Clinical outcomes and molecular profile of differentiated thyroid cancers with radioiodine-avid distant metastases

BACKGROUND

Radioiodine (RAI) remains the mainstay of therapy for RAI-avid (RAIA) distant metastatic thyroid carcinoma. We previously demonstrated that RAI-refractory distant metastatic thyroid cancers commonly harbor BRAF mutations. However, the molecular profile of RAIA metastatic thyroid cancer is unknown. Here we describe the mutational profile of thyroid tumors from follicular cell-derived cancer (FCDTC) patients presenting with RAIA distant metastases. In addition, we aimed to correlate clinical outcomes of RAI therapy with clinicopathological factors and tumor mutational status.

METHODS

We retrospectively identified 43 patients with FCDTC who had RAI uptake in the lungs and/or bones on their initial ¹³¹I postablation scan. Primary tumors were genotyped for known mutations in thyroid cancer genes. Structural response to RAI was assessed 6-18 months after each administered RAI activity and at the end of follow-up.

RESULTS

RAS, BRAF, RET/PTC, and PIK3CA mutations were found in 42, 23, 10, and 2% of tumors, respectively, and the remaining 23% were wild type. None of these patients achieved cure after repeat RAI therapies, and most patients (54%) experienced disease progression despite repeated RAI administration. There was an increased prevalence of RAS mutations in these RAIA tumors. RAS-mutant cancers were more likely to concentrate iodine on diagnostic whole body scans. Despite this, structural response to RAI was not influenced by tumor genotype.

CONCLUSIONS

RAIA metastatic FCDTC are overrepresented with RAS mutations, whereas RAI refractory metastatic thyroid cancers are enriched with BRAF mutations. Despite a seemingly preserved ability to concentrate iodine, RAI therapy is ineffective in achieving cure in most patients with RAIA metastatic FCDTC, even in RAS-mutant disease. These poor outcomes may be improved based on recent evidence that pretreatment with MAPK kinase 1/2 inhibitors enhances responses to RAI, particularly in patients with RAS-mutant tumors.

Repeatability of SUV measurements in serial PET

PURPOSE

The standardized uptake value (SUV) is a quantitative measure of FDG tumor uptake frequently used as a tool to monitor therapeutic response. This study aims to (i) assess the reproducibility and uncertainty of SUV max and SUV mean, due to purely statistical, i.e., nonbiological, effects and (ii) to establish the minimum uncertainty below which changes in SUV cannot be expected to be an indicator of physiological changes.

METHODS

Three sets of measurements were made using a GE Discovery STE PET/CT Scanner in 3D mode: (1) A uniform 68Ge 20 cm diameter cylindrical phantom was imaged. Thirty serial frames were acquired for durations of 3, 6, 10, 15, and 30 min. (2) Esser flangeless phantom (Data Spectrum, approximately 6.1 L) with fillable thin-walled cylinders inserts (diameters: 8, 12, 16, and 25 mm; height: approximately 3.8 mm) was scanned for five consecutive 3 min runs. The cylinders were filled with 18FDG with a 37 kBq/cc concentration, and with a target-to-background ratio (T/BKG) of 3/1. (3) Eight cancer patients with healthy livers were scanned approximately 1.5 h post injection. Three sequential 3 min scans were performed for one bed position covering the liver, with the patient and bed remaining at the same position for the entire length of the scan. Volumes of interest were drawn on all images using the corresponding CT and then transferred to the PET images. For each study (1-3), the average percent change in SUV mean and SUV max were determined for each run pair. Moreover, the repeatability coefficient was calculated for both the SUV mean and SUV max for each pair of runs. Finally, the overall ROI repeatability coefficient was determined for each pair of runs.

RESULTS

For the 68Ge phantom the average percent change in SUV max and SUV mean decrease as a function of increasing acquisition time from 4.7 +/- 3.1 to 1.1 +/- 0.6%, and from 0.14 +/- 0.09 to 0.04 +/- 0.03%, respectively. Similarly, the coefficients of repeatability also decrease between the 3 and 30 min acquisition scans, in the range of 10.9 +/- 3.9% - 2.6 +/- 0.9%, and 0.3 +/- 0.1% - 0.10 +/- 0.04%, for the SUV max and SUV mean, respectively. The overall ROI repeatability decreased from 18.9 +/- 0.2 to 6.0 +/- 0.1% between the 3 and 30 min acquisition scans. For the l8FDG phantom, the average percent change in SUV max and SUV mean decreases with target diameter from 3.6 +/- 2.0 to 1.5 +/- 0.8% and 1.5 +/- 1.3 to 0.26 +/- 0.15%, respectively, for targets from 8-25 mm in diameter and for a region in the background (BKG). The coefficients of repeatability for SUV max and SUV mean also decrease as a function of target diameter from 7.1 +/- 2.5 to 2.4 +/- 0.9 and 4.2 +/- 1.5 to 0.6 +/- 0.2, respectively, for targets from 8 mm to BKG in diameter. Finally, overall ROI repeatability decreased from 12.0 +/- 4.1 to 13.4 +/- 0.5 targets from 8 mm to BKG in diameter. Finally, for the measurements in healthy livers the average percent change in SUVmax and SUV mean were in the range of 0.5 +/- 0.2% - 6.2 +/- 3.9% and 0.4 +/- 0.1 and 1.6 +/- 1%, respectively. The coefficients of repeatability for SUV max and SUV men are in the range of 0.6 +/- 0.7% - 9.5 +/- 12% and 0.6 +/- 0.7% - 2.9 +/- 3.6%, respectively. The overall target repeatability varied between 27.9 +/- 0.5% and 41.1 +/- 1.0%.

