Radioimmunotherapy with Monoclonal Antibodies

Radioimmunotherapy (RIT) with labeled tumor-associated monoclonal antibodies (MAbs) is a promising concept in oncology, which essentially consists of biological targeting of ionising radiation to tumors. Some encouraging clinical results have been achieved with RIT. However, there are severe problems associated with both understanding the mechanisms and predicting the effectiveness of RIT. This paper reviews the results of some major clinical trials, especially in malignant lymphomas and in some solid tumors. Furthermore, problems with RIT are described such as the significance of dose inhomogeneity and dose-rate effects, the appropriate dose calculation method, the toxicity of RIT and the development of HAMAs. It is suggested that newer technologies including chimeric antibodies, multiple-step targeting protocols, bone marrow transplantation, parallel application of external radiation, heat or bioreductive drugs will enable RIT to make an essential contribution to strategies for combating cancer.

Late Cervical Lymph Node Recurrence in Differentiated Thyroid Carcinoma

Die postoperative Radiojodtherapie ist unumstrittener Bestandteil der Gesamtbehandlungsstrategie beim differenzierten Schilddrüsenkarzinom. Gelegentlich werden jedoch Jahre nach Erstdiagnose und Therapie zervikale Lymphknotenmetastasen manifest, ohne daß ein Rezidiv des Primärtumors oder Fernmetastasen nachweisbar sind. In diesen Fällen war die Radiojodtherapie offensichtlich nicht ausreichend, um eine endgültige Tumorzellsterilisation zu bewirken. Die vorliegende Arbeit suchte eine Erklärung für dieses Phänomen, indem die räumliche Dosisverteilung von 131J bei sehr kleinen Tumormanifestationen im Modell mit der Monte-Carlo-Methode simuliert wurde. Dabei zeigte sich, daß für Tumorgrößen unterhalb 1 mm Radius nur noch ein kleiner Bruchteil der gesamten β-Energie innerhalb des Tumors deponiert wird und zur Tumorvernichtung beiträgt: Für Radien von 1,0, 0,5, 0,2, 0,1, 0,05 und 0,02 mm stehen bei homogener 131J-Speicherung intratumoral nur jeweils 86, 73, 39, 16, 8 bzw. 4% der Gesamtenergie zur Verfügung. Dies könnte einer wirksamen Tumorzellvernichtung in kleinen, bei Erstdiagnose klinisch nicht nachweisbaren Tumormanifestationen entgegenstehen und somit Ursache für späte zervikale Lymphknotenmetastasen sein.

Stellenwert der 99mTc-M DP-Skelettszintigraphie beim Neuroblastom

The present study compares the reliability of MIBG and MDP bone scans in detecting bone metastases of neuroblastoma. Out of 57 patients, 23 had both 99mTc-MDP and 123I/131I-MIBG scans within a 2-week period. In 10 patients at primary diagnosis there was an underestimation of skeletal involvement by MIBG in 1/5, in 13 patients at follow-up in 3/9; 99mTc-MDP scans were able to visualize skeletal involvement in all those cases. There was only one false positive MDP scan. These results suggest that MIBG alone may fail to visualize skeletal involvement of neuroblastoma and should therefore be complemented by additional 99mTc-MDP scintigraphy

Radiosynovectomy for the treatment of rheumatoid arthritis of the elbow

The Aim of this retrospective study was to evaluate the efficiacy of radiosynovectomy (RSO) in patients with rheumatoid elbow arthritis. Patients and Methods: 40 joints of 31 patients were evaluated. At the time of therapy, patients had been suffering from elbow arthritis for 17.5 months (2-72 months). 95% of the joints (n = 38) had severe dally pain or continuous pain, 97.5% (n = 39) had moderate to severe limitation of the mobility and 10% (n = 4) had severe swelling. RSO was performed by intraarticular injection of 74 MBq colloidal rhenium-l 86 and 15 mg triamcinolonehex-acetonide. Before and six to 26 months after therapy (median follow-up 14.7 months) severity of the patients pain, mobility and swelling (transferred to a scoring system) were determined with a standardised questional. A clinical re-evaluation, along with an ar-throsonographical follow-up was performed in 28 joints. Results: A “good to very good” overall long-term response was achieved in 80% (n = 32) of the treated joints and a temporary response in 10% (n = 4). Only 10% (n = 4) had a non-satisfactory response due to advanced articular destruction. The range of motion for flexion-extension increased from 103.8 ± 20.0 degrees to 144.0 ±12.8 degrees (p <0.001). The respective scores for articular pain, impaired mobility and swelling decreased significantly (pain from 3.15 to 0.82, impaired mobility from 3.15 to 0.82, swelling from 2.40 to 0.65; p <0.00U. No deterioration or complication occurred. The effects lasted throughout the entire follow-up time for 36 joints (90%). Conclusion: For patients with rheumatoid involvement of the elbow joint, radiosynovectomy results in a significant decrease of articular pain and improvement of objective parameter, i.e. joint mobility. Thus, radiosynovectomy represents a feasible and effective therapeutic option for elbow arthritis.

