Sir Peter MacCallum Department of Oncology - Research Publications
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ItemVoxel-wise correlation of positron emission tomography/computed tomography with multiparametric magnetic resonance imaging and histology of the prostate using a sophisticated registration framework(WILEY, 2019-06)OBJECTIVES: To develop a registration framework for correlating positron emission tomography/computed tomography (PET/CT) images with multiparametric magnetic resonance imaging (mpMRI) and histology of the prostate, thereby enabling voxel-wise analysis of imaging parameters. PATIENTS AND METHODS: In this prospective proof-of-concept study, nine patients scheduled for radical prostatectomy underwent mpMRI and PET/CT imaging before surgery. One had PET imaging using 18 F-fluoromethylcholine, five using 68 Ga-labelled prostate-specific membrane antigen (PSMA)-HBED-CC (PMSA-11), and three using a trial 68 Ga-labelled THP-PSMA tracer. PET/CT data were co-registered with mpMRI via the CT scan and an in vivo three-dimensional T2-weighted (T2w) MRI, and then co-registered with ground truth histology data using ex vivo MRI of the prostate specimen. Maximum and mean standardised uptake values (SUVmax and SUVmean ) were extracted from PET data using tumour annotations from histology, and Kolmogorov-Smirnov tests were used to compare between tumour- and benign-voxel values. Correlation analysis was performed between mpMRI and PET SUV tumour voxel values using Pearson's correlation coefficient and R2 statistics. RESULTS: PET/CT data from all nine patients were successfully registered with mpMRI and histology data. SUVmax and SUVmean ranged from 2.21 to 12.11 and 1.08 to 4.21, respectively. All patients showed the PET SUV values in benign and tumour voxels were from statistically different distributions. Correlation analysis showed no consistent trend between the T2w or apparent diffusion coefficient values and PET SUV. However, parameters from dynamic contrast-enhanced (DCE) MRI including the maximum enhancement, volume transfer constant (Ktrans ), and the initial area under the contrast agent concentration curve for the first 60 s after injection (iAUGC60), showed consistent positive correlations with PET SUV. Furthermore, R2* values from blood oxygen level-dependent (BOLD) MRI showed consistent negative correlations with PET SUV-voxel values. CONCLUSION: We have developed a novel framework for registering and correlating PET/CT data at a voxel-level with mpMRI and histology. Despite registration uncertainties, perfusion and oxygenation parameters from DCE MRI and BOLD imaging showed correlations with PET SUV. Further analysis will be performed on a larger patient cohort to quantify these proof-of-concept findings. Improved understanding of the correlation between mpMRI and PET will provide supportive information for focal therapy planning of the prostate.
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ItemA pilot study of cardiopulmonary exercise testing and cardiac stress positron emission tomography before major non-cardiac surgery(WILEY, 2018-12)Cardiac events are a common cause of peri-operative morbidity. Cardiopulmonary exercise testing can objectively assess risk, but it does not quantify myocardial ischaemia. With appropriate dietary preparation to suppress basal myocardial glucose uptake, positron emission tomography with 18 F-fluorodeoxyglucose can identify post-ischaemic myocardium, providing an attractive complement to exercise testing. We aimed to investigate the feasibility of this diagnostic algorithm. Patients referred for cardiopulmonary exercise testing before major cancer surgery were prospectively recruited. Exercise testing and positron emission tomography imaging were performed after a high fat-low carbohydrate meal. Protocol feasibility (primary end-point) included compliance with pre-test diet instructions and the completion of tests. Stress myocardial perfusion imaging was performed if either exercise testing or positron emission tomography was equivocal or positive for ischaemia. We recorded cardiac complications for 30 postoperative days. We enrolled 26 participants, 20 of whom completed protocol. Twenty-one participants proceeded to surgery: myocardial injury or infarction was diagnosed in three participants, two of whom had positive or equivocal positron emission tomography but negative myocardial perfusion imaging. We have shown that pre-operative cardiac positron emission tomography after cardiopulmonary exercise testing is feasible; protocol deviations were minor and did not affect image quality. Our findings warrant further investigation to compare the diagnostic utility of cardiac positron emission tomography imaging with standard pre-operative stress tests.