CONCLUSIONS

The statistical fluctuations of the SUV mean are half as large as those of the SUV max in the absence of biological or physiological effects. In addition, for clinically applicable scan durations (i.e., approximately 3 min) and FDG concentrations, the SUV max and SUV mean have similar amounts of statistical fluctuation for small regions. However, the statistical fluctuations of the SUVmean rapidly decrease with respect tothe SUVmax as the statistical power of the data grows either due to longer scanning times or as the target regions encompass a larger volume.

Five-year survival is similar in thyroid cancer patients with distant metastases prepared for radioactive iodine therapy with either thyroid hormone withdrawal or recombinant human TSH

CONTEXT

Elevated levels of TSH markedly enhance the effectiveness of radioiodine (RAI) therapy in metastatic thyroid cancer.

OBJECTIVE

The objective of the study was to compare short-term overall survival in thyroid cancer patients with RAI-avid distant metastases prepared for RAI therapy with either traditional thyroid hormone withdrawal (THW) or recombinant human TSH (rhTSH) stimulation.

DESIGN

This was a retrospective chart review.

SETTING

The study was conducted at a tertiary care comprehensive cancer center.

PATIENTS

Patients included 175 patients with RAI avid metastatic disease to lung and/or bone.

INTERVENTIONS

In 58 patients, all RAI treatments (remnant ablation and therapy of metastatic disease) were done with rhTSH stimulation. In 35 patients, all RAI treatments were done after THW. In 82 patients, THW was used for initial RAI treatment(s) with subsequent administered activities given after rhTSH stimulation.

MAIN OUTCOME MEASURE

Overall survival was measured.

RESULTS

After a median follow-up of 5.5 yr, there were no significant differences in overall survival between patients prepared for RAI therapy with rhTSH alone, THW alone, or THW followed by rhTSH (Kaplan-Meier analysis, P = 0.80). In a multivariate analysis that included clinicopathological features and method of preparation (rhTSH or TWH), only age at diagnosis was an independent predictor of overall survival.

CONCLUSIONS

Preparation for RAI therapy using either THW or rhTSH stimulation was associated with similar 5-yr overall survival rates in patients with RAI avid thyroid cancer metastases to lung or bone.

Renal uptake of bismuth-213 and its contribution to kidney radiation dose following administration of actinium-225-labeled antibody

Clinical therapeutic studies using (225)Ac-labeled antibodies have begun. Of major concern is renal toxicity that may result from the three alpha-emitting progeny generated following the decay of (225)Ac. The purpose of this study was to determine the amount of (225)Ac and non-equilibrium progeny in the mouse kidney after the injection of (225)Ac-huM195 antibody and examine the dosimetric consequences. Groups of mice were sacrificed at 24, 96 and 144 h after injection with (225)Ac-huM195 antibody and kidneys excised. One kidney was used for gamma ray spectroscopic measurements by a high-purity germanium (HPGe) detector. The second kidney was used to generate frozen tissue sections which were examined by digital autoradiography (DAR). Two measurements were performed on each kidney specimen: (1) immediately post-resection and (2) after sufficient time for any non-equilibrium excess (213)Bi to decay completely. Comparison of these measurements enabled estimation of the amount of excess (213)Bi reaching the kidney (γ-ray spectroscopy) and its sub-regional distribution (DAR). The average absorbed dose to whole kidney, determined by spectroscopy, was 0.77 (SD 0.21) Gy kBq(-1), of which 0.46 (SD 0.16) Gy kBq(-1) (i.e. 60%) was due to non-equilibrium excess (213)Bi. The relative contributions to renal cortex and medulla were determined by DAR. The estimated dose to the cortex from non-equilibrium excess (213)Bi (0.31 (SD 0.11) Gy kBq(-1)) represented ∼46% of the total. For the medulla the dose contribution from excess (213)Bi (0.81 (SD 0.28) Gy kBq(-1)) was ∼80% of the total. Based on these estimates, for human patients we project a kidney-absorbed dose of 0.28 Gy MBq(-1) following administration of (225)Ac-huM195 with non-equilibrium excess (213)Bi responsible for approximately 60% of the total. Methods to reduce renal accumulation of radioactive progeny appear to be necessary for the success of (225)Ac radioimmunotherapy.

