First-in-Humans PET Imaging of Tissue Factor in Patients with Primary and Metastatic Cancers Using 18F-labeled Active-Site Inhibited Factor VII (18F-ASIS): Potential as Companion Diagnostic

Tissue factor (TF) expression in cancers correlates with poor prognosis. Recently, the first TF-targeted therapy was approved by the U.S. Food and Drug Administration for cervical cancer. To unfold the potential of TF-targeted therapies, correct stratification and selection of patients eligible for treatments may become important for optimization of patient outcomes. TF-targeted PET imaging based on ¹⁸F-radiolabeled active-site inhibited versions of the TF natural ligand coagulation factor VII (¹⁸F-ASIS) has in preclinical models convincingly demonstrated its use for noninvasive quantitative measurements of TF expression in tumor tissue. ¹⁸F-ASIS PET imaging thus has the potential to act as a diagnostic companion for TF-targeted therapies in the clinical setting. Methods: In this first-in-humans trial, we included 10 cancer patients (4 pancreatic, 3 breast, 2 lung, and 1 cervical cancer) for ¹⁸F-ASIS PET imaging. The mean and SD of administered ¹⁸F-ASIS activity was 157 ± 35 MBq (range, 93-198 MBq). PET/CT was performed after 1, 2, and 4 h. The primary objectives were to establish the safety, biodistribution, pharmacokinetics, and dosimetry of ¹⁸F-ASIS. Secondary objectives included quantitative measurements of SUVs in tumor tissue with PET and evaluation of the correlation (Pearson correlation) between tumor SUV_max and ex vivo TF expression in tumor tissue. Results: Administration of ¹⁸F-ASIS was safe, and no adverse events were observed. No clinically significant changes in vital signs, electrocardiograms, or blood parameters were observed after injection of ¹⁸F-ASIS. Mean ¹⁸F-ASIS plasma half-life was 3.2 ± 0.6 h, and the radiotracer was predominantly excreted in the urine. For injection activity of 200 MBq of ¹⁸F-ASIS, effective whole-body dose was 4 mSv and no prohibitive organ-specific absorbed doses were found. Heterogeneous radiotracer uptake was observed across patients and within tumors. We found a trend of a positive correlation between tumor SUV_max and ex vivo TF expression (r = 0.84, P = 0.08, n = 5). Conclusion: ¹⁸F-ASIS can be safely administered to cancer patients for PET imaging of TF expression in tumors. The trial marks the first test of a TF-targeted PET radiotracer in humans (first-in-class). The findings represent important first steps toward clinical implementation of ¹⁸F-ASIS PET imaging of TF expression.

No effects of a 6-week intervention with a glucagon-like peptide-1 receptor agonist on pancreatic volume and oedema in obese men without diabetes

AIM

To investigate the effect of a glucagon-like peptide-1 receptor agonist (GLP-1RA), liraglutide, on pancreatic volume, oedema, cellularity and DNA synthesis in humans.

MATERIALS AND METHODS

We performed an open-label study in 14 obese men (age 38 ± 11 years, body mass index 32 ± 4 kg/m² ) without diabetes. Subjects were examined at baseline, during titration (week 4) of liraglutide towards 3.0 mg/day, and 2 weeks after steady-state treatment (week 6) of a final dose of liraglutide. The primary endpoint was pancreatic volume determined by magnetic resonance imaging. Secondary endpoints included pancreatic oedema and cellularity, positron emission tomography-based [¹⁸ F]fluorothymidine (FLT) uptake (DNA synthesis) and plasma pancreatic enzymes.

RESULTS

Plasma amylase (+7 U/L [95% confidence intervals 3-11], P < .01) and lipase (+19 U/L [7-30], P < .01) increased during liraglutide treatment. Pancreatic volume did not change from baseline to steady state of treatment (+0.2 cm³ [-8-8], P = .96) and no change in pancreatic cellular infiltration was found (P = .22). During titration of liraglutide, FLT uptake in pancreatic tissue increased numerically (+0.08 [0.00-0.17], P = .0507).

