Non-specific irreversible 89Zr-mAb uptake in tumours: evidence from biopsy-proven target-negative tumours using 89Zr-immuno-PET

BACKGROUND

Distribution of mAbs into tumour tissue may occur via different processes contributing differently to the 89Zr-mAb uptake on PET. Target-specific binding in tumours is of main interest; however, non-specific irreversible uptake may also be present, which influences quantification. The aim was to investigate the presence of non-specific irreversible uptake in tumour tissue using Patlak linearization on 89Zr-immuno-PET data of biopsy-proven target-negative tumours. Data of two studies, including target status obtained from biopsies, were retrospectively analysed, and Patlak linearization provided the net rate of irreversible uptake (Ki).

RESULTS

Two tumours were classified as CD20-negative and two as CD20-positive. Four tumours were classified as CEA-negative and nine as CEA-positive. Ki values of CD20-negative (0.43 µL/g/h and 0.92 µL/g/h) and CEA-negative tumours (mdn = 1.97 µL/g/h, interquartile range (IQR) = 1.50-2.39) were higher than zero. Median Ki values of target-negative tumours were lower than CD20-positive (1.87 µL/g/h and 1.90 µL/g/h) and CEA-positive tumours (mdn = 2.77 µL/g/h, IQR = 2.11-3.65).

CONCLUSION

Biopsy-proven target-negative tumours showed irreversible uptake of 89Zr-mAbs measured in vivo using 89Zr-immuno-PET data, which suggests the presence of non-specific irreversible uptake in tumours. Consequently, for 89Zr-immuno-PET, even if the target is absent, a tumour-to-plasma ratio always increases over time.

How to obtain the image-derived blood concentration from 89Zr-immuno-PET scans

BACKGROUND

PET scans using zirconium-89 labelled monoclonal antibodies (89Zr-mAbs), known as 89Zr-immuno-PET, are made to measure uptake in tumour and organ tissue. Uptake is related to the supply of 89Zr-mAbs in the blood. Measuring activity concentrations in blood, however, requires invasive blood sampling. This study aims to identify the best delineation strategy to obtain the image-derived blood concentration (IDBC) from 89Zr-immuno-PET scans.

METHODS

PET imaging and blood sampling of two 89Zr-mAbs were included, 89Zr-cetuximab and 89Zr-durvalumab. For seven patients receiving 89Zr-cetuximab, PET scans on 1-2 h, 2 and 6 days post-injection (p.i.) were analysed. Five patients received three injections of 89Zr-durvalumab. The scanning protocol for the first two injections consisted of PET scanning on 2, 5 and 7 days p.i. and for the third injection only on 7 days p.i. Blood samples were drawn with every PET scan and the sample-derived blood concentration (SDBC) was used as gold standard for the IDBC. According to an in-house developed standard operating procedure, the aortic arch, ascending aorta, descending aorta and left ventricle were delineated. Bland-Altman analyses were performed to assess the bias (mean difference) and variability (1.96 times the standard deviation of the differences) between IDBC and SDBC.

RESULTS

Overall, the activity concentration obtained from the IDBC was lower than from the SDBC. When comparing IDBC with SDBC, variability was smallest for the ascending aorta (20.3% and 17.0% for 89Zr-cetuximab and 89Zr-durvalumab, respectively). Variability for the other regions ranged between 17.9 and 30.8%. Bias for the ascending aorta was - 10.9% and - 11.4% for 89Zr-cetuximab and 89Zr-durvalumab, respectively.

CONCLUSIONS

Image-derived blood concentrations should be obtained from delineating the ascending aorta in 89Zr-immuno-PET scans, as this results in the lowest variability with respect to sample-derived blood concentrations.

First exploration of the on-treatment changes in tumor and organ uptake of a radiolabeled anti PD-L1 antibody during chemoradiotherapy in patients with non-small cell lung cancer using whole body PET

BACKGROUND

In patients with locally advanced unresectable non-small cell lung cancer (NSCLC), durvalumab, an anti-programmed cell death ligand-1 (PD-L1) antibody, has shown improved overall survival when used as consolidation therapy following concurrent chemoradiotherapy (CRT). However, it is unclear whether CRT itself upregulates PD-L1 expression. Therefore, this study aimed to explore the changes in the uptake of the anti PD-L1 antibody [89Zr]Zr-durvalumab in tumors and healthy organs during CRT in patients with NSCLC.

METHODS

Patients with NSCLC scheduled to undergo CRT were scanned 7±1 days after administration of 37±1 MBq [89Zr]Zr-durvalumab at baseline, 1-week on-treatment and 1 week after finishing 6 weeks of CRT. First, [89Zr]Zr-durvalumab uptake was visually assessed in a low dose cohort with a mass dose of 2 mg durvalumab (0.13% of therapeutic dose) and subsequently, quantification was done in a high dose cohort with a mass dose of 22.5 mg durvalumab (1.5% of therapeutic dose). Tracer pharmacokinetics between injections were compared using venous blood samples drawn in the 22.5 mg cohort. Visual assessment included suspected lesion detectability. Positron emission tomography (PET) uptake in tumoral and healthy tissues was quantified using tumor to plasma ratio (TPR) and organ to plasma ratio, respectively.

RESULTS

In the 2 mg dose cohort, 88% of the 17 identified tumor lesions were positive at baseline, compared with 69% (9/13) for the 22.5 mg cohort. Although the absolute plasma concentrations between patients varied, the intrapatient variability was low. The ten quantitatively assessed lesions in the 22.5 mg cohort had a median TPR at baseline of 1.3 (IQR 0.7-1.5), on-treatment of 1.0 (IQR 0.7-1.4) and at the end of treatment of 0.7 (IQR 0.6-0.7). On-treatment, an increased uptake in bone marrow was seen in three out of five patients together with a decreased uptake in the spleen in four out of five patients.

CONCLUSIONS

This study successfully imaged patients with NSCLC with [89Zr]Zr-durvalumab PET before and during CRT. Our data did not show any increase in [89Zr]Zr-durvalumab uptake in the tumor 1-week on-treatment and at the end of treatment. The changes observed in bone marrow and spleen may be due to an CRT-induced effect on immune cells.

TRIAL REGISTRATION NUMBER

EudraCT number: 2019-004284-51.

Community Survey Results Show that Standardisation of Preclinical Imaging Techniques Remains a Challenge

PURPOSE

To support acquisition of accurate, reproducible and high-quality preclinical imaging data, various standardisation resources have been developed over the years. However, it is unclear the impact of those efforts in current preclinical imaging practices. To better understand the status quo in the field of preclinical imaging standardisation, the STANDARD group of the European Society of Molecular Imaging (ESMI) put together a community survey and a forum for discussion at the European Molecular Imaging Meeting (EMIM) 2022. This paper reports on the results from the STANDARD survey and the forum discussions that took place at EMIM2022.

PROCEDURES

The survey was delivered to the community by the ESMI office and was promoted through the Society channels, email lists and webpages. The survey contained seven sections organised as generic questions and imaging modality-specific questions. The generic questions focused on issues regarding data acquisition, data processing, data storage, publishing and community awareness of international guidelines for animal research. Specific questions on practices in optical imaging, PET, CT, SPECT, MRI and ultrasound were further included.

RESULTS

Data from the STANDARD survey showed that 47% of survey participants do not have or do not know if they have QC/QA guidelines at their institutes. Additionally, a large variability exists in the ways data are acquired, processed and reported regarding general aspects as well as modality-specific aspects. Moreover, there is limited awareness of the existence of international guidelines on preclinical (imaging) research practices.

CONCLUSIONS

Standardisation of preclinical imaging techniques remains a challenge and hinders the transformative potential of preclinical imaging to augment biomedical research pipelines by serving as an easy vehicle for translation of research findings to the clinic. Data collected in this project show that there is a need to promote and disseminate already available tools to standardise preclinical imaging practices.

Validation of simplified uptake measures against dynamic Patlak Ki for quantification of lesional 89Zr-Immuno-PET antibody uptake

PURPOSE

Positron emission tomography imaging of zirconium-89-labelled monoclonal antibodies (89Zr-Immuno-PET) allows for visualisation and quantification of antibody uptake in tumours in vivo. Patlak linearization provides distribution volume (VT) and nett influx rate (Ki) values, representing reversible and irreversible uptake, respectively. Standardised uptake value (SUV) and tumour-to-plasma/tumour-to-blood ratio (TPR/TBR) are often used, but their validity depends on the comparability of plasma kinetics and clearances. This study assesses the validity of SUV, TPR and TBR against Patlak Ki for quantifying irreversible 89Zr-Immuno-PET uptake in tumours.

METHODS

Ten patients received 37 MBq 10 mg 89Zr-anti-EGFR with 500 mg/m2 unlabelled mAbs. Five patients received two doses of 37 MBq 89Zr-anti-HER3: 8-24 mg for the first administration and 24 mg-30 mg/kg for the second. Seven tumours from four patients showed 89Zr-anti-EGFR uptake, and 18 tumours from five patients showed 89Zr-anti-HER3 uptake. SUVpeak, TPRpeak and TBRpeak values were obtained from one to six days p.i. Patlak linearization was applied to tumour time activity curves and plasma samples to obtain Ki.

RESULTS

For 89Zr-anti-EGFR, there was a small variability along the linear regression line between SUV (- 0.51-0.57), TPR (- 0.06‒0.11) and TBR (- 0.13‒0.16) on day 6 versus Ki. Similar doses of 89Zr-anti-HER3 showed similar variability for SUV (- 1.3‒1.0), TPR (- 1.1‒0.53) and TBR (- 1.5‒0.72) on day 5 versus Ki. However, for the second administration of 89Zr-anti-HER3 with a large variability in administered mass doses, SUV showed a larger variability (- 1.4‒2.3) along the regression line with Ki, which improved when using TPR (- 0.38-0.32) or TBR (- 0.56‒0.46).

CONCLUSION

SUV, TPR and TBR at late time points were valid for quantifying irreversible lesional 89Zr-Immuno-PET uptake when constant mass doses were administered. However, for variable mass doses, only TPR and TBR provided reliable values for irreversible uptake, but not SUV, because SUV does not take patient and mass dose-specific plasma clearance into account.

89Zr-immuno-PET using the anti-LAG-3 tracer [89Zr]Zr-BI 754111: demonstrating target specific binding in NSCLC and HNSCC

PURPOSE

Although lymphocyte activation gene-3 (LAG-3) directed therapies demonstrate promising clinical anti-cancer activity, only a subset of patients seems to benefit and predictive biomarkers are lacking. Here, we explored the potential use of the anti-LAG-3 antibody tracer [89Zr]Zr-BI 754111 as a predictive imaging biomarker and investigated its target specific uptake as well as the correlation of its tumor uptake and the tumor immune infiltration.

METHODS

Patients with head and neck (N = 2) or lung cancer (N = 4) were included in an imaging substudy of a phase 1 trial with BI 754091 (anti-PD-1) and BI 754111 (anti-LAG-3). After baseline tumor biopsy and [18F]FDG-PET, patients were given 240 mg of BI 754091, followed 8 days later by administration of [89Zr]Zr-BI 754111 (37 MBq, 4 mg). PET scans were performed 2 h, 96 h, and 144 h post-injection. To investigate target specificity, a second tracer administration was given two weeks later, this time with pre-administration of 40 (N = 3) or 600 mg (N = 3) unlabeled BI 754111, followed by PET scans at 96 h and 144 h post-injection. Tumor immune cell infiltration was assessed by immunohistochemistry and RNA sequencing.