An iterative technique to segment PET lesions using a Monte Carlo based mathematical model

PURPOSE

The need for an accurate lesion segmentation tool in 18FDG PET is a prerequisite for the estimation of lesion response to therapy, for radionuclide dosimetry, and for the application of 18FDG PET to radiotherapy planning. In this work, the authors have developed an iterative method based on a mathematical fit deduced from Monte Carlo simulations to estimate tumor segmentation thresholds.

METHODS

The GATE software, a GEANT4 based Monte Carlo tool, was used to model the GE Advance PET scanner geometry. Spheres ranging between 1 and 6 cm in diameters were simulated in a 10 cm high and 11 cm in diameter cylinder. The spheres were filled with water-equivalent density and simulated in both water and lung equivalent background. The simulations were performed with an infinite, 8/1, and 4/1 target-to-background ratio (T/B). A mathematical fit describing the correlation between the lesion volume and the corresponding optimum threshold value was then deduced through analysis of the reconstructed images. An iterative method, based on this mathematical fit, was developed to determine the optimum threshold value. The effects of the lesion volume and T/B on the threshold value were investigated. This method was evaluated experimentally using the NEMA NU2-2001 IEC phantom, the ACNP cardiac phantom, a randomly deformed aluminum can, and a spheroidal shape phantom implemented artificially in the lung, liver, and brain of patient PET images. Clinically, the algorithm was evaluated in six lesions from five patients. Clinical results were compared to CT volumes.

RESULTS

This mathematical fit predicts an existing relationship between the PET lesion size and the percent of maximum activity concentration within the target volume (or threshold). It also showed a dependence of the threshold value on the T/B, which could be eliminated by background subtraction. In the phantom studies, the volumes of the segmented PET targets in the PET images were within 10% of the nominal ones. Clinically, the PET target volumes were also within 10% of those measured from CT images.

CONCLUSIONS

This iterative algorithm enabled accurately segment PET lesions, independently of their contrast value.

New PET tracers for evaluation of solid tumor response to therapy

We take advantage of the special characteristics of human tumors to image tumor response including predicting susceptibility to specific cancer therapies. The metabolic phenotype of malignancy, includes increased glycolysis (2-[(18)F]fluoro-2-D-deoxyglucose [FDG]), increased proliferation (2-[(18)F]fluoro-L-thymidine [FLT]), increased amino acid transport, as well as other functions such as fatty acid synthesis which have yet to be fully exploited. The endocrine dependent malignancies offer rich opportunities for selective imaging, including radioligands that have high affinity for hormone receptors, like androgen receptor (AR) (16Beta-[(18)F]16beta-[(18)F]fluoro-5alpha-dihydrotestoste-rone [FDHT]) and estrogen receptor (ER) ([(18)F]fluoroestradiol [FES]) and tissue specific transporters such as sodium iodide symporter (NIS) ((124)I). As knowledge of cancer biology has grown, it has become possible to develop tracers which image the client proteins involved in response to specific drugs, e.g. Gallium-68-Fab'2 herceptin for HER 2 effected by HSP 90 inhibitor drugs. More and more radiolabeled drugs will be used to explore the pharmacology of anticancer therapies, such as [(18)F]Desatinib. These may or may not be excellent imaging agents, but as analogs or even true tracers for specific anti-cancer drugs, noninvasive imaging through positron emission tomography will provide highly useful information, relating cancer pharmacology within the local tumor, to treatment response.

Phase and amplitude binning for 4D-CT imaging

We compare the consistency and accuracy of two image binning approaches used in 4D-CT imaging. One approach, phase binning (PB), assigns each breathing cycle 2pi rad, within which the images are grouped. In amplitude binning (AB), the images are assigned bins according to the breathing signal's full amplitude. To quantitate both approaches we used a NEMA NU2-2001 IEC phantom oscillating in the axial direction and at random frequencies and amplitudes, approximately simulating a patient's breathing. 4D-CT images were obtained using a four-slice GE Lightspeed CT scanner operating in cine mode. We define consistency error as a measure of ability to correctly bin over repeated cycles in the same field of view. Average consistency error mue+/-sigmae in PB ranged from 18%+/-20% to 30%+/-35%, while in AB the error ranged from 11%+/-14% to 20%+/-24%. In PB nearly all bins contained sphere slices. AB was more accurate, revealing empty bins where no sphere slices existed. As a proof of principle, we present examples of two non-small cell lung carcinoma patients' 4D-CT lung images binned by both approaches. While AB can lead to gaps in the coronal images, depending on the patient's breathing pattern, PB exhibits no gaps but suffers visible artifacts due to misbinning, yielding images that cover a relatively large amplitude range. AB was more consistent, though often resulted in gaps when no data existed due to patients' breathing pattern. We conclude AB is more accurate than PB. This has important consequences to treatment planning and diagnosis.