CONCLUSIONS

Six weeks of treatment with liraglutide did not affect pancreatic volume, oedema or cellularity in obese men without diabetes.

18F-FDG PET/MR-imaging in a Göttingen Minipig model of atherosclerosis: Correlations with histology and quantitative gene expression

BACKGROUND AND AIMS

The advantage of combining molecular and morphological imaging, e.g. positron emission tomography and magnetic resonance imaging (PET/MRI), is reflected in the increased use of these modalities as surrogate end-points in clinical trials. This study aimed at evaluating plaque inflammation using ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG)-PET/MRI, and gene expression in a minipig model of atherosclerosis.

METHODS

Göttingen Minipigs were fed for 60 weeks with fat/fructose/cholesterol-rich diet (FFC), chow (Control) or FFC-diet changed to chow midway (diet normalization group; DNO). In all groups, ¹⁸F-FDG-PET/MRI of the abdominal aorta was assessed midway and at study-end. The aorta was analyzed using histology and gene expression.

RESULTS

At study-end, FFC had significantly higher FDG-uptake compared to Control (target-to-background maximal uptake, TBR_Max (95% confidence interval) CI_TBRMax: 0.092; 7.32) and DNO showed significantly decreased uptake compared to FFC (CI_TBRMax: -5.94;-0.07). No difference was observed between DNO and Control (CI_TBRMax: -2.71; 4.11). FFC displayed increased atherosclerosis and gene expression of inflammatory markers, including vascular cell adhesion molecule 1 (VCAM-1), cluster of differentiation 68 (CD68), matrix metalloproteinase 9 (MMP9), cathepsin K (CTSK) and secreted phosphoprotein 1 (SPP1) compared to Control and DNO (all, p < 0.05). FDG-uptake correlated with gene expression of inflammatory markers, including CD68, ρ_s = 0.58; MMP9, ρ_s = 0.46; SPP1, ρ_s = 0.44 and CTSK, ρ_s = 0.49; (p ≤ 0.01 for all).

CONCLUSIONS

In a model of atherosclerosis, ¹⁸F-FDG-PET/MRI technology allows for detection of inflammation in atherosclerotic plaques, consistent with increased inflammatory gene expression. Our findings corroborate clinical data and are important in pre-clinical drug development targeting plaque inflammation.

Cross-calibration of the Siemens mMR: easily acquired accurate PET phantom measurements, long-term stability and reproducibility

Background

We present a quick and easy method to perform quantitatively accurate PET scans of typical water-filled PET plastic shell phantoms on the Siemens Biograph mMR PET/MR system.

We perform regular cross-calibrations (Xcal) of our PET systems, including the PET/MR, using a Siemens mCT water phantom.

Long-term stability

The mMR calibration stability was evaluated over a 3-year period where 54 cross-calibrations were acquired, showing that the mMR on average underestimated the concentration by 16 %, consistently due to the use of MR-based μ-maps.

The mMR produced the narrowest calibration ratio range with the lowest standard deviation, implying it is the most stable of the six systems in the study over a 3-year period.

mMR accuracy with predefined μ-maps

With the latest mMR software version, VB20P, it is possible to utilize predefined phantom μ-maps. We evaluated both the system-integrated, predefined μ-map of the long mMR water phantom and our own user-defined CT-based μ-map of the mCT water phantom, which is used for cross-calibration.

For seven scans, which were reconstructed with correctly segmented μ-maps, the mMR produced cross-calibration ratios of 1.00–1.02, well within the acceptance range [0.95–1.05], showing high accuracy.

Conclusions

The mMR is the most stable PET system in this study, and the mean underestimation is no longer an issue with the easily accessible μ-map, which resulted in correct cross-calibration ratios in all seven tests. We will share the user-defined μ-map of the mCT phantom and the protocol with interested mMR users.

