The optimum time for tumour imaging with thallium-201

Following the intravenous injection of 75 MBq ²⁰¹Tl-chloride we have assessed the uptake kinetics in the myocardium and in the primary tumour in 56 patients with lung cancer, 26 with breast cancer and 13 with mediastinal lymphoma. The time of maximal tumour uptake ranged from 8–20 min post-injection and did not differ significantly between lung cancer (mean±SD=11.9±3.34 min), breast cancer (11.21±1.88 min) and lymphoma (11.76±3.25 min). The time of maximum cardiac uptake of ²⁰¹Tl was 11.61±3.25 min. There was no significant washout of ²⁰¹Tl from the tumours in the first hour after injection in the various malignant lesions studied. The time of maximal tumour to background activity was 18.3±0.59 min for lung cancer, 13.0±1.16 min for breast cancer and 16.7±1.04 min for lymphoma.The time course of ²⁰¹Tl uptake in the tumours suggests that the mechanism of uptake is similar to that in the myocardium. The optimal time of ²⁰¹Tl tumour imaging is from 20–60 min following injection and did not differ in various tumours studied.     

The use of thallium-201 in the preoperative detection of breast cancer: an adjunct to mammography and ultrasonography

Thallium-201 breast scans were performed preoperatively in 72 female patients with breast abnormalities detected by mammography and/or ultrasonography (7.5–13 MHz), in order to differentiate benign from malignant breast disease. Informed consent was obtained from each patient. Scintigraphy consisted of anterior and oblique planar images of the affected breast and axilla at 10 min and 3 h following the injection of²⁰¹Tl chloride (110 MBq). All²⁰¹Tl scans were interpreted without prior knowledge of surgery data. Pathological features of breast malignancies, such as tumour size, axillary lymph node metastases, tumour grading, lymphatic vascular channel invasion and receptor status, were analysed for their association with²⁰¹Tl uptake by tumour cells. A total of 76 breast lesions were assessed in the study. On final histological diagnosis, there were 56 malignant tumours, 14 benign nodules (9 fibroadenomas, two cases of adenosis, two cases of focal fibrosis and one case of epitheliosis) and six atypical lesions (atypical ductal or lobular hyperplasia). Thallium scintigraphy was shown to have high accuracy (92%) in detecting breast cancer, better than mammography (74%) and ultrasonography (84%). Almost all (51/56) breast cancers showed greater²⁰¹Tl activity than surrounding normal breast tissue while there was no significant increase in²⁰¹Tl activity above background in all but one (19/20) case of non-malignant disease.²⁰¹Tl activity within breast tumours, calculated as tumour/background (T/B) ratio, ranged between 1.2 and 2.5 with a mean value of 1.45. In our experience the concentration of thallium in the breast cancer seems to be primarily dependent on vascularity and tumour size rather than tumour grading, lymphatic/vascular invasion or receptor status.²⁰¹Tl scan sensitivity was 97% for malignant lesions larger than 1.5 cm (n=35) and 80% for lesions of 1.5 cm or less (n=21); however, five of the eight breast cancers smaller than 1.0 cm were also detectable by²⁰¹Tl scintigraphy, compared with five out of seven by mammography. Thallium scintigraphy would not be useful in evaluating the axilla for lymph node metastases (sensitivity 27%, specificity 77%).     

Indium-111 octreotide scintigraphy in patients with bone tumours of the extremities

Radiolabelled somatostatin analogues are of potential value in the imaging of somatostatin receptor-positive tumours. Recently, somatostatin receptors have been demonstrated in the osteoblast precursor cells. In this preliminary study, we evaluated the uptake characteristics of indium-111 octreotide in two benign and two malignant bone tumours. Tracer accumulation was observed in all four cases, and overall lesion to background ratio (mean±SD) was 2.74±0.84 and 2.98±1.49 at 4 h and 24 h, respectively. There was no clear relationship between I¹¹¹In-octreotide accumulation and the benign or malignant nature of the tumour. In one patient, tracer uptake was inhibited by unlabelled octreotide administration. These results suggest that¹¹¹In-octreotide can be taken up by benign and malignant bone tumours. The inhibition of tumour uptake by treatment with cold octreotide supports the concept that specific uptake mechanisms are responsible for¹¹¹In-octreotide deposition by bone tumours.     