Molecular imaging of EGFR kinase activity in tumors with 124I-labeled small molecular tracer and positron emission tomography

Positron emission tomography (PET) with epidermal growth factor receptor (EGFR) kinase-specific radiolabeled tracers could provide the means for noninvasive and repetitive imaging of heterogeneity of EGFR expression and signaling activity in tumors in individual patients before and during therapy with EGFR signaling inhibitors. We developed the synthesis and (124)I-radiolabeling of the (E)-But-2-enedioic acid [4-(3-[(124)I]iodoanilino)-quinazolin-6-yl]-amide-(3-morpholin-4-yl-propyl)-amide (morpholino-[(124)I]-IPQA), which selectively, irreversibly, and covalently binds the adenosine-triphosphate-binding site to the activated (phosphorylated) EGFR kinase, but not to the inactive EGFR kinase. The latter was demonstrated using in silico modeling with crystal structures of the wild type and different gain-of-function mutants of EGFR kinases. Also, this was demonstrated by selective radiolabeling of the EGFR kinase domain with morpholino-[(131)I]-IPQA in A431 human epidermoid carcinoma cells and Western blot autoradiography. In vitro radiotracer accumulation and washout studies demonstrated a rapid accumulation and progressive retention postwashout of morpholino-[(131)I]-IPQA in A431 epidermoid carcinoma and in U87 human glioma cells genetically modified to express the EGFRvIII mutant receptor, but not in the wild-type U87MG glioma cells under serum-starved conditions. Using morpholino-[(124)I]-IPQA, we obtained noninvasive PET images of EGFR activity in A431 subcutaneous tumor xenografts, but not in subcutaneous tumor xenografts grown from K562 human chronic myeloid leukemia cells in immunocompromised rats and mice. Based on these observations, we suggest that PET imaging with morpholino-[(124)I]-IPQA should allow for identification of tumors with high EGFR kinase signaling activity, including brain tumors expressing EGFRvIII mutants and nonsmall-cell lung cancer expressing gain-of-function EGFR kinase mutants. Because of significant hepatobiliary clearance and intestinal reuptake of the morpholino-[(124)I]-IPQA, additional [(124)I]-IPQA derivatives with improved water solubility may be required to optimize the pharmacokinetics of this class of molecular imaging agents.

Response to neoadjuvant chemotherapy as measured by PET predicts outcome after liver resection for colorectal metastases

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Background: Patients with hepatic colorectal metastases are often treated with neoadjuvant chemotherapy prior to liver resection. FDG PET is a standard imaging modality for such patients. We have shown the amount of FDG uptake in liver metastases is reduced by recent chemotherapy (chemo) administration and this is associated with a reduction in FDG uptake mediated by a reduction in hexokinase activity. We sought to determine if the amount of FDG uptake in the hepatic colorectal metastasis post chemo correlates with survival and to compare the prognostic significance of this single biologic scan to standard clinical predictors of outcome. Methods: A group of 149 patients enrolled in a prospective clinical trial examining the efficacy of FDG PET imaging in patients undergoing hepatic resection of colorectal cancer metastases to the liver formed the dataset. The maximal SUV within the liver was recorded for each patient, and the median of those maximums was determined across the patient group. Patients were then stratified by the median SUV, by the presence or absence of any chemo within 6 months of PET and by the clinical risk score (CRS) (a standard score for prognosis based on five clinical parameter (nodal status of primary, disease-free interval before liver metastases, size of largest liver tumor, number of tumors, and CEA). Multivariate analysis (MVA) and hazard ratios of death (HRD) were assessed. Results: The median of maximal SUVs was 7.9. In MVA in the patients without recent chemo, the CRS≥3 was an excellent predictor of survival (HRD=2.53; p=0.008), while SUV>8 was not (HRD=1.02; p=0.96). Conversely, in patients who had chemo within 6 months, SUV>8 (HRD 3.34; p=0.03) was a much superior predictor of outcome than CRS≥3 (HRD=1.25; p=0.57). Conclusions: In those patients without recent chemo CRS is the best predictor of survival confirming the utility of this scoring system, In those patients who had had chemo within 6 months of PET prior to surgery PET SUV was the best predictor of survival.

No significant financial relationships to disclose.

Deep Impact: observations from a worldwide Earth-based campaign

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.