Simultaneous PET/MRI with (13)C magnetic resonance spectroscopic imaging (hyperPET): phantom-based evaluation of PET quantification

Background

Integrated PET/MRI with hyperpolarized ¹³C magnetic resonance spectroscopic imaging (¹³C-MRSI) offers simultaneous, dual-modality metabolic imaging. A prerequisite for the use of simultaneous imaging is the absence of interference between the two modalities. This has been documented for a clinical whole-body system using simultaneous ¹H-MRI and PET but never for ¹³C-MRSI and PET. Here, the feasibility of simultaneous PET and ¹³C-MRSI as well as hyperpolarized ¹³C-MRSI in an integrated whole-body PET/MRI hybrid scanner is evaluated using phantom experiments.

Methods

Combined PET and ¹³C-MRSI phantoms including a NEMA [¹⁸F]-FDG phantom, ¹³C-acetate and ¹³C-urea sources, and hyperpolarized ¹³C-pyruvate were imaged repeatedly with PET and/or ¹³C-MRSI. Measurements evaluated for interference effects included PET activity values in the largest sphere and a background region; total number of PET trues; and ¹³C-MRSI signal-to-noise ratio (SNR) for urea and acetate phantoms. Differences between measurement conditions were evaluated using t tests.

Results

PET and ¹³C-MRSI data acquisition could be performed simultaneously without any discernible artifacts. The average difference in PET activity between acquisitions with and without simultaneous ¹³C-MRSI was 0.83 (largest sphere) and −0.76 % (background). The average difference in net trues was −0.01 %. The average difference in ¹³C-MRSI SNR between acquisitions with and without simultaneous PET ranged from −2.28 to 1.21 % for all phantoms and measurement conditions. No differences were significant. The system was capable of ¹³C-MRSI of hyperpolarized ¹³C-pyruvate.

Conclusions

Simultaneous PET and ¹³C-MRSI in an integrated whole-body PET/MRI hybrid scanner is feasible. Phantom experiments showed that possible interference effects introduced by acquiring data from the two modalities simultaneously are small and non-significant. Further experiments can now investigate the benefits of simultaneous PET and hyperpolarized ¹³C-MRI in vivo studies.

Prospective phase II trial of image-guided radiotherapy in Hodgkin lymphoma: benefit of deep inspiration breath-hold

BACKGROUND

Long-term Hodgkin lymphoma (HL) survivors have an increased risk of late cardiac morbidity and secondary lung cancer after chemotherapy and mediastinal radiotherapy. In this prospective study we investigate whether radiotherapy with deep inspiration breath-hold (DIBH) can reduce radiation doses to the lungs, heart, and cardiac structures without compromising the target dose.

PATIENTS AND METHODS

Twenty-two patients (14 female, 8 male), median age 30 years (18-65 years), with supra-diaphragmatic HL were enrolled and had a thoracic PET/CT with DIBH in addition to staging FDG-PET/CT in free breathing (FB) and a planning CT in both FB and DIBH. For each patient an involved-node radiotherapy plan was done for both DIBH and FB, and the doses to the lungs, heart, and female breasts were recorded prospectively. Mean doses to the heart valves and coronary arteries were recorded retrospectively. Patients were treated with the technique yielding the lowest doses to normal structures.

RESULTS

Nineteen patients were treated with DIBH and three with FB. DIBH reduced the mean estimated lung dose by 2.0 Gy (median: 8.5 Gy vs. 7.2 Gy) (p < 0.01) and the mean heart dose by 1.4 Gy (6.0 Gy vs. 3.9 Gy) (p < 0.01) compared to FB. The lung and heart V20Gy were reduced with a median of 5.3% and 6.3%. Mean doses to the female breasts were equal with FB and DIBH.

CONCLUSION

DIBH can significantly decrease the estimated mean doses to the heart and lungs without lowering the dose to the target in radiotherapy for patients with mediastinal HL.