Comparison of99mTc(V)-DMSA,201Tl and99mTc-MIBI imaging in the follow-up of patients with medullary carcinoma of the thyroid

Radionuclide scanning with tumour-seeking agents such as pentavalent technetium-99m dimercaptosuccinic acid [^99mTc(V)-DMSA], thallium-201 and technetium-99m sestamibi (MIBI) has been reported to be useful in the detection of medullary thyroid carcinoma (MTC). We undertook a study in 14 MTC patients to determine the comparative imaging potential of²⁰¹Tl, MIBI and^99mTc(V)-DMSA in the detection of recurrent or metastatic MTC. All patients underwent total thyroidectomy and had persistently elevated serum calcitonin levels after the surgery. Scintigraphic studies were carried out 20 min after the injection of 111 MBq of²⁰¹Tl or 555 MBq of MIBI and 2 h following the injection of 370 MBq of^99mTc(V)-DMSA. All scintigraphic findings were correlated with contemporaneous CT or MRI studies. CT, MRI and bone scans showed 42 (26 bone, 16 soft tissue) metastatic sites in 11 of the 14 patients. In the remaining three patients no lesions were detected during diagnostic evaluation.^99mTc(V)-DMSA showed all of the soft tissue metastases but could not show two bone lesions. On the other hand, MIBI imaging was false-negative in 22 (52%) sites and²⁰¹Tl was false-negative in 34 (80%) sites. Overall, lesion detection sensitivities for^99mTc(V)-DMSA, MIBI and²⁰¹Tl were 95%, 47% and 19% respectively. We conclude that^99mTc(V)-DMSA is clearly superior to MIBI and²⁰¹Tl in the follow-up of MTC patients.     

Somatostatin receptor imaging in intracranial tumours

The somatostatin analogue [¹¹¹In-DTPA-d-Phe¹]-octreotide (¹¹¹In-octreotide) allows scintigraphic visualization of somatostatin receptor-expressing tissue. While it is well known that a large variety of tissues express somatostatin receptors and ¹¹¹In-octreotide scintigraphy has a clearly defined role in various neuroendocrine diseases, the clinical value of ¹¹¹In-octreotide scintigraphy in brain tumours is still under clinical investigation. In 124 patients with 141 brain lesions (63 meningiomas, 24 pituitary adenomas, 10 gliomas WHO class I and II, 12 gliomas WHO class III and IV, 11 neurinomas and 2 neurofibromas, 7 metastases and 12 other varieties: three non-Hodgkin B-cell lymphomas, two epidermoids, one abscess, one angioleiomyoma, one chordoma, one haemangiopericytoma, one osteosarcoma, one plasmacytoma and one pseudocyst), ¹¹¹In-octreotide scintigraphy was performed 4–6 and 24 h after i.v. injection of 110–220 MBq ¹¹¹In-octreotide. Planar images of the head in four views with a 128×128 matrix and single-photon emission tomographic images (64×64 matrix) were acquired, and lesions were graded according to qualitative tracer uptake. Fifty-nine of the 63 meningiomas showed moderate to intense tracer uptake. Nine of 24 pituitary adenomas were visible; the remaining 15 did not show any tracer uptake. None of the class I and II gliomas with an intact blood-brain barrier were detected whereas 11/12 class III and IV gliomas showed ¹¹¹In-octreotide uptake. None of the neurinomas or neurofibromas were positive. Five of seven metastases were classified as positive, as were the osteosarcoma, two of three non-Hodgkin B-cell lymphomas, one abscess, one angioleiomyoma, one chordoma and one haemangiopericytoma. The other varieties (one non-Hodgkin B-cell lymphoma, two epidermoids, one plasmacytoma and one pseudocyst) did not show ¹¹¹In-octreotide uptake. The results demonstrate that a large variety of intracranial lesions express somatostatin receptors and therefore can be visualized by [¹¹¹In-DTPA-d-Phe¹]-octreotide scintigraphy. This technique can be valuable in the differentiation between meningiomas and pituitary adenomas, based on qualitative tracer uptake. [¹¹¹In-DTPA-d-Phe¹]-octreotide scintigraphy allows differentiation between meningiomas and neurinomas or neurofibromas and therefore provides complementary information to computed tomography or magnetic resonance imaging. Furthermore, this technique allows differentiation between scar tissue and recurrent meningiomas postoperatively and can help in non-invasive tumour differentiation of multiple intracranial lesions, which can be of value in defining the most adequate therapeutic strategy. Received 1 December 1997 and in revised form 17 March 1998     

