Impact of 18F-fluciclovine PET/CT on salvage radiotherapy plans for men with recurrence of prostate cancer postradical prostatectomy.

OBJECTIVES: Imaging options to localize biochemical recurrence (BCR) of prostate cancer after radical prostatectomy (RP) are limited, especially at low prostate-specific antigen (PSA) levels. The FALCON study evaluated the impact of 18F-fluciclovine PET/CT on management plans for patients with BCR. Here, we evaluate salvage radiotherapy decisions in patients post-RP. METHODS: We conducted a subgroup analysis of post-RP patients enrolled in FALCON who had a prescan plan for salvage radiotherapy (± androgen-deprivation therapy). Patients' treatment plans post-18F-fluciclovine PET/CT were compared with their prescan plans. Fisher exact test was used to determine the impact of PSA and Gleason sum on positivity and anatomical patterns of uptake. RESULTS: Sixty-five (63%) FALCON patients had undergone RP. Of these, 62 (median PSA, 0.32 ng/mL) had a prescan plan for salvage radiotherapy. Twenty-one (34%) had 18F-fluciclovine-avid lesions. Disease was confined to the prostate bed in 11 patients (52%) and to the pelvis in a further 5 (24%), while 5 (24%) had extrapelvic findings. Trends towards more disseminated disease with increasing PSA or Gleason sum were observed but did not reach statistical significance. Postscan, 25 (40%) patients had a management change; 17 (68%) were changed to the treatment modality (8 to systemic therapy, 8 to active surveillance, 1 other) and 8 (32%) were radiotherapy field modifications. CONCLUSIONS: Incorporating 18F-fluciclovine PET/CT into treatment planning may help identify patients suitable for salvage radiotherapy, help augment planned radiotherapy to better target lesions and support the clinician to optimise patient management.

Mitochondrial Inhibitor Atovaquone Increases Tumor Oxygenation and Inhibits Hypoxic Gene Expression in Patients with Non-Small Cell Lung Cancer.

PURPOSE: Tumor hypoxia fuels an aggressive tumor phenotype and confers resistance to anticancer treatments. We conducted a clinical trial to determine whether the antimalarial drug atovaquone, a known mitochondrial inhibitor, reduces hypoxia in non-small cell lung cancer (NSCLC). PATIENTS AND METHODS: Patients with NSCLC scheduled for surgery were recruited sequentially into two cohorts: cohort 1 received oral atovaquone at the standard clinical dose of 750 mg twice daily, while cohort 2 did not. Primary imaging endpoint was change in tumor hypoxic volume (HV) measured by hypoxia PET-CT. Intercohort comparison of hypoxia gene expression signatures using RNA sequencing from resected tumors was performed. RESULTS: Thirty patients were evaluable for hypoxia PET-CT analysis, 15 per cohort. Median treatment duration was 12 days. Eleven (73.3%) atovaquone-treated patients had meaningful HV reduction, with median change -28% [95% confidence interval (CI), -58.2 to -4.4]. In contrast, median change in untreated patients was +15.5% (95% CI, -6.5 to 35.5). Linear regression estimated the expected mean HV was 55% (95% CI, 24%-74%) lower in cohort 1 compared with cohort 2 (P = 0.004), adjusting for cohort, tumor volume, and baseline HV. A key pharmacodynamics endpoint was reduction in hypoxia-regulated genes, which were significantly downregulated in atovaquone-treated tumors. Data from multiple additional measures of tumor hypoxia and perfusion are presented. No atovaquone-related adverse events were reported. CONCLUSIONS: This is the first clinical evidence that targeting tumor mitochondrial metabolism can reduce hypoxia and produce relevant antitumor effects at the mRNA level. Repurposing atovaquone for this purpose may improve treatment outcomes for NSCLC.

Prostate cancer recurrence in patients with negative or equivocal conventional imaging: A role for 18F-fluciclovine-PET/CT in delineating sites of recurrence and identifying patients with oligometastatic disease.

