized to better image bone response to therapy, as, fluoride is avidly taken up by bone. Na18F Response Criteria in Solid Tumors (NAFCIST) has been developed as a novel method to evaluate treatment response using Na18F PET/CT. Current evidence supporting NAFCIST comes from a pilot study that evaluated alpha particle radium-223 in patients with osteosarcoma. In this review, practical guidance for utilizing NAFCIST in the context of bone tumors is illustrated to aid future studies.

Prostate-specific antigen flare induced by 223RaCl2 in patients with metastatic castration-resistant prostate cancer.

PURPOSE: Prostate-specific antigen (PSA) flare is a well-known phenomenon in patients with prostate cancer, but its impact during radium-223 dichloride (223RaCl2) therapy is still unclear. This radioisotope has shown to improve overall survival in metastatic castration-resistant prostate cancer (mCRPC). We sought to evaluate the impact of PSA flare on survival and its relation with metabolic parameters on 18F-labeled sodium fluoride PET/CT. METHODS: We conducted a retrospective study of 168 patients with mCRPC (median age 69; median PSA 29.7) receiving 223RaCl2. Overall survival (OS) and progression-free survival (PFS), estimated by the Kaplan-Meier method and compared using a log-rank test, were evaluated for patient groups corresponding to different definitions of PSA flare. Metabolic 18F-fluoride PET/CT data were analyzed as well. RESULTS: Immediate PSA decline was observed in 49 patients (29.2%), whereas no PSA response was observed in 59 patients (35.1%). PSA flare (defined as rise after the first cycle followed by decrease below the baseline) was observed in 20 patients (11.9%) and PSA flare followed by a decrease from peak but not below baseline was observed in 40 (23.8%). The first flare subgroup had a median PFS and OS of 20.8 and 23.9 months, respectively. These outcomes were not significantly different from patients with immediate PSA decrease, but were significantly better than in patients with persistent PSA elevation (3.1 months for PFS and 11.5 months for OS, p < 0.001). Moreover, the PSA flare group showed an alkaline phosphatase (ALP) decrease significantly greater than non-responders (p = 0.003). Metabolic 18F-fluoride PET/CT data were available in 35 patients at baseline and during 233RaCl2 therapy. The tumor burden reduction, expressed by ΔTLF10 and ΔFTV10, was more evident within PSA flare group below baseline than non-responders (p = 0.005 and 0.001, respectively). CONCLUSIONS: This report suggests that a flare does not necessarily indicate lack of response to 223RaCl2 therapy.

Clinical parameters model for predicting pathologic complete response following preoperative chemoradiation in patients with esophageal cancer.

BACKGROUND: Approximately 25% of patients with esophageal cancer (EC) who undergo preoperative chemoradiation, achieve a pathologic complete response (pathCR). We hypothesized that a model based on clinical parameters could predict pathCR with a high (≥60%) probability. PATIENTS AND METHODS: We analyzed 322 patients with EC who underwent preoperative chemoradiation. All the patients had baseline and postchemoradiation positron emission tomography (PET) and pre- and postchemoradiation endoscopic biopsy. Logistic regression models were used for analysis, and cross-validation via the bootstrap method was carried out to test the model. RESULTS: The 70 (21.7%) patients who achieved a pathCR lived longer (median overall survival [OS], 79.76 months) than the 252 patients who did not achieve a pathCR (median OS, 39.73 months; OS, P = 0.004; disease-free survival, P = 0.003). In a logistic regression analysis, the following parameters contributed to the prediction model: postchemoradiation PET, postchemoradiation biopsy, sex, histologic tumor grade, and baseline (EUS)T stage. The area under the receiver-operating characteristic curve was 0.72 (95% confidence interval [CI] 0.662-0.787); after the bootstrap validation with 200 repetitions, the bias-corrected AU-ROC was 0.70 (95% CI 0.643-0.728). CONCLUSION: Our data suggest that the logistic regression model can predict pathCR with a high probability. This clinical model could complement others (biomarkers) to predict pathCR.

Circulating tumor cells and bone metastases as detected by FDG-PET/CT in patients with metastatic breast cancer.