[The integrated PET/CT: technological advance in diagnostics of head and neck recurrencies and CUP?]

BACKGROUND

In the last years (18)F-Fluoro-deoxy-glucose (FDG)-positron emission tomography (PET) worked satisfactorily as auxiliary method in order to show recurrency of head and neck tumors and to detect primary tumors in case of CUP especially when CT and MR imaging failed to identify the tumor accurately. The correlation of FDG hypermetabolism and anatomical structures is now provided by a new technology which is integrating PET and CT: Integrated PET/CT represents a new technical development, which combines the advantages of CT and PET.

PATIENTS

In a retrospective investigation 84 non selected PET/CT studies of 83 patients with recurrent head and neck disease and CUP were critically analyzed.

RESULTS

33 cases had positive PET findings. 5 of these 33 cases showed false-positive findings. In 51 PET studies there was not found any sign of suspicious FDG hypermetabolism.

CONCLUSION

Integrated PET/CT delivers substantial progress in detecting tumor localization. False positive findings have to be considered and therefore indications should be strictly limited to special cases of head and neck tumor recurrency, cases with complex anatomical sites and CUP.

[Significance of PET and integrated PET/CT in the diagnostics of occult primary tumors]

BACKGROUND

In the last years (18)F-FDG-positron-emission-tomography (PET) worked satisfactorily as helpful auxiliary method in order to verify recurrency of head and neck tumors and to detect primary tumors in case of CUP syndrome especially when CT and MR imaging failed to identify the tumor accurately. Fusion of FDG hypermetabolism in PET scan and anatomical structures is achieved by integrating positron emission tomography with CT and provides improvement also in case of CUP syndrome. This retrospective study shows 47 patients with neck metastases where PET or PET/CT helped to detect primary tumor site.

PATIENTS

In a retrospective investigation 49 PET studies of 47 patients with CUP syndrome were analyzed.

RESULTS

9 cases had positive PET findings, 1 case false-positive. 5 cases were false-negative. In 40 PET studies there couldn't be found any sign of suspicious FDG hypermetabolism.

CONCLUSION

PET and PET/CT deliver a certain improvement in localization of primary tumor site and therapeutical strategy.

131 I-cG250 monoclonal antibody immunoscintigraphy versus [18 F]FDG-PET imaging in patients with metastatic renal cell carcinoma: a comparative study

The aims of this study were to establish the percentage of metastatic renal cell carcinoma (RCC) lesions detected by radioimmunoscintigraphy (RIS) with the chimeric monoclonal antibody 131I-cG250 versus positron emission tomography (PET) with 18F-labelled deoxyglucose ([18F]FDG), and to evaluate the use of these radionuclide imaging modalities compared with routinely used imaging techniques. Twenty patients with metastatic RCC disease were examined with [18F]FDG-PET and 131I-cG250 RIS within 1 week. Total body gamma camera images were obtained up to 120h after injection of 232MBq 131I-cG250. Total body PET scanning was performed 45-60 min after intravenous injection of 370MBq [18F]FDG. Nuclear medicine techniques were compared to routine imaging procedures. Routine imaging modalities revealed a total of 79 metastases. [18F]FDG-PET and 131I-cG250 RIS detected 33 previously unknown metastases, of which 32 were [18F]FDG positive and seven were 131I-cG250 positive. Of the 112 tumour lesions that were documented, [18F]FDG-PET detected 69% (77 out of 112), whereas 131I-cG250 RIS detected only 30% (34 out of 112). In conclusion, [18F]FDG-PET is superior to 131I-cG250 RIS in detecting metastases in patients with metastatic RCC, and therefore seems a promising tool for (re)staging patients with RCC. The usefulness of RIS with a diagnostic dose of 131I-cG250 seems to be restricted to selecting patients for radioimmunotherapy with 131I-cG250.

[Radiosynovectomy for the treatment of rheumatoid arthritis of the elbow joint]

The aim of this retrospective study was to evaluate the efficacy of radiosynovectomy (RSO) in patients with rheumatoid elbow arthritis.

PATIENTS AND METHODS

40 joints of 31 patients were evaluated. At the time of therapy, patients had been suffering from elbow arthritis for 17.5 months (2-72 months). 95% of the joints (n = 38) had severe daily pain or continuous pain, 97.5% (n = 39) had moderate to severe limitation of the mobility and 10% (n = 4) had severe swelling. RSO was performed by intraarticulär injection of 74 MBq colloidal rhenium-186 and 15 mg triamcinolonehexacetonide. Before and six to 26 months after therapy (median follow-up 14.7 months) severity of the patients pain, mobility and swelling (transferred to a scoring system) were determined with a standardised questionnaire. A clinical re-evaluation, along with an orthrosonographical follow-up was performed in 28 joints.