INTRODUCTION: Despite improvements in overall survival, biochemical recurrence of prostate cancer, characterized by rising prostate-specific antigen (PSA) levels after curative intent primary therapy, remains common. With the advent of highly sensitive molecular imaging, men with limited metastatic disease burden, or oligometastatic prostate cancer, are increasingly being identified. The LOCATE trial (NCT02680041) assessed the impact of positron emission tomography (PET) with 18F-fluciclovine on management of men with prostate cancer recurrence after curative intent primary therapy and negative/equivocal conventional imaging. Here, we use LOCATE data to characterize the sites of disease recurrence and explore the potential for 18F-fluciclovine-PET/CT to evaluate oligometastatic disease. METHODS: Eligible men (≥18 years; prior curative intent treatment of prostate cancer; recurrence based on rising PSA; negative/equivocal conventional imaging) underwent 18F-fluciclovine-PET/CT according to standard protocols. The primary outcome measure of the LOCATE trial was a revised management plan post-scan. We performed a secondary analysis of the LOCATE imaging data to characterize anatomical sites of disease recurrence and to explore the potential for 18F-fluciclovine-PET/CT to evaluate oligometastatic disease. Imaging results were stratified by baseline PSA levels and prior treatment(s) and the Fisher exact test used to analyze differences between groups. Oligometastatic disease was defined as 1-5 extraprostatic lesions (≤3 lesions in any single organ system) plus negative prostate/bed imaging (as a surrogate for primary tumor control). RESULTS: Of 213 enrolled patients, 164 (77%) had undergone prostatectomy as their initial treatment; their median PSA was 0.57ng/ml. For the 49 patients with an intact prostate, the median PSA was 5.5ng/ml. The overall 18F-fluciclovine-PET/CT detection rate was 57%. Detection rates were 84% in men with intact prostates and 49% in those who had undergone prostatectomy, with the difference being attributable to prostate/bed findings (71% vs. 18%, respectively). The detection rate in lymph nodes was 29% and in bone was 11%. In total, 53/213 (25%) had oligometastatic disease. Twenty (38%) oligometastatic patients had PSA ≤1.0 ng/ml. Forty-two (79%) experienced a change to their management plan following the scan, commonly to target a lesion identified by 18F-fluciclovine-PET/CT. The majority of management changes (74%) involved a new treatment modality; however, 10 patients (24%) experienced a modification of the existing plan for radiotherapy to incorporate a boost to an area guided by the 18F-fluciclovine-PET/CT results. CONCLUSION: Even at low PSA levels, 18F-fluciclovine-PET/CT identified a diverse pattern of recurrence missed with conventional imaging. One-quarter of men had oligometastatic disease, raising the potential for 18F-fluciclovine-PET/CT to guide targeted treatment of oligometastases.

18F-Fluciclovine Positron Emission Tomography in Men With Biochemical Recurrence of Prostate Cancer After Radical Prostatectomy and Planning to Undergo Salvage Radiation Therapy: Results from LOCATE.

PURPOSE: Conventional imaging rarely localizes the site(s) of prostate cancer recurrence in patients undergoing evaluation for salvage radiation therapy (sRT) after radical prostatectomy (RP). LOCATE (NCT02680041) was a prospective, multicenter study investigating the impact of 18F-fluciclovine positron emission tomography and computed tomography (PET/CT) on the management of patients with biochemical recurrence of prostate cancer after curative-intent radiation or RP and negative or equivocal conventional imaging. Our objective was to determine the impact of 18F-fluciclovine PET/CT on treatment decisions for men planning to undergo sRT for biochemical recurrence post-RP. METHODS AND MATERIALS: We conducted a subgroup analysis of post-RP patients enrolled in LOCATE who were planning to undergo sRT with or without hormonal therapy based on prescan documentation. 18F-Fluciclovine PET/CT was performed according to standardized procedures. The treatment plan postscan was compared with the prescan plan, and Fisher exact test was used to determine the impact of prescan prostate-specific antigen (PSA) and Gleason sum (GS) on positivity and anatomic patterns of uptake. RESULTS: A total of 114 patients (median prescan PSA 0.42 [interquartile range, 0.3-1.1] ng/mL) met selection criteria (54% of patients in LOCATE). Forty-eight (42%) had 18F-fluciclovine-avid lesions. Twelve patients (11%) had positive findings only in the prostate bed, 24 (21%) had positivity only in the pelvis (prostate bed or pelvic nodes), and 24 (21%) had extrapelvic findings. PSA >0.5 ng/mL and GS ≥8 were associated with a higher risk of extrapelvic positivity (P < .05). Postscan, 55 (48%) patients had a management change; 37 (32%) had a change in overall treatment approach (ie, omission of sRT); and 18 (16%) had sRT target modification. CONCLUSIONS: 18F-Fluciclovine PET/CT is positive in nearly half of patients planning to undergo post-RP sRT with negative/equivocal conventional imaging, with findings frequently leading to changes in management. PSA >0.5 ng/mL and GS ≥8 are associated with a higher risk of extrapelvic positive findings.