Simultaneous hyperpolarized (13)C-pyruvate MRI and (18)F-FDG-PET in cancer (hyperPET): feasibility of a new imaging concept using a clinical PET/MRI scanner

In this paper we demonstrate, for the first time, the feasibility of a new imaging concept - combined hyperpolarized (13)C-pyruvate magnetic resonance spectroscopic imaging (MRSI) and (18)F-FDG-PET imaging. This procedure was performed in a clinical PET/MRI scanner with a canine cancer patient. We have named this concept hyper PET. Intravenous injection of the hyperpolarized (13)C-pyruvate results in an increase of (13)C-lactate, (13)C-alanine and (13)C-CO2 ((13)C-HCO3) resonance peaks relative to the tissue, disease and the metabolic state probed. Accordingly, with dynamic nuclear polarization (DNP) and use of (13)C-pyruvate it is now possible to directly study the Warburg Effect through the rate of conversion of (13)C-pyruvate to (13)C-lactate. In this study, we combined it with (18)F-FDG-PET that studies uptake of glucose in the cells. A canine cancer patient with a histology verified local recurrence of a liposarcoma on the right forepaw was imaged using a combined PET/MR clinical scanner. PET was performed as a single-bed, 10 min acquisition, 107 min post injection of 310 MBq (18)F-FDG. (13)C-chemical shift imaging (CSI) was performed just after FDG-PET and 30 s post injection of 23 mL hyperpolarized (13)C-pyruvate. Peak heights of (13)C-pyruvate and (13)C-lactate were quantified using a general linear model. Anatomic (1)H-MRI included axial and coronal T1 vibe, coronal T2-tse and axial T1-tse with fat saturation following gadolinium injection. In the tumor we found clearly increased (13)C-lactate production, which also corresponded to high (18)F-FDG uptake on PET. This is in agreement with the fact that glycolysis and production of lactate are increased in tumor cells compared to normal cells. Yet, most interestingly, also in the muscle of the forepaw of the dog high (18)F-FDG uptake was observed. This was due to activity in these muscles prior to anesthesia, which was not accompanied by a similarly high (13)C-lactate production. Accordingly, this clearly demonstrates how the Warburg Effect directly can be demonstrated by hyperpolarized (13)C-pyruvate MRSI. This was not possible with (18)F-FDG-PET imaging due to inability to discriminate between causes of increased glucose uptake. We propose that this new concept of simultaneous hyperpolarized (13)C-pyruvate MRSI and PET may be highly valuable for image-based non-invasive phenotyping of tumors. This methods may be useful for treatment planning and therapy monitoring.

Positron emission tomography of the vulnerable atherosclerotic plaque in man--a contemporary review

Atherosclerosis is the primary underlying cause of cardiovascular disease (CVD). It is the leading cause of morbidity and mortality in the Western world today and is set to become the prevailing disease and major cause of death worldwide by 2020. In the 1950s surgical intervention was introduced to treat symptomatic patients with high-grade carotid artery stenosis due to atherosclerosis – a procedure known as carotid endarterectomy (CEA). By removing the atherosclerotic plaque from the affected carotid artery of these patients, CEA is beneficial by preventing subsequent ipsilateral ischemic stroke. However, it is known that patients with low to intermediate artery stenosis may still experience ischemic events, leading clinicians to consider plaque composition as an important feature of atherosclerosis. Today molecular imaging can be used for characterization, visualization and quantification of cellular and subcellular physiological processes as they take place in vivo; using this technology we can obtain valuable information on atherosclerostic plaque composition. Applying molecular imaging clinically to atherosclerotic disease therefore has the potential to identify atherosclerotic plaques vulnerable to rupture. This could prove to be an important tool for the selection of patients for CEA surgery in a health system increasingly focused on individualized treatment. This review focuses on current advances and future developments of in vivo atherosclerosis PET imaging in man.

Image artifacts from MR-based attenuation correction in clinical, whole-body PET/MRI

PURPOSE

Integrated whole-body PET/MRI tomographs have become available. PET/MR imaging has the potential to supplement, or even replace combined PET/CT imaging in selected clinical indications. However, this is true only if methodological pitfalls and image artifacts arising from novel MR-based attenuation correction (MR-AC) are fully understood.

RESULTS

Here we present PET/MR image artifacts following routine MR-AC, as most frequently observed in clinical operations of an integrated whole-body PET/MRI system.