RESULTS

Tracer uptake in tumors was clearly visible at the 4-mg mass dose (tumor-to-plasma ratio 1.63 [IQR 0.37-2.89]) and could be saturated by increasing mass doses (44 mg: 0.67 [IQR 0.50-0.85]; 604 mg: 0.56 [IQR 0.42-0.75]), demonstrating target specificity. Tumor uptake correlated to immune cell-derived RNA signatures.

CONCLUSIONS

[89Zr]Zr-BI-754111 PET imaging shows favorable technical and biological characteristics for developing a potential predictive imaging biomarker for LAG-3-directed therapies.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT03780725. Registered 19 December 2018.

Characterizing the Bone Marrow Environment in Advanced-Stage Myelofibrosis during Ruxolitinib Treatment Using PET/CT and MRI: A Pilot Study

Current diagnostic criteria for myelofibrosis are largely based on bone marrow (BM) biopsy results. However, these have several limitations, including sampling errors. Explorative studies have indicated that imaging might form an alternative for the evaluation of disease activity, but the heterogeneity in BM abnormalities complicates the choice for the optimal technique. In our prospective diagnostic pilot study, we aimed to visualize all BM abnormalities in myelofibrosis before and during ruxolitinib treatment using both PET/CT and MRI. A random sample of patients was scheduled for examinations at baseline and after 6 and 18 months of treatment, including clinical and laboratory examinations, BM biopsies, MRI (T1-weighted, Dixon, dynamic contrast-enhanced (DCE)) and PET/CT ([¹⁵O]water, [¹⁸F]NaF)). At baseline, all patients showed low BM fat content (indicated by T1-weighted MRI and Dixon), increased BM blood flow (as measured by [¹⁵O]water PET/CT), and increased osteoblastic activity (reflected by increased skeletal [¹⁸F]NaF uptake). One patient died after the baseline evaluation. In the others, BM fat content increased to various degrees during treatment. Normalization of BM blood flow (as reflected by [¹⁵O]water PET/CT and DCE-MRI) occurred in one patient, who also showed the fastest clinical response. Vertebral [¹⁸F]NaF uptake remained stable in all patients. In evaluable cases, histopathological parameters were not accurately reflected by imaging results. A case of sampling error was suspected. We conclude that imaging results can provide information on functional processes and disease distribution throughout the BM. Differences in early treatment responses were especially reflected by T1-weighted MRI. Limitations in the gold standard hampered the evaluation of diagnostic accuracy.

Optimal imaging time points considering accuracy and precision of Patlak linearization for 89Zr-immuno-PET: a simulation study

Purpose

Zirconium-89-immuno-positron emission tomography (⁸⁹Zr-immuno-PET) has enabled visualization of zirconium-89 labelled monoclonal antibody (⁸⁹Zr-mAb) uptake in organs and tumors in vivo. Patlak linearization of ⁸⁹Zr-immuno-PET quantification data allows for separation of reversible and irreversible uptake, by combining multiple blood samples and PET images at different days. As one can obtain only a limited number of blood samples and scans per patient, choosing the optimal time points is important. Tissue activity concentration curves were simulated to evaluate the effect of imaging time points on Patlak results, considering different time points, input functions, noise levels and levels of reversible and irreversible uptake.

Methods

Based on ⁸⁹Zr-mAb input functions and reference values for reversible (V_T) and irreversible (K_i) uptake from literature, multiple tissue activity curves were simulated. Three different ⁸⁹Zr-mAb input functions, five time points between 24 and 192 h p.i., noise levels of 5, 10 and 15%, and three reference K_i and V_T values were considered. Simulated K_i and V_T were calculated (Patlak linearization) for a thousand repetitions. Accuracy and precision of Patlak linearization were evaluated by comparing simulated K_i and V_T with reference values.

Results

Simulations showed that K_i is always underestimated. Inclusion of time point 24 h p.i. reduced bias and variability in V_T, and slightly reduced bias and variability in K_i, as compared to combinations of three later time points. After inclusion of 24 h p.i., minimal differences were found in bias and variability between different combinations of later imaging time points, despite different input functions, noise levels and reference values.

Conclusion

Inclusion of a blood sample and PET scan at 24 h p.i. improves accuracy and precision of Patlak results for ⁸⁹Zr-immuno-PET; the exact timing of the two later time points is not critical.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-022-00927-6.

Praluzatamab Ravtansine, a CD166-Targeting Antibody-Drug Conjugate, in Patients with Advanced Solid Tumors: An Open-Label Phase I/II Trial

PURPOSE

Praluzatamab ravtansine (CX-2009) is a conditionally activated Probody drug conjugate (PDC) comprising an anti-CD166 mAb conjugated to DM4, with a protease-cleavable linker and a peptide mask that limits target engagement in normal tissue and circulation. The tumor microenvironment is enriched for proteases capable of cleaving the linker, thereby releasing the mask, allowing for localized binding of CX-2009 to CD166. CX-2009 was evaluated in a phase I/II clinical trial for patients with advanced solid tumors.

PATIENTS AND METHODS

Eligible patients had metastatic cancer receiving ≥2 prior treatments. CX-2009 was administered at escalating doses every 3 weeks (0.25-10 mg/kg) or every 2 weeks (4-6 mg/kg). Primary objective was to determine the safety profile and recommended phase II dose (RP2D).

RESULTS

Of 99 patients enrolled, the most prevalent subtype was breast cancer (n = 45). Median number of prior therapies was 5 (range, 1-19). Dose-limiting toxicities were observed at 8 mg/kg every 3 weeks and 6 mg/kg every 2 weeks. On the basis of tolerability, the RP2D was 7 mg/kg every 3 weeks. Tumor regressions were observed at doses ≥4 mg/kg. In the hormone receptor-positive/HER2-nonamplified breast cancer subset (n = 22), 2 patients (9%) had confirmed partial responses, and 10 patients (45%) had stable disease. Imaging with zirconium-labeled CX-2009 confirmed uptake in tumor lesions and shielding of major organs. Activated, unmasked CX-2009 was measurable in 18 of 22 posttreatment biopsies.

CONCLUSIONS

CD166 is a novel, ubiquitously expressed target. CX-2009 is the first conditionally activated antibody-drug conjugate to CD166 to demonstrate both translational and clinical activity in a variety of tumor types.

PET-CT Imaging of Polymeric Nanoparticle Tumor Accumulation in Patients

Several FDA/EMA-approved nanomedicines have demonstrated improved pharmacokinetics and toxicity profiles compared to their conventional chemotherapeutic counterparts. The next step to increase therapeutic efficacy depends on tumor accumulation, which can be highly heterogeneous. A clinical tool for patient stratification is urgently awaited. Therefore, a docetaxel-entrapping polymeric nanoparticle (⁸⁹ Zr-CPC634) is radiolabeled, and positron emission tomography/computed tomography (PET/CT) imaging is performed in seven patients with solid tumors with two different doses of CPC634: an on-treatment (containing 60 mg m^-2 docetaxel) and a diagnostic (1-2 mg docetaxel) dose (NCT03712423). Pharmacokinetic half-life for ⁸⁹ Zr-CPC634 is mean 97.0 ± 14.4 h on-treatment, and 62.4 ± 12.9 h for the diagnostic dose (p = 0.003). At these doses accumulation is observed in 46% and 41% of tumor lesions with a median accumulation in positive lesions 96 h post-injection of 4.94 and 4.45%IA kg^-1 (p = 0.91), respectively. In conclusion, PET/CT imaging with a diagnostic dose of ⁸⁹ Zr-CPC634 accurately reflects on-treatment tumor accumulation and thus opens the possibility for patient stratification in cancer nanomedicine with polymeric nanoparticles.

Noise sensitivity of 89Zr-Immuno-PET radiomics based on count-reduced clinical images

PURPOSE

Low photon count in ⁸⁹Zr-Immuno-PET results in images with a low signal-to-noise ratio (SNR). Since PET radiomics are sensitive to noise, this study focuses on the impact of noise on radiomic features from ⁸⁹Zr-Immuno-PET clinical images. We hypothesise that ⁸⁹Zr-Immuno-PET derived radiomic features have: (1) noise-induced variability affecting their precision and (2) noise-induced bias affecting their accuracy. This study aims to identify those features that are not or only minimally affected by noise in terms of precision and accuracy.

METHODS

Count-split ⁸⁹Zr-Immuno-PET patient scans from previous studies with three different ⁸⁹Zr-labelled monoclonal antibodies were used to extract radiomic features at 50% (S50p) and 25% (S25p) of their original counts. Tumour lesions were manually delineated on the original full-count ⁸⁹Zr-Immuno-PET scans. Noise-induced variability and bias were assessed using intraclass correlation coefficient (ICC) and similarity distance metric (SDM), respectively. Based on the ICC and SDM values, the radiomic features were categorised as having poor [0, 0.5), moderate [0.5, 0.75), good [0.75, 0.9), or excellent [0.9, 1] precision and accuracy. The number of features classified into these categories was compared between the S50p and S25p images using Fisher's exact test. All p values < 0.01 were considered statistically significant.

RESULTS

For S50p, a total of 92% and 90% features were classified as having good or excellent ICC and SDM respectively, while for S25p, these decreased to 81% and 31%. In total, 148 features (31%) showed robustness to noise with good or moderate ICC and SDM in both S50p and S25p. The number of features classified into the four ICC and SDM categories between S50p and S25p was significantly different statistically.

CONCLUSION

Several radiomic features derived from low SNR ⁸⁹Zr-Immuno-PET images exhibit noise-induced variability and/or bias. However, 196 features (43%) that show minimal noise-induced variability and bias in S50p images have been identified. These features are less affected by noise and are, therefore, suitable candidates to be further studied as prognostic and predictive quantitative biomarkers in ⁸⁹Zr-Immuno-PET studies.

3D Convolutional Neural Network-Based Denoising of Low-Count Whole-Body 18F-Fluorodeoxyglucose and 89Zr-Rituximab PET Scans

Acquisition time and injected activity of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET should ideally be reduced. However, this decreases the signal-to-noise ratio (SNR), which impairs the diagnostic value of these PET scans. In addition, ⁸⁹Zr-antibody PET is known to have a low SNR. To improve the diagnostic value of these scans, a Convolutional Neural Network (CNN) denoising method is proposed. The aim of this study was therefore to develop CNNs to increase SNR for low-count ¹⁸F-FDG and ⁸⁹Zr-antibody PET. Super-low-count, low-count and full-count ¹⁸F-FDG PET scans from 60 primary lung cancer patients and full-count ⁸⁹Zr-rituximab PET scans from five patients with non-Hodgkin lymphoma were acquired. CNNs were built to capture the features and to denoise the PET scans. Additionally, Gaussian smoothing (GS) and Bilateral filtering (BF) were evaluated. The performance of the denoising approaches was assessed based on the tumour recovery coefficient (TRC), coefficient of variance (COV; level of noise), and a qualitative assessment by two nuclear medicine physicians. The CNNs had a higher TRC and comparable or lower COV to GS and BF and was also the preferred method of the two observers for both ¹⁸F-FDG and ⁸⁹Zr-rituximab PET. The CNNs improved the SNR of low-count ¹⁸F-FDG and ⁸⁹Zr-rituximab PET, with almost similar or better clinical performance than the full-count PET, respectively. Additionally, the CNNs showed better performance than GS and BF.