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ItemA prospective randomized multicentre study of the impact of gallium-68 prostate-specific membrane antigen (PSMA) PET/CT imaging for staging high-risk prostate cancer prior to curative-intent surgery or radiotherapy (proPSMA study): clinical trial protocol(WILEY, 2018-11)BACKGROUND: Accurate staging of patients with prostate cancer (PCa) is important for therapeutic decision-making. Relapse after surgery or radiotherapy of curative intent is not uncommon and, in part, represents a failure of staging with current diagnostic imaging techniques to detect disease spread. Prostate-specific membrane antigen (PSMA) positron-emission tomography (PET)/computed tomography (CT) is a new whole-body scanning technique that enables visualization of PCa with high contrast. The hypotheses of this study are that: (i) PSMA-PET/CT has improved diagnostic performance compared with conventional imaging; (ii) PSMA-PET/CT should be used as a first-line diagnostic test for staging; (iii) the improved diagnostic performance of PSMA-PET/CT will result in significant management impact; and (iv) there are economic benefits if PSMA-PET/CT is incorporated into the management algorithm. OBJECTIVES AND METHODS: The proPSMA trial is a prospective, multicentre study in which patients with untreated high-risk PCa will be randomized to gallium-68-PSMA-11 PET/CT or conventional imaging, consisting of CT of the abdomen/pelvis and bone scintigraphy with single-photon emission CT/CT. Patients eligible for inclusion are those with newly diagnosed PCa with select high-risk features, defined as International Society of Urological Pathology grade group ≥3 (primary Gleason grade 4, or any Gleason grade 5), prostate-specific antigen level ≥20 ng/mL or clinical stage ≥T3. Patients with negative, equivocal or oligometastatic disease on first line-imaging will cross over to receive the other imaging arm. The primary objective is to compare the accuracy of PSMA-PET/CT with that of conventional imaging for detecting nodal or distant metastatic disease. Histopathological, imaging and clinical follow-up at 6 months will define the primary endpoint according to a predefined scoring system. Secondary objectives include comparing management impact, the number of equivocal studies, the incremental value of second-line imaging in patients who cross over, the cost of each imaging strategy, radiation exposure, inter-observer agreement and safety of PSMA-PET/CT. Longer-term follow-up will also assess the prognostic value of a negative PSMA-PET/CT. OUTCOME AND SIGNIFICANCE: This trial will provide data to establish whether PSMA-PET/CT should replace conventional imaging in the primary staging of select high-risk localized PCa, or whether it should be used to provide incremental diagnostic information in selected cases.
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ItemDeep Learning Renal Segmentation for Fully Automated Radiation Dose Estimation in Unsealed Source Therapy(FRONTIERS MEDIA SA, 2018-06-14)BACKGROUND: Convolutional neural networks (CNNs) have been shown to be powerful tools to assist with object detection and-like a human observer-may be trained based on a relatively small cohort of reference subjects. Rapid, accurate organ recognition in medical imaging permits a variety of new quantitative diagnostic techniques. In the case of therapy with targeted radionuclides, it may permit comprehensive radiation dose analysis in a manner that would often be prohibitively time-consuming using conventional methods. METHODS: An automated image segmentation tool was developed based on three-dimensional CNNs to detect right and left kidney contours on non-contrast CT images. Model was trained based on 89 manually contoured cases and tested on a cohort of patients receiving therapy with 177Lu-prostate-specific membrane antigen-617 for metastatic prostate cancer. Automatically generated contours were compared with those drawn by an expert and assessed for similarity based on dice score, mean distance-to-agreement, and total segmented volume. Further, the contours were applied to voxel dose maps computed from post-treatment quantitative SPECT imaging to estimate renal radiation dose from therapy. RESULTS: Neural network segmentation was able to identify right and left kidneys in all patients with a high degree of accuracy. The system was integrated into the hospital image database, returning contours for a selected study in approximately 90 s. Mean dice score was 0.91 and 0.86 for right and left kidneys, respectively. Poor performance was observed in three patients with cystic kidneys of which only few were included in the training data. No significant difference in mean radiation absorbed dose was observed between the manual and automated algorithms. CONCLUSION: Automated contouring using CNNs shows promise in providing quantitative assessment of functional SPECT and possibly PET images; in this case demonstrating comparable accuracy for radiation dose interpretation in unsealed source therapy relative to a human observer.
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ItemChanges in biodistribution on 68Ga-DOTA-Octreotate PET/CT after long acting somatostatin analogue therapy in neuroendocrine tumour patients may result in pseudoprogression(E-MED, 2018-01-24)BACKGROUND: To evaluate the effects of long-acting somatostatin analogue (SSA) therapy on 68Ga-DOTA-octreotate (GaTate) uptake at physiological and metastatic sites in neuroendocrine tumour (NET) patients. METHODS: Twenty-one patients who underwent GaTate PET/CT before and after commencement of SSA therapy were reviewed. Maximum standardized uptake values (SUVmax) were measured in normal organs. Changes in uptake of 49 metastatic lesions in 12 patients with stable disease were also compared. Serum chromogranin-A (CgA) levels were available for correlation between scans in 17/21 patients. RESULTS: Mean thyroid, spleen and liver SUVmax decreased significantly following SSA therapy from a baseline of 5.9 to 3.5, 30.3 to 23.1 and 10.3 to 8.0, respectively (p = < 0.0001 for all). Pituitary SUVmax increased from 10.2 to 11.0 (p = 0.004) whereas adrenal and salivary gland SUVmax did not change. Tumour SUVmax increased in 7 of 12 patients with stable disease; CgA was stable or decreasing in 5 of these patients. 30/49 (61%) metastatic lesions had an increase in SUVmax and lesion-to-liver uptake ratio increased in 40/49 (82%) following SSA therapy. CONCLUSION: Long-acting SSA therapy decreases GaTate uptake in the thyroid, spleen and liver but in most cases increases intensity of uptake within metastases. This has significant implications for interpretation of GaTate PET/CT following commencement of therapy as increased intensity alone may not represent true progression. Our findings also suggest pre-dosing with SSA prior to PRRT may enable higher doses to be delivered to tumour whilst decreasing dose to normal tissues.
