An Evaluation of Thallium-201 as a Tumour Imaging Agent

Sehweil, Ali Mahmoud (1988) An Evaluation of Thallium-201 as a Tumour Imaging Agent. PhD thesis, University of Glasgow.

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I evaluated thalllum-201 chloride as a tumour imaging agent. I studied the time course of Tl--201 uptake in various tumours in order to establish the best time for imaging tumours following injection of the tracer. The results show that uptake occurs rapidly in tumours with a peak value obtained 8 to 20 minutes post-injectIon in various tumours studied. The mean time of tumour uptake (+SD) was 11.2 (+3.34) minutes for lung carcinoma, 11.21 (+1.88) minutes for breast carcinoma and 11.76 (+3.25) minutes for lymphoma. There were no significant differences in different tumour types. Tumour to background ratios also rapidly attained peak values and remained relatively constant over the hour following injection. The mean (+SD) time of maximal tumour/background activity was assessed and found for lung cancer to be 18.3 (+0.59) minutes, breast cancer 13.0 (+1.16) minutes, and lymphoma 16.7 (+1.04) minutes. The mean tumour to background ratios did not change significantly over the first hour once the peak value was obtained at around ten minutes. The tumour to background ratios were also compared in the early and four hours delayed ten minutes and found to be mean (+SD) 1.8 (+0.30) for the initial image and 1.67 (+0.33) for the delayed image. These values are not sig- nificantly different. From these data I concluded that tumour imaging with T1-201 is best performed 20 to 60 minutes post Injection. I did not find any evidence that delayed four hour imaging was advantageous because tumour to background was not significantly changed and the count in tumour decreased. I studied the mechanism of tumour uptake of Tl-201 by in vivo and in vitro studies. In a series of patients with lung cancer (n-50), breast cancer (n=24), and mediastinal lymphoma (n-13), the time course of tumour uptake of Tl-201 paralleled that In the myocardium with almost identical times being obtained in tumours and myocardium. The time from injection to peak myocardial activity ranged from 8 to 20 minutes. The mean time to peak myocardial activity (+SD) was 11.61 (+ 3.25). The mean (+SD) washout of Tl-201 from the tumour over four hours post injection was 25.4 (+ 33.5) percent of the activity present in the early static image. The mean washout of Tl-201 from the myocardium over four hours was 29.7 (+16.7). In a patient with hepatic metastases from colonic cancer undergoing laparotomy, Tc99m labeled microspheres and Tl-201 were Injected into the hepatic artery and biopsies of metastatic and normal liver tissue obtained. The tumour to normal liver tissue activity ratios for Tl-201 were one-tenth of those for TC 99m microspheres. Measurement of Tl-201 activty under control condtions and after digoxin intervention in non-small cell lung cancer line SK-MTS. The cells were incubated for 30 minutes with Tl-201 and without the addition of digoxin, which acts as a sodium-potassium pump blocker. The cells exposed to digoxin showed markedly decreased uptake of Tl-201 compared to the cells not exposed. Results of the studies indicate that Tl-201 uptake in tumours in not a purely flow dependent process. The mechanism of intracellular uptake of Tl-201 demonstrates the viability and metabolic activity of the pathological cells. It appears to be similar to the myocardium by substitution of Tl-201 for potassium in the ATP-ase dependent sodium-potassium pump. I carried out a clinical evaluation of Tl-201 chloride in the diagnosis and staging of various common malignancies. I evaluated the ability of Tl-201 chloride to detect primary lung cancer (n-147) and to demonstrate mediastinal spread of the disease. Thallium-201 images were compared with the results of CT Scanning and surgical mediastinal exploration. Thallium-201 was accurate In locating 126 of 147 of the primary lung tumours (86%) but disappointing in detecting mediastinal tumour spread (15%). Ten patients with benign lung disease were examined. Tl-201 chloride was also found to concentrate in active sarcoidosis (one case) and active TB (two cases). The specificity of 70 percent was obtained. Forty-five patients with histologically proven lung cancer underwent Tl-201 and Ga-67 studies. Thirty-nine (87%) showed positive uptake of Tl-201 into the primary tumour, while 36 (80%) had positive Ga-67 uptake In the tumour. Ga-67 was superior over Tl-201 In detecting mediastinal spread of the disease in 16 out of 28 (58%) patients with mediastinal gallium uptake, while five out of 28 (18%) patients showed positive Tl-201 uptake. I concluded that Tl-201 chloride concentrates In both malignant and benign active metabolic tissue. Tl-201 is highly sensitive in locating primary lung cancer but lacks sensitivity in determining mediastinal spread of the disease. I evaluated Tl-201 chloride in patients with breast cancer (n=26) and In patients with malignant lymphoma (n-15), and found that Tl-201 is highly sensitive in detecting primary tumours and disappointing in detecting nodal spread of the disease. Thallium-201 was also evaluated in patients with bone and soft tissue tumours (n=9), brain tumours and in patients with mass lesions of the liver. Thallium-201 was found to be useful In detecting bone and soft tissue tumours (100% sensitivity), brain tumours (100%) and was not affected by steroid therapy. Thallium-201 was found to be equally useful to gallium-67 for imaging primary hepatomas. It surpasses gallium-67 imaging in distinction of pseudotumours of the liver. In addition, It has the advantage over gallium-67 of early imaging. Finally, sequential Tl-201 scans were found to be useful in evaluating patients with malignant disease and determining local tumour response after ant I-tumour therapy, especially when the scan was positive pre-treatment. There was a good correlation between the changes In Tl-201 uptake and the change In the primary tumour size after treatment as determined radiographically.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Nuclear physics and radiation, Biophysics, Medical imaging
Date of Award: 1988
Depositing User: Enlighten Team
Unique ID: glathesis:1988-77769
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 11:53
Last Modified: 14 Jan 2020 11:53

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