Mechanism of 201Tl uptake in tumours

We have studied the mechanism of tumour uptake of ²⁰¹Tl by in vivo and in vitro studies. In a series of patients with breast cancer (n=26), lung cancer (n=56) and lymphoma (n=15), the time course of tumour uptake of ²⁰¹Tl paralleled that in the myocardium with almost identical times of peak uptake being obtained in tumours and myocardium. In a patient with hepatic metastases from colonic cancer undergoing laparotomy, ^99mTc labelled microspheres and ²⁰¹Tl were injected into the hepatic artery and biopsies of metastatic and normal liver tissue obtained. The tumour to normal liver activity ratios for ²⁰¹Tl were one tenth of those for ^99mTc microspheres. In the final part of the study, cells from a lung cancer tissue culture line were incubated for 30 min with ²⁰¹Tl with and without the addition of cardiac glycoside, which acts a sodium potassium pump blocker. The cells exposed to the cardiac glycoside showed markedly decreased uptake of ²⁰¹Tl compared to the cells not so exposed (0.6%±0.1% vs 11.8±0.7.2% of the administered dose). The mechanism of ²⁰¹Tl uptake of tumours is similar to that in the myocardium. Sodium potassium pump activity appears to be more important than tumour blood flow. ²⁰¹Tl uptake may provide a useful means of studying tumour viability.     

Identification of AIDS-related tuberculosis with concordant gallium-67 and three-hour delayed thallium-201 scintigraphy

Concordant gallium-67 and thallium-201 uptake has been described in malignant lesions. More recently,²⁰¹Tl accumulation has been described in some benign conditions. The authors report three HIV-positive patients who underwent⁶⁷Ga and²⁰¹Tl scintigraphy. These studies revealed concordant⁶⁷Ga and²⁰¹Tl uptake and tumour was erroneously diagnosed. All three patients were finally diagnosed as having tuberculosis.     

Technetium-99m sestamibi uptake in human breast carcinoma cell lines displaying glutathione-associated drug-resistance

An in vitro study was designed to evaluate the uptake of sestamibi (MIBI) in P-glycoprotein (Pgp) and glutathione-associated (GSH) multidrug-resistant (MDR) cell lines. MIBI uptake was studied in various human breast carcinoma cell lines, i.e. in wild-type (MCF7/wt) cells, in adriamycin-resistant (MCF7/adr) cells which express Pgp and in melphalan-resistant (MCF7/mph) cells with increased levels of GSH. The effects of buthiomine sulphoximine (BSO) and verapamil on MIBI uptake were also studied in the MCF7/mph and MCF7/adr cells respectively. The cells were incubated for 1 h with a dose of 0.1 MBq thallium-201 and technetium-99m MIBI. Both MIBI and²⁰¹Tl uptakes were higher for MCF7/mph cells than for the other cells studied. The mean MIBI uptake in MCF7/adr cells was significantly lower than that in MCF7/wt cells (1.9%±0.5% vs 3.1%.0.6%;P <0.01). Verapamil treatment increased the MIBI uptake in MCF7/adr cells (to 2.6%.0.3%;P <0.05). Treatment of MCF7/mph cells with BSO resulted in a significant reduction in GSH content (from 243.2±81.1 nmoUmg protein to 17.6±4.4 nmol/mg protein;P <0.001). However, MIBI uptake in BSO-treated and untreated MCF7/mph cells was similar (4.43%±0.5% and 5.93%±1.7%, respectively;P >0.1). This study suggests that the uptake of MIBI is not diminished by glutathione-associated drug resistance and that MIBI uptake in a tumour sample does not necessarily indicate that a cancer is sensitive to drugs.     

