Genotoxicity Associated with 131I and 99mTc Exposure in Nuclear Medicine Staff: A Physical and Biological Monitoring Study

Nuclear medicine staff are constantly exposed to low doses of ionizing radiation. This study investigated the level of genotoxic effects in hospital employees exposed to routinely used ¹³¹I and ^99mTc in comparison with a control group. The study compared the results of physical and biological monitoring in peripheral blood lymphocytes. The effects of confounding factors, such as smoking status and physical activity, were also considered. Physical dosimetry monitoring revealed differences in the individual annual effective dose as measured by finger ring dosimeter and whole-body dosimeter between the ¹³¹I- and ^99mTc-exposed groups. The DNA damage studies revealed differences between the groups in terms of excess premature chromosome condensation (PCC) fragments and tail DNA. Physical activity and smoking status differentiated the investigated groups. When assessed by the level of physical activity, the highest mean values of tail DNA were observed for the ^99mTc group. When assessed by work-related physical effort, excess PCC fragments were significantly higher in the ¹³¹I group than in the control group. In the investigated groups, the tail DNA values were significantly different between non-smokers and past or current smokers, but excess PCC fragments did not significantly differ by smoking status. It is important to measure exposure to low doses of ionizing radiation and assess the potential risk from this exposure. Such investigations support the need to continue epidemiological and experimental studies to improve our understanding of the mechanisms of the health effects of radionuclides and to develop predictive models of the behavior of these complex systems in response to low-dose radiation.

Classification of the Multiple Stages of Parkinson's Disease by a Deep Convolution Neural Network Based on 99mTc-TRODAT-1 SPECT Images

Single photon emission computed tomography (SPECT) has been employed to detect Parkinson's disease (PD). However, analysis of the SPECT PD images was mostly based on the region of interest (ROI) approach. Due to limited size of the ROI, especially in the multi-stage classification of PD, this study utilizes deep learning methods to establish a multiple stages classification model of PD. In the retrospective study, the 99mTc-TRODAT-1 was used for brain SPECT imaging. A total of 202 cases were collected, and five slices were selected for analysis from each subject. The total number of images was thus 1010. According to the Hoehn and Yahr Scale standards, all the cases were divided into healthy, early, middle, late four stages, and HYS I~V six stages. Deep learning is compared with five convolutional neural networks (CNNs). The input images included grayscale and pseudo color of two types. The training and validation sets were 70% and 30%. The accuracy, recall, precision, F-score, and Kappa values were used to evaluate the models' performance. The best accuracy of the models based on grayscale and color images in four and six stages were 0.83 (AlexNet), 0.85 (VGG), 0.78 (DenseNet) and 0.78 (DenseNet).

Combining Diagnostic Imaging and Pathology for Improving Diagnosis and Prognosis of Cancer

In the era of personalized medicine, the management of oncological patients requires a translational and multidisciplinary approach. During early phases of cancer development, biochemical alterations of cell metabolism occur much before the formation of detectable tumour masses. Current molecular imaging techniques, targeted to the study of molecular kinetics, employ molecular tracers capable of detecting cancer lesions with both high sensitivity and specificity while also providing essential information for both prognosis and therapy. On the contrary, complementary and crucial information is provided by histopathological examination and ancillary techniques such as immunohistochemistry. Thus, the successful collaboration between diagnostic imaging and anatomic pathology can represent a fundamental step in the "tortuous" but decisive path towards personalized medicine.

Scintigraphic assessment of arterial embolism at mixed thrombin and technetium 99m injection therapy for femoral pseudoaneurysms

BACKGROUND

Clinically evident arterial thrombosis is rare following thrombin injection therapy for femoral pseudoaneurysm. However, it is unclear to what extent injected thrombin may pass to the ipsilateral lower limb arteries.

AIMS

To assess if technetium 99m injected at the time of thrombin injection for femoral artery pseudoaneurysm therapy passes into the adjacent lower limb arteries.

METHODS

This was a prospective trial with institutional review board approval. Four consecutive patients with common femoral pseudoaneurysms and failed manual compression were enrolled. Under real-time colour flow doppler ultrasound, a mixture of 1000 IU thrombin and approximately 200 MBq technetium 99m was injected in 0.1-mL doses into the pseudoaneurysm until thrombosis occurred. Gamma camera imaging of the syringe before injection, the injected groin after thrombosis and the syringe after injection were performed. Analysis of the gamma camera information was performed to determine the amount of technetium 99m deposited in the arterial tree.

RESULTS

All the procedures were technically successful. A mean of 33% (range 3-50%; SD 21) of the administered technetium 99m dose was deposited in the arterial circulation during pseudoaneurysm therapy. No clinically evident arterial thrombosis was identified.

CONCLUSION

Technetium 99m is routinely deposited in the arterial circulation following injection of a mixture of thrombin and technetium for therapy of common femoral artery pseudoaneurysms. This suggests that arterial passage of thrombin is more common than clinically evident.

Pyeloduodenal fistula diagnosed with technetium-99m scintigraphy and managed with a conservative strategy

We present a case of pyeloduodenal fistula in an 89-year-old woman with history of nephrolithiasis and recurrent urinary tract infection (UTI) who presented to the emergency department with back pain. CT revealed a malrotated right kidney with a large renal stone and possible fistulous connection between the second portion of the duodenum and the right renal collecting system. Technetium-99m scintigraphy confirmed presence of the fistula. The patient declined intervention and was discharged from the hospital with oral antibiotic suppressive therapy. The patient remained clinically stable at time of follow-up 3 months later. Spontaneous pyeloduodenal fistula is an aetiology of recurrent upper or lower UTIs or persistent bacteriuria though uncommonly recognised. Diagnosis may be achieved using several modalities, including technetium-99m scintigraphy. Nephrectomy and primary fistula closure has traditionally been the treatment of choice for this condition; however, conservative management is an option for patients with intact renal function.

Molecular radiotheragnostics in thyroid disease

Molecular radiotheragnostics directly links nuclear medicine diagnostic imaging to therapy. The imaging study is used to detect a specific molecular target associated with a disease process. A radiotherapeutic molecule with a similar biodistribution to the diagnostic agent can then be used to deliver targeted therapy.Molecular radiotheragnostics have been applied to manage both benign and malignant thyroid disease since the 1940s. The specific molecular pathway targeted is the sodium/iodide symporter (NIS) located on the basolateral membrane of the thyroid follicular cell. Radiolabelling of iodide or a similar ion allows targeting of the NIS system with radiopharmaceuticals for imaging (123I-radioiodine and 99mTc-pertechnetate) and treatment (131I-radioiodine) by virtue of their gamma ray and beta-particle emissions, respectively.Scintigraphic imaging directly guides 131I-radioiodine treatment planning to maximise therapeutic benefit while minimising adverse reactions, in a personalised medicine approach.

Breastdosimetry of 99mTc-balloon in complementary radiotherapy

Dose reinforcement in primary tumor cavity can complement conventional radiotherapy in patients with early breast cancer. In this study, a dosimetric analysis was conducted by pertechnetate-^99mTc-filled balloon brachytherapy (TBB).

METHODS

Dosimetry based on radiochromic films and on a computational voxel thorax model was performed. Calibration protocol achieved a mathematical relationship between dose and optical density in films placed on the surface at a distance of 0-9cm, 1cm between them, in which dose values were provided by MCNP® code. Moreover, experimental spatial dose distribution was prepared. A female thorax voxel model was developed in the SISCODES®/MCNP® codes. Additionally, experimental and computational doses at 8-10mm from balloon surface were compared.

RESULTS

Dose from ^99mTc-balloon, with 16mm diameter, 32.22GBq activity, and 24h exposure time, achieved 8.08±0.42 (Ue) and 8.82±1.76 (Ue) Gy, at a distance of 10mm from the balloon surface for the experimental data and computational modeling, respectively, thus showing nonsignificant difference. The spatial dose distribution in the chest wall, glandular tissue, breast skin, and lung was presented. The dosimetric findings supported the TBB modality presenting a suitable spatial dose distribution in the tumor bed and preserving the adjacent health tissues.