BACKGROUND: We evaluated the relationship between the detection and prognostic significance of circulating tumor cells (CTCs) and sites of metastases detected by 2-[fluorine-18]fluoro-2-deoxy-D-glucose-positron emission tomography/computed tomography (FDG-PET/CT) in patients with metastatic breast cancer (MBC). PATIENTS AND METHODS: From May 2004 to January 2008, 195 patients with relapsed/progressive MBC underwent whole-body FDG-PET/CT and provided blood samples for assessment of CTC count. RESULTS: Higher CTC numbers were detected in patients with bone metastases relative to those with no bone lesions (mean 65.7 versus 3.3, P = 0.0122) and in patients with multiple bone metastases relative to those with one or two bone lesions (mean 77.7 versus 2.6, P < 0.001). CTCs predicted overall survival (OS) in 108 patients with multiple sites of metastases including bone (P = 0.0008) but not in 58 without bone metastases (P = 0.4111) and in 29 with bone involvement only (P = 0.3552). All 15 patients but one with human epidermal growth factor receptor 2 (HER-2) positive tumors who were treated with trastuzumab-based regimens had <5 CTCs at progression. In multivariate analysis, CTCs, but not bone metastases, remained a significant predictor of OS. CONCLUSION: Presence of extensive bone metastases as detected by FDG-PET/CT is associated with increased CTC numbers in MBC.

The evolving role of PET-CT in the management of esophageal cancer.

Esophageal cancer, although uncommon in the United States, has been increasing in frequency, and despite advances in therapy, the diagnosis still carries a poor prognosis. Many patients present with locally advanced disease and receive multimodality therapy with combined chemoradiation before surgery. Imaging plays an important role in the initial selection of patients for tri-modality therapy and in evaluating responses to neoadjuvant chemoradiation prior to surgery. There is increasing use of 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG)-positron emission tomography (PET)/computed tomography (CT) in management of esophageal cancer to identify distant metastasis at presentation and to assess response to therapy. Standardized imaging protocols with semiquantitative analysis may also provide prognostic information and be used to individualize patient therapy. This review will discuss the role of imaging studies in the management of esophageal cancer patients, with particular attention to FDG-PET/CT.

Unusual adrenal metastasis and abdominal carcinomatosis secondary to Hurthle cell carcinoma of the thyroid.

Hurthle cell carcinoma (HCC) of the thyroid is an uncommon and relatively rare differentiated thyroid neoplasm. To our knowledge, no reported case of adrenal metastases with abdominal carcinomatosis secondary to HCC of the thyroid has been demonstrated by F-18 FDG PET/CT imaging. One report of adrenal uptake on I-131 whole-body scan with HCC exists. In this case report, we describe a patient with HCC who had a left adrenal metastasis with abdominal carcinomatosis that was discovered using F-18 FDG PET/CT imaging.

Attenuation correction of PET cardiac data with low-dose average CT in PET/CT.

We proposed a low-dose average computer tomography (ACT) for attenuation correction (AC) of the PET cardiac data in PET/CT. The ACT was obtained from a cine CT scan of over one breath cycle per couch position while the patient was free breathing. We applied this technique on four patients who underwent tumor imaging with 18F-FDG in PET/CT, whose PET data showed high uptake of 18F-FDG in the heart and whose CT and PET data had misregistration. All four patients did not have known myocardiac infarction or ischemia. The patients were injected with 555-740 MBq of 18F-FDG and scanned 1 h after injection. The helical CT (HCT) data were acquired in 16 s for the coverage of 100 cm. The PET acquisition was 3 min per bed of 15 cm. The duration of cine CT acquisition per 2 cm was 5.9 s. We used a fast gantry rotation cycle time of 0.5 s to minimize motion induced reconstruction artifacts in the cine CT images, which were averaged to become the ACT images for AC of the PET data. The radiation dose was about 5 mGy for 5.9 s cine duration. The selection of 5.9 s was based on our analysis of the respiratory signals of 600 patients; 87% of the patients had average breath cycles of less than 6 s and 90% had standard deviations of less than 1 s in the period of breath cycle. In all four patient studies, registrations between the CT and the PET data were improved. An increase of average uptake in the anterior and the lateral walls up to 48% and a decrease of average uptake in the septal and the inferior walls up to 16% with ACT were observed. We also compared ACT and conventional slow scan CT (SSCT) of 4 s duration in one patient study and found ACT was better than SSCT in depicting average respiratory motion and the SSCT images showed motion-induced reconstruction artifacts. In conclusion, low-dose ACT improved registration of the CT and the PET data in the heart region in our study of four patients. ACT was superior than SSCT for depicting average respiration motion in a patient study.