RESULTS

A "good to very good" overall long-term response was achieved in 80% (n = 32) of the treated joints and a temporary response in 10% (n = 4). Only 10% (n = 4) had a non-satisfactory response due to advanced articular destruction. The range of motion for flexion-extension increased from 103.8 +/- 20.0 degrees to 144.0 +/- 12.8 degrees (p < 0.001). The respective scores for articular pain, impaired mobility and swelling decreased significantly (pain from 3.15 to 0.82, impaired mobility from 3.15 to 0.82, swelling from 2.40 to 0.65; p < 0.001). No deterioration or complication occurred. The effects lasted throughout the entire follow-up time for 36 joints (90%).

CONCLUSION

For patients with rheumatoid involvement of the elbow joint, radiosynovectomy results in a significant decrease of articular pain and improvement of objective parameter, i.e. joint mobility. Thus, radiosynovectomy represents a feasible and effective therapeutic option for elbow arthritis.

Clinical relevance of positron emission tomography (PET) in treatment control and relapse of Hodgkin's disease

BACKGROUND

In Hodgkin's disease accurate restaging is important to assess treatment results and may eventually provide a basis for further therapeutic strategies. A typical dilemma after treatment of Hodgkin's disease with radiographically persistent lymphoma is the differentiation between sterilized residual mass and viable tumor. Positron emission tomography (PET) has been described as a reliable tool to identify active lymphoma. Aim of the present study was to assess the accuracy and clinical relevance of PET for treatment control and in the situation of a suspected relapse of Hodgkin's disease.

PATIENTS AND METHODS

63 patients (32 men, 31 women, mean age 41.5 years) with Hodgkin's disease were investigated with FDG-PET. In 51 patients 63 PET studies were performed as a treatment control (group 1) after primary therapy. 17 patients (5 of whom preexamined in group 1) underwent 18 PET scans for confirmation of suspected relapse (group 2). PET was performed with a dedicated whole-body ring scanner. In a retrospective analysis, all FDG-PET scans were compared with conventional imaging methods and related to the final diagnosis obtained by histology and/or clinical follow-up (mean 22.4 months).

RESULTS

Group 1: FDG-PET showed an accuracy of 91%, whereas the accuracy of conventional imaging was 62%. Group 2: The accuracy for PET was 83% and 56% for conventional imaging.

CONCLUSION

The present data suggest that PET is a sensitive and reliable tool for detection of involved areas of active Hodgkin's disease. The accuracy of PET for restaging purpose seems to be superior than conventional imaging.

Whole body positron emission tomography in the treatment of Hodgkin disease

BACKGROUND

In Hodgkin disease (HD), accurate assessment of the extent of disease is essential because it provides the basis for different treatment strategies. In addition to conventional imaging methods (CIM), positron emission tomography with fluorine-18-fluorodeoxyglucose (FDG-PET) may permit reliable differentiation between lymphoma and nonmalignant tissue and thus improve determination of the stage of the disease. The aim of the current study was to assess the clinical value of FDG-PET for primary staging, treatment monitoring, and assessment in a suspected case of recurrent HD.

METHODS

Eighty-one patients with HD underwent 106 FDG-PET studies using a dedicated whole body PET ring scanner. In 25 patients PET was part of the primary staging, 63 PET studies were undertaken for treatment monitoring after the completion of treatment, and in 18 patients PET was performed in cases of suspected recurrence of HD. PET scans were compared with CIM and verified histologically and/or by follow-up evaluation (mean follow-up duration, 20.4 months).

RESULTS

With regard to primary staging, in a patient to patient analysis, both PET scans and CIM were positive (i.e., showed pathologic foci indicative of HD) in 24 of 25 cases. In a staging-relevant lesion to lesion analysis, accuracy in the determination of the stage of disease was 96% for PET versus 56% for CIM. PET led to a lower stage classification in 28% and a higher stage classification in 12% of cases, compared with the stage assumed with CIM. With regard to treatment monitoring, PET showed an accuracy of 91% compared with 62% for CIM. The negative predictive value of PET was 96%. With regard to suspected recurrence, PET findings were true-positive in 10 of 12 PET scans and true-negative in 5 of 6 PET scans, resulting in accuracy of 83%, which compares favorably with the accuracy rate of 56% for CIM.

CONCLUSIONS

It may be concluded that FDG-PET is capable of determining the stage of HD with great accuracy and is capable of correctly detecting manifestations of HD in treatment monitoring and cases of suspected recurrence, in which CIM occasionally result in equivocal findings. The results of the current study suggest that FDG-PET should become a routine tool in the staging/restaging of HD.

Absence of somatostatin receptor expression in vivo is correlated to di- or tetraploid 1p36-deleted neuroblastomas

BACKGROUND

Poor prognosis in childhood neuroblastoma is associated with deletions of chromosome region 1p36 and di/tetraploid DNA content.

PROCEDURE

Forty-six patients with histopathologically proven neuroblastoma were investigated for in vivo expression of somatostatin receptors (SR) by 111In-pentetreotide scintigraphy. All tumors were analyzed for cytometric DNA content and chromosome 1p36 integrity.