Thallium-201 single-photon emission tomography in the treatment follow-up of nasopharyngeal carcinoma

In order to assess the usefulness of thallium-201 single-photon emission tomography (SPET) in the treatment follow-up of nasopharyngeal carcinoma (NPC), a total of 75²⁰¹Tl SPET studies were performed in 18 patients with histologically proven NPC. The findings were compared with those of magnetic resonance imaging (MRI) before and after therapy. Four patients received radiotherapy alone while the other 14 received concurrent chemo-radiotherapy. Treatment response was classified as complete (CR) or partial (PR) based on the findings of MRI and²⁰¹Tl SPET. Intense²⁰¹Tl uptake by the tumour was seen in all 18 patients before treatment. After treatment, MRI showed seven CRs and 11 PRs, whereas²⁰¹Tl SPET showed 13 CRs and five PRs. In 12 patients, the results of²⁰¹Tl SPET were in agreement with those of MRI. In six patients MRI showed PR but²⁰¹Tl showed CR. Follow-up (mean 10.6 months) MRI and²⁰¹Tl SPET studies of these six patients revealed that tumour gradually decreased and finally vanished in three patients. This preliminary study indicates that²⁰¹Tl SPET has potential in the assessment of early response to treatment of patients with NPC when compared with MRI.     

Different thallium-201 single-photon emission tomographic patterns in benign and aggressive meningiomas

To evaluate the possibility of preoperatively obtaining an index of aggressiveness for intracranial meningiomas, we prospectively studied 22 patients with computed tomography or magnetic resonance imaging evidence of meningeal tumour, using single-photon emission tomography (SPET) of the brain and thallium-201 (²⁰¹Tl). On a brain-dedicated SPET scanner, a rapid acquisition protocol with early, short scans was started simultaneously with the intravenous administration of 111 MBq²⁰¹Tl, covering the initial intratumoral distribution of the tracer. Twenty minutes post injection, a delayed SPET scan was also obtained. On the reconstructed and attenuation-corrected images we calculated the²⁰¹Tl concentration in tumour and normal contralateral brain tissue, and compared intratumoral tracer concentration in the initial and the final part of the rapid acquisition protocol. Benign and malignant meningiomas were classified as such based on histological examination. In malignant lesions, the ratio of the²⁰¹Tl concentration at 2–4 min post injection to that at 14–16 min was found to be significantly higher than in non-aggressive neoplasms (mean±1 SD: 1.14±0.31 and 0.56±0.13, respectively,P <0.01). Conversely, in the delayed scan, most lesions showed high tracer concentration, and the two groups could not be distinguished. In addition, three recurrent meningiomas displayed the same imaging behaviour as the malignant group, i.e. had similar²⁰¹Tl concentration values at 2–4 and at 14–16 min. Our findings suggest that the comparative assessment of intratumoral²⁰¹T1 concentration at 2–4 and at 14–16 min post injection could provide a fast, simple method to differentiate preoperatively intracranial meningiomas with different biological behaviour.     