Attenuation correction of PET images with respiration-averaged CT images in PET/CT.

UNLABELLED: Attenuation correction (AC) of PET images with helical CT (HCT) in PET/CT matches only the spatial resolution of CT and PET, not the temporal resolution. We therefore proposed the use of respiration-averaged CT (ACT) to match the temporal resolution of CT and PET and evaluated the improvement of tumor quantification in PET images of the thorax with ACT. METHODS: First, we examined 100 consecutive clinical PET/CT studies for the frequency and magnitude of misalignment at the diaphragm position between the HCT and the PET data. Patients were injected with 555-740 MBq of (18)F-FDG and scanned 1 h after injection. The HCT data were acquired at the following settings: 120 kV, 300 mA, pitch of 1.35:1, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. Patients were instructed to hold their breath at midexpiration during HCT of the thorax. The PET acquisition was 3 min per bed. Second, we retrospectively analyzed studies of 8 patients (1 with esophageal cancer and 7 with lung cancer). Each study included regular PET/CT followed by 4-dimensional (4D) CT for radiation treatment planning. We compared the results of AC of the PET data with HCT and ACT. There were 13 tumors in these 8 patients. The 4D CT data were acquired at the following settings: 120 kV, 50-150 mA, cine duration of 1 breathing cycle plus 1 s, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. The acquisition was taken when the patient was in the free-breathing state. We averaged the 10 phases of the 4D CT data to obtain ACT for AC of the PET data. Both the ACT and the HCT data were used for AC of the same PET data. RESULTS: There was a misalignment between the HCT and the PET data in 50 of 100 patient studies. In 34 studies, the misalignment was greater than 2 cm. In a comparison of HCT and ACT, 5 tumors had differences in standardized uptake values (SUV) between HCT-and ACT-attenuation-corrected PET of less than 20%, and 4 tumors had differences in SUV of more than 50%. The latter 4 tumors were found in the patient with esophageal cancer and in 2 of the patients with lung cancer. The PET data from these 3 patients had a misalignment of 2-4.5 cm relative to the HCT data. Breathing artifacts were significantly reduced by ACT. Seven of the 8 patients had a lower diaphragm position on HCT than on ACT, suggesting that the patients tended to hold a deeper breath during HCT than during ACT. CONCLUSION: The high rate of misalignment suggested a potential mismatch between the HCT and the PET data with the limited-breath-hold CT protocol. In the comparison of HCT and ACT, significant differences (>50%) in SUV were attributable to different breathing states between HCT and PET. The PET data corrected by ACT did not show breathing artifacts, suggesting that ACT may be more accurate than HCT for AC of the PET data.

Qualitative and quantitative comparison between images obtained with filtered back projection and iterative reconstruction in prostate cancer lesions of (18)F-FDG PET.

BACKGROUND: Recently, iterative reconstruction with segmented attenuation corrections (IRSAC) has been introduced for reconstruction of (18)F-FDG PET images. IRSAC produces images that are more pleasing to the eye, but qualitative and quantitative comparisons between IRSAC and filtered back projection (FBP) have not been reported for metastatic cancer. Since quantitative data has been widely used as an adjunct to interpretation of PET scans, comparison between IRSAC and FBP is needed. The purpose of this study was to compare image quality and the maximum standardized uptake value (SUVmax) obtained with FBP and with IRSAC in metastatic lesions from prostate cancer. METHODS: Twenty (18)F-FDG PET scans (10 baseline and 10 follow-up) were performed in 10 patients with prostate cancer (ages 66-85 yrs, mean 73.6 yrs). Acquisition began 45 min after injection of 370 MBq of (18)F-FDG. Images were reconstructed using FBP and IRSAC, and submitted to visual and quantitative analysis. SUVmax was obtained for all metastases, on FBP and IRSAC. A Jaszczak phantom study was also performed. RESULTS: IRSAC images showed better image quality than FBP especially in regions of high activity concentrations. IRSAC detected 106 lesions on both baseline and follow-up scans, while FBP detected 100 and 95 lesions on baseline and follow-up scans, respectively. Therefore, 17 more lesions were seen on IRSAC. The mean SUVmax values on baseline scans for FBP and IRSAC were systematically different, at 4.46+/-1.99 and 5.13+/-2.67, respectively. On follow-up scans values were 3.89+/-1.72 for FBP and 4.29+/-1.93 for IRSAC. Comparison of FBP with IRSAC on baseline and follow-up scans were statistically significant (baseline: paired "t"-test p=0.0017; follow-up: paired "t"-test p=0.0008). Phantom studies reveal that these differences can be explained by the type of reconstruction filters used, and IRSAC was more accurate than FBP. CONCLUSIONS: IRSAC detects smaller volumes in phantoms, patient images are easier to interpret and more metastatic lesions were detected. In addition, IRSAC provides reproducible quantitative data, comparable to data provided by FBP. IRSAC SUV and FBP SUV are in close agreement but there was a statistically significant difference between the two, and therefore threshold values of SUV will probably need to be re-determined with IRSAC, and are likely to be 10 to 19% higher than currently reported.