Quantitation of respiratory motion during 4D-PET/CT acquisition

We report on the variability of the respiratory motion during 4D-PET/CT acquisition. The respiratory motion for five lung cancer patients was monitored by tracking external markers placed on the abdomen. CT data were acquired over an entire respiratory cycle at each couch position. The x-ray tube status was recorded by the tracking system, for retrospective sorting of the CT data as a function of respiration phase. Each respiratory cycle was sampled in ten equal bins. 4D-PET data were acquired in gated mode, where each breathing cycle was divided into ten 500 ms bins. For both CT and PET acquisition, patients received audio prompting to regularize breathing. The 4D-CT and 4D-PET data were then correlated according to their respiratory phases. The respiratory periods, and average amplitude within each phase bin, acquired in both modality sessions were then analyzed. The average respiratory motion period during 4D-CT was within 18% from that in the 4D-PET sessions. This would reflect up to 1.8% fluctuation in the duration of each 4D-CT bin. This small uncertainty enabled good correlation between CT and PET data, on a phase-to-phase basis. Comparison of the average-amplitude within the respiration trace, between 4D-CT and 4D- PET, on a bin-by-bin basis show a maximum deviation of approximately 15%. This study has proved the feasibility of performing 4D-PET/CT acquisition. Respiratory motion was in most cases consistent between PET and CT sessions, thereby improving both the attenuation correction of PET images, and co-registration of PET and CT images. On the other hand, in two patients, there was an increased partial irregularity in their breathing motion, which would prevent accurately correlating the corresponding PET and CT images.

Four-dimensional (4D) PET/CT imaging of the thorax

We have reported in our previous studies on the methodology, and feasibility of 4D-PET (Gated PET) acquisition, to reduce respiratory motion artifact in PET imaging of the thorax. In this study, we expand our investigation to address the problem of respiration motion in PET/CT imaging. The respiratory motion of four lung cancer patients were monitored by tracking external markers placed on the thorax. A 4D-CT acquisition was performed using a "step-and-shoot" technique, in which computed tomography (CT) projection data were acquired over a complete respiratory cycle at each couch position. The period of each CT acquisition segment was time stamped with an "x-ray ON" signal, which was recorded by the tracking system. 4D-CT data were then sorted into 10 groups, according to their corresponding phase of the breathing cycle. 4D-PET data were acquired in the gated mode, where each breathing cycle was divided into ten 0.5 s bins. For both CT and PET acquisitions, patients received audio prompting to regularize breathing. The 4D-CT and 4D-PET data were then correlated according to respiratory phase. The effect of 4D acquisition on improving the co-registration of PET and CT images, reducing motion smearing, and consequently increase the quantitation of the SUV, were investigated. Also, quantitation of the tumor motions in PET, and CT, were studied and compared. 4D-PET with matching phase 4D-CTAC showed an improved accuracy in PET-CT image co-registration of up to 41%, compared to measurements from 4D-PET with clinical-CTAC. Gating PET data in correlation with respiratory motion reduced motion-induced smearing, thereby decreasing the observed tumor volume, by as much as 43%. 4D-PET lesions volumes showed a maximum deviation of 19% between clinical CT and phase- matched 4D-CT attenuation corrected PET images. In CT, 4D acquisition resulted in increasing the tumor volume in two patients by up to 79%, and decreasing it in the other two by up to 35%. Consequently, these corrections have yielded an increase in the measured SUV by up to 16% over the clinical measured SUV, and 36% over SUV's measured in 4D-PET with clinical-CT Attenuation Correction (CTAC) SUV's. Quantitation of the maximum tumor motion amplitude, using 4D-PET and 4D-CT, showed up to 30% discrepancy between the two modalities. We have shown that 4D PET/CT is clinically a feasible method, to correct for respiratory motion artifacts in PET/CT imaging of the thorax. 4D PET/CT acquisition can reduce smearing, improve the accuracy in PET-CT co-registration, and increase the measured SUV. This should result in an improved tumor assessment for patients with lung malignancies.

Cytoreduction with iodine-131-anti-CD33 antibodies before bone marrow transplantation for advanced myeloid leukemias

The monoclonal antibodies M195 and HuM195 target CD33, a glycoprotein found on myeloid leukemia cells. When labeled with iodine-131 ((131)I), these antibodies can eliminate large disease burdens and produce prolonged myelosuppression. We studied whether (131)I-labeled M195 and HuM195 could be combined safely with busulfan and cyclophosphamide (BuCy) as conditioning for allogeneic BMT. A total of 31 patients with relapsed/refractory acute myeloloid leukemia (AML) (n=16), accelerated/myeloblastic chronic myeloid leukemia (CML) (n=14), or advanced myelodysplastic syndrome (n=1) received (131)I-M195 or (131)I-HuM195 (122-437 mCi) plus busulfan (16 mg/kg) and cyclophosphamide (90-120 mg/kg) followed by infusion of related-donor bone marrow (27 first BMT; four second BMT). Hyperbilirubinemia was the most common extramedullary toxicity, occurring in 69% of patients during the first 28 days after BMT. Gamma camera imaging showed targeting of the radioisotope to the bone marrow, liver, and spleen, with absorbed radiation doses to the marrow of 272-1470 cGy. The median survival was 4.9 months (range 0.3-90+ months). Three patients with relapsed AML remain in complete remission 59+, 87+, and 90+ months following bone marrow transplantation (BMT). These studies show the feasibility of adding CD33-targeted radioimmunotherapy to a standard BMT preparative regimen; however, randomized trials will be needed to prove a benefit to intensified conditioning with radioimmunotherapy.