Potential and pitfalls of 89Zr-immuno-PET to assess target status: 89Zr-trastuzumab as an example

Background

⁸⁹Zirconium-immuno-positron emission tomography (⁸⁹Zr-immuno-PET) is used for assessment of target status to guide antibody-based therapy. We aim to determine the relation between antibody tumor uptake and target concentration to improve future study design and interpretation.

Methods

The relation between tumor uptake and target concentration was predicted by mathematical modeling of ⁸⁹Zr-labeled antibody disposition in the tumor. Literature values for trastuzumab kinetics were used to provide an example.

Results

⁸⁹Zr-trastuzumab uptake initially increases with increasing target concentration, until it levels off to a constant value. This is determined by the total administered mass dose of trastuzumab. For a commonly used imaging dose of 50 mg ⁸⁹Zr-trastuzumab, uptake can discriminate between immunohistochemistry score (IHC) 0 versus 1–2–3.

Conclusion

The example for ⁸⁹Zr-trastuzumab illustrates the potential to assess target expression. The pitfall of false-positive findings depends on the cut-off to define clinical target positivity (i.e., IHC 3) and the administered mass dose.

PD-L1 PET/CT imaging with radiolabeled durvalumab in patients with advanced stage non-small cell lung cancer

Background: Better biomarkers are needed to predict treatment outcome in NSCLC patients treated with anti PD-(L)1 checkpoint inhibitors. PD-L1 immunohistochemistry has limited predictive value, possibly due to tumor heterogeneity of PD-L1 expression. Noninvasive PD-L1 imaging using ⁸⁹Zr-durvalumab might provide a better reflection of tumor PD-L1 expression and can therefore support treatment decision making. Patients and Methods: NSCLC patients eligible for second line immunotherapy treatment were enrolled. Patients received two injections of ⁸⁹Zr-durvalumab; one without a preceding dose of unlabeled durvalumab ('tracer dose only') and one with a preceding dose of 750 mg durvalumab, directly prior to tracer injection. Up to four PET/CT scans were obtained after tracer injection. Post-imaging acquisition, patients were treated with 750mg durvalumab every two weeks. Tracer biodistribution and tumor uptake were visually assessed and quantified as standardized uptake value (SUV) and both imaging acquisitions were compared. Tumor tracer uptake was correlated with PD-L1 expression and clinical outcome, defined as treatment response to durvalumab treatment. Results: Thirteen patients were included and ten completed all scheduled PET scans. No tracer related adverse events were observed and all patients started durvalumab treatment. Biodistribution analysis showed ⁸⁹Zr-durvalumab accumulation in the blood pool, liver and spleen. Serial imaging showed that image acquisition 120 hours post injection delivered the best tumor to blood pool ratio. Most tumor lesions were visualized with the tracer-dose only versus the co-injection imaging acquisition (25% vs 13.5% of all lesions). Uptake heterogeneity was observed within (range SUVpeak 0.2 to 15.1) and between patients. Tumor uptake was higher in patients with treatment response or stable disease, compared to patients with disease progression according to RECIST 1.1. However, this difference was not statistically significant (median SUVpeak 4.9 vs 2.4, P = 0.06). SUVpeak correlated better with the combined tumor and immune cell PD-L1 score than with PD-L1 expression on tumor cells, although both were not statistically significant (P = 0.06 and P = 0.93, respectively). Conclusion: ⁸⁹Zr-durvalumab was safe without any tracer related adverse events and more tumor lesions were visualized using the tracer dose only imaging acquisition. ⁸⁹Zr-durvalumab tumor uptake was higher in patients with response to durvalumab treatment, but did not correlate with tumor PD-L1 IHC.

First-in-human study of 89Zr-pembrolizumab PET/CT in patients with advanced stage non-small-cell lung cancer

Background: Tumor programmed-death ligand-1 (PD-L1) proportion score is the current method to select non-small-cell lung cancer (NSCLC) patients for single agent treatment with pembrolizumab, a programmed cell death-1 (PD-1) monoclonal antibody. However, not all patients respond to therapy. Better understanding of in vivo drug behavior may help to select patients that benefit most. Methods: NSCLC patients eligible for pembrolizumab monotherapy as first or later line therapy were enrolled. Patients received two injections of ⁸⁹Zr-pembrolizumab; one without a preceding dose of pembrolizumab and one with 200 mg pembrolizumab, directly prior to tracer injection. Up to four PET/CT scans were obtained after tracer injection. Post-imaging acquisition, patients were treated with 200 mg pembrolizumab, every three weeks. Tumor uptake and tracer biodistribution were visually assessed and quantified as standardized uptake value (SUV). Tumor tracer uptake was correlated with PD-1 and PD-L1 expression and response to pembrolizumab treatment. Results: Twelve NSCLC patients were included. One patient experienced grade 3 myalgia after tracer injection. ⁸⁹Zr-pembrolizumab was observed in the blood pool, liver and spleen. Tracer uptake was visualized in 47,2% of 72 tumor lesions measuring ≥20 mm long axis diameter, and substantial uptake heterogeneity was observed within and between patients. Uptake was higher in patients with response to pembrolizumab treatment (n = 3) compared to patients without a response (n = 9), although this was not statistically significant (median SUVpeak 11.4 vs 5.7, P = 0.066). No significant correlations were found with PD-L1 or PD-1 immunohistochemistry. Conclusion: ⁸⁹Zr-pembrolizumab injection was safe with only one grade 3 adverse event, possibly immune related, out of 12 patients. ⁸⁹Zr-pembrolizumab tumor uptake was higher in patients with response to pembrolizumab treatment, but did not correlate with PD-L1 or PD-1 immunohistochemistry.

Application of [18F]FLT-PET in pulmonary arterial hypertension: a clinical study in pulmonary arterial hypertension patients and unaffected bone morphogenetic protein receptor type 2 mutation carriers

Pulmonary arterial hypertension is a heterogeneous group of diseases characterized by vascular cell proliferation leading to pulmonary vascular remodelling and ultimately right heart failure. Previous data indicated that 3′-deoxy-3′-[18F]-fluorothymidine (¹⁸FLT) positron emission tomography (PET) scanning was increased in pulmonary arterial hypertension patients, hence providing a possible biomarker for pulmonary arterial hypertension as it reflects vascular cell hyperproliferation in the lung. This study sought to validate ¹⁸FLT-PET in an expanded cohort of pulmonary arterial hypertension patients in comparison to matched healthy controls and unaffected bone morphogenetic protein receptor type 2 mutation carriers. ¹⁸FLT-PET scanning was performed in 21 pulmonary arterial hypertension patients (15 hereditary pulmonary arterial hypertension and 6 idiopathic pulmonary arterial hypertension), 11 unaffected mutation carriers and 9 healthy control subjects. In-depth kinetic analysis indicated that there were no differences in lung ¹⁸FLT k3 phosphorylation among pulmonary arterial hypertension patients, unaffected bone morphogenetic protein receptor type 2 mutation carriers and healthy controls. Lung ¹⁸FLT uptake did not correlate with haemodynamic or clinical parameters in pulmonary arterial hypertension patients. Sequential ¹⁸FLT-PET scanning in three patients demonstrated uneven regional distribution in ¹⁸FLT uptake by 3D parametric mapping of the lung, although this did not follow the clinical course of the patient. We did not detect significantly increased lung ¹⁸FLT uptake in pulmonary arterial hypertension patients, nor in the unaffected bone morphogenetic protein receptor type 2 mutation carriers, as compared to healthy subjects. The conflicting results with our preliminary human ¹⁸FLT report may be explained by a small sample size previously and we observed large variation of lung ¹⁸FLT signals between patients, challenging the application of ¹⁸FLT-PET as a biomarker in the pulmonary arterial hypertension clinic.

Performance of nanoScan PET/CT and PET/MR for quantitative imaging of 18F and 89Zr as compared with ex vivo biodistribution in tumor-bearing mice

INTRODUCTION

The assessment of ex vivo biodistribution is the preferred method for quantification of radiotracers biodistribution in preclinical models, but is not in line with current ethics on animal research. PET imaging allows for noninvasive longitudinal evaluation of tracer distribution in the same animals, but systemic comparison with ex vivo biodistribution is lacking. Our aim was to evaluate the potential of preclinical PET imaging for accurate tracer quantification, especially in tumor models.

METHODS

NEMA NU 4-2008 phantoms were filled with ¹¹C, ⁶⁸Ga, ¹⁸F, or ⁸⁹Zr solutions and scanned in Mediso nanoPET/CT and PET/MR scanners until decay. N87 tumor-bearing mice were i.v. injected with either [¹⁸F]FDG (~ 14 MBq), kept 50 min under anesthesia followed by imaging for 20 min, or with [⁸⁹Zr]Zr-DFO-NCS-trastuzumab (~ 5 MBq) and imaged 3 days post-injection for 45 min. After PET acquisition, animals were killed and organs of interest were collected and measured in a γ-counter to determine tracer uptake levels. PET data were reconstructed using TeraTomo reconstruction algorithm with attenuation and scatter correction and regions of interest were drawn using Vivoquant software. PET imaging and ex vivo biodistribution were compared using Bland-Altman plots.

RESULTS

In phantoms, the highest recovery coefficient, thus the smallest partial volume effect, was obtained with ¹⁸F for both PET/CT and PET/MR. Recovery was slightly lower for ¹¹C and ⁸⁹Zr, while the lowest recovery was obtained with ⁶⁸Ga in both scanners. In vivo, tumor uptake of the ¹⁸F- or ⁸⁹Zr-labeled tracer proved to be similar irrespective whether quantified by either PET/CT and PET/MR or ex vivo biodistribution with average PET/ex vivo ratios of 0.8-0.9 and a deviation of 10% or less. Both methods appeared less congruent in the quantification of tracer uptake in healthy organs such as brain, kidney, and liver, and depended on the organ evaluated and the radionuclide used.

CONCLUSIONS

Our study suggests that PET quantification of ¹⁸F- and ⁸⁹Zr-labeled tracers is reliable for the evaluation of tumor uptake in preclinical models and a valuable alternative technique for ex vivo biodistribution. However, PET and ex vivo quantification require fully described experimental and analytical procedures for reliability and reproducibility.

The Role of 89Zr-Immuno-PET in Navigating and Derisking the Development of Biopharmaceuticals

The identification of molecular drivers of disease and the compelling rise of biotherapeutics have impacted clinical care but have also come with challenges. Such therapeutics include peptides, monoclonal antibodies, antibody fragments and nontraditional binding scaffolds, activatable antibodies, bispecific antibodies, immunocytokines, antibody-drug conjugates, enzymes, polynucleotides, and therapeutic cells, as well as alternative drug carriers such as nanoparticles. Drug development is expensive, attrition rates are high, and efficacy rates are lower than desired. Almost all these drugs, which in general have a long residence time in the body, can stably be labeled with ⁸⁹Zr for whole-body PET imaging and quantification. Although not restricted to monoclonal antibodies, this approach is called ⁸⁹Zr-immuno-PET. This review summarizes the state of the art of the technical aspects of ⁸⁹Zr-immuno-PET and illustrates why it has potential for steering the design, development, and application of biologic drugs. Appealing showcases are discussed to illustrate what can be learned with this emerging technology during preclinical and especially clinical studies about biologic drug formats and disease targets. In addition, an overview of ongoing and completed clinical trials is provided. Although ⁸⁹Zr-immuno-PET is a young tool in drug development, its application is rapidly expanding, with first clinical experiences giving insight on why certain drug-target combinations might have better perspectives than others.

Correction to: [89Zr]Zr-cetuximab PET/CT as biomarker for cetuximab monotherapy in patients with RAS wild-type advanced colorectal cancer

Missing Electronic Supplementary Materials.