Effect of 18F-Fluciclovine Positron Emission Tomography on the Management of Patients With Recurrence of Prostate Cancer: Results From the FALCON Trial.

PURPOSE: Early and accurate localization of lesions in patients with biochemical recurrence (BCR) of prostate cancer may guide salvage therapy decisions. The present study, 18F-Fluciclovine PET/CT in biochemicAL reCurrence Of Prostate caNcer (FALCON; NCT02578940), aimed to evaluate the effect of 18F-fluciclovine on management of men with BCR of prostate cancer. METHODS AND MATERIALS: Men with a first episode of BCR after curative-intent primary therapy were enrolled at 6 UK sites. Patients underwent 18F-fluciclovine positron emission tomography/computed tomography (PET/CT) according to standardized procedures. Clinicians documented management plans before and after scanning, recording changes to treatment modality as major and changes within a modality as other. The primary outcome measure was record of a revised management plan postscan. Secondary endpoints were evaluation of optimal prostate specific antigen (PSA) threshold for detection, salvage treatment outcome assessment based on 18F-fluciclovine-involvement, and safety. RESULTS: 18F-Fluciclovine was well tolerated in the 104 scanned patients (median PSA = 0.79 ng/mL). Lesions were detected in 58 out of 104 (56%) patients. Detection was broadly proportional to PSA level; ≤1 ng/mL, 1 out of 3 of scans were positive, and 93% scans were positive at PSA >2.0 ng/mL. Sixty-six (64%) patients had a postscan management change (80% after a positive result). Major changes (43 out of 66; 65%) were salvage or systemic therapy to watchful waiting (16 out of 66; 24%); salvage therapy to systemic therapy (16 out of 66; 24%); and alternative changes to treatment modality (11 out of 66, 17%). The remaining 23 out of 66 (35%) management changes were modifications of the prescan plan: most (22 out of 66; 33%) were adjustments to planned brachytherapy/radiation therapy to include a 18F-fluciclovine-guided boost. Where 18F-fluciclovine guided salvage therapy, the PSA response rate was higher than when 18F-fluciclovine was not involved (15 out of 17 [88%] vs 28 out of 39 [72%]). CONCLUSIONS: 18F-Fluciclovine PET/CT located recurrence in the majority of men with BCR, frequently resulting in major management plan changes. Incorporating 18F-fluciclovine PET/CT into treatment planning may optimize targeting of recurrence sites and avoid futile salvage therapy.

[18F]Fluciclovine PET/CT: joint EANM and SNMMI procedure guideline for prostate cancer imaging-version 1.0.

The aim of this guideline is to provide standards for the recommendation, performance, interpretation, and reporting of [18F]Fluciclovine PET/CT for prostate cancer imaging. These recommendations will help to improve accuracy, precision, and repeatability of [18F]Fluciclovine PET/CT for prostate cancer essentially needed for implementation of this modality in science and routine clinical practice.

Quantitative and Qualitative Analyses of Biodistribution and PET Image Quality of a Novel Radiohybrid PSMA, 18F-rhPSMA-7, in Patients with Prostate Cancer.