Diagnostic and prognostic value of [(18)F]fluorodeoxyglucose positron emission tomography for recurrent head and neck squamous cell carcinoma

PURPOSE

Patients with recurrent head and neck squamous cell carcinoma (HNSCC) present a diagnostic and therapeutic challenge. We evaluated the diagnostic accuracy and prognostic value of [(18)F]fluorodeoxyglucose positron emission tomography (PET) in this patient population.

PATIENTS AND METHODS

We performed a retrospective review of 143 patients with previously treated HNSCC who underwent 181 PET scans at our institution from May 1996 through April 2001 to detect recurrent disease. Disease recurrence within 6 months was used as the gold standard for assessing true disease status at PET.

RESULTS

With equivocal sites considered positive, the sensitivity and specificity of PET for detecting recurrence overall were 96% and 72%, respectively. PET was highly sensitive and specific at regional and distant sites. At local sites, sensitivity was high, but specificity was lower because of false-positive findings. One fifth of all false-positive PET scans occurred at sites of known inflammation or infection. The area under the curve for a receiver operator characteristic curve on the basis of standardized uptake value (SUV) was 0.882 +/- 0.025. PET interpretation, SUV, and physical examination were independent predictors of relapse-free and overall survival in a time-dependent, multivariate proportional hazards model. An increase in SUV by one unit increased the relative risk (RR) of relapse by 11% and the RR of death by 14%. A positive PET interpretation increased the RR of relapse by four-fold and the RR of death by seven-fold.

CONCLUSION

PET was a highly sensitive method of detecting recurrent HNSCC and provided important prognostic information for relapse-free and overall survival.

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.

Effect of respiratory gating on reducing lung motion artifacts in PET imaging of lung cancer

Positron emission tomography (PET) has shown an increase in both sensitivity and specificity over computed tomography (CT) in lung cancer. However, motion artifacts in the 18F fluorodioxydoglucose (FDG) PET images caused by respiration persists to be an important factor in degrading PET image quality and quantification. Motion artifacts lead to two major effects: First, it affects the accuracy of quantitation, producing a reduction of the measured standard uptake value (SUV). Second, the apparent lesion volume is overestimated. Both impact upon the usage of PET images for radiation treatment planning. The first affects the visibility, or contrast, of the lesion. The second results in an increase in the planning target volume, and consequently a greater radiation dose to the normal tissues. One way to compensate for this effect is by applying a multiple-frame capture technique. The PET data are then acquired in synchronization with the respiratory motion. Reduction in smearing due to gating was investigated in both phantoms and patient studies. Phantom studies showed a dependence of the reduction in smearing on the lesion size, the motion amplitude, and the number of bins used for data acquisition. These studies also showed an improvement in the target-to-background ratio, and a more accurate measurement of the SUV. When applied to one patient, respiratory gating showed a 28% reduction in the total lesion volume, and a 56.5% increase in the SUV. This study was conducted as a proof of principle that a gating technique can effectively reduce motion artifacts in PET image acquisition.

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.

Resistance of [18f]-fluorodeoxyglucose-avid metastatic thyroid cancer lesions to treatment with high-dose radioactive iodine

Radioactive iodine (131I) is an important therapeutic option for the treatment of metastatic thyroid carcinoma. Survival in patients with metastases that concentrate radioiodine is better than those whose metastatic lesions do not take up radioiodine. Survival is markedly reduced in patients who have metastatic lesions that concentrate 18F-fluorodeoxyglucose (FDG) on positron emission tomography (PET). In this retrospective study, we evaluated the ability of 131I to destroy FDG-avid metastatic lesions in thyroid cancer patients. Twenty-five patients with positive FDG-PET scans received at least one dose of 131I treatment before a second FDG-PET was performed. The average interval between the two PET scans was 12.9 months. The average interval between the 131I treatment and the follow-up FDG-PET was 10.1 months. We measured posttherapy changes in lesional volume, in standard uptake values (SUV) of FDG, and in serum thyroglobulin (Tg) levels. The total volume of FDG-avid metastases rose significantly (p = 0.036) from a mean of 159 mL to 235 mL after 131I therapy, the maximum SUV rose from 9.3 to 11.9, the median Tg at the time of the second PET scan was 132% of that at baseline. Statistical analyses demonstrated no significant changes in maximum SUV, or serum Tg levels after 131I in the FDG-PET-positive group. In a control group of FDG-PET-negative patients, the serum Tg decreased to 38% of baseline after 131I therapy (p < 0.001). We conclude that high-dose 131I therapy appears to have little or no effect on the viability of metastatic FDG-avid thyroid cancer lesions.