Value of CMR and PET in Predicting Ventricular Arrhythmias in Ischemic Cardiomyopathy Patients Eligible for ICD

OBJECTIVES

This study presents a head-to-head comparison of the value of cardiac magnetic resonance (CMR)-derived left-ventricular (LV) function and scar burden and positron emission tomography (PET)-derived perfusion and innervation in predicting ventricular arrhythmias (VAs).

BACKGROUND

Improved risk stratification of VA is important to identify patients who should benefit of prophylactic implantable cardioverter-defibrillator (ICD) implantation. Perfusion abnormalities, sympathetic denervation, and scar burden have all been linked to VA, although comparative studies are lacking.

METHODS

Seventy-four patients with ischemic cardiomyopathy and left-ventricular ejection fraction (LVEF) ≤35%, referred for primary prevention ICD placement were enrolled prospectively. Late gadolinium-enhanced (LGE) CMR was performed to assess LV function and scar characteristics. [¹⁵O]H₂O and [¹¹C]hydroxyephedrine positron emission tomography (PET) were performed to quantify resting and hyperemic myocardial blood flow (MBF), coronary flow reserve (CFR), and sympathetic innervation. During follow-up of 5.4 ± 1.9 years, the occurrence of sustained VA, appropriate ICD therapy, and mortality were evaluated.

RESULTS

In total, 20 (26%) patients experienced VA. CMR and PET parameters showed considerable overlap between patients with VA and patients without VA, caused by substantial heterogeneity within groups. Univariable analyses showed that lower LVEF (hazard ratio [HR]: 0.92; p = 0.03), higher left-ventricular end-diastolic volume index (LVEDVi) (HR 1.02; p < 0.01), and larger scar border zone (HR 1.11; p = 0.03) were related to VA. Scar core size, resting MBF, hyperemic MBF, perfusion defect size, innervation defect size, and the innervation-perfusion mismatch were not found to be associated with VA.

CONCLUSIONS

In patients with ischemic cardiomyopathy, lower LVEF, higher LVEDVi, and larger scar border zone were related to VA. PET-derived perfusion and sympathetic innervation, as well as CMR-derived scar core size were not associated with VA. These results suggest that improved prediction of VA by advanced imaging remains challenging for the individual patient.

Quantification of PD-L1 Expression with 18F-BMS-986192 PET/CT in Patients with Advanced-Stage Non-Small Cell Lung Cancer

The aim of this work was to quantify the uptake of ¹⁸F-BMS-986192, a programmed cell death ligand 1 (PD-L1) adnectin PET tracer, in patients with non-small cell lung cancer. To this end, plasma input kinetic modeling of dynamic tumor uptake data with online arterial blood sampling was performed. In addition, the accuracy of simplified uptake metrics such as SUV was investigated. Methods: Data from a study with ¹⁸F-BMS-986192 in patients with advanced-stage non-small cell lung cancer eligible for nivolumab treatment were used if a dynamic scan was available and lesions were present in the field of view of the dynamic scan. After injection of ¹⁸F-BMS-986192, a 60-min dynamic PET/CT scan was started, followed by a 30-min whole-body PET/CT scan. Continuous arterial and discrete arterial and venous blood sampling were performed to determine a plasma input function. Tumor time-activity curves were fitted by several plasma input kinetic models. Simplified uptake parameters included tumor-to-blood ratio as well as several SUV measures. Results: Twenty-two tumors in 9 patients were analyzed. The arterial plasma input single-tissue reversible compartment model with fitted blood volume fraction seems to be the most preferred model as it best fitted 11 of 18 tumor time-activity curves. The distribution volume (V _T ) ranged from 0.4 to 4.8 mL⋅cm^-3 Similar values were obtained with an image-derived input function. From the simplified measures, SUV normalized for body weight at 50 and 67 min after injection correlated best with V _T , with an R ² of more than 0.9. Conclusion: A single-tissue reversible model can be used to quantify tumor uptake of the PD-L1 PET tracer ¹⁸F-BMS-986192. SUV at 60 min after injection, normalized for body weight, is an accurate simplified parameter for uptake assessment of baseline studies. To assess its predictive value for response evaluation during programmed cell death protein 1 or PD-L1 immune checkpoint inhibition, further validation of SUV against V _T based on an image-derived input function is recommended.

[89Zr]Zr-cetuximab PET/CT as biomarker for cetuximab monotherapy in patients with RAS wild-type advanced colorectal cancer

PURPOSE

One-third of patients with RAS wild-type mCRC do not benefit from anti-EGFR monoclonal antibodies. This might be a result of variable pharmacokinetics and insufficient tumor targeting. We evaluated cetuximab tumor accumulation on [⁸⁹Zr]Zr-cetuximab PET/CT as a potential predictive biomarker and determinant for an escalating dosing strategy.

PATIENTS AND METHODS

PET/CT imaging of [⁸⁹Zr]Zr-cetuximab (37 MBq/10 mg) after a therapeutic pre-dose (500 mg/m² ≤ 2 h) cetuximab was performed at the start of treatment. Patients without visual tumor uptake underwent dose escalation and a subsequent [⁸⁹Zr]Zr-cetuximab PET/CT. Treatment benefit was defined as stable disease or response on CT scan evaluation after 8 weeks.

RESULTS

Visual tumor uptake on [⁸⁹Zr]Zr-cetuximab PET/CT was observed in 66% of 35 patients. There was no relationship between PET positivity and treatment benefit (52% versus 80% for PET-negative, P = 0.16), progression-free survival (3.6 versus 5.7 months, P = 0.15), or overall survival (7.1 versus 9.4 months, P = 0.29). However, in 67% of PET-negative patients, cetuximab dose escalation (750-1250 mg/m²) was applied, potentially influencing outcome in this group. None of the second [⁸⁹Zr]Zr-cetuximab PET/CT was positive. Eighty percent of patients without visual tumor uptake had treatment benefit, making [⁸⁹Zr]Zr-cetuximab PET/CT unsuitable as a predictive biomarker. Tumor SUV_peak did not correlate to changes in tumor size on CT (P = 0.23), treatment benefit, nor progression-free survival. Cetuximab pharmacokinetics were not related to treatment benefit. BRAF mutations, right-sidedness, and low sEGFR were correlated with intrinsic resistance to cetuximab.

CONCLUSION

Tumor uptake on [⁸⁹Zr]Zr-cetuximab PET/CT failed to predict treatment benefit in patients with RAS wild-type mCRC receiving cetuximab monotherapy. BRAF mutations, right-sidedness, and low sEGFR correlated with intrinsic resistance to cetuximab.

3'-Deoxy-3'-[18F]Fluorothymidine Positron Emission Tomography Depicts Heterogeneous Proliferation Pathology in Idiopathic Pulmonary Arterial Hypertension Patient Lung

BACKGROUND

Pulmonary vascular cell hyperproliferation is characteristic of pulmonary vascular remodeling in pulmonary arterial hypertension. A noninvasive imaging biomarker is needed to track the pathology and assess the response to novel treatments targeted at resolving the structural changes. Here, we evaluated the application of radioligand 3'-deoxy-3'-[18F]-fluorothymidine (¹⁸FLT) using positron emission tomography.

METHODS AND RESULTS

We performed dynamic ¹⁸FLT positron emission tomography in 8 patients with idiopathic pulmonary arterial hypertension (IPAH) and applied in-depth kinetic analysis with a reversible 2-compartment 4k model. Our results show significantly increased lung ¹⁸FLT phosphorylation (k₃) in patients with IPAH compared with nonpulmonary arterial hypertension controls (0.086±0.034 versus 0.054±0.009 min^-1; P<0.05). There was heterogeneity in the lung ¹⁸FLT signal both between patients with IPAH and within the lungs of each patient, compatible with histopathologic reports of lungs from patients with IPAH. Consistent with ¹⁸FLT positron emission tomographic data, TK1 (thymidine kinase 1) expression was evident in the remodeled vessels in IPAH patient lung. In addition, hyperproliferative pulmonary vascular fibroblasts isolated from patients with IPAH exhibited upregulated expression of TK1 and the thymidine transporter, ENT1 (equilibrative nucleoside transporter 1). In the monocrotaline and SuHx (Sugen hypoxia) rat pulmonary arterial hypertension models, increased lung ¹⁸FLT uptake was strongly associated with peripheral pulmonary vascular muscularization and the proliferation marker, Ki-67 score, together with prominent TK1 expression in remodeled vessels. Importantly, lung ¹⁸FLT uptake was attenuated by 2 antiproliferative treatments: dichloroacetate and the tyrosine kinase inhibitor, imatinib.

CONCLUSIONS

Dynamic ¹⁸FLT positron emission tomography imaging can be used to report hyperproliferation in pulmonary hypertension and merits further study to evaluate response to treatment in patients with IPAH.

Abstract 1136: Tumor uptake and biodistribution of 89Zirconium-labeled ipilimumab in patients with metastatic melanoma during ipilimumab treatment

Introduction

Ipilimumab, a monoclonal antibody targeting CTLA-4, is approved for the treatment of metastatic melanoma and significantly improves overall survival. Because of the high costs and the potential serious toxicity of ipilimumab, it is of great importance to identify biomarkers that correlate with clinical activity and that can be used to select patients who will benefit from CTLA-4 blockade therapy.

We hypothesize that patients who do not respond to treatment with ipilimumab have lower drug levels in tumor tissues as compared to patients with a good response to therapy. In addition, we hypothesize that immune related adverse events (irAEs) are associated with high drug levels in the affected tissue. As irAEs usually occur approximately 6-8 weeks after the first injection of ipilimumab, we hypothesize that the drug levels in potentially affected tissues will increase at the second injection.

Experimental procedures

To visualize in vivo localization of ipilimumab in patients diagnosed with metastatic melanoma, 37 MBq, 10 mg 89Zr-labeled ipilimumab was injected within 2 hours after their first ipilimumab dose (3 mg/kg). Whole body PET/CT scans were obtained at 2h, 72h and 144h post injection and this procedure was repeated three weeks later at the second ipilimumab cycle. Biodistribution and tumor uptake were assessed visually by a nuclear physician. Focal uptake in tumor lesions exceeding local background was determined in volumes of interest (VOI) and SUVpeak values were obtained. Biodistribution was quantified by defining vital organs (i.e. lungs, kidneys, spleen, liver) and calculating mean %ID/kg. Blood was drawn for dosimetry and immunophenotyping at several time points during the trial. Presented here are initial results of the first three patients, up to 29 patients are planned to be included.

Results

Biodistribution of 89Zr-labeled ipilimumab showed a pattern distinctive for 89Zr-labeled antibodies with uptake in liver and spleen, as well as prolonged circulating antibody in the bloodstream corresponding to the pharmacokinetics of ipilimumab. Visual evaluation confirmed uptake of 89Zr-labeled ipilimumab in 5/12 evaluable tumor lesions, visible at both first and second injection of ipilimumab. Tumor uptake was comparable for 72h and 144h post injection with a mean of 6.9 %ID/kg (range 3.3-10.1) and a SUVpeak of 4.4 (range 2.3-8.9). There were no significant differences in tumor uptake between first and second dose of ipilimumab (mean 7.31 and 6.54 %ID/kg respectively).

Conclusions

Preliminary data of this ongoing study showed that the tracer is able to visualize and quantify uptake of ipilimumab in tumors. Correlations between tumor uptake and response to treatment will be presented. Furthermore, special interest will be given to uptake in lymphoid organs and locations for irAEs.

