Sir Peter MacCallum Department of Oncology - Research Publications
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Item68Ga PSMA-11 PET with CT urography protocol in the initial staging and biochemical relapse of prostate cancer(BMC, 2017-12-21)BACKGROUND: 68Ga-labelled prostate specific membrane antigen (PSMA) ligand PET/CT is a promising modality in primary staging (PS) and biochemical relapse (BCR) of prostate cancer (PC). However, pelvic nodes or local recurrences can be difficult to differentiate from radioactive urine. CT urography (CT-U) is an established method, which allows assessment of urological malignancies. The study presents a novel protocol of 68Ga-PSMA-11 PET/CT-U in PS and BCR of PC. METHODS: A retrospective review of PSMA PET/CT-U preformed on 57 consecutive patients with prostate cancer. Fifty mL of IV contrast was administered 10 min (range 8-15) before the CT component of a combined PET/CT study, acquired approximately 60 min (range 40-85) after administration of 166 MBq (range 91-246) of 68Ga-PSMA-11. PET and PET/CT-U were reviewed by two nuclear medicine physicians and CT-U by a radiologist. First, PET images were reviewed independently followed by PET/CT-U images. Foci of activity which could not unequivocally be assessed as disease or urinary activity were recorded. PET/CT-U was considered of potential benefit in final interpretation when the equivocal focal activity in PET images corresponded to opacified ureter, bladder, prostate bed, seminal vesicles, or urethra. Student's T test and Pearson's correlation coefficient was used for assessment of variables including lymph node size and standardized uptake value. RESULTS: Overall 50 PSMA PET/CT-U studies were performed for BCR and 7 for PS. Median PSA with BCR and PS were 2.0 ± 11.4 ng/ml (0.06-57.3 ng/ml) and 18 ± 35.3 ng/ml (6.8-100 ng/ml), respectively. The median Gleason-score for both groups was 7 (range 6-10). In BCR group, PSMA PET was reported positive in 36 (72%) patients, CT-U in 11(22%) patients and PET/CT-U in 33 (66%) patients. In PS group, PSMA PET detected the primary site in all seven patients, of which one patient with metastatic nodal disease had negative CT finding. Of 40 equivocal foci (27/57 patients) on PET, 11 foci (10/57 patients, 17.5%) were localized to enhanced urine on PET/CT-U, hence considered of potential benefit in interpretation. Of those, 3 foci (3 patients) were solitary sites of activity on PSMA imaging including two local and one nodal site and 4 foci (3 patients) were in different nodal fields. CONCLUSIONS: PET/CT-U protocol is a practical approach and may assist in interpretation of 68Ga-PSMA-11 imaging by delineation of the contrast opacified genitourinary system and matching focal PSMA activity with urinary contrast.
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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.