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ItemIntra-individual comparison of 68Ga-PSMA-11 and 18F-DCFPyL normal-organ biodistribution(BMC, 2019-05-15)PURPOSE: Detailed data comparing the biodistribution of PSMA radioligands is still scarce, raising concerns regarding the comparability of different compounds. We investigated differences in normal-organ biodistribution and uptake variability between the two most commonly PSMA tracers in clinical use, 68Ga-PSMA-11 and 18F-DCFPyL. METHODS: This retrospective analysis included 34 patients with low tumor burden referred for PET/CT imaging with 68Ga-PSMA-11 and subsequently 18F-DCFPyL. Images were acquired with 4 cross-calibrated PET/CT systems. Volumes of interest were placed on major salivary and lacrimal glands, liver, spleen, duodenum, kidneys, bladder, blood-pool and muscle. Normal-organ biodistribution of both tracers was then quantified as SUVpeak and compared using paired tests, linear regression and Bland-Altman analysis. Between-patient variability was also assessed. Clinical and protocol variables were investigated for possible interference. RESULTS: For both tracers the highest uptake was found in the kidneys and bladder and low background activity was noted across all scans. In the quantitative analysis there was significantly higher uptake of 68Ga-PSMA-11 in the kidneys, spleen and major salivary glands (p < 0.001), while the liver exhibited slightly higher 18F-DCFPyL uptake (p = 0.001, mean bias 0.79 ± 1.30). The lowest solid-organ uptake variability was found in the liver (COV 21.9% for 68Ga-PSMA-11, 22.5% for 18F-DCFPyL). There was a weak correlation between 18F-DCFPyL uptake time and liver SUVpeak (r = 0.488, p = 0.003) and, accordingly, patients scanned at later time-points had a larger mean bias between the two tracers' liver uptake values (0.05 vs 1.46, p = 0.001). CONCLUSION: Normal tissue biodistribution patterns of 68Ga-PSMA-11 and 18F-DCFPyL were similar, despite subtle differences in quantitative values. Liver uptake showed an acceptable intra-patient agreement and low inter-patient variability between the two tracers, allowing its use as a reference organ for thresholding scans in the qualitative comparison of PSMA expression using these different tracers.
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ItemThe role of 18F-FDG-PET/CT in evaluating retroperitoneal masses -Keeping your eye on the ball!(BMC, 2019-05-29)BACKGROUND: Testicular germ cell tumour is the commonest malignancy affecting males aged between 15 and 35, with an increased relative risk amongst those with a history of cryptorchidism. In patients presenting with locoregional metastatic disease, retroperitoneal and pelvic soft tissue masses are common findings on ultrasound and computed tomography, which has several differential diagnoses within this demographic cohort. On staging 18F-FDG-PET/CT, understanding the typical testicular lymphatic drainage pathway facilitates prompt recognition of the pathognomonic constellation of unilateral absence of testicular scrotal activity, and FDG-avid nodal masses along the drainage pathway. We describe the cases of three young males presenting with abdominopelvic masses, in whom FDG-PET/CT was helpful in formulating a unifying diagnosis of metastatic seminoma, retrospectively corroborated by a history of testicular maldescent. CASE PRESENTATIONS: In all three cases, the patients were males aged in their 30s and 40s who were brought to medical attention for back and lower abdominal pain of varying duration. Initial imaging evaluation with computed tomography and/or ultrasound revealed large abdominopelvic soft tissue masses, with lymphoproliferative disorders or soft tissue sarcomas being high on the list of differential diagnoses. As such, they were referred for staging FDG-PET/CT, all of whom demonstrated the pathognomonic constellation of, 1) unilateral absence of scrotal testicular activity, and 2) FDG-avid nodal masses along the typical testicular lymphatic drainage pathway. These characteristic patterns were corroborated by a targeted clinical history and examination which revealed a history of cryptorchidism, and elevated β-hCG in two of three patients. All were subsequently confirmed as metastatic seminoma on biopsy and open resection. CONCLUSION: These cases highlight the importance of clinical history and examination for the clinician, as well as a sound knowledge of the typical testicular lymphatic drainage pathway for the PET physician, which would assist with prompt recognition of the characteristic imaging patterns on FDG-PET/CT. It further anecdotally supports the utility of FDG-PET/CT in evaluating undiagnosed abdominopelvic masses, as well as a potential role in the initial staging of germ cell tumours in appropriately selected patients.