Standardized uptake value in pediatric patients: an investigation to determine the optimum measurement parameter.

Although the standardized uptake value (SUV) is currently used in fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) imaging, concerns have been raised over its accuracy and clinical relevance. Dependence of the SUV on body weight has been observed in adults and this should be of concern in the pediatric population, since there are significant body changes during childhood. The aim of the present study was to compare SUV measurements based on body weight, body surface area and lean body mass in the pediatric population and to determine a more reliable parameter across all ages. Sixty-eight pediatric FDG-PET studies were evaluated. Age ranged from 2 to 17 years and weight from 11 to 77 kg. Regions of interest were drawn at the liver for physiologic comparison and at FDG-avid malignant lesions. SUV based on body weight (SUV(bw)) varied across different weights, a phenomenon less evident when body surface area (SUV(bsa)) normalization is applied. Lean body mass-based SUV (SUV(lbm)) also showed a positive correlation with weight, which again was less evident when normalized to bsa (SUV(bsa-lbm)). The measured liver SUV(bw) was 1.1+/-0.3, a much lower value than in our adult population (1.9+/-0.3). The liver SUV(bsa) was 7.3+/-1.3. The tumor sites had an SUV(bw) of 4.0+/-2.7 and an SUV(bsa) of 25.9+/-15.4 (65% of the patients had neuroblastoma). The bsa-based SUVs were more constant across the pediatric ages and were less dependent on body weight than the SUV(bw). These results indicate that SUV calculated on the basis of body surface area is a more uniform parameter than SUV based on body weight in pediatric patients and is probably the most appropriate approach for the follow-up of these patients.

FDG-PET standardized uptake values in normal anatomical structures using iterative reconstruction segmented attenuation correction and filtered back-projection.

Filtered back-projection (FBP) is the most commonly used reconstruction method for PET images, which are usually noisy. The iterative reconstruction segmented attenuation correction (IRSAC) algorithm improves image quality without reducing image resolution. The standardized uptake value (SUV) is the most clinically utilized quantitative parameter of [fluorine-18]fluoro-2-deoxy-D-glucose (FDG) accumulation. The objective of this study was to obtain a table of SUVs for several normal anatomical structures from both routinely used FBP and IRSAC reconstructed images and to compare the data obtained with both methods. Twenty whole-body PET scans performed in consecutive patients with proven or suspected non-small cell lung cancer were retrospectively analyzed. Images were processed using both IRSAC and FBP algorithms. Nonquantitative or gaussian filters were used to smooth the transmission scan when using FBP or IRSAC algorithms, respectively. A phantom study was performed to evaluate the effect of different filters on SUV. Maximum and average SUVs (SUVmax and SUVavg) were calculated in 28 normal anatomical structures and in one pathological site. The phantom study showed that the use of a nonquantitative smoothing filter in the transmission scan results in a less accurate quantification and in a 20% underestimation of the actual measurement. Most anatomical structures were identified in all patients using the IRSAC images. On average, SUVavg and SUVmax measured on IRSAC images using a gaussian filter in the transmission scan were respectively 20% and 8% higher than the SUVs calculated from conventional FBP images. Scatterplots of the data values showed an overall strong relationship between IRSAC and FBP SUVs. Individual scatterplots of each site demonstrated a weaker relationship for lower SUVs and for SUVmax than for higher SUVs and SUVavg. A set of reference values was obtained for SUVmax and SUVavg of normal anatomical structures, calculated with both IRSAC and FBP image reconstruction algorithms. The use of IRSAC and a gaussian filter for the transmission scan seems to give more accurate SUVs than are obtained from conventional FBP images using a nonquantitative filter for the transmission scan.