Technetium-99m-tetrofosmin uptake in malignant lung tumours

Technetium-99m-tetrofosmin is a new myocardial imaging agent which has yielded promising results compared to thallium-201. The tumour-seeking properties of the routinely used cardiac radiopharmaceuticals²⁰¹Tl and^99mTc-methoxyisobutylisonitrile are well known. Here we report the results of a pilot study demonstrating^99mTc-tetrofosmin uptake in malignant lung tumours. Five patients with bronchial carcinoma, each in different stages of chemo- or radiotherapy, were imaged. Dynamic and static acquisitions were performed to evaluate the uptake and kinetics of^99mTc-tetrofosmin in the lesions. In four of the five patients localized tumour uptake of^99mTc-tetrofosmin was observed. Time to peak tumour activity and tracer washout in the tumour, myocardium and contralateral normal lung at 30 min post injection (p.i.) were determined. Tumour/normal lung, heart/tumour and heart/contralateral normal lung ratios were calculated for 5–10, 25–30 and 85–90 min p.i. The peak concentration in all tumours was reached at the end of the first minute. The mean tumour and contralateral normal lung washout rates of^99mTc-tetrofosmin at 30 min p.i. were 18.3%±9.2% and 19.5%±5.85% respectively. The tumour/contralateral normal lung ratio remained higher than 1.25 until 90 min p.i. in all four patients. It is concluded that^99mTc-tetrofosmin seems to be of value in lung tumour imaging, although larger studies are necessary to ascertain its sensitivity, specificity and usefulness in clinical practice.     

Relationship between thallium-201 uptake by supratentorial glioblastomas and their morphological characteristics on magnetic resonance imaging

Single-photon emission tomography (SPET) with thallium-201 is used in the assessment of patients with gliomas because the amount of²⁰¹Tl accumulated by the tumoral cells increases in proportion to the degree of tumour malignancy, thus making it possible to differentiate high-grade from low-grade gliomas or recurrences from radiation necrosis. However, in large areas of tissue such as those examined in²⁰¹Tl SPET studies, the uptake of²⁰¹Tl may vary considerably even in tumours with the same histological diagnosis, as occurs in glioblastomas (GBMs). In order to evaluate the possible influence of the macroscopic characteristics of tumours on²⁰¹Tl uptake, we studied a series of 13 patients with histologically proven GBMs, comparing magnetic resonance imaging (MRI) parameters such as tumour dimensions, perilesional oedema, intratumoral necrosis and contrast enhancement with the degree of²⁰¹Tl uptake. The patients underwent both²⁰¹Tl SPET and MRI before surgery. The²⁰¹Tl index (tumour/contralateral unaffected brain) was calculated using two different region of interest (ROI) methods: the first employed irregular large ROIs (3.2±13.9 cm²) including pixels with more than 50% maximum activity; the second employed regular square small ROls (2.7 cm²) centered on the maximum activity of the lesion. Of the MRI morphological parameters studied, only necrosis significantly reduced the degree of²⁰¹Tl uptake in GBMs when larger ROIs were used. However, by using small regular ROIs the influence of necrosis on²⁰¹Tl uptake was found to be less relevant. Since necrosis is related to tumour proliferative activity and represents a negative prognostic factor in astrocytoma, a possible underestimation of²⁰¹Tl uptake due to intratumoral necrosis must be carefully evaluated.     

The optimum time for tumour imaging with thallium-201

Following the intravenous injection of 75 MBq 201Tl-chloride we have assessed the uptake kinetics in the myocardium and in the primary tumour in 56 patients with lung cancer, 26 with breast cancer and 13 with mediastinal lymphoma. The time of maximal tumour uptake ranged from 8-20 min post-injection and did not differ significantly between lung cancer (mean +/- SD = 11.9 +/- 3.34 min), breast cancer (11.21 +/- 1.88 min) and lymphoma (11.76 +/- 3.25 min). The time of maximum cardiac uptake of 201Tl was 11.61 +/- 3.25 min. There was no significant washout of 201Tl from the tumours in the first hour after injection in the various malignant lesions studied. The time of maximal tumour to background activity was 18.3 +/- 0.59 min for lung cancer, 13.0 +/- 1.16 min for breast cancer and 16.7 +/- 1.04 min for lymphoma. The time course of 201Tl uptake in the tumours suggests that the mechanism of uptake is similar to that in the myocardium. The optimal time of 201Tl tumour imaging is from 20-60 min following injection and did not differ in various tumours studied.     