CONCLUSION

TBB is a viable adjuvant brachytherapy modality for breast cancer in patients who have an appropriate indication.

Assessment of Using 99Mo and 99mTc Isotopes in Kuwait Medical Sector

The Ministry of Health (MOH) in the state of Kuwait currently depends on importing the radioisotope molybdenum (Mo) in its isotopic form (Mo) to fulfill its demands. The present study was conducted on all nuclear medicine departments in the state of Kuwait. Daily, weekly, and monthly data were analyzed to statistically determine the current and future demands for the isotope Tc. This analysis was performed by collecting and analyzing data on MOH consumption of Tc for different diagnostic applications. The overall results indicate a partial decrease of 1.012% in the overall total demand for Tc up to the year 2018 for the state of Kuwait.

Approach to Oligometastatic Prostate Cancer

Oligometastatic prostate cancer has increasingly been recognized as a unique clinical state with therapeutic implications. It has been proposed that patients with oligometastases may have a more indolent course and that outcome may be further improved with metastasis-directed local ablative therapy. In addition, there are differing schools of thoughts regarding whether oligometastases represent isolated lesions-where targeted therapy may render a patient disease free-or whether they coexist with micrometastases, where targeted therapy in addition to systemic therapy is required for maximal clinical impact. As such, the approach to the patient with oligometastatic prostate cancer requires multidisciplinary consideration, with surgery, radiotherapy, and systemic therapy potentially of benefit either singularly or in combination. Indeed, mounting evidence suggests durable disease-free intervals and, in some cases, possibly cure, may be achieved with such a multimodal strategy. However, selecting patients that may benefit most from treatment of oligometastases is an ongoing challenge. Moreover, with the advent of new, highly sensitive imaging technologies, the spectrum based on CT of the abdomen and pelvis and technetium bone scan of localized to oligometastatic to widespread disease has become increasingly blurred. As such, new MRI- and PET-based modalities require validation. As some clinical guidelines advise against routine prostate-specific antigen screening, the possibility of more men presenting with locally advanced or de novo oligometastatic prostate cancer exists; thus, knowing how best to treat these patients may become more relevant at a population level. Ultimately, the arrival of prospective clinical data and better understanding of biology will hopefully further inform how best to treat men with this disease.

An alternate approach to the production of radioisotopes for nuclear medicine applications

There is a growing need for the production of radioisotopes for both diagnostic and therapeutic medical applications. Radioisotopes that are produced using the (n,γ) or (γ,n) reactions, however, typically result in samples with low specific activity (radioactivity∕gram) due to the high abundance of target material of the same element. One method to effectively remove the isotopic impurity is electro-magnetic mass separation. An Ion Source Test Facility has been constructed at TRIUMF to develop high-intensity, high-efficiency, reliable ion sources for purification of radioactive isotopes, particularly those used in nuclear medicine. In progress studies are presented.

Use of a 99mTc labeled anti-TNFalpha monoclonal antibody in Crohn's disease: in vitro and in vivo studies

AIM

Crohn's disease (CD) is a chronic inflammatory bowel disease characterized by a cellular-mediated immune response driven by cytokines secreted mainly by T helper 1 cells (Th1). In active phases of the disease, an increased production and release of tumor necrosis factor a (TNFalpha) by macrophages and monocytes of the lamina propria has been described. The aim of this study was to detect the presence of TNFalpha within the gut mucosa in patients with active CD by using (99m)Tc-labelled chimeric human/mouse monoclonal antibody anti-TNFalpha (Infliximab, Remicade).

METHODS

Infliximab has been labeled with (99m)Tc after reduction of disulfide bound by 2-ME method. In vitro binding assay and biodistribution in animal of [(99m)Tc]Infliximab has been performed to evaluate the retention of its biological activity. Ten patients with active CD refractory to conventional medical therapies were studied. Images of the abdomen were acquired at 6 to 20 h after i.v. injection of about 10 mCi of [(99m)Tc]Infliximab and a week later, all patients were also studied with [(99m)Tc]HMPAO-labeled autologous white blood cells (WBC).

RESULTS

A product with high labeling efficiency (>95%) and stability has been obtained. In vitro tests with stimulated T-cells expressing TNFalphalpha indicated that [(99m)Tc] Infliximab retains its binding activity to cell bound TNFalpha as compared to unlabelled Infliximab. The degree of [(99m)Tc]Infliximab uptake by the inflamed bowel evaluated at 20 h postinjection was much less than that seen with labeled WBC and with a different distribution. Three of these patients received anti-TNFalpha (Infliximab) for therapeutic purposes with good clinical results despite the scintigraphy with (99m)Tc-Infliximab was negative in 2 of them.

CONCLUSION

Scintigraphy with [(99m)Tc]Infliximab shows the presence of little TNFalpha in the affected bowel of patients with active CD. Therefore, the clinical benefit that patients have from Infliximab therapy is unlikely the consequence of a local a reduction of TNFalpha and the mechanism of action of Infliximab, in therapeutic doses, deserves further investigations.

Pretargeting CWR22 prostate tumor in mice with MORF-B72.3 antibody and radiolabeled cMORF

PURPOSE

We have now applied our MORF/cMORF pretargeting technology to the targeting of CWR22 prostate tumor in nude mice.

METHODS

The antiTAG-72 antibody B72.3 was conjugated with an 18 mer MORF while the cMORF was radiolabeled with (99m)Tc. The specific binding of the antibody to the CWR22 cells was first confirmed in an assay placing the radiolabeled B72.3 antibody in competition with increasing concentrations of native B72.3. Thereafter, a group of four CWR22 tumored mice intravenously received the MORF-B72.3 and, 3 days later, the (99m)Tc-cMORF, and were killed at 3 h postradioactivity injection. The dosage of the labeled cMORF was selected on the basis of previous experience in LS174T tumored mice. As controls, four animals received only the radiolabeled cMORF and another four received only the (111)In-B72.3. The maximum percent tumor accumulation (MPTA) of the labeled cMORF was subsequently determined by a dosage study of labeled cMORF. Both a multipinhole SPECT image and a planar gamma camera image were obtained of a representative mouse.

RESULTS

The CWR22 tumor was confirmed to be TAG-72-positive. The MPTA of the labeled cMORF in the CWR22 tumor was 2.22%ID/g compared to only 0.12%ID/g in control mice without pretargeting. Both the planar and tomographic images confirmed the success of the CWR22 pretargeting.

CONCLUSIONS

The MORF/cMORF pretargeting approach has been successfully applied to tumor targeting of the prostate xenograft CWR22. However, the MPTA in this tumor model is lower than that in the LS174T tumor model investigated earlier, possibly due to a lower tumor blood supply.

Polymer-peptide conjugates for angiogenesis targeted tumor radiotherapy

INTRODUCTION

New methods of delivering radiotherapy to sites of occult or disseminated cancer are needed to control the disease and address the failure of conventional therapy. Because tumor cells rely on angiogenesis for survival, we assessed the effectiveness of beta-emitter radiotherapy delivered by polymer-peptide conjugates that target tumor neovasculature. This molecularly targeted radiation is intended to damage both the endothelial bed and surrounding neoplastic cells.

METHODS

N-(2-Hydroxypropyl) methacrylamide (HPMA), a biocompatible and water-soluble copolymer, was derivatized to incorporate side chains for (99m)Tc and (90)Y chelation and was further conjugated to a alpha(V)beta(3) integrin-targeting peptide (RGD4C). The HPMA copolymer-RGD4C conjugate was characterized by its side-chain contents, in vitro endothelial cell adhesion assay and its biodistribution and antitumor effectiveness in a SCID mouse xenograft model of human prostate carcinoma.