RESULTS

SR expression was detected in 28 tumors (61%) and correlated with young age, localized clinical stage, and favorable outcome. Fourteen tumors showed deletion at chromosome 1p36, thirteen of which did not show SR expression (P< 0.001). A triploid DNA content was correlated with the presence of SR (23 of 25, P< 0.001). No tumor with deletion of chromosome 1p36 and di/tetra DNA content showed SR expression (chi2 = 29.88, d.o.f. = 2, P < 0.001).

CONCLUSIONS

We conclude that SR expression is related to genetic features of prognostic significance. This may be assessed with a minimally invasive scintigraphic method.

Combined (111)In-pentetreotide scintigraphy and (123)I-mIBG scintigraphy in neuroblastoma provides prognostic information

BACKGROUND

High-affinity somatostatin receptors (SRs) have been characterized in neuroblastomas and may be used as target structures for in vivo detection of SR.

PROCEDURE

Eighty-eight children with histologically proven neuroblastoma were investigated at diagnosis or relapse by (123)I-mIBG and (111)In-pentetreotide scintigraphy. All tumors were investigated for MYCN copy number, chromosome 1p36 status, and 68/88 also for DNA content, followed for a median follow-up of 35 months (range 1-88 months).

RESULTS

SR expression was detected in 56/88 tumors and (123)I-mIBG showed positivity in 83/88. (111)In-pentetreotide was less sensitive in detecting tumor tissue than was (123)I-mIBG (64% vs. 94%, P = 0.005). Survival (SUR) and event-free survival probability (EFS) according to Kaplan-Meier was significantly better for children with positive SR scintigraphy than for the children with a negative SR scan (SUR: 90% vs. 48% at 4 years log rank P < 0.003, EFS: 83% vs. 39% at 4 years, log rank P < 0.0002).

CONCLUSIONS

(123)I-mIBG scintigraphy remains the best scintigraphic method for detecting neuroblastoma tumor tissue, whereas additional SR scintigraphy is able to provide significant prognostic information with a minimum of invasiveness.

Technetium-99m human immunoglobulin (HIG): a new substance for scintigraphic detection of bone and joint infections

Technetium (99m-Tc)-labelled, polyclonal human immunoglobulin (HIG) has been described as a new agent to detect local infection and inflammation. In this study, we tested 99m-Tc HIG in 55 patients with suspected chronic (n = 42) and acute (n = 13) skeletal infection. Diagnosis was proven operatively (n = 44) and clinically (n = 11), including microbiological culture tests (n = 46). A gamma camera scan was performed 4 and 24 hours after I.v. injection of 500 MBq 99m-Tc-HIG. 99m-Tc-HIG scanning achieved a sensitivity of 91% and a specificity of 93%. We found one false negative and five false positive scintigraphic results in 55 patients. No clinical or biochemical side effects were encountered after 99m-Tc-HIG injection. We recommend this technique especially for localisation of low-grade, chronic osteomyelitis. The mechanisms and kinetics of 99m-Tc-HIG, however, are worth investigating more extensively.

Somatostatin in neuroblastoma and ganglioneuroma

Neuroblastoma, a childhood tumour of the sympathetic nervous system, may in some cases differentiate to a benign ganglioneuroma or regress due to apoptosis. Somatostatin may inhibit neuroblastoma growth and induce apoptosis in vitro and was therefore investigated. Using a radioimmunoassay, we found that all ganglioneuromas contained high somatostatin concentrations (> 16 pmol/g), significantly higher than neuroblastomas (n = 117, median 2.8 pmol/g), healthy adrenals, Wilms' tumours, phaeochromocytomas and other neuroendocrine tumours (P < 0.001). Neuroblastomas contained more somatostatin than control tumours (P < 0.001-0.05). Neuroblastomas amplified for the MYCN oncogene contained less somatostatin than non-amplified tumours (1.2 pmol/g versus 4.0 pmol/g, respectively; P = 0.026). In a clinically unfavourable neuroblastoma subset (age > 12 months, stage 3 or 4) 16 children with high concentrations of somatostatin in primary tumours had a better prognosis than 23 with low somatostatin (46.7% versus 0% survival at 5 years, P < 0.005). Scintigraphy using 111In-pentetreotide identified tumours expressing high-affinity somatostatin receptors in vivo. However, no significant correlation was found between somatostatin receptor expression and peptide content in 15 tumours. Similarly, human SH-SY5Y neuroblastoma xenografts grown in nude rats showed low somatostatin concentrations, but were positive for somatostatin receptor scintigraphy. Treatment of these rats with the somatostatin analogue octreotide seemed to upregulate in vivo receptor expression of somatostatin and vasoactive intestinal peptide more effectively than 13-cis retinoic acid. In conclusion, somatostatin in neuroblastoma is associated with differentiation to benign ganglioneuromas in vivo and favourable outcome in advanced tumours. Furthermore, somatostatin receptor scintigraphy may identify tumours with high-affinity receptors in children that might benefit from targeted therapy using synthetic somatostatin analogues.