Statistical issues in analysis of diagnostic imaging experiments with multiple observations per patient

Many diagnostic imaging experiments are characterized by the presence of several observations for each patient studied. Evaluation of metastases with different imaging modalities in patients with cancer or examination of multiple artery segments in patients with heart abnormalities are some examples of such studies. Data obtained from multiple observations per patient are cluster correlated and should not be analyzed by using standard statistical methods because of correlations within a subject. In this article, positron emission tomographic studies are used as a framework to review statistical methods for the analysis of clustered data. Some simple statistical methods that account for correlation within a subject and that can be applied to conventional and well-known statistical methods, such as the chi(2) and t tests, are introduced. One of these methods is illustrated by using a brief analysis of data from a positron emission tomographic study, which demonstrates how resulting conclusions may be incorrect if appropriate techniques are not applied. Alternative methods that can handle multiple observations and dependency within a subject for diagnostic imaging studies are discussed.

Lack of correlation of functional scintigraphy with (99m)technetium-methoxyisobutylisonitrile with histological necrosis following induction chemotherapy or measures of P-glycoprotein expression in high-grade osteosarcoma

In osteosarcoma, some studies have suggested P-glycoprotein expression is a prognostic factor. The clearance of (99m)technetium hexakis-2-methoxyisobutylisonitrile ((99m)Tc-MIBI) has been used in some tumor systems as an in vivo measure of P-glycoprotein-mediated efflux. In this study we explored the correlation between (99m)Tc-MIBI clearance and histological necrosis following induction chemotherapy and P-glycoprotein expression in osteosarcoma. The primary tumors of 20 patients with high-grade osteosarcoma were imaged at diagnosis with (99m)Tc-MIBI, and the uptake ratios and biological half-lives were calculated. P-Glycoprotein expression in the tumor tissue was determined immunohistochemically and by measuring mRNA expression of the multidrug resistance-1 gene. The histological necrosis following induction chemotherapy was assessed by the Huvos grading system. The biological half-life of (99m)Tc-MIBI ranged from 1.4 to 52.5 h. Seven of the 20 tumor samples had a favorable extent of necrosis following induction chemotherapy. The (99m)Tc-MIBI half-life and uptake ratio showed no correlation with histological necrosis following induction chemotherapy. The (99m)Tc-MIBI half-life and uptake ratio did not correlate with either measure of P-glycoprotein expression. The results of this pilot study indicate that (99m)Tc-MIBI imaging is not an effective predictor of histological necrosis following induction chemotherapy in high-grade osteosarcoma. (99m)Tc-MIBI imaging did not correlate with measures of P-glycoprotein expression in the tumor tissue.

Radioiodine ablation of thyroid remnants after preparation with recombinant human thyrotropin

Radioiodine ablation (RA) of normal thyroid remnants after thyroidectomy for differentiated thyroid carcinoma improves the sensitivity of subsequent radioiodine scans and serum thyroglobulin measurements for detection of residual thyroid carcinoma. Local cancer recurrences are also lower after RA. One standard preparation for RA involves rendering the patient hypothyroid in order to stimulate endogenous thyrotropin (TSH) secretion and sodium iodide symporter (NIS) activity. An alternative approach is to prescribe thyroxine after thyroidectomy and to stimulate NIS with exogenous recombinant human thyrotropin (rhTSH). This latter approach was used in 10 patients at our medical center. Complete resolution of all visible 131I thyroid bed uptake was achieved in all when follow-up scans were performed 5 to 13 months later. This approach has the potential to successfully ablate thyroid remnants without the need to induce hypothyroidism.

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.

PET imaging of (86)Y-labeled anti-Lewis Y monoclonal antibodies in a nude mouse model: comparison between (86)Y and (111)In radiolabels

Absorbed doses in (90)Y radioimmunotherapy are usually estimated by extrapolating from (111)In imaging data. PET using (86)Y (beta(+) 33%; half-life, 14.7 h) as a surrogate radiolabel could be a more accurate alternative. The aim of this study was to evaluate an (86)Y-labeled monoclonal antibody (mAb) as a PET imaging agent and to compare the biodistribution of (86)Y- and (111)In-labeled mAb.

METHODS

The humanized anti-Lewis Y mAb hu3S193 was labeled with (111)In or (86)Y through CHX-A"-diethylenetriaminepentaacetic acid chelation. In vitro cell binding and cellular retention of radiolabeled hu3S193 were evaluated using HCT-15 colon carcinoma cells, a cell line expressing Lewis Y. Nude mice bearing HCT-15 xenografts were injected with (86)Y-hu3S193 or (111)In-hu3S193. The biodistribution was studied by measurements of dissected tissues as well as by PET and planar imaging.

RESULTS

The overall radiochemical yield in hu3S193 labeling and purification was 42% +/- 2% (n = 2) and 76% +/- 3% (n = 6) for (86)Y and (111)In, respectively. Both radioimmunoconjugates specifically bound to HCT-15 cells. When cellular retention of hu3S193 was studied using (111)In-hu3S193, 80% of initially cell-bound (111)In activity was released into the medium as high-molecular-weight compounds within 8 h. When coadministered, in vivo tumor uptake of (86)Y-hu3S193 and (111)In-hu3S193 reached maximum values of 30 +/- 6 and 29 +/- 6 percentage injected dose per gram and tumor sites were easily identifiable by PET and planar imaging, respectively.