RESULTS

The conjugate contained about 16 RGD4C moieties per polymer backbone. Tumor accumulation significantly increased (P < .01) over time from 1.05 +/- 0.03 % injected dose (%ID)/g tissue at 1 h to 4.32 +/-0.32% at 72 h. The activity in major normal tissues significantly decreased (P < .05) during that period. At 21 days, the control tumors increased 442% in volume from baseline. In contrast, a 7% and a 63% decrease of tumor volume were observed for the 100- and 250-microCi (90)Y treatment groups, respectively. Histopathological examination revealed increased apoptosis in the treated tumors with no acute signs of radiation-induced toxicity to other organs.

CONCLUSION

This copolymer-peptide conjugate targets tumor angiogenic vessels and delivers sufficient radiotherapy to arrest tumor growth.

99mTc/188Re-labelled lipid nanocapsules as promising radiotracers for imaging and therapy: formulation and biodistribution

PURPOSE

This study focuses on a promising carrier system for imaging and therapeutic purposes using lipid nanocapsules. To assess their potential for clinical use, we labelled nanocapsules with (99m)Tc and (188)Re and analysed some kinetic biodistribution parameters after intravenous injection in rats.

METHODS

Lipophilic complexes [(99m)Tc/(188)Re(S(3)CPh)(2)(S(2)CPh)] ((99m)Tc/(188)Re-SSS) were encapsulated within the nanoparticles during their manufacture with quantitative yield and satisfactory radiochemical purity. Rats were injected intravenously with 3.7 MBq (99m)Tc/(188)Re-labelled nanocapsules and sacrificed at 5, 15 and 30 min and 1, 2, 4, 8, 12, 16, 20 and 24 h.

RESULTS

Dynamic scintigraphic acquisitions showed predominant hepatic uptake, and ex vivo counting indicated a long circulation time of labelled nanocapsules, with a half-life of 21+/-1 min for (99m)Tc and 22+/-2 min for (188)Re. Very weak urinary elimination was observed, indicating good stability of (99m)Tc and (188)Re labelling.

CONCLUSION

(99m)Tc/(188)Re-SSS nanocapsules can be obtained with high yield and satisfactory radiochemical purity. The biodistributions of (99m)Tc/(188)Re-labelled nanocapsules are close to those of classical PEG-coated particles and show good stability of (188)Re/(99m)Tc-SSS labelling.

Teleradiotherapy of joints in rheumatoid arthritis: lack of efficacy

BACKGROUND

Low dose radiotherapy is commonly used for painful rheumatic conditions in clinical practice. Teleradiotherapy may be a cheap, painless procedure which is applicable to many joints at a time.

OBJECTIVE

To determine if the local application of x rays to inflamed joints in rheumatoid arthritis (RA) affects the signs and symptoms of inflammation.

METHODS

In a randomised, controlled, double blind study, roentgen irradiation was administered in a total dose of 20 Gy during 2 weeks to single joints in six patients with RA who were receiving constant and stable pharmacological treatment with DMARDs and NSAIDs. Single inflamed joints on the contralateral side of the body were used as controls and received sham irradiation. Swelling and tenderness was assessed by blinded investigators before and until 3 months after the irradiation; general disease activity and pain scales were included in the assessment.

RESULTS

No change in the scores for tenderness, swelling, pain, or disease activity was seen. The trial was stopped for ethical reasons.

CONCLUSION

Local roentgen treatment of RA at a substantial dose of 20 Gy was ineffective in this pilot trial.

Radiation dosimetry of 99mTc-labeled C225 in patients with squamous cell carcinoma of the head and neck

This study assessed the radiation dosimetry of 99mTc-labeled ethylene dicysteine (EC) C225 (EC-C225), a promising radioligand for functional tumor imaging.

METHODS

Whole-body scanning was performed on 6 patients with head and neck squamous cell carcinoma up to 24 h after administration of 99mTc-EC-C225. Alternate patients who had been randomized to receive C225 in a phase III trial received 99mTc-EC-C225 before their 20-mg test dose or after their 400 mg/m2 loading dose of unlabeled C225 (patients 1/3/5 and 2/4/6, respectively). Radiation dosimetry was assessed using the MIRD method.

RESULTS

The critical organ was the kidney, with an average radiation-absorbed dose for all 6 patients of 0.0274 mGy/MBq. The average total-body absorbed dose was 0.0022 mGy/MBq (0.243 cGy/1,110 MBq).

CONCLUSION

The new radiopharmaceutical 99mTc-EC-C225 appears to have reasonable dosimetric properties for a diagnostic nuclear medicine agent. Correlation of the imaging results with clinical findings is the next step.

Samarium-153 and technetium-99m-labeled monoclonal antibodies in angiogenesis for tumor visualization and inhibition

BACKGROUND

Angiogenesis is the development of new blood vessels from pre-existing ones. Vascular endothelial growth factor (VEGF) is one of the most important angiogenic activators. Our studies are focused on the detection of VEGF by use of radiolabeled anti-endothelial monoclonal antibodies, which have the ability to localize in newly-formed vasculature of a cancerous origin.

MATERIALS AND METHODS

The anti-endothelial monoclonal antibody VG76e was labeled with Samarium-153 and Technetium-99m. Biodistribution of the radiolabeled species was assessed in normal female Swiss mice, while tumor uptake was also evaluated.

RESULTS

VG76e was labeled with 99mTc and 153Sm, resulting in a single product with a labeling yield of over 95%. Biodistribution studies showed non-specific uptake in any organ, with elimination via the hepatobiliary system. Finally, satisfactory tumor uptake was observed for both radiolabeled derivatives.

CONCLUSION

Monoclonal antibodies raised against epithelial growth factors or their receptors, when labeled with appropriate radionuclides, may be a useful tool for early tumor detection and eventually for therapy.

Targeting bcl-2 by triplex-forming oligonucleotide--a promising carrier for gene-radiotherapy

Triplex forming oligonucleotides (TFO) provide a promising tool for gene therapy. DNA damaging agents have been successfully coupled to TFOs and induce site-directed DNA damages. Here, we attempted to apply this antigen strategy using a TFO incorporated with a Conversion-electron-emitter, (99m)technetium, to target bcl-2 gene, the prototypical inhibitor of apoptosis. In the bcl-2 promoter region, we found two TFO binding sites which bind corresponding TFOs with very high specificity and affinity. Both partially and completely phosphorothioated TFOs form stable triplexes and significantly inhibit gene transcription in vitro. We also found that purine motif TFO with a thymidine opposite a thymidine interruption at the polypurine strand can form a stable triplex. In addition, (99m)technetium-conjugated TFOs were found to form a stable triplex and to inhibit bcl-2 gene transcription in vitro. Our results suggest a promising application of this triplex-forming oligonucleotide based Conversion-electron-emitter mediated gene radiotherapy in diseases related to bcl-2 overexpression.

Accuracy of the quantification of organ activity from planar gamma camera images

The accuracy in determination of organ activity of (99m)Tc was investigated, with activity estimated from gamma camera images of phantoms, using the conjugate view method. The accuracy depends on several parameters such as the choice of background correction method, the accuracy in determination of the effective attenuation coefficient and the thickness of the body and organs and on the determination of the gamma camera sensitivity. The background correction method has a major influence on the quantification of the activity. Methods which take the volume of the source organ into consideration are recommended. The discrepancy in the determined organ activity varied between an underestimation of 26% and an overestimation of 16% in the MIRD phantom, depending on which organ was studied and on the correction method used. To correct for absorption and scattering, an effective attenuation coefficient was used. A theoretical analysis showed that a change in the effective attenuation coefficient of 0.01 cm(-1) resulted in a 15% change in the calculated activity. Also the thickness of the body and the organ of interest influences the calculated activity. A 2 cm deviation in the body thickness causes a deviation of approximately 10% in the calculated activity. The quantification is improved if the attenuation coefficient is determined by transmission measurements.