Radiohybrid PSMA (rhPSMA) ligands, a new class of theranostic prostate-specific membrane antigen (PSMA)-targeting agents, feature fast 18F synthesis and utility for labeling with radiometals. Here, we assessed the biodistribution and image quality of 18F-rhPSMA-7 to determine the best imaging time point for patients with prostate cancer. Methods: In total, 202 prostate cancer patients who underwent a clinically indicated 18F-rhPSMA-7 PET/CT were retrospectively analyzed, and 12 groups based on the administered activity and uptake time of PET scanning were created: 3 administered activities (low, 222-296 MBq; moderate, 297-370 MBq; and high, 371-444 MBq) and 4 uptake time points (short, 50-70 min; intermediate, 71-90 min; long, 91-110 min; and extra long, ≥111 min). For quantitative analyses, SUVmean and organ- or tumor-to-background ratio were determined for background, healthy organs, and 3 representative tumor lesions. Qualitative analyses assessed overall image quality, nonspecific blood-pool activity, and background uptake in bone or marrow using 3- or 4-point scales. Results: In quantitative analyses, SUVmean showed a significant decrease in the blood pool and lungs and an increase in the kidneys, bladder, and bones as the uptake time increased. SUVmean showed a trend to increase in the blood pool and bones as the administered activity increased. However, no significant differences were found in 377 tumor lesions with respect to the administered activity or uptake time. In qualitative analyses, the overall image quality was stable along with the uptake time, but the proportion rated to have good image quality decreased as the administered activity increased. All other qualitative image parameters showed no significant differences for the administered activities, but they showed significant trends with increasing uptake time: less nonspecific blood activity, more frequent background uptake in the bone marrow, and increased negative impact on clinical decision making. Conclusion: The biodistribution of 18F-rhPSMA-7 was similar to that of established PSMA ligands, and tumor uptake of 18F-rhPSMA-7 was stable across the administered activities and uptake times. An early imaging time point (50-70 min) is recommended for 18F-rhPSMA-7 PET/CT to achieve the highest overall image quality.

Hypoxia-induced switch in SNAT2/SLC38A2 regulation generates endocrine resistance in breast cancer.

Tumor hypoxia is associated with poor patient outcomes in estrogen receptor-α-positive (ERα+) breast cancer. Hypoxia is known to affect tumor growth by reprogramming metabolism and regulating amino acid (AA) uptake. Here, we show that the glutamine transporter, SNAT2, is the AA transporter most frequently induced by hypoxia in breast cancer, and is regulated by hypoxia both in vitro and in vivo in xenografts. SNAT2 induction in MCF7 cells was also regulated by ERα, but it became predominantly a hypoxia-inducible factor 1α (HIF-1α)-dependent gene under hypoxia. Relevant to this, binding sites for both HIF-1α and ERα overlap in SNAT2's cis-regulatory elements. In addition, the down-regulation of SNAT2 by the ER antagonist fulvestrant was reverted in hypoxia. Overexpression of SNAT2 in vitro to recapitulate the levels induced by hypoxia caused enhanced growth, particularly after ERα inhibition, in hypoxia, or when glutamine levels were low. SNAT2 up-regulation in vivo caused complete resistance to antiestrogen and, partially, anti-VEGF therapies. Finally, high SNAT2 expression levels correlated with hypoxia profiles and worse outcome in patients given antiestrogen therapies. Our findings show a switch in the regulation of SNAT2 between ERα and HIF-1α, leading to endocrine resistance in hypoxia. Development of drugs targeting SNAT2 may be of value for a subset of hormone-resistant breast cancer.

Integrated Pharmacodynamic Analysis Identifies Two Metabolic Adaption Pathways to Metformin in Breast Cancer.