Incidental focal thyroid uptake on FDG positron emission tomographic scans may represent a second primary tumor.

PURPOSE: This article discusses the value of incidental thyroid uptake of fluorodeoxyglucose (FDG) on whole-body positron emission tomography (PET) scans performed in patients with cancer. This issue has been reported diversely in the literature. MATERIALS AND METHODS: Whole-body PET scans of four patients with cancer (two of them women; age, 49 to 78 years) in whom focal thyroid uptake was visualized and subsequently correlated with thyroid carcinoma based on cytologic or histopathologic data were reviewed. The clinical outcomes of these patients were analyzed retrospectively. Maximum and average standardized uptake values (SUVs) of thyroid accumulation were recalculated in all patients. RESULTS: Two of the four patients referred for FDG PET scans had lung adenocarcinomas, one had prostate carcinoma, and one had an unknown primary tumor. Focal thyroid uptake was visualized, with maximum and average SUVs ranging from 3.7 and 2.3 to 53 and 34, respectively. These findings were correlated with cytologic (two patients) or histopathologic data (two patients) that indicated thyroid carcinoma. In two patients, their treatment was changed and total thyroidectomy was performed; in one of them the SUVs of the focal thyroid accumulation (maximum and average values of 7.9 and 4.8, respectively) were less than the cutoff values for thyroid cancer noted in the literature. The clinical condition of the other two patients did not permit additional investigation or treatment for thyroid carcinoma. CONCLUSION: Increased focal thyroid uptake on whole-body FDG PET scans should not be overlooked, even when it is not marked, and should prompt further investigation to rule out cancer.

Local detection of prostate cancer by positron emission tomography with 2-fluorodeoxyglucose: comparison of filtered back projection and iterative reconstruction with segmented attenuation correction.

BACKGROUND: To compare filtered back projection (FBP) and iterative reconstruction with segmented attenuation correction (IRSAC) in the local imaging of prostate cancer by positron emission tomography with 2-fluorodeoxyglucose (FDG-PET). METHODS: We retrospectively identified 13 patients with primary (n=7) or recurrent (n=6) prostate cancer who had increased uptake in the prostate on FDG-PET performed without urinary catheterization, contemporaneous biopsy confirming the presence of active tumor in the prostate, and correlative cross-sectional imaging by MRI (n=8) or CT (n=5). FDG-PET images were reconstructed by FBP and IRSAC. Two independent nuclear medicine physicians separately rated FBP and IRSAC images for visualization of prostatic activity on a 4-point scale. Results were compared using biopsy and cross-sectional imaging findings as the standard of reference. RESULTS: IRSAC images were significantly better that FBP in terms of visualization of prostatic activity in 12 of 13 patients, and were equivalent in 1 patient (p<0.001, Wilcoxon signed ranks test). In particular, 2 foci of tumor activity in 2 different patients seen on IRSAC images were not visible on FBP images. In 11 patients who had a gross tumor mass evident on cross-sectional imaging, there was good agreement between PET and cross-sectional anatomic imaging with respect to tumor localization. CONCLUSIONS: In selected patients, cancer can be imaged within the prostate using FDG-PET, and IRSAC is superior to FBP in image reconstruction for local tumor visualization.

The indications of FDG-PET in neck oncology.

FDG-PET imaging in neck oncology has a definite clinical impact in the post-therapy setting, assisting in the management of thyroid cancers and SCC of the neck. Quantitation of FDG uptake in suspicious areas may be helpful but should be regarded cautiously. Overall, wider incorporation of FDG imaging in clinical routine depends also on cost availability issues of FDG and of imaging devices. Dual-coincidence scanners for FDG imaging are much cheaper than dedicated PET scanners and are installed in growing numbers in many centers. These devices have inferior sensitivity; however, series published with these scanners produce encouraging results. Easier and more acceptable clinical application will also be facilitated by the systematic use of coregistration with anatomic images. Both prerequisites might be fulfilled by the emergence on the market of a gamma camera-mounted anatomic X-ray tomograph, which in addition to dual-coincidence scintigraphic imaging provides radiographic images of comparable quality to third-generation CT systems. This type of hybrid gamma camera-CT scanner has great potential in a region of complex anatomy, such as the head and neck.