CONCLUSION

A clinical adoption of integrated PET/MRI should entail the joint image display and interpretation of MR data, MR-based attenuation maps and uncorrected plus attenuation-corrected PET images in order to recognize potential pitfalls from MR-AC and to ensure clinically accurate image interpretation.

Colloid volume loading does not mitigate decreases in central blood volume during simulated haemorrhage while heat stressed

Heat stress results in profound reductions in the capacity to withstand a simulated haemorrhagic challenge; however, this capacity is normalized if the individual is volume loaded prior to the challenge. The present study tested the hypothesis that volume loading during passive heat stress attenuates the reduction in regional blood volumes during a simulated haemorrhagic challenge imposed via lower-body negative pressure (LBNP). Seven subjects underwent 30 mmHg LBNP while normothermic, during passive heat stress (increased internal temperature ∼1◦C), and while continuing to be heated after intravenous colloid volume loading (11 ml kg⁻¹). Relative changes in torso and regional blood volumes were determined by gamma camera imaging with technetium-99m labelled erythrocytes. Heat stress reduced blood volume in all regions (ranging from 7 to 16%), while subsequent volume loading returned those values to normothermic levels. While normothermic,LBNP reduced blood volume in all regions (torso: 22 ± 8%; heart: 18 ± 6%; spleen: 15 ± 8%). During LBNP while heat stressed, the reductions in blood volume in each region were markedly greater when compared to LBNP while normothermic (torso: 73 ± 2%; heart: 72 ± 3%; spleen: 72 ± 5%, all P<0.001 relative to normothermia). Volume loading during heat stress did not alter the extent of the reduction in these blood volumes to LBNP relative to heat stress alone (torso: 73 ± 1%; heart: 72 ± 2%; spleen: 74 ± 3%, all P>0.05 relative to heat stress alone). These data suggest that blood volume loading during passive heat stress (via 11 ml kg⁻¹ of a colloid solution) normalizes regional blood volumes in the torso, but does not mitigate the reduction in central blood volume during a simulated haemorrhagic challenge combined with heat stress.

Radiation exposure to surgical staff during F-18-FDG-guided cancer surgery

PURPOSE

High-energy gamma probes have recently become commercially available, developed for (18)F-FDG probe-guided surgery. The radiation received by the staff in the operating room might limit the use of it, but has never been determined. We therefore wanted to measure the absorbed staff doses at operations where patients had received a preoperative injection of (18)F-FDG.

METHODS

Thirty-four patients with different cancers (breast cancer, melanoma, gastrointestinal cancers, respectively) were operated. At every operation the surgeon was monitored with a TLD tablet on his finger of the operating hand and a TLD tablet on the abdomen. The surgeon and anaesthesiologist were also monitored using electronic dosimeters placed in the trousers lining at 25 operations.

RESULTS

The dose rate to the surgeon's abdominal wall varied between 7.5-13.2 microSv/h, depending on tumour location. The doses to the anaesthesiologists and the finger doses to the surgeon were much lower. About 350-400 MBq, i.e. ca. eight times higher activities than those used in the present study are supposed to be necessary for guiding surgery. It can be calculated from the body doses measured that a surgeon can perform between 150-260 h of surgery without exceeding permissible limits for professional workers.

CONCLUSIONS

The radiation load to the operating staff will generally be so small that it does not present any limitation for FDG-guided surgery. However, it is recommended to monitor the surgical staff considering that the surgeon may be exposed to other radiation sources, and since the staff often includes women of child-bearing age.

How few cancer cells can be detected by positron emission tomography? A frequent question addressed by an in vitro study

PURPOSE

Positron emission tomography (PET) has gained widespread use in cancer diagnosis and treatment, but how many malignant cells are required for a tumour to be detected by PET?

METHODS

Three human cancer cell lines [glioblastoma and two subtypes of small cell lung cancer (SCLC)] in concentrations from 10(4) to 10(7) were seeded on six-well plates or plastic tubes and treated with [(18)F]fluorodeoxy-glucose (FDG) in vitro. FDG retention was measured in a PET/CT scanner and in a calibrated well counter. The clinical situation was simulated using a cylinder phantom with a background concentration of FDG.