Late-phase clinical trials investigating metformin as a cancer therapy are underway. However, there remains controversy as to the mode of action of metformin in tumors at clinical doses. We conducted a clinical study integrating measurement of markers of systemic metabolism, dynamic FDG-PET-CT, transcriptomics, and metabolomics at paired time points to profile the bioactivity of metformin in primary breast cancer. We show metformin reduces the levels of mitochondrial metabolites, activates multiple mitochondrial metabolic pathways, and increases 18-FDG flux in tumors. Two tumor groups are identified with distinct metabolic responses, an OXPHOS transcriptional response (OTR) group for which there is an increase in OXPHOS gene transcription and an FDG response group with increased 18-FDG uptake. Increase in proliferation, as measured by a validated proliferation signature, suggested that patients in the OTR group were resistant to metformin treatment. We conclude that mitochondrial response to metformin in primary breast cancer may define anti-tumor effect.

Bayesian penalised likelihood reconstruction (Q.Clear) of 18F-fluciclovine PET for imaging of recurrent prostate cancer: semi-quantitative and clinical evaluation.

OBJECTIVE: 18F-Fluciclovine (FACBC) is an amino acid PET radiotracer approved for recurrent prostate cancer imaging. We investigate the use of Bayesian penalised likelihood (BPL) reconstruction for 18F-fluciclovine PET. METHODS: 15 18F-fluciclovine scans were reconstructed using ordered subset expectation maximisation (OSEM), OSEM + point spread function (PSF) modelling and BPL using ß-values 100-600. Lesion maximum standardised uptake value (SUVmax), organ SUVmean and standard deviation were measured. Deidentified reconstructions (OSEM, PSF, BPL using ß200-600) from 10 cases were visually analysed by two readers who indicated their most and least preferred reconstructions, and scored overall image quality, noise level, background marrow image quality and lesion conspicuity. RESULTS: Comparing BPL to OSEM, there were significant increments in lesion SUVmax and signal-to-background up to ß400, with highest gain in ß100 reconstructions (mean ΔSUVmax 3.9, p < 0.0001). Organ noise levels increased on PSF, ß100 and ß200 reconstructions. Across BPL reconstructions, there was incremental reduction in organ noise with increasing ß, statistically significant beyond ß300-500 (organ-dependent). Comparing with OSEM and PSF, lesion signal-to-noise was significantly increased in BPL reconstructions where ß ≥ 300 and  ≥ 200 respectively. On visual analysis, ß 300 had the first and second highest scores for image quality, ß500 and ß600 equal highest scores for marrow image quality and least noise, PSF and ß 200 had first and second highest scores for lesion conspicuity. For overall preference, one reader preferred ß 300 in 9/10 cases and the other preferred ß 200 in all cases. CONCLUSION: BPL reconstruction of 18F-fluciclovine PET images improves signal-to-noise ratio, affirmed by overall reader preferences. On balance, ß300 is suggested for 18F-fluciclovine whole body PET image reconstruction using BPL. Advances in knowledge: The optimum ß is different to that previously published for 18F-fluorodeoxyglucose, and has practical implications for a relatively new tracer in an environment with modern reconstruction technologies.

Recurrent Malignant Melanoma Detected on 18F-Fluciclovine PET/CT Imaging for Prostate Cancer.

A 66-year-old man presented with biochemical recurrence of prostate cancer and underwent F-fluciclovine PET/CT to detect sites of recurrence. He had a history of resected truncal stage IIIC malignant melanoma, with bilateral axillary node involvement on sentinel node biopsy, in complete remission for 3 years. F-fluciclovine PET/CT demonstrated an incidental fluciclovine-avid right axillary node (SUVmax = 4.3). Diagnostic sampling confirmed recurrent malignant melanoma.

Predicting Pathologic Response of Esophageal Cancer to Neoadjuvant Chemotherapy: The Implications of Metabolic Nodal Response for Personalized Therapy.