Sequential scintigraphic strategy for the differentiation of brain tumours

Both thallium-201 and iodine-123 α-methyltyrosine (¹²³I-IMT) have been shown to be useful in the diagnostic evaluation of brain tumours. The aim of this study was to investigate the respective contributions of ²⁰¹Tl and ¹²³I-IMT single-photon emission tomography (SPET) in the non-invasive evaluation of intracerebral tumours. We analysed 65 patients with the following brain tumours: 8 non-neoplastic lesions, 4 meningiomas, 12 low-grade gliomas, 28 high-grade gliomas, 11 metastases and 2 high-grade lymphomas. ²⁰¹Tl SPET and ¹²³I-IMT SPET were performed [start of ²⁰¹Tl SPET: 15 min p.i. (early) and 180 min p.i. (delayed); start of ¹²³I-IMT SPET: 15 min p.i.]. The intensity of uptake was quantified as the ratio between tracer accumulation in the tumour and in the contralateral hemisphere. None of the non-neoplastic lesions or low-grade gliomas expressed marked ²⁰¹Tl uptake. All malignant tumours except one small metastasis and all meningiomas except one small, cystic and degenerated lesion showed significant ²⁰¹Tl accumulation [Tl(15’)>2.0]; ¹²³I-IMT uptake was either absent or intermediate in non-malignant lesions except in two low-grade gliomas; the highest levels were observed in high-grade gliomas followed by metastases and lymphomas (mean IMT: 2.7 vs 2.1 vs 1.8), with metastases showing a high variability in ¹²³I-IMT uptake (range: 0.8–3.6). Using ²⁰¹Tl to distinguish non-neoplastic lesions from malignant tumours and meningiomas, 63 of 65 patients were characterised correctly. In the latter group, high-grade gliomas were correctly identified in 27 of 28 cases by their amino acid uptake. It is concluded that the combination of ²⁰¹Tl and ¹²³I-IMT surpasses the accuracy of each single test in the differentiation of space-occupying lesions of the brain. Based on these preliminary results, a sequential strategy is proposed involving an initial ²⁰¹Tl SPET study and an additional ¹²³I-IMT SPET study in the event of positive ²⁰¹Tl uptake. Received 1 October 1999 and in revised form 8 January 2000     

Use of somatostatin analogue scintigraphy in the localization of recurrent medullary thyroid carcinoma

Detection of recurrence of medullary thyroid carcinoma (MTC) remains a diagnostic problem. Increased serum tumour marker levels frequently indicate recurrence while conventional imaging techniques (CIT) are non-diagnostic. In this study, we performed indium-111 octreotide scintigraphy and CIT in a series of 20 patients with MTC presenting with elevated serum tumour markers after surgery. ¹¹¹In-octreotide whole-body studies detected 15 pathological uptake foci in 11 of the 20 patients studied and CIT detected 17 lesions in 11 of the 20 patients. Ten patients underwent reoperation, five of them with positive ¹¹¹In-octreotide scintigraphy and CIT and two with positive isotopic exploration and negative CIT. Surgical findings demonstrated that the results of isotopic study and CIT had been false-positive for MTC in one case (sarcoidosis). The six patients with true-positive ¹¹¹In-octreotide studies had significantly higher basal calcitonin (CT) and carcinoembryonic antigen (CEA) levels than the patients with negative isotopic studies. The expression of somatostatin receptor (SSTR) subtypes by PC-PCR could be investigated in four cases with a positive isotopic study. Among the three cases with a true-positive study, SSTR2, the SSTR subtype that preferentially binds to the somatostatin analogue octreotide, was detected in two, SSTR5 was demonstrated in the three, and SSTR3 was detected in one. No subtype of SSTR was detected in the case with a final diagnosis of sarcoidosis. We conclude that ¹¹¹In-octreotide has limited sensitivity in detecting recurrence in patients with MTC, although its sensitivity may improve with high serum CT levels. This radionuclide imaging technique should be employed when conventional imaging techniques are negative or inconclusive or when the presence of somatostatin receptors may provide the basis for treatment with somatostatin analogues. Received 5 April and in revised form 27 July 1998     