Citation Format: Iris H. Miedema, Gerben J. Zwezerijnen, Guus A. van Dongen, Daniëlle J. Vugts, Marc C. Huisman, Otto S. Hoekstra, Tanja D. de Gruijl, Hendrik M. Verheul, Catharina W. Menke, Alfons J. van den Eertwegh. Tumor uptake and biodistribution of 89Zirconium-labeled ipilimumab in patients with metastatic melanoma during ipilimumab treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1136.

Interobserver reproducibility of tumor uptake quantification with 89Zr-immuno-PET: a multicenter analysis

PURPOSE

In-vivo quantification of tumor uptake of 89-zirconium (⁸⁹Zr)-labelled monoclonal antibodies (mAbs) with PET provides a potential tool in strategies to optimize tumor targeting and therapeutic efficacy. A specific challenge for ⁸⁹Zr-immuno-PET is low tumor contrast. This is expected to result in interobserver variation in tumor delineation. Therefore, the aim of this study was to determine interobserver reproducibility of tumor uptake measures by tumor delineation on ⁸⁹Zr-immuno-PET scans.

METHODS

Data were obtained from previously published clinical studies performed with ⁸⁹Zr-rituximab, ⁸⁹Zr-cetuximab and ⁸⁹Zr-trastuzumab. Tumor lesions on ⁸⁹Zr-immuno-PET were identified as focal uptake exceeding local background by a nuclear medicine physician. Three observers independently manually delineated volumes of interest (VOI). Maximum, peak and mean standardized uptake values (SUV_max, SUV_peak and SUV_mean) were used to quantify tumor uptake. Interobserver variability was expressed as the coefficient of variation (CoV). The performance of semi-automatic VOI delineation using 50% of background-corrected AC_peak was described.

RESULTS

In total, 103 VOI were delineated (3-6 days post injection (D3-D6)). Tumor uptake (median, interquartile range) was 9.2 (5.2-12.6), 6.9 (4.0-9.6) and 5.5 (3.3-7.8) for SUV_max, SUV_peak and SUV_mean. Interobserver variability was 0% (0-12), 0% (0-2) and 7% (5-14), respectively (n = 103). The success rate of the semi-automatic method was 45%. Inclusion of background was the main reason for failure of semi-automatic VOI.

CONCLUSIONS

This study shows that interobserver reproducibility of tumor uptake quantification on ⁸⁹Zr-immuno-PET was excellent for SUV_max and SUV_peak using a standardized manual procedure for tumor segmentation. Semi-automatic delineation was not robust due to limited tumor contrast.

Comparison of Coronary CT Angiography, SPECT, PET, and Hybrid Imaging for Diagnosis of Ischemic Heart Disease Determined by Fractional Flow Reserve

Importance

At present, the choice of noninvasive testing for a diagnosis of significant coronary artery disease (CAD) is ambiguous, but nuclear myocardial perfusion imaging with single-photon emission tomography (SPECT) or positron emission tomography (PET) and coronary computed tomography angiography (CCTA) is predominantly used for this purpose. However, to date, prospective head-to-head studies are lacking regarding the diagnostic accuracy of these imaging modalities. Furthermore, the combination of anatomical and functional assessments configuring a hybrid approach may yield improved accuracy.

Objectives

To establish the diagnostic accuracy of CCTA, SPECT, and PET and explore the incremental value of hybrid imaging compared with fractional flow reserve.

Design, Setting, and Participants

A prospective clinical study involving 208 patients with suspected CAD who underwent CCTA, technetium 99m/tetrofosmin-labeled SPECT, and [15O]H2O PET with examination of all coronary arteries by fractional flow reserve was performed from January 23, 2012, to October 25, 2014. Scans were interpreted by core laboratories on an intention-to-diagnose basis. Hybrid images were generated in case of abnormal noninvasive anatomical or functional test results.

Main Outcomes and Measures

Hemodynamically significant stenosis in at least 1 coronary artery as indicated by a fractional flow reserve of 0.80 or less and relative diagnostic accuracy of SPECT, PET, and CCTA in detecting hemodynamically significant CAD.

Results

Of the 208 patients in the study (76 women and 132 men; mean [SD] age, 58 [9] years), 92 (44.2%) had significant CAD (fractional flow reserve ≤0.80). Sensitivity was 90% (95% CI, 82%-95%) for CCTA, 57% (95% CI, 46%-67%) for SPECT, and 87% (95% CI, 78%-93%) for PET, whereas specificity was 60% (95% CI, 51%-69%) for CCTA, 94% (95% CI, 88%-98%) for SPECT, and 84% (95% CI, 75%-89%) for PET. Single-photon emission tomography was found to be noninferior to PET in terms of specificity (P < .001) but not in terms of sensitivity (P > .99) using the predefined absolute margin of 10%. Diagnostic accuracy was highest for PET (85%; 95% CI, 80%-90%) compared with that of CCTA (74%; 95% CI, 67%-79%; P = .003) and SPECT (77%; 95% CI, 71%-83%; P = .02). Diagnostic accuracy was not enhanced by either hybrid SPECT and CCTA (76%; 95% CI, 70%-82%; P = .75) or by PET and CCTA (84%; 95% CI, 79%-89%; P = .82), but resulted in an increase in specificity (P = .004) at the cost of a decrease in sensitivity (P = .001).

Conclusions and Relevance

This controlled clinical head-to-head comparative study revealed PET to exhibit the highest accuracy for diagnosis of myocardial ischemia. Furthermore, a combined anatomical and functional assessment does not add incremental diagnostic value but guides clinical decision-making in an unsalutary fashion.

First-in-human imaging of nanoparticle entrapped docetaxel (CPC634) in patients with advanced solid tumors using 89Zr-Df-CPC634 PET/CT

3093

Background: CPC634 is a nanoparticle entrapping docetaxel designed to improve tumor accumulation and tolerability compared to conventionally administered docetaxel by taking advantage of the presumed enhanced permeability and retention (EPR) effect. In vivo imaging with zirconium-89 (89Zr)-desferal (Df)-CPC634 will provide valuable information on its biodistribution and will quantify tumor retention. Methods: Patients with solid tumors not amenable to standard therapy received 37 MBq, 0.1-2mg of 89Zr-Df-CPC634 tracer and whole body PET/CT scans were obtained at 2, 24 and 96h post-injection (p.i.). Patients were administered CPC634 (60mg/m2) two weeks later followed by a second tracer injection and scans at 24 and 96h p.i. Biodistribution was quantified by delineating organs of interest and calculating mean %ID/kg. Visual tumor retention was defined as focal uptake in tumor lesions exceeding local background and quantified as standardized uptake peak values (SUVpeak) in volumes of interest. Results: Five patients were included. Biodistribution of 89Zr-Df-CPC634 showed significant retention in healthy liver, and spleen compared to lung (respectively 2.54, 1.61 and 0.56 mean %ID/kg at 96h p.i.), supporting apparent opsonization of nanoparticles in cells of the reticuloendothelial system. Visual retention was observed in 16/37 evaluable tumor lesions with the highest intensity at 96h p.i, compatible with the assumed EPR effect. Tumor retention showed intra- and interpatient heterogeneity, with a mean %ID/kg of 3.43 [1.14-9.32]. Pre-administering unlabeled CPC634 did not change the mean tumor retention of 89Zr-Df-CPC634 (at 96h p.i. mean 3.50 %ID/kg [1.64-9.97]), however, four additional lesions were visible in comparison to tracer only. Conclusions: The biodistribution of 89Zr-Df-CPC634 was consistent with a prolonged exposure of nanoparticle containing docetaxel. 89Zr-Df-CPC634 showed high retention in tumors confirming the EPR effect of these nanoparticle in humans, and supporting their further development for tumor targeting of therapeutic agents. A Phase II efficacy study in platinum resistant ovarian cancer (NTC03742713) is currently ongoing. Clinical trial information: NCT03712423.

Noise-Induced Variability of Immuno-PET with Zirconium-89-Labeled Antibodies: an Analysis Based on Count-Reduced Clinical Images

Purpose

Positron emission tomography (PET) with Zirconium-89 (Zr-89)-labeled antibodies can be used for in vivo quantification of antibody uptake. Knowledge about measurement variability is required to ensure correct interpretation. However, no clinical studies have been reported on measurement variability of Zr-89 immuno-PET. As variability due to low signal-to-noise is part of the total measurement variability, the aim of this study was to assess noise-induced variability of Zr-89 -immuno-PET using count-reduced clinical images.

Procedures

Data were acquired from three previously reported clinical studies with [⁸⁹Zr]antiCD20 (74 MBq, n = 7), [⁸⁹Zr]antiEGFR (37 MBq, n = 7), and [⁸⁹Zr]antiCD44 (37 MBq, n = 13), with imaging obtained 1 to 6 days post injection (D0–D6). Volumes of interest (VOIs) were manually delineated for liver, spleen, kidney, lung, brain, and tumor. For blood pool and bone marrow, fixed-size VOIs were used. Original PET list mode data were split and reconstructed, resulting in two count-reduced images at 50 % of the original injected dose (e.g., 37 MBq_74inj).

Repeatability coefficients (RC) were obtained from Bland-Altman analysis on standardized uptake values (SUV) derived from VOIs applied to these images.

Results

The RC for the combined manually delineated organs for [⁸⁹Zr] antiCD20 (37 MBq_74inj) increased from D0 to D6 and was less than 6 % at all time points. Blood pool and bone marrow had higher RC, up to 43 % for 37 MBq_74inj at D6. For tumor, the RC was up to 42 % for [⁸⁹Zr]antiCD20 (37 MBq_74inj). For [⁸⁹Zr]antiCD20, (18 MBq_74inj), [⁸⁹Zr]antiEGFR (18 MBq_37inj), and [⁸⁹Zr]antiCD44 (18 MBq_37inj), measurement variability was independent of the investigated antibody.

Conclusions

Based on this study, noise-induced variability results in a RC for Zr-89-immuno-PET (37 MBq) around 6 % for manually delineated organs combined, increasing up to 43 % at D6 for blood pool and bone marrow, assuming similar biodistribution of antibodies. The signal-to-noise ratio leads to tumor RC up to 42 %.

Electronic supplementary material

The online version of this article (10.1007/s11307-018-1200-4) contains supplementary material, which is available to authorized users.

Standardization of Small Animal Imaging-Current Status and Future Prospects

The benefit of small animal imaging is directly linked to the validity and reliability of the collected data. If the data (regardless of the modality used) are not reproducible and/or reliable, then the outcome of the data is rather questionable. Therefore, standardization of the use of small animal imaging equipment, as well as of animal handling in general, is of paramount importance. In a recent paper, guidance for efficient small animal imaging quality control was offered and discussed, among others, the use of phantoms in setting up a quality control program (Osborne et al. 2016). The same phantoms can be used to standardize image quality parameters for multi-center studies or multi-scanners within center studies. In animal experiments, the additional complexity due to animal handling needs to be addressed to ensure standardized imaging procedures. In this review, we will address the current status of standardization in preclinical imaging, as well as potential benefits from increased levels of standardization.