Radiolabeling morpholinos with 90Y, 111In, 188Re and 99mTc

This laboratory is investigating morpholinos (MORF), a DNA analogue, for radiopharmaceutical applications. While we routinely radiolabel with (99m)Tc, we have now labeled MORFs with (111)In, (188)Re and (90)Y in anticipation of therapeutic studies.

METHODS

A 25 mer MORF with a primary amine on the 3' equivalent end attached via a 10 member linker was conjugated with an isothiocyanate backbone derivative of DOTA (for labeling with (111)In and (90)Y) and with NHS-MAG(3) (for labeling with (188)Re and (99m)Tc). The in vitro stability of labeled MORFs were investigated and biodistribution was carried out in normal mice.

RESULTS

As evident by size exclusion HPLC, ITLC and Sep-Pak analysis, all four radiolabeled MORFs were successfully radiolabeled. In each case, the labeled MORFs showed one sharp peak in HPLC that shifted completely to earlier retention times following addition of a polymer conjugated with the complementary MORF. In saline at room temperature and in 37 degrees C serum, the radioactivity profile of (111)In, (188)Re and (99m)Tc was unchanged over 48 h while over the same period, the (90)Y profile showed a pronounced lower molecular weight peak which did not shift and was shown to be most probably due to (90)Y-DOTA resulting from radiolysis. In addition, the recovery of (188)Re on HPLC decreased as samples aged probably due to oxidation to perrhenate which was retained by the HPLC column. The biodistributions at 1, 3 and 6 h in normal mice showed no important differences among all four labels with the exception that levels of radioactivity in stomach and thyroid were higher in the case of (188)Re due to in vivo oxidation of the radiolabel to perrhenate.

CONCLUSIONS

When radiolabeled with DOTA, (90)Y-labeled MORF showed increased instabilities relative to that of (111)In and when radiolabeled with MAG(3), (188)Re showed in vitro and in vivo instabilities compared to (99m)Tc, but all labels were still largely intact after 48 h in saline or serum. Possibly because of the rapid clearance of MORFs, no important differences in biodistribution among (90)Y, (111)In and (99m)Tc labels were evident in normal mice. These strategies for labeling MORF with (90)Y and (188)Re therefore appear to be suitable for therapeutic applications although both show some evidence of instabilities.

Tumor targeting with radiolabeled alpha(v)beta(3) integrin binding peptides in a nude mouse model

The alpha(v)beta(3) integrin is expressed on proliferating endothelial cells such as those present in growing tumors, as well as on tumor cells of various origin. Tumor-induced angiogenesis can be blocked in vivo by antagonizing the alpha(v)beta(3) integrin with small peptides containing the Arg-Gly-Asp (RGD) amino acid sequence. This tripeptidic sequence, naturally present in extracellular matrix proteins, is the primary binding site of the alpha(v)beta(3) integrin. Because of selective expression of alpha(v)beta(3) integrin in tumors, radiolabeled RGD peptides are attractive candidates for alpha(v)beta(3) integrin targeting in tumors. We studied the in vivo behavior of the radiolabeled dimeric RGD peptide E-[c(RGDfK)](2) in the NIH:OVCAR-3 s.c. ovarian carcinoma xenograft model in BALB/c nude mice. Conjugation of the 1,4,7,10-tetraazadodecane-N,N',N",N"'-tetraacetic acid (DOTA) and hydrazinonicotinamide (HYNIC) chelators enabled efficient radiolabeling with (111)In/(90)Y and (99m)Tc, respectively. The radiolabeled peptide was rapidly excreted renally. Uptake in nontarget organs such as liver and spleen was considerable. Tumor uptake peaked at 7.5% injected dose (ID)/g ((111)In-DOTA-E-[c(RGDfK)](2)) or 6.0%ID/g ((99m)Tc-HYNIC-E-[c(RGDfK)](2)) at 2 and 1 h postinjection, respectively. Integrin alpha(v)beta(3) receptor binding specificity was demonstrated by reduced tumor uptake after injection of the scrambled control peptide (111)In-DOTA-E-[c(RDKfD)](2) (0.28%ID/g at 2 h p.i.) and after coinjection of excess nonradioactive (115)In-DOTA-E-[c(RGDfK)](2) (0.22%ID/g at 2 h p.i.). A single injection of (90)Y-DOTA-E-[c(RGDfK)](2) at the maximum-tolerated dose (37 MBq) in mice with small s.c. tumors caused a significant growth delay as compared with mice treated with 37 MBq (90)Y-labeled scrambled peptide or untreated mice (median survival of 54 versus 33.5 versus 19 days, respectively). In conclusion, the radiolabeled RGD peptides (111)In-DOTA-E-[c(RGDfK)](2) and (99m)Tc-HYNIC-E-[c(RGDfK)](2) demonstrated high and specific tumor uptake in a human tumor xenograft. Injection of (90)Y-DOTA-E-[c(RGDfK)](2) induced a significant delay in tumor growth. Potentially, these peptides can be used for peptide receptor radionuclide imaging as well as therapy.

Pretargeting for cancer radioimmunotherapy with bispecific antibodies: role of the bispecific antibody's valency for the tumor target antigen

The use of a divalent effector molecule improves bispecific antibody (bsMAb) pretargeting by enabling the cross-linking of monovalently bound bsMAb on the cell surface, thereby increasing the functional affinity of a bsMAb. In this work, it was determined if a bsMAb with divalency for the primary target antigen would improve bsMAb pretargeting of a divalent hapten. The pretargeting of a (99m)Tc-labeled divalent DTPA-peptide, IMP-192, using a bsMAb prepared by chemically coupling two Fab' fragments, one with monovalent specificity to the primary target antigen, carcinoembryonic antigen (CEA), and to indium-loaded DTPA [DTPA(In)], was compared to two other bsMAbs, both with divalency to CEA. One conjugate used the whole anti-CEA IgG, while the other used the anti-CEA F(ab')(2) fragment to make bsMAbs that had divalency to CEA, but with different molecular weights to affect their pharmacokinetic behavior. The rate of bsMAb blood clearance was a function of molecular weight (IgG x Fab' < F(ab')(2) x Fab' < Fab' x Fab' conjugate). The IgG x Fab' bsMAb conjugate had the highest uptake and longest retention in the tumor. However, when used for pretargeting, the F(ab')(2) x Fab' conjugate allowed for superior tumor accretion of the (99m)Tc-IMP-192 peptide, because its more rapid clearance from the blood enabled early intervention with the radiolabeled peptide when tumor uptake of the bsMAb was at its peak. Excellent peptide targeting was also seen with the Fab' x Fab' conjugate, albeit tumor uptake was lower than with the F(ab')(2) x Fab' conjugate. Because the IgG x Fab' bsMAb cleared from the blood so slowly, when the peptide was given at the time of its maximum tumor accretion, the peptide was captured predominantly by the bsMAb in the blood. Several strategies were explored to reduce the IgG x Fab' bsMAb remaining in the blood to take advantage of its 3-4-fold higher tumor accretion than the other bsMAb conjugates. A number of agents were tested, including those that could clear the bsMAb from the blood (e.g., galactosylated or nongalactosylated anti-id antibody) and those that could block the anti-DTPA(In) binding arm [e.g., DTPA(In), divalent-DTPA(In) peptide, and DTPA coupled to bovine serum albumin (BSA) or IgG]. When clearing agents were given 65 h after the IgG x Fab' conjugate (time of maximum tumor accretion for this bsMAb), (99m)Tc-IMP-192 levels in the blood were significantly reduced, but a majority of the peptide localized in the liver. Increasing the interval between the clearing agent and the time the peptide was given to allow for further processing of the bsMAb-clearing agent complex did not improve targeting. At the dose and level of substitution tested, galacosylated BSA-DTPA(In) was cleared too quickly to be an effective blocking agent, but BSA- and IgG-DTPA(In) conjugates were able to reduce the uptake of the (99m)Tc-IMP-192 in the blood and liver. Tumor/nontumor ratios compared favorably for the radiolabeled peptide using the IgG x Fab'/blocking agent combination and the F(ab')(2) x Fab' (no clearing/blocking agent), and peptide uptake 3 h after the blocking agent even exceeded that of the F(ab')(2) x Fab'. However, this higher level of peptide in the tumor was not sustained over 24 h, and actually decreased to levels lower than that seen with the F(ab')(2) x Fab' by this time. These results demonstrate that divalency of a bsMAb to its primary target antigen can lead to higher tumor accretion by a pretargeted divalent peptide, but that the pharmacokinetic behavior of the bsMAb also needs to be optimized to allow for its clearance from the blood. Otherwise, blocking agents will need to be developed to reduce unwanted peptide uptake in normal tissues.