RESULTS

The theoretical detection limit was found to be around 10(5) malignant cells. In a cylinder phantom the detection limit was increased by a factor of 10. The FDG retention by the glioblastoma cell line was significantly higher than the activity of the SCLC cell line. FDG retention measured by PET and a gamma counter was closely correlated to the number of cells and a linear relationship was found.

DISCUSSION

The detection limit of PET is in the magnitude of 10(5) to 10(6) malignant cells. The experimental set-up was robust and well suited as a platform for further investigations of factors influencing the detection limit of PET.

Radiation doses to staff involved in sentinel node operations for breast cancer

BACKGROUND

The use of radioactive compounds for sentinel node biopsy is now a generally accepted part of the surgical treatment of breast cancer and melanoma, with the risk of radiation exposure to the operating team. The aim of this investigation was to study the levels of this exposure in relation to the permissible radiation dose limits.

METHODS

The radiation exposure to the hands and bodies of the operating surgeons (the 'risk persons') was measured by thermoluminescent dosimeters in 79 operations and to the pathologists handling the specimens in 17 cases. Radioactivity and dose rate measurement from tumours and breast specimens were also performed.

RESULTS

During an operation the mean skin dose (+/-SD) to the thermoluminescent dosimeters placed at the hand and the abdominal wall were 0.04 +/- 0.04 mSv (79 operations) and 0.01 +/- 0.02 mSv (67 operations) respectively. For the pathologist, the mean hand dose per operation was below the detection limit (17 operations). Correlation between the measured dose rate and the radioactive content of the tumours was 0.998.

CONCLUSIONS

The radiation exposure to the staff involved in sentinel node (SN) biopsy for breast cancer using radioactive labelled tracers will be considerably below the permissible limits, even with high numbers of SN biopsy procedures. Pregnant staff members should participate in <100 SN operations.

PET/CT with intravenous contrast can be used for PET attenuation correction in cancer patients

PURPOSE

If the CT scan of a combined PET/CT study is performed as a full diagnostic quality CT scan including intravenous (IV) contrast agent, the quality of the joint PET/CT procedure is improved and a separate diagnostic CT scan can be avoided. CT with IV contrast can be used for PET attenuation correction, but this may result in a bias in the attenuation factors. The clinical significance of this bias has not been established. Our aim was to perform a prospective clinical study where each patient had CT performed with and without IV contrast agent to establish whether PET/CT with IV contrast can be used for PET attenuation without reducing the clinical value of the PET scan.

METHODS

A uniform phantom study was used to document that the PET acquisition itself is not significantly influenced by the presence of IV contrast medium. Then, 19 patients referred to PET/CT with IV contrast underwent CT scans without, and then with contrast agent, followed by an 18F-fluorodeoxyglucose whole-body PET scan. The CT examinations were performed with identical parameters on a GE Discovery LS scanner. The PET data were reconstructed with attenuation correction based on the two CT data sets. A global comparison of standard uptake value (SUV) was performed, and SUVs in tumour, in non-tumour tissue and in the subclavian vein were calculated. Clinical evaluation of the number and location of lesions on all PET/CT scans was performed twice, blinded and in a different random order, by two independent nuclear medicine specialists.

RESULTS

In all patients, the measured global SUV of PET images based on CT with IV contrast agent was higher than the global activity using non-contrast correction. The overall increase in the mean SUV (for two different conversion tables tested) was 4.5+/-2.3% and 1.6+/-0.5%, respectively. In 11/19 patients, focal uptake was identified corresponding to malignant tumours. Eight out of 11 tumours showed an increased SUVmax (2.9+/-3.1%) on the PET images reconstructed using IV contrast. The clinical evaluation performed by the two specialists comparing contrast and non-contrast CT attenuated PET images showed weighted kappa values of 0.92 (doctor A) and 0.82 (doctor B). No contrast-introduced artefacts were found.

CONCLUSION

This study demonstrates that CT scans with IV contrast agent can be used for attenuation correction of the PET data in combined modality PET/CT scanning, without changing the clinical diagnostic interpretation.