F8-IL10: A New Potential Antirheumatic Drug Evaluated by a PET-Guided Translational Approach

Antibody fragment F8-mediated interleukin 10 (IL10) delivery is a novel treatment for rheumatoid arthritis (RA). F8 binds to the extra-domain-A of fibronectin (ED-A). In this study, in vivo biodistribution and arthritis targeting of radiolabeled F8-IL10 were investigated in RA patients, followed by further animal studies. Therefore, three RA patients (DAS28 > 3.2) received 0.4 mg of 30–74 megabecquerel [¹²⁴I]I–F8–IL10 for PET-CT and blood sampling. In visually identified PET-positive joints, target-to-background was calculated. Healthy mice, rats, and arthritic rats were injected with iodinated F8-IL10 or KSF-IL10 control antibody. Various organs were excised, weighed, and counted for radioactivity. Tissue sections were stained for fibronectin ED-A. In RA patients, [¹²⁴I]I–F8–IL10 was cleared rapidly from the circulation with less than 1% present in blood after 5 min. PET-CT showed targeting in 38 joints (11–15 per patient) and high uptake in the liver and spleen. Mean target-to-background ratios of PET-positive joints were 2.5 ± 1.2, 1.5 times higher for clinically active than clinically silent joints. Biodistribution of radioiodinated F8-IL10 in healthy mice showed no effect of the radioiodination method. [¹²⁴I]I–F8–IL10 joint uptake was also demonstrated in arthritic rats, ∼14-fold higher than that of the control antibody [¹²⁴I]I-KSF-IL10 (p < 0.001). Interestingly, liver and spleen uptake were twice as high in arthritic than in healthy rats and were related to increased (∼7×) fibronectin ED-A expression in these tissues. In conclusion, [¹²⁴I]I–F8–IL10 uptake was observed in arthritic joints in RA patients holding promise for visualization of inflamed joints by PET-CT imaging and therapeutic targeting. Patient observations and, subsequently, arthritic animal studies pointed to awareness of increased [¹²⁴I]I–F8–IL10 uptake in the liver and spleen associated with moderate systemic inflammation. This translational study demonstrated the value of in vivo biodistribution and PET-CT-guided imaging in development of new and potential antirheumatic drugs’.

Whole body PD-L1 PET in patients with NSCLC and melanoma

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Background: PD-(L)1 immunotherapy is effective in multiple tumors, including NSCLC and melanoma, but tumor PD-L1 IHC correlates only moderately with treatment outcome. This study aims to assess 1) safety of 18F-BMS-986192 (18F-PD-L1) in human, 2) PD-L1 quantification in tumors using 18F-PD-L1 PET, 3) PD-L1 PET correlation with IHC and treatment outcome, and 4) intra and inter subject tracer uptake variability. Methods: Pts with NSCLC (N = 10) and melanoma (N = 3) were included. At baseline, pts received a static or multiphase dynamic whole body PET scan after injecting 200 MBq 18F-BMS-986192. For NSCLC pts, (1) SUV(max, peak and mean) were measured for each delineable tumor (N = 32, 1-7 tumors/pt), (2) PD-L1 IHC (28.8 assay) was performed on the biopsy, and (3) response to Nivolumab therapy assessed by RECIST 1.1. Intra and inter subject variability and intraclass correlation were calculated using SUVs of all assessed tumors. Equal variance for PD-L1 status was evaluated by a Levene’s test. Four (3 female) pts underwent dosimetry study (ICRP 60). Results: No AEs related to radiotracer was observed. Dosimetry study demonstrated whole body exposure of 30 mGy at dose > 1400 MBq. Biodistribution among pts is comparable. PD-L1 IHC from 13 biopsied lesions were evaluated, 5 < 1%, 4 ≥1%, and 4 ≥50%. Tumor tracer uptake was measured in NSCLC pts and categorized by PDL-1 IHC as ≥50% or < 50%. Clinical trial information: 2015-004760-11. Tumor SUVs did not correlate with RECIST 1.1 assessment. Lesion heterogeneity was reflected in both inter and intra pt variability (CVinter = 41%, CVintra = 53%, ICC = 0.41 for SUVpeak). Levene’s test showed no significance in variability between the two PD-L1 categories. Conclusions: PET-imaging with 18F-BMS-986192 is safe and feasible in pts with NSCLC and melanoma. Pts with higher PD-L1 PET SUV have higher PD-L1 by IHC. Intra pt variability is similar to inter pt variability. With limited number of pts, no clear correlation of PET PD-L1 and tumor response is observed. A prospective study with this tracer is underway to further investigate 18F-BMS-986192 in understanding of PD-L1 expression.[Table: see text]

Assessment of target-mediated uptake with immuno-PET: analysis of a phase I clinical trial with an anti-CD44 antibody

BACKGROUND

Ideally, monoclonal antibodies provide selective treatment by targeting the tumour, without affecting normal tissues. Therefore, antibody imaging is of interest, preferably in early stages of drug development. However, the imaging signal consists of specific, as well as non-specific, uptake. The aim of this study was to assess specific, target-mediated uptake in normal tissues, with immuno-PET in a phase I dose escalation study, using the anti-CD44 antibody RG7356 as example.

RESULTS

Data from thirteen patients with CD44-expressing solid tumours included in an imaging sub-study of a phase I dose escalation clinical trial using the anti-CD44 antibody RG7356 was analysed. 89Zirconium-labelled RG7356 (1 mg; 37 MBq) was administered after a variable dose of unlabelled RG7356 (0 to 675 mg). Tracer uptake in normal tissues (liver, spleen, kidney, lung, bone marrow, brain and blood pool) was used to calculate the area under the time antibody concentration curve (AUC) and expressed as tissue-to-blood AUC ratios. Within the dose range of 1 to 450 mg, tissue-to-blood AUC ratios decreased from 10.6 to 0.75 ± 0.16 for the spleen, 7.5 to 0.86 ± 0.18 for the liver, 3.6 to 0.48 ± 0.13 for the bone marrow, 0.69 to 0.26 ± 0.1 for the lung and 1.29 to 0.56 ± 0.14 for the kidney, indicating dose-dependent uptake. In all patients receiving ≥ 450 mg (n = 7), tumour uptake of the antibody was observed.

CONCLUSIONS

This study demonstrates how immuno-PET in a dose escalation study provides a non-invasive technique to quantify dose-dependent uptake in normal tissues, indicating specific, target-mediated uptake.

Pharmacokinetics of cetuximab and tumor uptake of 89Zr-cetuximab as potential predictive biomarkers for benefit of cetuximab in patients with advanced colorectal cancer

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Background: One third of patients with RAS wild-type metastatic colorectal cancer (mCRC) do not benefit from anti-EGFR inhibitors. Thus, predictive biomarkers to identify patients with primary resistant mCRC are urgently needed. Methods: Patients with chemotherapy refractory mCRC received 500 mg/m2 cetuximab 2-weekly (NCT02117466 and NCT01691391). Patients underwent a 89Zr-cetuximab PET/CT 6 days post-injection after a therapeutic dose of cetuximab. In case of lack of tumor targeting on 89Zr-cetuximab PET, the cetuximab dose was escalated. Pharmacokinetic (PK) analyses included 89Zr-cetuximab plasma levels, EGFR saturation in skin, soluble EGFR (sEGFR), and tumor uptake and biodistribution on 89Zr-cetuximab PET. We defined treatment benefit as response or stable disease (according to RECIST v1.1) at 2 months. Results: Of the 44 patients, median age was 64 years, 25% had a right-sided primary tumor, 5 patients had a BRAF mutated (mt) tumor and 62% had treatment benefit. Cetuximab treatment dose was escalated to maximally 1250 mg/m2 in 8 patients. Visual and semiquantitative data of 89Zr-cetuximab uptake in the tumor, biodistribution and plasma activity 6 days post-injection were not correlated with treatment benefit. Although EGFR saturation in skin after 2 cycles cetuximab had a wide range (21 – 98%), saturation did not correlate with treatment benefit. On-treatment levels of sEGFR were higher than baseline (median 4.1 vs 2.0 ng/ml; p < 0.001), but levels and change of sEGFR did not correlate with PK or treatment efficacy. PFS and OS correlated with right-sided mCRC (p < 0.001 and p = 0.002 respectively) and the presence of a BRAF mt (p < 0.001 and p = 0.004 respectively). In a multivariate Cox-regression only BRAF mt remained correlated with PFS and OS (p = 0.003 and p = 0.027). Conclusions: Interpatient variances in PK and tumor uptake of 89Zr-cetuximab as performed in this setting do not predict treatment benefit of cetuximab in patients with mCRC. In contrast, BRAF status correlated with treatment benefit and warrants further research to confirm the predictive value. Clinical trial information: NCT02117466 and NCT01691391.

Whole body PD-1 and PD-L1 PET with 89Zr-nivolumab and 18F- BMS-986192 in pts with NSCLC

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Background: Tumor PD-L1 IHC relates moderately with treatment outcome following anti-PD-(L)1 monotherapy in pts with NSCLC. Aim: 1. To assess safety of the PET procedures. 2. To quantify PD-1 and PD-L1 expression in tumors with 89Zirconium-labeled nivolumab (89Zr-nivo) and 18F-labeled BMS-986192 (18F-PD-L1) PET. 3. To assess intra- and inter-patient tracer uptake differences in tumors. 4. To correlate PET results with IHC and treatment outcome. Methods: NSCLC pts eligible for treatment with nivolumab were included. Pts received a dynamic and static whole body 18F-PD-L1 and a static 89Zr-nivo PET scan. A baseline tumor biopsy was required and up to two additional biopsies were allowed in case PET showed heterogeneous tumor uptake. SUVpeak was calculated for all delineable tumor lesions and related to PD-(L)1 IHC (28.8 assay) and response after 6 wks of nivolumab treatment. Results: 7 pts (5 ≥1%, 2 ≥50% and 2 negative by PD-L1 IHC) were enrolled and 11 lesions analyzed. No toxicity related to radiotracer administration was identified. Tumor uptake of both tracers was visualized in all pts. There was substantial variability among pts for 18F-PD-L1 (mean SUV 5.4, range 2.2 - 14.4) and 89Zr-nivo (mean SUV 5.0, range 1.6 - 9.7). Intra-patient tracer uptake heterogeneity was also seen: mean 2.5-fold (±0.96) and 2.3-fold (±0.86) differences between lesions for 18F-PD-L1 and 89Zr-nivo SUV, respectively. For lesions with < 50% PD-L1 IHC mean 18F-PD-L1 SUV was 3.4 (±2.9) as compared to 7.1 (±6.0) for lesions with ≥50% PD-L1 IHC (p = 0.22). For lesions with low PD-1 expression mean 89Zr-nivo SUV was 6.9 (±2.7) as compared to 8.1 (±2.0) for lesions with high PD-1 expression (p = 0.44). Five pts were evaluable for response evaluation: 1 PR, 2 SD and 2 PD with 18F-PD-L1 SUV values (most PET avid lesion) of 14.4 (PR), 2.0 and 5.4 (SD) and 6.4 and 6.6 (PD). Conclusion: 1.PET-imaging with both tracers is safe and feasible, with good tumor-to-normal tissue contrast. 2. Tumor uptake demonstrated substantial heterogeneity among pts and among tumors within the same pts. 3. Although higher 18F-PD-L1 tumor uptake was seen in pts with ≥50% tumor PD-L1 IHC and the highest 18F-PD-L1 SUV was measured in the responding pt, the dataset is still very small. Clinical trial information: 2015-004760-11.