Assessment of antiangiogenic effect using 99mTc-EC-endostatin

PURPOSE

Tumor vascular density may provide a prognostic indicator of metastatic potential or survival. The purpose of this study was to develop 99mTc-ethylenedicysteine-endostatin (99mTc-EC-endostatin) for the evaluation of anti-angiogenesis therapy.

METHOD

99mTc-EC-endostatin was prepared by conjugating ethylenedicysteine (EC) to endostatin, followed by adding pertechnetate and tin chloride. Radiochemical purity was > 95%. In vitro cell viability, affinity and TUNEL assays were performed. Tissue distribution and planar imaging of radiolabeled endostatin were determined in tumor-bearing rats. To assess anti-angiogenic treatment response, rats were treated with endostatin, paclitaxel and saline, followed by imaging with 99mTc-EC-endostatin. Tumor response to endostatin therapy in tumor-bearing animal models was assessed by correlating tumor uptake dose with microvessel density, VEGF, bFGF and IL-8 expression during endostatin therapy.

RESULTS

In vitro cell viability and TUNEL assays indicated no marked difference between EC-endostatin and endostatin. Cellular uptake assay suggests that endostatin binds to endostatin receptor. Biodistribution of 99mTc-EC-endostatin in tumor-bearing rats showed increased tumor-to-tissue count density ratios as a function of time. Tumor uptake (%ID/g) of 99mTc-EC-endostatin was 0.2-0.5. Planar images confirmed that the tumors could be visualized clearly with 99mTc-EC-endostatin. The optimal time for imaging using radiolabeled endostatin was 2 hrs. 99mTc-EC-endostatin could assess treatment response. There was a correlation between tumor uptake and cellular targets expression.

CONCLUSION

The results indicate that it is feasible to use 99mTc-EC-endostatin to assess efficiency of anti-angiogenesis therapy.

The value of immunoscintigraphy in the detection of recurrent colorectal cancer

The aim of this prospective study was to determine whether anti-carcinoembryonic antigen (anti-CEA) scintigraphy is a useful additional technique in the diagnosis recurrence of colorectal cancer. Forty patients with suspected recurrence of colorectal cancer, underwent immunoscintigraphy (IS) and helical computed tomography (CT) in the 2 weeks before surgery. Surgical findings were used to evaluate the performance of the imaging techniques. Suspected areas on IS and CT were systematically explored. Helical CT was found to be superior to IS for the liver, the sensitivity and specificity of CT being 100% and 90%, respectively, vs 53% and 100% for IS. However, IS was better than CT for the detection of extra-hepatic abdominal recurrence: sensitivity and specificity of IS were 100 and 82% respectively vs 33 and 82% for CT. Seven cases of peritoneal carcinomatosis were overlooked by helical CT. Our results indicate that IS improves detection of extra-hepatic abdominal recurrence of colorectal cancer. Immunoscintigraphy is valuable as a guide to the treatment strategy and operative procedures.

Proposal for a gamma-emitting stent for the prevention and treatment of coronary artery restenosis

Radioactive stents have failed to prevent restenosis despite the demonstrated success of other radionuclide therapies using beta- or gamma-emitting radionuclides in the coronary arteries. This may be due to the rapid dose reduction at the end of the stent that occurs with a stent coated with 32P, which is a pure beta-emitter. A gamma-emitter will give a greater dose beyond the end of the stent and would therefore be expected to produce better results. However, it is essential that the gamma-emitter is not contaminated with beta particles of either sign nor with conversion electrons. This requirement generally demands the use of a high energy gamma-emitter, preferably with an energy greater than 500 keV. High energy gammas have other advantages, including a high radiation dose delivered per decay which reduces the total activity required and reduced dose near to the source due to electron disequilibrium. The ideal dose distribution is one that provides a uniform dose to the proliferating tissues and a reduced dose elsewhere. Although the target tissues are not well defined it is believed that the adventitia is the source of the proliferating cells. Hence the target tissue is between 0.5 and 2 mm depth into the artery. It is shown that 96Tc is a very suitable radionuclide for the production of radioactive stents giving a significantly greater dose compared with 32P both at depth and beyond the end of the stent for the same dose at the surface of the stent. Furthermore, 96Tc should be able to be made with a standard medical cyclotron and may be coated on to a stainless steel stent by a simple process that takes approximately 30 minutes to perform. Its half-life of 4.3 days will allow radioactive stents to be transported over significant distances and will result in a treatment time with a mean value of approximately 1 week. This will allow the rapid reestablishment of the endothelial layer which may be a further advantage of this radioactive stent.

An automated technique for SPECT marker-based image registration in radionuclide therapy

An automated technique for marker-based image registration in radionuclide therapy is described. This technique is based on localization of the centroids of external markers and on establishing correspondence between the individual markers of the two studies to be registered. Localization of the centroids of markers relies on segmenting the markers using iterative thresholding. Thresholding is locally adaptive in order to account for study-dependent conditions (e.g. crossover between adjacent markers and markers with varying radioactive concentrations). Following marker segmentation, the centroids of the markers are computed based on an intensity-weighted method. Finally, prior to the least-squares fit registration, the markers of the two sets are matched to achieve one-to-one correspondence. The technique was applied to both simulated and patient studies resulting in mean residual three-dimensional registration errors (+/- 1SD) of 1.7 +/- 0.1 mm and 3.5 +/- 0.3 mm respectively. The technique was compared with a semi-automated approach and no significant difference was found between the mean residual three-dimensional registration errors (t = 0.281. p = 0.8). This automated marker-based image registration technique provides robust and accurate registration. Although it was developed as part of a programme to generate three-dimensional dose distributions for radionuclide therapy, it could be useful for other clinical applications.

Phase I clinical evaluation of a neutralizing monoclonal antibody against epidermal growth factor receptor

Ior egf/r3, a neutralizing monoclonal antibody (mAb) against Epidermal Growth Factor Receptor (EGFR) was generated at the Cuban Institute of Oncology. Immunoscintigraphic studies in 148 patients with this 99-m Technetium (99Tc) labeled mAb, showed a high sensitivity and specificity for in vivo detection of epithelial tumors. To study safety, pharmacokinetic and immunogenicity of ior egf/r3 at high doses, a phase I clinical trial was conducted. Nineteen patients with advanced epithelial tumors received 4 mAb intravenous infusions at 6 dose levels: from 50 to 500 mg. Previously, immunoscintigraphic images using the same mAb labeled with 99Tc were acquired. Blood samples were collected for pharmacokinetic analysis and HAMA response. After mAb therapy, objective response was classified according to WHO criteria. Ior egf/r3 was well tolerated in spite of the high-administered doses. Only a severe adverse reaction consisting of hypotension and lethargy was observed. In 13 patients, selective accumulation of 99Tc-labeled mAb was observed at the site of the primary tumor or the metastasis. Pharmacokinetic analysis revealed that elimination half-life and the area under the time-concentration curve increased linearly with dose. HAMA response was detected in 17 patients. After 6 months of mAb therapy, 4 patients had stable disease. One patient had a tumor partial remission after 3 cycles of ior egf/r3.