Comparison of MIBG and pentetreotide scintigraphy in children with neuroblastoma. Is the expression of somatostatin receptors a prognostic factor?

BACKGROUND

Neuroblastoma (NB) is the fourth most common pediatric malignancy and recent reports suggest a prognostic role of somatostatin receptor scintigraphy (SRS) in this disease.

MATERIALS AND METHODS

Twenty two patients (pts. mean age 43.9 months) with NB were investigated by 1-123-MIBG and SRS (In-111-pentetreotide). Twenty-seven comparative scans were evaluated and compared for catecholamin excretion, Ultrasound, CT and MRI data. The patients were then divided into three groups. I: patients with manifest disease, II: patients with relapse or minimal disease and III: patients with no evidence of disease.

RESULTS

MIBG and SRS scans were concordant in 85% (12 true positive, 7 true negative, 4 false negative). In 4 pts only the MIBG scan was positive. In 9 pts with stage I-III disease or complete remission no relapse was recorded during 19.8 months. In 4 out of 5 pts who died SRS failed to localize the tumor sites but three MIBG scans were positive. Five out of 6 pts with a relapse free interval of 7.9 months had positive SRS and MIBG scans.

CONCLUSIONS

in NB SRS can be applied as a specific imaging modality. However, in some pts SRS failed due to the lack of receptor expression. Somatostatin receptor expression seems to be related with a more favourable clinical outcome.

[Value of 99mTc-MIBI scintigraphy in diagnostic localization of hyperparathyroidism. A prospective study]

We evaluated the sensitivity of praeoperative parathyroid imaging using 99mTc-MIBI scintigraphy in planar as well as SPECT technique to detect and localize abnormal parathyroid glands in 36 patients with hyperparathyroidism. Seven out of these patients had been previously operated in the thyroid area. With a sensitivity of 76% (22/29) solid adenomas could be localized correctly. Surgical success was estimated by the weight of the adenomas, by histology and postoperative laboratory findings. Compared to other imaging procedures 99mTc-MIBI-scintigraphy seems to be most sensitive in detecting and localizing abnormal parathyroid glands, especially in previously operated patients. Praeoperative standard in nuclear medicine up to now is Tl-Tc-subtraction scintigraphy, which is technically more difficult, sensitive to artefacts and exposes the patient to more radiation. Based on our experience we would therefore suggest to screen all previously operated patients with 99mTc-MIBI scintigraphy on a routine basis.

Efficient symptomatic control of carcinoid tumors with somatostatin in patients with disease progression under alpha-interferon therapy

BACKGROUND/AIMS

We report--as a retrospective observation--on eight patients with malignant carcinoid tumors.

MATERIALS AND METHODS

All patients were initially treated with alpha-interferon and received the longacting somatostatin analogue octreotide (SMS 201-995) after disease progression. Tumor growth was monitored by CT-scan or ultrasound. In addition, serum CgA and urinary 5-HIAA values were determined.

RESULTS

All patients responded with relief of symptoms within a few days after the start of octreotide therapy. A regression of the tumor size did not occur, however four patients showed no significant progress over a period of nine to more than eighteen months. The endocrine parameter chromogranin A--determined by immunoluminometric assay (ILMA)--was elevated in all eight patients regardless of symptoms and showed a close correlation with the course of disease. The urinary 5-HIAA values were only elevated in seven patients. In addition, 123I-SMS 204-090 scintigraphy could be performed in six patients. Using this method most of the primary tumors and metastases could be detected.

CONCLUSIONS

Only octreotide therapy showed a sufficient symptomatic control and has to be considered as progress in drug therapy for patients with malignant carcinoid tumors. In addition, chromogranin A is an interesting endocrine parameter for the follow-up of the secretory activity.

Somatostatin receptor imaging in persistent medullary thyroid carcinoma

OBJECTIVE

Somatostatin is secreted from thyroid C-cells and seems to play an important part in the regulation of calcitonin secretion. We therefore evaluated the usefulness of somatostatin receptor scintigraphy in the localization of tumour tissue in patients with persistent medullary thyroid carcinoma.

DESIGN

A prospective clinical study.

PATIENTS

The series consisted of 26 patients with elevated calcitonin levels after total thyroidectomy for histologically proven medullary thyroid carcinoma.

METHODS

Somatostatin receptor scintigraphy using 111In-pentetreotide (Octreoscan) was performed in all patients and the results correlated with histology, ultrasonography, computerized tomography, magnetic resonance imaging, plain radiography, bone scintigraphy and selective venous catheterization. Calcitonin and carcinoembryonic antigen levels were measured.

RESULTS

The sensitivity of somatostatin receptor scintigraphy for localization of persistent medullary thyroid carcinoma was 57% in patients with histologically proven disease. The results depended on tumour mass (low sensitivity (33%) in minimal residual disease) and on the location of metastases (insensitive in detecting liver metastases).