Ga-67 uptake in cutaneous lesions of graft-versus-host disease.

Acute graft-versus-host disease (GVHD) usually involves the skin, gastrointestinal tract, and liver. A 47-year-old woman with fever of unknown origin was referred for a Ga-67 scan. The study showed diffuse uptake of Ga-67 throughout the skin. Subsequently, a skin biopsy confirmed the diagnosis of acute GVHD. The incidence, diagnosis, and pathophysiology of the dermatitis in acute GVHD are discussed.

Sequential dose-intensive paclitaxel, ifosfamide, carboplatin, and etoposide salvage therapy for germ cell tumor patients.

PURPOSE: To evaluate the efficacy and toxicity of sequential, dose-intensified chemotherapy with paclitaxel/ifosfamide and carboplatin/etoposide administered plus peripheral blood-derived stem-cell (PBSC) support for patients with germ cell tumors (GCT) who have unfavorable prognostic features in response to conventional-dose salvage programs. Carboplatin was dose escalated by target area under the curve (AUC; in [milligrams per milliliter] x minutes) among patient cohorts, and pharmacokinetic studies were performed for comparison. PATIENTS AND METHODS: Thirty-seven previously treated patients who had cisplatin-resistant GCT and unfavorable prognostic features for response to conventional-dose salvage therapy were treated. Two cycles of paclitaxel 200 mg/m(2) plus ifosfamide 6 g/m(2) were given 2 weeks apart with leukapheresis, followed by three cycles of carboplatin plus etoposide given 14 to 21 days apart with reinfusion of PBSCs. The dose of etoposide was 1, 200 mg/m(2), and the carboplatin target AUC ranged among cohorts from 12 to 32 (mg/mL) x min. Pharmacokinetic studies of carboplatin were performed for comparison of target to measured AUC. RESULTS: Twenty-one patients (57%) achieved a complete response and an additional two patients (5%) achieved a partial response with normal tumor markers; therefore, 23 (62%) achieved a favorable response. Eight patients relapsed, and 15 (41%) of the favorable responses remained durable at a median follow-up of 30 months. Myelosuppression was the major toxicity; 58% of carboplatin/etoposide cycles were associated with hospitalization for nadir fever. The AUC of carboplatin measured in serum was lower than the target AUC; this may be related to underestimation of the glomerular filtration rate used in the dosing formula. CONCLUSION: Dose-intense therapy with sequential, accelerated chemotherapy of paclitaxel/ifosfamide and carboplatin/etoposide administered with PBSC support was relatively well tolerated. The durable complete response proportion was substantial in patients with unfavorable prognostic features for achieving durable complete response to conventional-dose salvage programs. Optimal dosing of carboplatin in the high-dose setting warrants further investigation.

Compassionate use of recombinant human thyrotropin to facilitate radioiodine therapy: case report and review of literature.

OBJECTIVE: To describe the use of recombinant human thyrotropin (thyroid-stimulating hormone) (rhTSH) to assist in radioiodine therapy in a patient with thyroid carcinoma who was unable to produce sufficient endogenous thyrotropin when hypothyroid and to review the related literature. METHODS: The study patient underwent formal dosimetric analysis and received radioiodine in conjunction with rhTSH. Follow-up scanning studies were performed. RESULTS: We found good localization of radioiodine on the posttherapy scans after administration of (131)I while the patient continued to receive thyroxine replacement after two intramuscularly administered injections of rhTSH. Some of his metastatic lesions disappeared and his serum thyroglobulin level decreased after the first rhTSH-assisted dose of (131)I was administered. His blood radioiodine clearance rate was unexpectedly more rapid in the hypothyroid state than when he was euthyroid (taking thyroxine) after administration of rhTSH. His whole-body clearance rate was more delayed when he was hypothyroid. Swelling of some of the metastatic thyroid cancer lesions developed when the patient was hypothyroid and after rhTSH was administered, the latter being much more rapid in onset. CONCLUSION: Therapeutic doses of radioiodine can be delivered with the assistance of rhTSH administration while patients continue to take suppressive doses of thyroxine. Metastatic thyroid carcinoma lesions can swell rapidly after administration of rhTSH. The commercially available form of rhTSH is approved only for diagnostic use. Its safety and efficacy in assisting radioiodine therapy have not been fully determined.