Only a minority of esophageal cancers demonstrates a pathologic tumor response (pTR) to neoadjuvant chemotherapy (NAC). 18F-FDG PET/CT is often used for restaging after NAC and to assess response. Increasingly, it is used during therapy to identify unresponsive tumors and predict pTR, using avidity of the primary tumor alone. However, definitions of such metabolic tumor response (mTR) vary. We aimed to comprehensively reevaluate metabolic response assessment using accepted parameters, as well as novel concepts of metabolic nodal stage (mN) and metabolic nodal response (mNR). METHODS: This was a single-center retrospective U.K. cohort study. All patients with esophageal cancer staged before NAC with PET/CT and after with CT or PET/CT and undergoing resection from 2006 to 2014 were identified. pTR was defined as Mandard tumor regression grade 1-3; imaging parameters included metrics of tumor avidity (SUVmax/mean/peak), composites of avidity and volume (including metabolic tumor volume), nodal SUVmax, and our new concepts of mN stage and mNR. RESULTS: Eighty-two (27.2%) of 301 patients demonstrated pTR. No pre-NAC PET parameters predicted pTR. In 220 patients restaged by PET/CT, the optimal tumor ΔSUVmax threshold was a 77.8% reduction. This was as sensitive as the current PERCIST 30% reduction, but more specific with a higher negative predictive value (P < 0.001). ΔSUVmax and Δlength independently predicted pTR, and composite avidity/spatial metrics outperformed avidity alone. Although both mTR and mNR were associated with pTR, in 82 patients with 18F-FDG-avid nodes before NAC we observed mNR in 10 (12.2%) not demonstrating mTR. CONCLUSION: Current definitions of metabolic response are suboptimal and too simplistic. Composite avidity/volume measures improve prediction. mNR may further improve response assessment, by specifically assessing metastatic tumor subpopulations, likely responsible for disease relapse, and should be urgently assessed when considering aborting therapy on the basis of mTR alone.

18F-FDG PET/CT assessment of histopathologically confirmed mediastinal lymph nodes in non-small cell lung cancer using a penalised likelihood reconstruction.

PURPOSE: To investigate whether using a Bayesian penalised likelihood reconstruction (BPL) improves signal-to-background (SBR), signal-to-noise (SNR) and SUVmax when evaluating mediastinal nodal disease in non-small cell lung cancer (NSCLC) compared to ordered subset expectation maximum (OSEM) reconstruction. MATERIALS AND METHODS: 18F-FDG PET/CT scans for NSCLC staging in 47 patients (112 nodal stations with histopathological confirmation) were reconstructed using BPL and compared to OSEM. Node and multiple background SUV parameters were analysed semi-quantitatively and visually. RESULTS: Comparing BPL to OSEM, there were significant increases in SUVmax (mean 3.2-4.0, p<0.0001), SBR (mean 2.2-2.6, p<0.0001) and SNR (mean 27.7-40.9, p<0.0001). Mean background SNR on OSEM was 10.4 (range 7.6-14.0), increasing to 12.4 (range 8.2-16.7, p<0.0001). Changes in background SUVs were minimal (largest mean difference 0.17 for liver SUVmean, p<0.001). There was no significant difference between either algorithm on receiver operating characteristic analysis (p=0.26), although on visual analysis, there was an increase in sensitivity and small decrease in specificity and accuracy on BPL. CONCLUSION: BPL increases SBR, SNR and SUVmax of mediastinal nodes in NSCLC compared to OSEM, but did not improve the accuracy for determining nodal involvement. KEY POINTS: • Penalised likelihood PET reconstruction was applied for assessing mediastinal nodes in NSCLC. • The new reconstruction generated significant increases in signal-to-background, signal-to-noise and SUVmax. • This led to an improvement in visual sensitivity using the new algorithm. • Higher SUV max thresholds may be appropriate for semi-quantitative analyses with penalised likelihood.

Restaging oesophageal cancer after neoadjuvant therapy with (18)F-FDG PET-CT: identifying interval metastases and predicting incurable disease at surgery.