CONCLUSIONS

Somatostatin receptor scintigraphy is of value as an additional diagnostic tool in localizing medullary thyroid carcinoma, especially pulmonary metastases. It is of minor importance in detecting minimal residual disease.

Radioimmunotherapy with monoclonal antibodies. A new horizon in nuclear medicine therapy?

Radioimmunotherapy (RIT) with labeled tumor-associated monoclonal antibodies (MAbs) is a promising concept in oncology, which essentially consists of biological targeting of ionising radiation to tumors. Some encouraging clinical results have been achieved with RIT. However, there are severe problems associated with both understanding the mechanisms and predicting the effectiveness of RIT. This paper reviews the results of some major clinical trials, especially in malignant lymphomas and in some solid tumors. Furthermore, problems with RIT are described such as the significance of dose inhomogeneity and dose-rate effects, the appropriate dose calculation method, the toxicity of RIT and the development of HAMAs. It is suggested that newer technologies including chimeric antibodies, multiple-step targeting protocols, bone marrow transplantation, parallel application of external radiation, heat or bioreductive drugs will enable RIT to make an essential contribution to strategies for combating cancer.

[Somatostatin receptor scintigraphy in the primary diagnosis and follow-up care of gastrinoma]

Somatostatin receptor scintigraphy (SRS) was performed in 14 patients (five men, nine women; mean age 51.5 [20-71] years) with Zollinger-Ellison syndrome (ZES), a gastrinoma proven in 7 and suspected on clinical or biochemical grounds in 7. The results were compared with those obtained by other methods (ultrasound, computed tomography, angiography). All 12 known tumour manifestations were demonstrated by SRS in seven patients with histologically confirmed gastrinoma. In four patients previously non-localized tumour was revealed by SRS, while in seven other patients the procedure led to modification of the treatment (primary tumour resection: n = 3, resection of metastases: n = 2, percutaneous radiation or chemoembolization: one each). These results suggest the following indications for SRS: (1) staging or re-staging in histologically proven gastrinoma and (2) search for primary tumour in clinically and biochemically suspected ZES.

Comparison of systemic radiotherapy with I-131-labeled monoclonal antibody BW575/9 to external beam radiotherapy in human neuroblastoma xenografts

The therapeutic effectiveness of external beam radiotherapy (XRT) and radioimmunotherapy (RIT) was investigated in a human neuroblastoma (SK-N-SH) xenotransplanted to nude mice. This tumor model seems especially suitable for comparison of the relative biological effectiveness of RIT vs. XRT, as--in contrast to most tumor models--it shows an unusually homogenous uptake of the labeled MAb, thus providing a homogenous intratumoral dose distribution. XRT was performed using single fractions of 800, 1600, 2000 and 2400 cGy and RIT was delivered by intravenous injection of 15, 19 and 26 MBq of the I-131-labeled monoclonal antibody (MAb) BW575/9. Therapeutic efficiency of the two radiation modalities was assessed in terms of tumor volume doubling time (VDT). Miniature thermoluminescent (mini-TLD) dosimetry and MIRD-based dose calculations were used to evaluate the absorbed doses delivered by RIT and to assess the degree of homogeneity of the dose distribution. RIT with 19 MBq of the I-131 BW575/9 delivered a tumor dose of 2820 cGy measured by TLD and resulted in a tumor VDT of 32 days (vs. one day in controls). An equivalent effect on VDT was achieved by a single fraction XRT of 1600 cGy. The relative efficiency of XRT compared with RIT (ratio of dose XRT/dose RIT required to give the same VDT) was 0.57. Application of 26 MBq of the MAb (= 3200 cGy) resulted in complete tumor regression after ten days as did XRT with 2400 cGy, corresponding to a relative efficiency of 0.75.

Systemic radiotherapy with monoclonal antibodies. An experimental study with human neuroblastoma xenografts in nude mice

In this experimental study, feasibility and efficiency of systemic radiotherapy with the I-131 labelled monoclonal antibody BW575/9 (radioimmunotherapy) are investigated using human SK-N-SH neuroblastoma transplanted into nude mice. Series of six nude mice were treated with intravenous application of 400 microCi (group 1), 700 microCi (group 2) of the I-131 labelled and of the unlabelled MAb (group 3). An untreated group (group 4) served as control. Tumors of group (3) and (4) showed an identical growth. In group (1), tumor growth was arrested for seven days. In group (2), the tumor showed complete regression after eight days which lasted for 55 days. Thereafter, the tumor started to regrow. This growth characteristics are correlated with the doses achieved in the tumor using a medical internal radiation dose (MIRD) formulation. The biodistribution data necessary for MIRD calculation were obtained by previously performed experiments with the I-125 labelled MAb. The doses assessed in the tumor turned out to be five to ten times greater than those in normal tissues (liver, bone, etc.) These results confirm feasibility, selectivity and efficiency of radioimmunotherapy in the above described model. Moreover, this in vivo model seems suitable for further investigations concerning fundamental issues of radioimmunotherapy.