Scintigraphic evaluation of synovial inflammation in rheumatoid arthritis with (99m)technetium-labelled human polyclonal immunoglobulin G

The aim of this study was to investigate whether (99m)technetium-labelled polyclonal human immunoglobulin G (99mTc-IgG) scintigraphy reflects synovial inflammation in patients with rheumatoid arthritis (RA). We evaluated 29 patients with RA for this reason and found a highly significant correlation between total scintigraphic scores and total tenderness scores (r = 0.781, P < 0.001). A significant correlation was also found between 99mTc-IgG scintigraphic scores and tenderness in all joints other than the shoulders. The 99mTc-IgG scintigraphy had a sensitivity of 69% and specificity of 88% in cases with tenderness and 72% and 81%, respectively, in cases with swelling. Total scintigraphic scores were correlated with serum levels of C-reactive protein (r = 0.401, P < 0.05) but not with erythrocyte sedimentation rate (r = 0.149, P > 0.05). The correlation between disease activity scores and total scintigraphic scores was also found to be significant (r = 0.812, P < 0.001). We suggest that 99mTc-IgG scintigraphy is a reliable and objective method in detecting synovial activity and can be appropriate for observing disease prognosis in clinical trials with RA.

Current and potential therapeutic uses of lanthanide radioisotopes

In the last 25 years, diagnostic nuclear medicine has come to depend on the versatile chemistry of a single radioisotope, technetium-99m (Tc-99m). Different chelating molecules can be used to guide Tc-99m through various physiological pathways in the body to gain information about disease states. No single radioisotope similarly dominates therapeutic applications. In the field of radioisotope therapy, much discussion and debate have focused on what radioisotope might be "ideal" for treatment of malignant tumors. The ideal may not be a single radioisotope, but rather the class of very closely related radiolanthanides and lanthanide-like radioisotopes. These radioisotopes possess strikingly similar chemistries and thus all may be conjugated to biomolecules using a single chelate, the DOTA moiety (and its chemical analogs). They also provide a wide range of physical characteristics, such as half-lives and beta energies, that can be chosen to match the biological properties of the conjugated biomolecule and the malignant tumor. Thus, the radiolanthanide-DOTA bioconjugate model provides a set of physically diverse, but chemically very similar, therapeutic radiopharmaceutical agents, the individual members of which can be tailored to treat specific types of cancers.

In vivo targeting of malignant melanoma by 125Iodine- and 99mTechnetium-labeled single-chain Fv fragments against high molecular weight melanoma-associated antigen

Monoclonal antibodies (MAbs) against high-molecular-weight melanoma-associated antigen (HMW-MAA) have been used in vivo to target melanoma. More recently, single chain Fv (scFv) antibody fragments against HMW-MAA have been described that may improve melanoma targeting. However, there have been few in vivo studies with antimelanoma scFvs because these have proved difficult to label with isotopes (e.g., 99mTc) suitable for imaging. We have generated a series of scFvs against HMW-MAA by chain shuffling and antibody phage selection on melanoma cells. In preliminary experiments we identified one scFv (RAFT3) as suitable for in vivo melanoma targeting. Direct radiolabeling of RAFT3 scFv with 99mTc was simple, yielding a radiochemical purity of >90%. The label remained stable for 24 h in vitro. 125I- and 99mTc-labeled RAFT3 scFv were tested in a nude mouse xenograft model for human melanoma and were compared with the parent MAb LHM2 and its F(ab')2 fragment versus nonmelanoma-specific MAb and scFv. RAFT3 scFv accumulated specifically in the tumor and showed greater tumor specificity compared with LHM2 with faster pharmacokinetics (t(1/2)alpha, 8 min; t(1/2)beta, 189 min; and t(1/2)alpha, 37 min; t(1/2)beta, 384 min, respectively) and reduced background in liver, lung, and spleen. Nonspecific accumulation of 99mTc-labeled RAFT3 scFv in the kidney was high but tumor:normal tissue ratios were better compared with 125I-labeled RAFT3 scFv and LHM2 F(ab')2. Overall, tumor-targeting efficiency at equivalent time points was scFv > IgG > F(ab')2 in good agreement with previously described scFvs engineered for 99mTc labeling. We discuss the potential use of RAFT3 scFv for imaging and therapy of metastatic melanoma.

Quantitative planar imaging method for measurement of renal activity by using a conjugate-emission image and transmission data

We are proposing a method to accurately measure renal activity in renography using Tc-99m labeled tracers. This method uses a conjugate-view image and transmission data for attenuation correction, the triple energy window (TEW) method for scatter correction, and background correction techniques that consider the source volume for accurate background activity correction. To examine this method in planar imaging, we performed two renal phantom studies with various uniform background activity concentrations. One study used two ideal box-shaped kidney phantoms with a thickness of 2 or 4 cm in a water tank and the other study employed two real kidney-shaped phantoms in a fillable abdominal cavity. For these studies the kidney phantom-to-background activity concentration ratio (S) was changed from 5 to infinity. The transmission data were obtained with an external Tc-99m line array source. The anterior- and posterior-view emission images were acquired with a dual-headed gamma camera simultaneously and the TEW method was used to correct scatter for the emission and transmission images. The results showed that this method with both the accurate background correction and scatter correction could give depth-independent count rates and could estimate the true count rate with errors of less than 5% for all S values. However, if either accurate background correction or scatter correction was performed alone, the absolute error increased to about 50% for the smaller S values. Our proposed method allows one to accurately and simply measure the renal radioactivity by planar imaging using the conjugate-emission image and transmission data.

Radioimmunotherapy for the intensification of conditioning before stem cell transplantation: differences in dosimetry and biokinetics of 188Re- and 99mTc-labeled anti-NCA-95 MAbs

A new concept is the intensification of preparative regimens for patients with advanced leukemia using monoclonal antibodies (MAbs) with an affinity for beta emitter-labeled bone marrow. 188Re is a high-energy beta emitter that has therapeutic promise. Our first aim was to clarify whether the therapeutic application of 188Re-MAb against nonspecific cross-reacting antigen 95 (NCA-95) can be predicted from biokinetic data derived from 99mTc-labeled NCA-95. Our second aim was to show that a radiation absorbed dose of > or =12 Gy in the bone marrow can be achieved using 188Re-MAb.

METHODS

Dosimetric data were obtained for both radiotracers from multiple planar whole-body scans (double-head gamma camera), blood samples, and urine measurements from 12 patients with advanced leukemia. Radiation absorbed doses were calculated using MIRDOSE 3 software.

RESULTS

Radiation absorbed doses to bone marrow, liver, spleen, lung, and kidney were 2.24, 0.50, 1.93, 0.05, and 0.90 mGy/MBq, respectively, using 99mTc-MAb and 1.45, 0.43, 1.32, 0.07, and 0.71 mGy/MBq, respectively, using 188Re-MAb. These differences were statistically significant for bone marrow, spleen, and kidney. The main differences were less accumulation of 188Re-MAb in bone marrow (31%+/-13% compared with 52%+/-13%) and faster elimination through urine (25%+/-3% compared with 15%+/-5% after 24 h). On the basis of these data, a mean marrow dose of 14+/-7 Gy was achieved in 12 patients suffering from leukemia after application of approximately 10+/-2 GBq 188Re-MAb.

CONCLUSION

Myeloablative radiation absorbed doses can easily be achieved using 188Re-MAb. 99mTc- and 188Re-MAb showed similar whole-body distributions. However, direct prediction of radiation absorbed doses from the 99mTc-MAb, assuming identical biokinetic behavior, is not valid for the 188Re-MAb in a single patient. Therefore, individual dosimetry using 188Re-MAb is needed to calculate therapeutic activity.