201Tl scintigraphy in the staging of lung cancer, breast cancer and lymphoma

To evaluate 201Tl in the detection of the primary tumour, lymph node involvement and mediastinal spread we have studied a total of 188 patients with histologically proven lung cancer, breast cancer or malignant lymphoma. Ten patients with benign lung disease were also examined. Static images were performed 20 min after intravenous injection of 75 MBq of thallous (201Tl) chloride. The results were compared with those of standard staging procedures including CT scanning and mediastinal exploration. Thallium-201 imaging was highly sensitive in detecting the primary tumour (lung cancer 86%, breast carcinoma 100%, lymphoma 85%), but showed low sensitivity in detecting mediastinal spread or lymph node involvement. Thallium-201 uptake was also observed in active sarcoidosis (one case) and active TB (two cases). We conclude that 201Tl imaging is unlikely to have a clinically useful role in the diagnosis or staging of lung cancer, breast cancer or lymphoma.     

Early and delayed thallium-201 scintigraphy in thyroid nodules: the relationship between early thallium-201 uptake and perfusion

Seventy-six patients with thyroid nodules were studied. Initially, 74 MBq of thallium-201 was injected. The thyroid gland was imaged 15 min (early) and 3 h (delayed) after the injection. Thereafter, 185 MBq technetium-99m pertechnetate was injected. Immediately after the injection, a 1-min perfusion image was acquired, followed by an image at 20 min. Increased early and delayed²⁰¹Tl uptake compared with the contralateral thyroid tissue was adopted as the criterion for malignancy. Sensitivity, specificity and negative predictive values were found to be 85%, 64% and 78%, respectively, in operated patients, but these values were 86%, 87% and 95%, respectively, in the whole group, including patients followed with fine-needle aspiration biopsy. With the purpose of investigating the relationship between perfusion and early²⁰¹Tl uptake, both perfusion and early images were graded comparing nodular activity with contralateral thyroid activity. There was a poor correlation between perfusion and²⁰¹Tl uptake. The correlation was even worse in hyperactive nodules. It is concluded that early and delayed²⁰¹Tl imaging should not be used in the differential diagnosis of cold nodules and that early²⁰¹Tl uptake seems to be more closely related to factors other than perfusion.     

The effect of steroid on thallium-201 uptake by malignant gliomas

In order to assess the effect of steroid on thallium-201 uptake by glioma,²⁰¹TI single-photon emission tomography was performed before and after steroid administration in four patients with recurrent malignant glioma. After steroid administration the²⁰¹Tl index, expressed as the ratio of²⁰¹Tl uptake in the tumour to that in the contralateral cerebral hemisphere, was 0.77±0.11 of the value before steroid (mean±SD:P<0.05 by pairedt test). The²⁰¹Tl index has been used as a possible indicator for the differentiation of malignant gliomas from relatively benign tumours or radiation necrosis. The present results indicate that the effect of steroid has to be taken into account when semi-quantitative analysis, e.g. by means of the²⁰¹Tl index, is used in patients with brain tumours.     