The potential value of somatostatin receptor scintigraphy in medullary thyroid carcinoma

In a prospective study, ten patients with recurrent medullary thyroid carcinoma (markedly elevated calcitonin levels) were investigated by means of somatostatin receptor scintigraphy (SRS) with 111Inpentetreotide. Scintigraphically, 30 sites of pathological uptake were found, mostly located in the neck and upper mediastinum. So far, 18 suspected tumour sites underwent histological examination and 14 of them could be verified as metastases of medullary thyroid carcinoma (MTC). The remaining four putative tumour lesions turned out to be false positive scintigraphic findings caused by chronic inflammation and somatostatin receptor positive tumours other than MTC. We conclude that SRS is a promising imaging modality for localization of MTC recurrence and may thus make a contribution to better management of this patient group.

Monoclonal antibody accumulation in experimental and spontaneous lung metastases of human malignant melanoma in rodents

Monoclonal antibody (mAb) uptake in metastatic lung lesions was depicted and evaluated by digital autoradiography. The models examined were experimental metastases of a human melanoma in nude mice and spontaneous metastases of human melanoma in immunocompromised young rats. By comparing uptake patterns in local (s.c.) tumours and in lung processes of various sizes it was found that patterns were essentially similar in both types of malignant tissue. From the point of view of visualization, however, the high blood content of lung tissue resulted in high background and low contrast. This could be overcome by the use of rapidly cleared antibody fragments.

[Systemic radiotherapy using monoclonal antibodies. Options and problems]

Radiolabeled monoclonal antibodies (MAbs), by virtue of their tumor specificity, offer the prospect of localized, highly targeted radiation treatment of malignant tumors. To date, a large number of radioimmunotherapy (RIT) studies have been reported in experimental and clinical settings showing the potential of this therapeutic strategy. This includes RIT-trials in hepatoma, cholangiocarcinoma, ovarian carcinoma, brain tumors, melanoma, neuroblastoma and especially Hodgkin's and non-Hodgkin's lymphomas. Despite very promising results in some of these studies, radioimmunotherapy is currently still in a developmental status. Selective accumulation of MAbs at tumor sites-a prerequisite for effective radioimmunotherapy-is a complex process. Many factors such as antigen heterogeneity, distinct antibody features (affinity, subclass, fragment size, etc.), labeling techniques, tumor physiology and competing antigens were identified in the last years using theoretical and experimental tumor models. Strategies to improve these critical parameters are currently under investigation in order to increase the efficacy of radioimmunotherapy.

Improved visualization of carcinoid liver metastases by indium-111 pentetreotide scintigraphy following treatment with cold somatostatin analogue

Five patients with hepatic metastases of midgut carcinoid underwent somatostatin receptor scintigraphy with indium-111 pentetreotide before and during treatment with octreotide. Octreotide treatment changed the biodistribution of 111In-pentetreotide significantly. Whereas the radioactivity in liver, spleen and kidney decreased, hepatic metastases showed increased contrast. In one patient, liver metastases could only be detected during octreotide treatment. These data suggest that the diagnostic reliability of somatostatin receptor scintigraphy in carcinoid liver metastases is not necessarily compromised by octreotide therapy. Because of different biodistributions, the detection of liver metastases may even be improved during octreotide therapy.

[Somatostatin receptor scintigraphy. A new imaging procedure for the specific demonstration of carcinoids of the small intestine]

Scintigraphy with a radiolabelled somatostatin analog represents a new highly specific approach in the diagnostic work-up of receptor-positive APUD tumours and their metastases. We present our preliminary results with somatostatin receptor scintigraphy in 15 patients with histologically proven midgut carcinoid. 5 out of 6 primary tumour sites (83%) and 90% of the known metastatic lesions could be detected; unknown metastatic lesions were seen in 5 patients. Compared with other nuclear medicine procedures somatostatin receptor scintigraphy is able to detect all tumour sites within hours. This advantage will promote the acceptance of this sensitive and specific imaging modality by the clinicians with regard to preoperative work-up and symptomatic therapy with a somatostatin analog.

Monoclonal antibody uptake in B-cell lymphomas: experimental studies in nude mouse xenografts

Accumulation of radiolabelled monoclonal antibodies (mAb) in human B-lymphoma xenografts was found to result in two distinct patterns. The basic elements leading to these patterns were elucidated by autoradiographic and immunohistological analysis applied to the nude mouse xenografts BJAB and OCI.LY1. With BJAB, accumulation occurred exclusively in peripheral cell layers of the lymphoma nodule, while central areas were not accessible irrespective of mAb dose. This feature was the consequence of an inefficient transport across intratumoral vessels together with peripheral mAb supply through a subcapsular pseudosinus. With OCI.LY1, intratumoral vessels showed generalized leakiness. Furthermore, interstitial transport was operative to a fair extent, such that in early images multiple sites of mAb extravasation were obvious, which coalesced during the course of prolonged uptake. The pattern of peripheral mAb uptake resulted in a low overall tumour uptake, while multifocal uptake yielded substantial accumulation values.