OBJECTIVES: It is unknown whether restaging oesophageal cancer after neoadjuvant therapy with positron emission tomography-computed tomography (PET-CT) is more sensitive than contrast-enhanced CT for disease progression. We aimed to determine this and stratify risk. METHODS: This was a retrospective study of patients staged before neoadjuvant chemotherapy (NAC) by (18)F-FDG PET-CT and restaged with CT or PET-CT in a single centre (2006-2014). RESULTS: Three hundred and eighty-three patients were restaged (103 CT, 280 PET-CT). Incurable disease was detected by CT in 3 (2.91 %) and PET-CT in 17 (6.07 %). Despite restaging unsuspected incurable disease was encountered at surgery in 34/336 patients (10.1 %). PET-CT was more sensitive than CT (p = 0.005, McNemar's test). A new classification of FDG-avid nodal stage (mN) before NAC (plus tumour FDG-avid length) predicted subsequent progression, independent of conventional nodal stage. The presence of FDG-avid nodes after NAC and an impassable tumour stratified risk of incurable disease at surgery into high (75.0 %; both risk factors), medium (22.4 %; either), and low risk (3.87 %; neither) groups (p < 0.001). Decision theory supported restaging PET-CT. CONCLUSIONS: PET-CT is more sensitive than CT for detecting interval progression; however, it is insufficient in at least higher risk patients. mN stage and response (mNR) plus primary tumour characteristics can stratify this risk simply. KEY POINTS: • Restaging (18) F-FDG-PET-CT after neoadjuvant chemotherapy identifies metastases in 6 % of patients • Restaging (18) F-FDG-PET-CT is more sensitive than CT for detecting interval progression • Despite this, at surgery 10 % of patients had unsuspected incurable disease • New concepts (FDG-avid nodal stage and response) plus tumour impassability stratify risk • Higher risk (if not all) patients may benefit from additional restaging modalities.

Novel penalised likelihood reconstruction of PET in the assessment of histologically verified small pulmonary nodules.

OBJECTIVES: Investigate the effect of a novel Bayesian penalised likelihood (BPL) reconstruction algorithm on analysis of pulmonary nodules examined with 18F-FDG PET/CT, and to determine its effect on small, sub-10-mm nodules. METHODS: 18F-FDG PET/CTs performed for nodule evaluation in 104 patients (121 nodules) were retrospectively reconstructed using the new algorithm, and compared to time-of-flight ordered subset expectation maximisation (OSEM) reconstruction. Nodule and background parameters were analysed semi-quantitatively and visually. RESULTS: BPL compared to OSEM resulted in statistically significant increases in nodule SUVmax (mean 5.3 to 8.1, p < 0.00001), signal-to-background (mean 3.6 to 5.3, p < 0.00001) and signal-to-noise (mean 24 to 41, p < 0.00001). Mean percentage increase in SUVmax (%ΔSUVmax) was significantly higher in nodules ≤10 mm (n = 31, mean 73%) compared to >10 mm (n = 90, mean 42 %) (p = 0.025). Increase in signal-to-noise was higher in nodules ≤10 mm (224%, mean 12 to 27) compared to >10 mm (165%, mean 28 to 46). When applying optimum SUVmax thresholds for detecting malignancy, the sensitivity and accuracy increased using BPL, with the greatest improvements in nodules ≤10 mm. CONCLUSION: BPL results in a significant increase in signal-to-background and signal-to-noise compared to OSEM. When semi-quantitative analyses to diagnose malignancy are applied, higher SUVmax thresholds may be warranted owing to the SUVmax increase compared to OSEM. KEY POINTS: • Novel Bayesian penalised likelihood PET reconstruction was applied for lung nodule evaluation. • This was compared to current standard of care OSEM reconstruction. • The novel reconstruction generated significant increases in lung nodule signal-to-background and signal-to-noise. • These increases were highest in small, sub-10-mm pulmonary nodules. • Higher SUV max thresholds may be warranted when using semi-quantitative analyses to diagnose malignancy.

Does a novel penalized likelihood reconstruction of 18F-FDG PET-CT improve signal-to-background in colorectal liver metastases?