Ion exchange tumor targeting: a new approach

Connective tissues are distinguished by the types, concentrations, and organizations of material in the extracellular matrix. Many physiological functions are determined largely by the nature and organization of the extracellular components. The components are characterized by their content and distribution of charged, mostly anionic groups. The distinct roles played by the charges are sometimes modeled by analogy to the transport theory of ion exchange resins. The intent of this study was to investigate whether the properties of the tumor matrix could be used for selective, charge-dependent accumulation of charge-modified dextran. Ten patients with diagnosed superficial urinary bladder carcinoma were included in the study. They received intravesical instillations of technetium-99m-labeled charge-modified dextran derivatives (approximately 0.1-1 mg; approximately 50 MBq in saline; 30-min incubation). After treatment and resection, samples were taken from normal and diseased tissue. The result clearly demonstrated a charge-dependent difference in the quotient of radioactive uptake in tumor tissue: normal tissue. Instillations of cationic dextran yielded a high quotient, up to 3000. Normal tissue had background activity. Anionic dextran yielded a low quotient, 1.8-2, with increased background (i.e. uptake in normal tissue). Neutral dextran gave a quotient of up to 90. No radioactivity could be detected in blood. The tumors in this study apparently displayed cation-exchanging properties. We will continue this investigation and determine whether this is a general property of bladder carcinomas and whether other carcinomas display ion exchange properties. If this is the case, the finding could have important implications for the local treatment of several cancers.

[Progress of nuclear oncology]

Radionuclides used for cancer patients are produced by cyclotron or nuclear reactor. Thyroid cancer patients with lung and/or bone metastasis have been successfully treated with 131I for more than 50 years. But for the diagnosis of cancer patients, 99mTc is superior to 131I, and many 99mTc labeled compounds have been developed, such as for the diagnosis of bone metastasis, liver and kidney diseases and so on. Recently PET studies using 18F-labeled FDG have been widely performed and excellent results are reported in many cancer patients such as lung, colorectal, malignant lymphoma, malignant melanoma and so on. Radionuclides with beta emitter are suitable for the therapy of various cancers. 131I labeled anti-CD-20 monoclonal antibodies and 131I-MIBG are used for the therapy of lymphoma and pheochromocytoma, respectively. For the palliation of metastatic bone pain, 89Sr, 153Sm or 186Re is promising, because these radionuclides can be administered on an outpatients basis.

[Primary lymphoma of the thyroid with contralateral recurrence--case report]

Primary lymphomas located in the thyroid gland are rare clinical findings. The therapy and the subsequent monitoring of the disease continue to be a subject of debate. We present the case of a 63-year-old female patient in whom a hemi-thyroidectomy was performed because of a growing goiter. Histological examination of the excised tissue revealed a large-cell B-lymphocytic lymphoma which extended to neighboring lymph nodes. The patient received chemotherapy which led to remission of disease for two years. The disease re-occurred in the remaining thyroid lobe. Subsequently, the patient was treated with involved-field radiation therapy which lead to long term remission. We conclude that total thyroidectomy should be considered in the treatment of lymphomas located in the thyroid gland.

Radioisotope concentrator gene therapy using the sodium/iodide symporter gene

We demonstrate a novel method of concentrating radiation for tumor imaging or killing. The rat sodium/iodide symporter gene (rNIS) was cloned into a retroviral vector for transfer into cancer cells to mimic the iodide uptake of thyroid follicular cells. In vitro iodide transport shows that the symporter functions similarly in rNIS-transduced tumor cells and rat thyroid follicular cells. rNIS-transduced and control nontransduced (NV) human A375 melanoma xenografts established in vivo in athymic nude mice were imaged using a gamma camera after i.p. injections of 123I. The rNIS-transduced human A375 melanoma tumors are visually distinguishable from and accumulate significantly more radionuclides than NV tumors. In vitro clonogenic assays confirm efficacy and clearly show that rNIS-transduced A375 human melanoma, BNL.1 ME murine transformed liver, CT26 murine colon carcinoma, and IGROV human ovarian carcinoma can be selectively killed by the induced accumulation of 131I. Thus, NIS-based gene therapy may have both diagnostic and therapeutic applications for cancer.

Absolute organ activity estimated by five different methods of background correction

Accurate absorbed dose estimates in radionuclide therapy require patient-specific dosimetry. In patient-based dosimetry, estimation of absolute organ uptake is essential. The methods used should be reasonably accurate as well as easy to perform in routine clinical practice. One of the major sources of uncertainty in quantification of organ or tumor activity from planar images is the activity present in the tissue surrounding the source.

METHODS

To estimate organ activity as a function of organ-to-background activity concentration ratio, a cylindrical phantom, filled with 5.6 liters of water was used to simulate the abdomen of a patient. Two other cylinders of 150 ml each, representing the kidneys, were each filled with 19 MBq 99mTC and were positioned in the abdomen phantom. The phantom was imaged with a dual-head gamma camera with the kidneys placed at posterior depths of 1-, 5- and 10-cm at kidney-to-background activity concentration ratios of infinity, 10:1, 5:1 and 2:1. The conjugate view geometric mean counting method was used to quantify activity. Five methods for background correction were applied: (1) no correction; (2) conventional background correction (simple subtraction of the background counting rate from the source region counting rate); (3) Kojima method (background corrected for organ thickness and depth); (4) Thomas method (analytical solution); and (5) Buijs method (background corrected for organ and total-body thickness).

RESULTS

Since the results were identical for both kidneys, only the left kidney activity measurements are presented. The accuracy of the five background correction methods is given as the percentage difference between the actual and measured activity in the left kidney. For Method 1, the percentage difference ranged from 2% with an infinite kidney-to-background activity concentration ratio to +413% with a 2:1 ratio. For Method 2, these values ranged from -1% to -80%, for Method 3 from +11% to -18%, for Method 4 from -2% to +120% and for Method 5 from -4% to +39%.

CONCLUSION

Even though quantitative SPECT is the most rigorous method for activity quantification in conditions of low organ-to-background activity concentration ratio, planar scintigraphy can be applied accurately if appropriate attention is paid to background correction. Using relatively simple background subtraction methods, the quantitative planar imaging technique can result in reasonably accurate activity estimates (Methods 3 and 5). The use of Kojima's method is preferable, especially at very low source-to-background activity concentration ratios.

Calculating internal dose by convolution from SPECT/MR fusion images

A new computer program was developed to calculate the absorbed dose. The program is based on the use of the convolution method and abdominal SPECT/MR fusion images. The applicability of the method was demonstrated by using data from (111)In-labeled thrombocyte and 99mTc-labeled colloid studies of three healthy volunteers. Dose distributions in the volunteers and the average absorbed doses in liver and spleen were calculated. The average doses for 99mTc-labeled colloid study were 0.07 +/- 0.02 (liver) and 0.046 +/- 0.005 mGy/MBq (spleen). The results are in good agreement with a Monte Carlo (MC) based method (0.074 for liver and 0.077 mGy/MBq for spleen) used by the International Commission on Radiological Protection (ICRP). For (111)In-labeled thrombocyte study the doses were 0.33 +/- 0.05 (liver) and 8.9 +/- 1.2 mGy/MBq (spleen) versus 0.730 and 7.50, respectively. The differences in dose estimates in the (111)In-labeled thrombocyte study are mainly due to the approximation used in activity quantitation. Convolution of the activity distribution with a point dose kernel is an effective method for calculating absorbed dose distribution in a homogeneous media. Activity distribution must be aligned to anatomical data in order to utilize the calculated dose distribution. The program developed is applicable to and practical for clinical use provided that the input data needed are available.