Late cervical lymph node recurrence in differentiated thyroid carcinoma. An inherent problem of 131I beta dose distribution in small tumor deposits?

In differentiated thyroid carcinoma, postoperative radioiodine therapy is an undisputed element of the integral therapeutic concept. Sometimes, however, and years after initial diagnosis and therapy, cervical lymph node metastases occur without any evidence of local relapse or distant metastases, indicating that radioiodine therapy has not achieved definite tumor cell sterilization. A Monte Carlo computer simulation of the spatial energy dose distribution of 131I in small functioning tumor manifestations was performed to explain this phenomenon. It appeared that only a small fraction of the total beta-energy dose can be deposited inside the tumor if the latter becomes smaller than 1 mm in diameter: for tumors with homogeneous 131I uptake and diameters of 1.0, 0.5, 0.2, 0.1, 0.05 and 0.02 mm, this value does not exceed 86, 73, 39, 16, 8 and 4%, respectively. These data suggest a potential therapeutic gap for small tumor manifestations not apparent at the time of initial diagnosis and could explain the occasional occurrence of late cervical lymph node metastases.

[Atypical scintigraphic appearance of an osteosarcoma. An explanation using x-ray and histologic findings]

In a 10-year old girl with a telangiectasic osteosarcoma of the proximal right tibia, sequential bone scintigraphy with 99mTc-DPD showed the tumor as an atypical photopenic lesion in the osseous phase. Considering conventional radiographs, angiographic features and histologic aspects, possible explanations for this unusual finding are discussed.

Atypisches szintigraphisches Erscheinungsbild eines Osteosarkoms

Ein 10 Jahre altes Mädchen mit einem teleangiektatischen Osteosarkom der rechten proximalen Tibia wird vorgestellt. Bei der prätherapeutisch durchgeführten 3-Phasen-Skelettszintigraphie stellte sich die Tumorregion in der ossären Phase als photopenische Läsion dar. Unter Berücksichtigung der röntgenologischen, angiographischen und histologischen Charakteristika dieses Tumortyps wird eine mögliche Erklärung des szintigraphisch atypischen Befundes versucht.

Non-invasive detection of reduced regional myocardial perfusion at rest in patients with unstable angina pectoris: increased regional 81mKr deposition following intravenous injection of 81Rb

The present study was to investigate whether combined imaging of 81Rb and 81mKr distributions after i.v. injection of 81Rb at rest might improve the differentiation between ischemic and irreversibly damaged myocardium as compared to 201Tl scintigraphy at rest. In 21 patients who had undergone diagnostic cardiac catheterization for evaluation of chest pain, 148 MBq ultrapure 81Rb were injected i.v. at rest immediately following 201Tl scintigraphy at rest. Of 14 patients with earlier myocardial infarction, 10 patients revealed decreased regional tracer uptake of 81Rb and/or 81mKr, compared to 12 patients with regional 201Tl uptake abnormalities. In 3 patients with unstable angina pectoris, however, an evident mismatch between either the regional 201Tl or 81Rb distributions and the distribution of 81mKr was observed: in contrast to the reduced uptake of 201Tl and/or 81Rb, 81mKr activity was increased in 3 myocardial segments with normal left ventricular performance but supplied by coronary arteries with high-grade stenoses. In patients with contraindications to exercise tests (e.g. unstable angina) 81Rb/81mKr rest scintigraphy may therefore assist the differentiation between malperfused but potentially viable and irreversibly damaged myocardium.

[Postoperative external radiotherapy of differentiated thyroid carcinoma: when is radioiodine therapy alone inadequate? The dosimetric considerations with a Monte Carlo simulation]

Indication for postoperative external radiation of differentiated thyroid cancer has remained an issue of controversial discussion and is generally restricted to those cases where local tumor control by I-131 therapy alone seems doubtful. This may be the case when lymph node metastases are present or occult micrometastasis are suspected, as the beta(-)-radiation caused by the incorporated I-131 may be deposited partly outside the tumor. This problem of dose distribution is analysed in a simulation model by Monte Carlo techniques where tumors are tissue equivalent spheres of various size (r = 20 microns to 2 cm). Homogeneous I-131 distribution in the whole tumor volume (a) is analysed as well as peripheral deposition confined to the tumour surface (b). In tumors of r = 0.5 mm or less, the percentage of the total dose deposited inside the tumor rapidly decreases, r = 20 microns: 4.1% (a) and 0.9% (b), respectively. Furthermore, extensive dose inhomogeneities appear in tumors of similar sizes. As in local lymph node metastases tumoricidal radiation doses are not necessarily achievable by I-131 therapy alone, postoperative external radiation should be taken into account in the above mentioned clinical situations.