Clearance of thallium-201 from the peripheral blood: Comparison of immediate and standard thallium-201 reinjection

As several reinjection procedures have shown encouraging results in terms of imaging, we investigated whether the kinetics of thallium-201 would differ between the standard stress-redistribution-reinjection approach and the stress-immediate reinjection approach. In 53 consecutive patients with undiagnosed chest pain, 75 MBq (2 mCi)²⁰¹Tl was injected at maximal exercise. In 26 of these patients (group I), 37 MBq (1 mCi)²⁰¹Tl was reinjected immediately after completing the exercise images (the immediate reinjection procedure) and in 27 patients (group II), 37 MBq (1 mCi)²⁰¹Tl was reinjected after completing 3-h redistribution images (the standard reinjection procedure). Mean peak²⁰¹Tl blood activity after exercise was 17.7±12.5 kBq/ml (4.8±3.4 mCi/ml) for group I versus 16.4±9.2 kBq/ml (4.4±2.5 mCi/ml) for group II (NS). The relative increase in²⁰¹Tl blood activity after reinjection of half the initial dose [37 MBq (1 mCi)] exceeded 50% of the initial peak in both groups. The relative amount of²⁰¹Tl delivered to the myocardium was assessed by the area under the curve after both exercise and reinjection, and was 117%±72% for group I and 112%±73% for group II (NS). Blood clearance of²⁰¹Tl was at least biexponential. Mean early decay constants (₁) after exercise and reinjection were 0.30±0.18 min^–1 and 0.22±0.046 min^–1 respectively for group I (T _1/2 2.3 min and 3.2 min respectively, NS), and 0.30±0.12 min^–1 and 0.24±0.07 min^–1 respectively for group II (T _1/2 2.3 min and 2.9 min respectively, NS). For both procedures no significant differences were found between ₁ after exercise and ₁ after injection. The mean late clearance (₂) from the blood was 0.032±0.056 min^–1 and 0.012±0.012 min^–1 respectively for group I (T _1/2 21.6 min and 57.7 min respectively, NS), and 0.036±0.030 min^–1 and 0.014±0.014 min^–1 respectively for group II (T _1/2 19.3 min and 49.5 min respectively, NS). Also, no significant differences were found between ₂ after exercise for both groups and between ₂ after reinjection for both groups. We conclude that reinjection of 37 MBq (1 mCi)²⁰¹Tl (half the initial dose) results in a relative increase in the initial peak and a relative increase in the amount of²⁰¹Tl delivered to the myocardium of more than 50% for both the standard and the immediate reinjection procedure. The clearance of²⁰¹Tl from the blood was not influenced by exercise or by the time of reinjection. Based on²⁰¹Tl kinetics as measured in the peripheral blood, there is no reason to postpone reinjection until 3–4 h following exercise.     

Indium-111 bleomycin complex for radiochemotherapy of head and neck cancer — dosimetric and biokinetic aspects

Bleomycin (BLM) is used for the treatment of head and neck cancer. In order to improve the effectiveness of this chemotherapeutic drug, BLM was combined with indium-111. A complex of these agents (¹¹¹In-BLMC), formed at low pH, was injected intravenously into ten head and neck cancer patients in escalating activities of 75, 175 and 375 MBq. The internally delivered dose to the tumours varied from 0.20 to 2.73 mGy at 75 MBq, from 0.33 to 2.51 mGy at 175 MBq, and from 0.87 to 31.3 mGy at the 375 MBq activity level. Uptake of radioactivity was 0.45±0.24×10^–3% ID/g in primary tumours and 0.52±0.20×l0^–3% ID/g in metastases (at 48 h). Tumour volumes varied from 0.51 to 49.0 cm³. The radioactivity half-lives in the tumours were 30±7 h. The activity distribution and penetration into tumour tissue were not affected by increasing the injected activity. There was a positive correlation between BLMC uptake and Ki-67/Mib activity as well as number of mitoses in tumour tissue. These data indicate that¹¹¹In-BLMC has potential as a radiochemotherapeutic agent in head and neck cancer and that adjuvant Auger-electron therapy is possible using^114m-In-labelled BLMC.