CONCLUSION

At 2 d after injection of (111)In-hu3S193 and (86)Y-hu3S193 radioimmunoconjugates, the uptake of (111)In and (86)Y activity was generally similar in most tissues. After 4 d, however, the concentration of (86)Y activity was significantly higher in several tissues, including tumor and bone tissue. Accordingly, the quantitative information offered by PET, combined with the presumably identical biodistribution of (86)Y and (90)Y radiolabels, should enable more accurate absorbed dose estimates in (90)Y radioimmunotherapy.

Relative therapeutic efficacy of (125)I- and (131)I-labeled monoclonal antibody A33 in a human colon cancer xenograft

A33, a monoclonal antibody that targets colon carcinomas, was labeled with (125)I or (131)I and the relative therapeutic efficacy of the 2 radiolabeled species was compared in a human colon cancer xenograft system.

METHODS

Nude mice bearing human SW1222 colon carcinoma xenografts were administered escalating activities of (125)I-A33 (9.25-148 MBq) or (131)I-A33 (0.925-18.5 MBq), (125)I- and (131)I-labeled control antibodies, unlabeled antibody, or no antibody. The effects of treatment were assessed using the endpoints of tumor growth delay and cure.

RESULTS

Tumor growth delay increased with administered activity for all radiolabeled antibodies. Approximately 4.5 times more activity was required for (125)I-A33 to produce therapeutic effects that were equivalent to those of (131)I-A33. This ratio was approximately 7 for a nonspecific, noninternalizing isotype-matched, radiolabeled control antibody. Unlabeled A33 antibody had no effect on tumor growth. Approximately 10 times more activity of (125)I-A33 produced toxicity similar to that of (131)I-A33, and this ratio fell to approximately 6 for radiolabeled control antibody.

CONCLUSION

Treatment with (125)I-A33 resulted in a relative therapeutic gain of approximately 2 compared with (131)I-A33 in this experimental system.

Extending positron emission tomography scan utility to high-risk neuroblastoma: fluorine-18 fluorodeoxyglucose positron emission tomography as sole imaging modality in follow-up of patients

PURPOSE

Although positron emission tomography (PET) with fluorine-18 fluorodeoxyglucose ((18)F-FDG) has a major impact on the treatment of adult cancer, the reported experience with extracranial tumors of childhood is limited. We describe a role for PET in patients with neuroblastoma (NB).

PATIENTS AND METHODS

In 51 patients with high-risk NB, 92 PET scans were part of a staging evaluation that included iodine-123 or iodine-131 metaiodobenzylguanidine (MIBG) scan, bone scan, computed tomography (and/or magnetic resonance imaging), urine catecholamine measurements, and bone marrow (BM) examinations. The minimum number of tests sufficient to detect NB was determined.

RESULTS

Of 40 patients who were not in complete remission, only 1 (2.5%) had NB that would have been missed had a staging evaluation been limited to PET and BM studies, and 13 (32.5%) had NB detected by PET but not by BM and urine tests. PET was equal or superior to MIBG scans for identifying NB in soft tissue and extracranial skeletal structures, for revealing small lesions, and for delineating the extent and localizing sites of disease. In 36 evaluations of 22 patients with NB in soft tissue, PET failed to identify only two long-standing MIBG-negative abdominal masses. PET and MIBG scans showed more skeletal lesions than bone scans, but the normally high physiologic brain uptake of FDG blocked PET visualization of cranial vault lesions. Similar to MIBG, FDG skeletal uptake was diffusely increased with extensive or progressing BM disease but faint or absent with minimal or nonprogressing BM disease.

CONCLUSION

In the absence or after resolution of cranial vault lesions, and once the primary tumor is resected, PET and BM tests suffice for monitoring NB patients at high risk for progressive disease in soft tissue and bone/BM.

Positron emission tomography imaging for herpes virus infection: Implications for oncolytic viral treatments of cancer

Molecular therapy using viruses would benefit greatly from a non-invasive modality for assessing dissemination of viruses. Here we investigated whether positron emission tomography (PET) scanning using [(124)I]-5-iodo-2'-fluoro-1-beta-d-arabinofuranosyl-uracil (FIAU) could image cells infected with herpes simplex viruses (HSV). Using replication-competent HSV-1 oncolytic viruses with thymidine kinase (TK) under control of different promoters, we demonstrate that viral infection, proliferation and promoter characteristics all interact to influence FIAU accumulation and imaging. In vivo, as few as 1 x 107 viral particles injected into a 0.5-cm human colorectal tumor can be detected by [(124)I]FIAU PET imaging. PET signal intensity is significantly greater at 48 hours compared with that at 8 hours after viral injection, demonstrating that PET scanning can detect changes in TK activity resulting from local viral proliferation. We also show the ability of FIAU-PET scanning to detect differences in viral infectivity at 0.5 log increments. Non-invasive imaging might be useful in assessing biologically relevant distribution of virus in therapies using replication-competent HSV.