PURPOSE: Iterative reconstruction algorithms are widely used to reconstruct positron emission tomography computerised tomography (PET/CT) data. Lesion detection in the liver by 18F-fluorodeoxyglucose PET/CT (18F-FDG-PET/CT) is hindered by 18F-FDG uptake in background liver parenchyma. The aim of this study was to compare semi-quantitative parameters of histologically-proven colorectal liver metastases detected by 18F-FDG-PET/CT using data based on a Bayesian penalised likelihood (BPL) reconstruction, with data based on a conventional time-of-flight (ToF) ordered subsets expectation maximisation (OSEM) reconstruction. METHODS: A BPL reconstruction algorithm was used to retrospectively reconstruct sinogram PET data. This data was compared with OSEM reconstructions. A volume of interest was placed within normal background liver parenchyma. Lesions were segmented using automated thresholding. Lesion maximum standardised uptake value (SUVmax), standard deviation of background liver parenchyma SUV, signal-to-background ratio (SBR), and signal-to-noise ratio (SNR) were collated. Data was analysed using paired Student's t-tests and the Pearson correlation. RESULTS: Forty-two liver metastases from twenty-four patients were included in the analysis. The average lesion SUVmax increased from 8.8 to 11.6 (p<0.001) after application of the BPL algorithm, with no significant difference in background noise. SBR increased from 4.0 to 4.9 (p<0.001) and SNR increased from 10.6 to 13.1 (p<0.001) using BPL. There was a statistically significant negative correlation between lesion size and the percentage increase in lesion SUVmax (p=0.03). CONCLUSIONS: This BPL reconstruction algorithm improved SNR and SBR for colorectal liver metastases detected by 18F-FDG-PET/CT, increasing the lesion SUVmax without increasing background liver SUV or image noise. This may improve the detection of FDG-avid focal liver lesions and the diagnostic performance of clinical 18F-FDG-PET/CT in this setting, with the largest impact for small foci.

Phantom and Clinical Evaluation of the Bayesian Penalized Likelihood Reconstruction Algorithm Q.Clear on an LYSO PET/CT System.

UNLABELLED: Q.Clear, a Bayesian penalized-likelihood reconstruction algorithm for PET, was recently introduced by GE Healthcare on their PET scanners to improve clinical image quality and quantification. In this work, we determined the optimum penalization factor (beta) for clinical use of Q.Clear and compared Q.Clear with standard PET reconstructions. METHODS: A National Electrical Manufacturers Association image-quality phantom was scanned on a time-of-flight PET/CT scanner and reconstructed using ordered-subset expectation maximization (OSEM), OSEM with point-spread function (PSF) modeling, and the Q.Clear algorithm (which also includes PSF modeling). Q.Clear was investigated for ß (B) values of 100-1,000. Contrast recovery (CR) and background variability (BV) were measured from 3 repeated scans, reconstructed with the different algorithms. Fifteen oncology body (18)F-FDG PET/CT scans were reconstructed using OSEM, OSEM PSF, and Q.Clear using B values of 200, 300, 400, and 500. These were visually analyzed by 2 scorers and scored by rank against a panel of parameters (overall image quality; background liver, mediastinum, and marrow image quality; noise level; and lesion detectability). RESULTS: As ß is increased, the CR and BV decreases; Q.Clear generally gives a higher CR and lower BV than OSEM. For the smallest sphere reconstructed with Q.Clear B400, CR is 28.4% and BV 4.2%, with corresponding values for OSEM of 24.7% and 5.0%. For the largest hot sphere, Q.Clear B400 yields a CR of 75.2% and a BV of 3.8%, with corresponding values for OSEM of 64.4% and 4.0%. Scorer 1 and 2 ranked B400 as the preferred reconstruction in 13 of 15 (87%) and 10 of 15 (73%) cases. The least preferred reconstruction was OSEM PSF in all cases. In most cases, lesion detectability was highest ranked for B200, in 9 of 15 (67%) and 10 of 15 (73%), with OSEM PSF ranked lowest. Poor lesion detectability on OSEM PSF was seen in cases of mildly (18)F-FDG-avid mediastinal nodes in lung cancer and small liver metastases due to background noise. Conversely, OSEM PSF was ranked second highest for lesion detectability in most pulmonary nodule evaluation cases. The combined scores confirmed B400 to be the preferred reconstruction. CONCLUSION: Our phantom measurement results demonstrate improved CR and reduced BV when using Q.Clear instead of OSEM. A ß value of 400 is recommended for oncology body PET/CT using Q.Clear.