Change in metabolic tumor activity on 18F-FDG PET after a single dose of cetuximab to predict for treatment benefit, PFS, and OS in patients with advanced colorectal cancer

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Background: Despite RAS selection, one third of patients with metastatic RAS wild-type colorectal cancer (mCRC) do not benefit from anti-EGFR inhibitors. Therefore, an additional or more accurate predictive biomarker is needed to identify patients with primary resistant mCRC. Methods: In the IMPACT-CRC trial (NCT02117466) patients with chemotherapy refractory mCRC received 500 mg/m2 cetuximab every 2 weeks. Before the first dose and just before the second dose, patients underwent a 18F-FDG PET/CT (FDG PET). PET scans were quantitatively assessed by manual tumor delineation of ≤ 5 lesions, 2 per organ. Outcome is reported in total lesion glycolysis (TLG), defined as metabolic tumor volume times mean standard uptake value of the tumor. An optimal threshold to assess metabolic response was defined as decrease in TLG ≥15%. Quantitative data were correlated with CT evaluation after 8 weeks of treatment according to RECIST v1.1. Results: Out of 35 patients, 1 was excluded due to an infusion reaction. Median age was 64 years, 74% was male, 4 patients had a BRAF mutated tumor and 9 patients had right-sided primary tumors. 62% of patients had stable disease or partial response on CT after 8 weeks. At the time of this analysis, 88% of patients had progressive disease and 71% had died. Of the patients with right-sided tumors 11% had treatment benefit, compared to 80% in the left-sided group (p = 0.001). None of the 9 metabolic non-responders had treatment benefit, whereas 83% of the metabolic responders had treatment benefit according to RECIST v1.1. After adjustment for age, WHO score, BRAF mutation, sex and primary tumor site, FDG PET response remained correlated with PFS and OS (p = 0.002 and p = 0.014). Conclusions: Early evaluation of metabolic response after 1 dose of cetuximab is highly and independently predictive for treatment benefit with a 100% negative predictive value. Implementation of early FDG-PET evaluation in daily clinical practice can prevent unnecessary toxicity, costs of ineffective treatment and allows timely treatment adjustment for patients with mCRC undergoing anti-EGFR treatment. Clinical trial information: NCT02117466.

Human Dosimetry of the N-Methyl-d-Aspartate Receptor Ligand 11C-GMOM

The methylguanidine derivative ¹¹C-GMOM (¹¹C-labeled N-(2-chloro-3-thiomethylphenyl)-N'-(3-methoxyphenyl)-N'-methylguanidine) has been used successfully to quantify N-methyl-d-aspartate (NMDA) receptor binding in humans. The purpose of the present study was to estimate the ¹¹C-GMOM radiation dose in healthy humans. Methods: After ¹¹C-GMOM injection, 3 female and 2 male subjects underwent 10 consecutive whole-body PET scans in approximately 77 min. Seven source organs were defined manually, scaled to a sex-specific reference, and residence times were calculated for input into OLINDA/EXM software. Accepted tissue-weighting factors were used to calculate the effective dose. Results: The mean absorbed radiation doses in source organs ranged from 7.7 μGy·MBq^-1 in the brain to 12.7 μGy·MBq^-1 in the spleen. The effective dose (±SD) was 4.5 ± 0.5 μSv·MBq^-1Conclusion: The effective dose of ¹¹C-GMOM is at the lower end of the range seen for other ¹¹C-labeled ligands, allowing for serial PET scanning in a single subject.

Performance of 89Zr-Labeled-Rituximab-PET as an Imaging Biomarker to Assess CD20 Targeting: A Pilot Study in Patients with Relapsed/Refractory Diffuse Large B Cell Lymphoma

Purpose

Treatment of patients with diffuse large B cell lymphoma (DLBCL) includes rituximab, an anti-CD20 monoclonal antibody (mAb). Insufficient tumor targeting might cause therapy failure. Tumor uptake of ⁸⁹Zirconium (⁸⁹Zr)-mAb is a potential imaging biomarker for tumor targeting, since it depends on target antigen expression and accessibility. The aim of this pilot study was to describe the performance of ⁸⁹Zr-labeled-rituximab-PET to assess CD20 targeting in patients with relapsed/refractory DLBCL.

Methods

Six patients with biopsy-proven DLBCL were included. CD20 expression was assessed using immunohistochemistry (IHC). 74 MBq ⁸⁹Zr-rituximab (10 mg) was administered after the therapeutic dose of rituximab. Immuno-PET scans on day 0, 3 and 6 post injection (D0, D3 and D6 respectively) were visually assessed and quantified for tumor uptake.

Results

Tumor uptake of ⁸⁹Zr-rituximab and CD20 expression were concordant in 5 patients: for one patient, both were negative, for the other four patients visible tumor uptake was concordant with CD20-positive biopsies. Intense tumor uptake of ⁸⁹Zr-rituximab on PET (SUV_peak = 12.8) corresponded with uniformly positive CD20 expression on IHC in one patient. Moderate tumor uptake of ⁸⁹Zr-rituximab (range SUV_peak = 3.2–5.4) corresponded with positive CD20 expression on IHC in three patients. In one patient tumor uptake of ⁸⁹Zr-rituximab was observed (SUV_peak = 3.8), while the biopsy was CD20-negative.

Conclusions

This study suggests a positive correlation between tumor uptake of ⁸⁹Zr-rituximab and CD20 expression in tumor biopsies, but further studies are needed to confirm this. This result supports the potential of ⁸⁹Zr-rituximab-PET as an imaging biomarker for CD20 targeting. For clinical application of ⁸⁹Zr-rituximab-PET to guide individualized treatment, further studies are required to assess whether tumor targeting is related to clinical benefit of rituximab treatment in individual patients.

Myocardial denervation coincides with scar heterogeneity in ischemic cardiomyopathy: A PET and CMR study

BACKGROUND

Mismatch between myocardial innervation and perfusion assessed with positron emission tomography (PET) is a potential risk marker for ventricular arrhythmias in patients with ischemic cardiomyopathy. This mismatch zone originates from residual viable myocardium that has sustained ischemic nerve injury. Heterogenic scar size assessed with late gadolinium-enhanced (LGE) cardiac magnetic resonance imaging (CMR) is also a risk marker of ventricular arrhythmias. These two imaging parameters may represent identical morphological tissue features. The current study explored the relation between innervation-perfusion mismatch and heterogenic scar size.

METHODS

Twenty-eight patients (26 males, age 67 ± 8 years) with ischemic cardiomyopathy and a left ventricular ejection fraction below 35%, eligible for ICD implantation were included. All patients underwent both [11C]-hydroxyephedrine and [15O]-water PET studies to assess myocardial sympathetic innervation and perfusion. LGE CMR was conducted to assess total myocardial scar size, scar core size, and heterogenic scar size.

RESULTS

Perfusion defect size was 16.6 ± 9.9% and innervation defect size was 33.7 ± 10.8%, which resulted in an innervation-perfusion mismatch of 17.6 ± 8.9%. Total scar size, scar core size, and heterogenic scar size were 21.2 ± 8.6%, 14.7 ± 6.6%, and 6.5 ± 2.9%, respectively. No relation between scar core size and perfusion deficit size was observed (r = 0.18, P = .36). Total scar size was correlated with the innervation defect size (r = 0.52, P = .004) and the heterogenic scar zone displayed a significant correlation with the innervation-perfusion mismatch area (r = 0.67, P < .001).

CONCLUSIONS

Denerved residual viable myocardium in ischemic cardiomyopathy as observed with innervation-perfusion PET is related to the heterogenic scar zone as assessed with LGE CMR.

Molecular Drug Imaging: 89Zr-Bevacizumab PET in Children with Diffuse Intrinsic Pontine Glioma

Predictive tools for guiding therapy in children with brain tumors are urgently needed. In this first molecular drug imaging study in children, we investigated whether bevacizumab can reach tumors in children with diffuse intrinsic pontine glioma (DIPG) by measuring the tumor uptake of ⁸⁹Zr-labeled bevacizumab by PET. In addition, we evaluated the safety of the procedure in children and determined the optimal time for imaging. Methods: Patients received ⁸⁹Zr-bevacizumab (0.1 mg/kg; 0.9 MBq/kg) at least 2 wk after completing radiotherapy. Whole-body PET/CT scans were obtained 1, 72, and 144 h after injection. All patients underwent contrast (gadolinium)-enhanced MRI. The biodistribution of ⁸⁹Zr-bevacizumab was quantified as SUVs. Results: Seven DIPG patients (4 boys; 6-17 y old) were scanned without anesthesia. No adverse events occurred. Five of 7 primary tumors showed focal ⁸⁹Zr-bevacizumab uptake (SUVs at 144 h after injection were 1.0-6.7), whereas no significant uptake was seen in the healthy brain. In 1 patient, multiple metastases all showed positive PET results. We observed inter- and intratumoral heterogeneity of uptake, and ⁸⁹Zr-bevacizumab uptake was present predominantly (in 4/5 patients) within MRI contrast-enhanced areas, although ⁸⁹Zr-bevacizumab uptake in these areas was variable. Tumor targeting results were quantitatively similar at 72 and 144 h after injection, but tumor-to-blood-pool SUV ratios increased with time after injection (P = 0.045). The mean effective dose per patient was 0.9 mSv/MBq (SD, 0.3 mSv/MBq). Conclusion:⁸⁹Zr-bevacizumab PET studies are feasible in children with DIPG. The data suggest considerable heterogeneity in drug delivery among patients and within DIPG tumors and a positive, but not 1:1, correlation between MRI contrast enhancement and ⁸⁹Zr-bevacizumab uptake. The optimal time for scanning is 144 h after injection. Tumor ⁸⁹Zr-bevacizumab accumulation assessed by PET scanning may help in the selection of patients with the greatest chance of benefit from bevacizumab treatment.

89Zr-cetuximab PET imaging in patients with advanced colorectal cancer

Monoclonal antibodies (mAbs) against the epidermal growth factor receptor (EGFR) are used in the treatment of advanced colorectal cancer (mCRC). Approximately 50% of patients benefit despite patient selection for RAS wild type (wt) tumors. Based on the hypothesis that tumor targeting is required for clinical benefit of anti-EGFR treatment, biodistribution and tumor uptake of (89)Zr-cetuximab by Positron Emission Tomography (PET), combining the sensitivity of PET with the specificity of cetuximab for EGFR was evaluated. Ten patients with wt K-RAS mCRC received 37 ± 1 MBq (89)Zr-cetuximab directly (<2 h) after the first therapeutic dose of cetuximab. PET-scans were performed from 1 hour to 10 days post injection (p.i.). Biodistribution was determined for blood and organs. Uptake in tumor lesions was quantified by Standardized Uptake Value (SUV) and related to response. In 6 of 10 patients (89)Zr-cetuximab uptake in tumor lesions was detected. Four of 6 patients with (89)Zr-cetuximab uptake had clinical benefit, while progressive disease was observed in 3 of 4 patients without (89)Zr-cetuximab uptake. Taken together, tumor uptake of 89Zr-cetuximab can be visualized by PET imaging. The strong relation between uptake and response warrants further clinical validation as an innovative selection method for cetuximab treatment in patients with wt RAS mCRC.

Impact of New Scatter Correction Strategies on High-Resolution Research Tomograph Brain PET Studies

PURPOSE

The aim of this study is to evaluate the impact of different scatter correction strategies on quantification of high-resolution research tomograph (HRRT) data for three tracers covering a wide range in kinetic profiles.

PROCEDURES

Healthy subjects received dynamic HRRT scans using either (R)-[(11)C]verapamil (n = 5), [(11)C]raclopride (n = 5) or [(11)C]flumazenil (n = 5). To reduce the effects of patient motion on scatter scaling factors, a margin in the attenuation correction factor (ACF) sinogram was applied prior to 2D or 3D single scatter simulation (SSS).

RESULTS

Some (R)-[(11)C]verapamil studies showed prominent artefacts that disappeared with an ACF-margin of 10 mm or more. Use of 3D SSS for (R)-[(11)C]verapamil showed a statistically significant increase in volume of distribution compared with 2D SSS (p < 0.05), but not for [(11)C]raclopride and [(11)C]flumazenil studies (p > 0.05).

CONCLUSIONS

When there is a patient motion-induced mismatch between transmission and emission scans, applying an ACF-margin resulted in more reliable scatter scaling factors but did not change (and/or deteriorate) quantification.

An automatic delineation method for bone marrow absorbed dose estimation in (89)Zr PET/CT studies

Background

The study aims to develop and validate an automatic delineation method for estimating red bone marrow (RM) activity concentration and absorbed dose in ⁸⁹Zr positron emission tomography/computed tomography (PET/CT) studies. Five patients with advanced colorectal cancer received 37.1 ± 0.9 MBq [⁸⁹Zr] cetuximab within 2 h after administration of a therapeutic dose of 500 mg m⁻² unlabelled cetuximab. Per patient, five PET/CT scans were acquired on a Gemini TF-64 PET/CT scanner at 1, 24, 48, 96 and 144 h post injection. Low dose CT data were used to manually generate volumes of interest (VOI) in the lumbar vertebrae (LV). In addition, LV VOI were generated automatically using an active contour method in a low dose CT. RM activity was then determined by mapping the low dose CT-derived RM VOI onto the corresponding PET scans. Finally, these activities were used to derive residence times and, subsequently, the self and total RM absorbed doses using OLINDA/EXM 1.1.

Results

High correlations (r² > 0.85) between manual and automated VOI methods were obtained for both RM activity concentrations and total absorbed doses. On average, the automatic method provided values that were lower than 5 % compared to the manual method.

Conclusions

An automated and efficient VOI method, based on an active contour approach, was developed, enabling accurate estimates of RM activity concentrations and total absorbed doses.

Electronic supplementary material

The online version of this article (doi:10.1186/s40658-016-0149-0) contains supplementary material, which is available to authorized users.

Noninvasive Quantification of Myocardial 11C-Meta-Hydroxyephedrine Kinetics

(11)C-meta-hydroxyephedrine ((11)C-HED) kinetics in the myocardium can be quantified using a single-tissue-compartment model together with a metabolite-corrected arterial blood sampler input function (BSIF). The need for arterial blood sampling, however, limits clinical applicability. The purpose of this study was to investigate the feasibility of replacing arterial sampling with imaging-derived input function (IDIF) and venous blood samples.

METHODS

Twenty patients underwent 60-min dynamic (11)C-HED PET/CT scans with online arterial blood sampling. Thirteen of these patients also underwent venous blood sampling. Data were reconstructed using both 3-dimensional row-action maximum-likelihood algorithm (3DR) and a time-of-flight (TF) list-mode reconstruction algorithm. For each reconstruction, IDIF results were compared with BSIF results. In addition, IDIF results obtained with venous blood samples and with a transformed venous-to-arterial metabolite correction were compared with results obtained with arterial metabolite corrections.

RESULTS

Correlations between IDIF- and BSIF-derived K1 and VT were high (r(2) > =0.89 for 3DR and TF). Slopes of the linear fits were significantly different from 1 for K1, for both 3DR (slope = 0.94) and TF (slope = 1.06). For VT, the slope of the linear fit was different from 1 for TF (slope = 0.93) but not for 3DR (slope = 0.98). Use of venous blood data introduced a large bias in VT (r(2) = 0.96, slope = 0.84) and a small bias in K1 (r(2) = 0.99, slope = 0.98). Use of a second-order polynomial venous-to-arterial transformation was robust and greatly reduced bias in VT (r(2) = 0.97, slope = 0.99) with no effect on K1 CONCLUSION: IDIF yielded precise results for both 3DR and TF. Venous blood samples can be used for absolute quantification of (11)C-HED studies, provided a venous-to-arterial transformation is applied. A venous-to-arterial transformation enables noninvasive, absolute quantification of (11)C-HED studies.

Immuno-Positron Emission Tomography with Zirconium-89-Labeled Monoclonal Antibodies in Oncology: What Can We Learn from Initial Clinical Trials?

Selection of the right drug for the right patient is a promising approach to increase clinical benefit of targeted therapy with monoclonal antibodies (mAbs). Assessment of in vivo biodistribution and tumor targeting of mAbs to predict toxicity and efficacy is expected to guide individualized treatment and drug development. Molecular imaging with positron emission tomography (PET) using zirconium-89 (⁸⁹Zr)-labeled monoclonal antibodies also known as ⁸⁹Zr-immuno-PET, visualizes and quantifies uptake of radiolabeled mAbs. This technique provides a potential imaging biomarker to assess target expression, as well as tumor targeting of mAbs. In this review we summarize results from initial clinical trials with ⁸⁹Zr-immuno-PET in oncology and discuss technical aspects of trial design. In clinical trials with ⁸⁹Zr-immuno-PET two requirements should be met for each ⁸⁹Zr-labeled mAb to realize its full potential. One requirement is that the biodistribution of the ⁸⁹Zr-labeled mAb (imaging dose) reflects the biodistribution of the drug during treatment (therapeutic dose). Another requirement is that tumor uptake of ⁸⁹Zr-mAb on PET is primarily driven by specific, antigen-mediated, tumor targeting. Initial trials have contributed toward the development of ⁸⁹Zr-immuno-PET as an imaging biomarker by showing correlation between uptake of ⁸⁹Zr-labeled mAbs on PET and target expression levels in biopsies. These results indicate that ⁸⁹Zr-immuno-PET reflects specific, antigen-mediated binding. ⁸⁹Zr-immuno-PET was shown to predict toxicity of RIT, but thus far results indicating that toxicity of mAbs or mAb-drug conjugate treatment can be predicted are lacking. So far, one study has shown that molecular imaging combined with early response assessment is able to predict response to treatment with the antibody-drug conjugate trastuzumab-emtansine, in patients with human epithelial growth factor-2 (HER2)-positive breast cancer. Future studies would benefit from a standardized criterion to define positive tumor uptake, possibly supported by quantitative analysis, and validated by linking imaging data with corresponding clinical outcome. Taken together, these results encourage further studies to develop ⁸⁹Zr-immuno-PET as a predictive imaging biomarker to guide individualized treatment, as well as for potential application in drug development.

Calibration of PET/CT scanners for multicenter studies on differentiated thyroid cancer with (124)I

BACKGROUND

Studies on imaging of differentiated thyroid cancer (DTC) using (124)I often require a multicenter approach, as the prevalence of DTC is low. Calibration of participating scanners is required to obtain comparable quantification. As determination of a well-defined range of recovery coefficients is complicated for various reasons, a simpler approach based on the assumption that the iodine uptake is highly focal with a background that significantly lacks radioactivity might be more efficient. For each scanner, a linear conversion between known and observed activity can be derived, allowing quantification that can be traced to a common source for all scanners within one study-protocol. The aim of this paper is to outline a procedure using this approach in order to set up a multicenter calibration of PET/CT scanners for (124)I.

METHODS

A cylindrical polyethylene phantom contained six 2-ml vials with reference activities of ~2, 10, 20, 100, 400, and 2000 kBq, produced by dilution from a known activity. The phantom was scanned twice on PET/CT scanners of participating centers within 1 week. For each scanner, the best proportional and linear fit between measured and known activities were derived and based on statistical analyses of the results of all scanners; it was determined which fit should be applied. In addition, a Bland-Altman analysis was done on calibrated activities with respect to reference activities to asses the relative precision of the scanners.

RESULTS

Nine Philips (vendor A) and nine Siemens (vendor B) PET/CT scanners were calibrated in a time period of 3 days before and after the reference time. No significant differences were detected between the two subsequent scans on any scanner. Six fitted intercepts of vendor A were significantly different from zero, so the linear model was used. Intercepts ranged from -8 to 26 kBq and slopes ranged from 0.80 to 0.98. Bland-Altman analysis of calibrated and reference activities showed that the relative error of calibrated activities was smaller than that of uncalibrated activities.

CONCLUSIONS

A simplified multicenter calibration procedure for PET/CT scans that show highly focal uptake and negligible background is feasible and results in more precise quantification. Our procedure can be used in multicenter (124)I PET scans focusing on (recurrent) DTC.

Non-invasive imaging to identify susceptibility for ventricular arrhythmias in ischaemic left ventricular dysfunction

OBJECTIVE

Non-invasive imaging of myocardial perfusion, sympathetic denervation and scar size contribute to enhanced risk prediction of ventricular arrhythmias (VA). Some of these imaging parameters, however, may be intertwined as they are based on similar pathophysiology. The aim of this study was to assess the predictive role of myocardial perfusion, sympathetic denervation and scar size on the inducibility of VA in patients with ischaemic cardiomyopathy in a head-to-head fashion.

METHODS

52 patients with ischaemic heart disease and left ventricular ejection fraction (LVEF) ≤35%, referred for primary prevention implantable cardioverter-defibrillator (ICD) implantation, were included. Late gadolinium-enhanced cardiovascular MRI was performed to assess LV volumes, function and scar size. Using [(15)O]H2O and [(11)C]hydroxyephedrine positron emission tomography, both resting and hyperaemic myocardial blood flow (MBF), and sympathetic innervation were assessed. After ICD implantation, an electrophysiological study (EPS) was performed and was considered positive in case of sustained VA.

RESULTS

Patients with a positive EPS (n=25) showed more severely impaired global hyperaemic MBF (p=0.003), larger sympathetic denervation size (p=0.048) and tended to have larger scar size (p=0.07) and perfusion defect size (p=0.06) compared with EPS-negative patients (n=27). No differences were observed in LV volumes, LVEF and innervation-perfusion mismatch size. Multivariable analysis revealed that impaired hyperaemic MBF was the single best independent predictor for VA inducibility (OR 0.78, 95% CI 0.65 to 0.94, p=0.007). A combination of risk markers did not yield incremental predictive value over hyperaemic MBF alone.

CONCLUSIONS

Of all previously validated approaches to evaluate the arrhythmic substrate, global impaired hyperaemic MBF was the only independent predictor of VA inducibility. Moreover, a combined approach of different imaging variables did not have incremental value.

Comparison of HRRT and HR+ scanners for quantitative (R)-[11C]verapamil, [11C]raclopride and [11C]flumazenil brain studies

PURPOSE

This study was conducted to directly compare the high-resolution research tomograph (HRRT) (high-resolution brain) and HR+ (standard whole-body) positron emission tomography (PET) only scanners for quantitative brain studies using three tracers with vastly different tracer distributions.

PROCEDURES

Healthy volunteers underwent successive scans on HR+ and HRRT scanners (in random order) using either (R)-[(11)C]verapamil (n = 6), [(11)C]raclopride (n = 7) or [(11)C]flumazenil (n = 7). For all tracers, metabolite-corrected plasma-input functions were generated.

RESULTS

After resolution matching, HRRT-derived kinetic parameter values correlated well with those of HR+ for all tracers (intraclass correlation coefficients ≥0.78), having a good absolute interscanner test-retest variability (≤15 %). However, systematic differences can be seen for HRRT-derived kinetic parameter values (range -13 to +15 %).

CONCLUSION

Quantification of kinetic parameters based on plasma-input models leads to comparable results when spatial resolution between HRRT and HR+ data is matched. When using reference-tissue models, differences remain that are likely caused by differences in attenuation and scatter corrections and/or image reconstruction.