Cancer imaging with radiolabeled antibodies: new advances with technetium-99m-labeled monoclonal antibody Fab' fragments, especially CEA-Scan and prospects for therapy

The use of radiolabeled anticancer antibodies to detect cancer sites by external scintigraphy has had a relatively long history. With the advent of monoclonal antibodies (MAbs), which precluded the need for purifying the antibodies by laborious purification steps, there was a surge of interest and efforts to develop these reagents for both imaging and therapy applications (1). Today, many thousands of patients have received different forms and doses of MAbs for various purposes, and four MAb-based products have been licensed for manufacture and sale in the U.S. (2,3). This article describes the most recent MAb product to be approved in the U.S. for colorectal cancer imaging, including discussions of using this agent and its therapeutic counterpart in several cancer types.

Parathyroid imaging

Developments in technology mean that it is now possible to localize abnormal parathyroid glands by a variety of imaging methods. There remain a number of unresolved issues. With all commonly used methods (radionuclide imaging, ultrasound, computed tomography and magnetic resonance imaging), there are wide variations in sensitivity of detection of glands, and in many cases this variation is not explained satisfactorily. The necessity for imaging is questioned by many parathyroid surgeons, particularly before a first operation. However, parathyroid surgery is itself changing, with a trend towards more limited neck exploration, which requires localization of the glands pre-operatively. This review describes the methods available for localizing parathyroid glands, with their advantages and limitations, and discusses the role of the techniques prior to surgery.

Technetium-99m, rhenium-186, and rhenium-188 direct-labeled antibodies

BACKGROUND

Antibody sulfhydryl groups can act as effective carriers of reduced technetium and rhenium species for radioimmunodetection and radioimmunotherapy.

METHODS

Intact immunoglobulin G and fragments were labeled with the isotopes and examined in vitro and in vivo.

RESULTS

Technetium bound to intact immunoglobulin G was found to be the most stable species in vitro, but in vivo, clearances of technetium and rhenium bound to intact antibody were similar. Serum clearances were faster than those seen for the corresponding radioiodinated antibodies. In vivo clearance rates of the radiolabeled fragments were similar, with kidney uptake and retention seen. Rhenium-labeled antibodies, despite a greater tendency toward in vitro reoxidation than technetium-labeled antibodies, did not show enhanced kidney clearance in animal models. Rhenium-188 and technetium-99m were obtained from similar generator systems in carrier-free form. Using rhenium-188 spiked with cold rhenium, it was determined that approximately one rhenium atom per molecule of antibody can be conjugated directly. Rhenium-186 also was coupled at almost a 1:1 ratio to antibody.

CONCLUSIONS

Only radiolysis concerns will limit the amount of rhenium-188 conjugated to antibody. Large doses of antibody will be necessary to deliver rhenium-186 at this isotope's currently available specific activity. Otherwise, higher specific activity rhenium-186, and/or greater loading capacity of rhenium-186 onto antibody, will be needed to generate the type of product that will be usable at a clinical dose of several hundred millicuries.

[The regional blood flow in intracranial tumors: a comparison of HMPAO-SPECT with a newer magnetic resonance tomographic procedure]

We compared the value of gadolinium-enhanced first-pass MRI perfusion studies and HMPAO-SPECT for the assessment of regional cerebral blood flow in a prospective study of 23 intracranial tumour patients. In five tumours with homogeneous hypoperfusion and eight tumours with homogeneous hyperperfusion, tumour blood flow patterns in MRI and HMPAO-SPECT were similar. By contrast, in ten patients with inhomogeneous tumour blood flow pattern only MRI was able to differentiate between tumour areas with no or low flow, tumour tissue with high flow, and perifocal oedema with reduced flow. In HMPAO-SPECT, these inhomogeneous tumours were represented as areas of homogeneously reduced tracer retention corresponding to different tumour constituents and perifocal oedema. In conclusion, the high spatial resolution of MRI enables a detailed analysis of tumour blood flow.

89Strontium in bone metastases from hormone resistant prostate cancer: palliation effect and biochemical changes

Hematological and biochemical parameters were evaluated in 31 patients receiving 150 MBq 89Strontium (89Sr) intravenously due to painful skeletal metastases from hormone resistant prostate cancer. Two and 3 months after the injection prostate specific antigen (PSA) had increased by a median of 36% and 100%, respectively, as compared to the pretreatment value whereas alkaline phosphatase (APHOS) had decreased by about 20% (median). The leucocyte and platelet counts were reduced by about 20-35%, without reaching grade greater than or equal to 2 toxicity. Pain relief was reported in 14 of 29 evaluable patients at 2 months and in 11 of 23 patients at 3 months. It is concluded that 89Sr represents a worthwhile therapeutic modality in the palliation treatment of patients with hormone resistant prostate cancer, though the biological significance of frequently increasing PSA and decreasing APHOS is not yet completely understood.

Quantitative measurements of cerebral blood flow using SPECT and [99mTc]-d,l-HM-PAO compared to xenon-133

The uptake and retention in a 2 cm thick brain section was recorded serially by SPECT after i.v. injection of [99mTc]-d,l-HM-PAO (HM-PAO). In 16 patients, the fraction of the administered dose retained by the brain was 5.2 +/- 1%, showing a peak after 40-50s, then decreasing by 10% within the first 10 min and then by only 0.4% per hour. The image contrast was measured in each patient as the regional hemispheric asymmetry difference in percent of the highest value of the two regions. It decreased from 31% at 30-40 s to 25% at 10 min. At 24 h, a value of 19% was reached. Using the images obtained at 10 min after injection, a region to region comparison of the original and corrected HM-PAO images to the xenon-133 regional cerebral blood flow (rCBF) images was performed. Forty-four patients with stroke, epilepsy, dementia, basal ganglia disease, and tumors and control subjects were included in this comparison. The algorithm proposed by Lassen et al. was used to correct the original images for back diffusion of tracer (brain to blood); a good correlation very close to the line of identity between the corrected HM-PAO and xenon-133 data was obtained when using a conversion/clearance ratio of 1.5 and when the noninvolved hemisphere was used as a reference region (r = 0.86, p less than 0.0001). Serial arterial and cerebral venous blood sampling was performed over 10 min following i.v. injection of HM-PAO in six patients. An overall brain retention fraction of 0.37 +/- 0.03 (mean +/- SEM) was calculated from the data. An average CBF of 0.62 +/- 0.12 ml/g/min was determined on the basis of the Fick principle; this compared to a value of 0.59 +/- 0.09 ml/g/min (mean +/- SEM) measured by the xenon-133 inhalation method. The two sets of CBF values correlated linearly with a correlation coefficient of 0.97 (p less than 0.01). Inserting the average CBF value for the hemisphere as measured by the Fick principle into the algorithm described by Lassen et al. yields absolute rCBF values (ml/g/min) directly from the corrected HM-PAO images.(ABSTRACT TRUNCATED AT 400 WORDS)

Technetium-labelled leucocytes using diethyldithiocarbamate: preliminary report on in vitro studies

Diethyldithiocarbamate (DDC) forms a lipid soluble complex with 99Tcm-pertechnetate which is rapidly incorporated into leucocytes in vitro. In seven healthy volunteers, a 'crude' leucocyte suspension was obtained by sedimnetaion and centrifugation and incubated with 99Tcm-DDC complex. Labelling efficiency was found to be 73 +/- 14% (SD). The mean activity remaining on the cells after hourly incubations with plasma was 77 +/- 5%. Percoll-saline differential cell analysis showed that 69 +/- 3% of the activity was associated with the granulocytes, 12 +/- 4% with the lymphocytes/monocytes, 11 +/- 4% with the platelets and 8 +/- 1% with contaminating erythrocytes (n = 3). The mean labelling efficiency decreased by 14% when the leucocyte count was reduced from 42 X 10(6) to 21 X 10(6) cells. Over the range 21 X 10(6) to 5.2 X 10(6) cells there was no decrease in labelling efficiency.

Scintigraphic evaluation of reflex sympathetic dystrophy: comparative study of the course of the disease under two therapeutic regimens

A study was made of 26 patients diagnosed as phase I reflex sympathetic dystrophy. In all of them, a bone:soft tissue uptake index was quantified by scintigraphic scanning before treatment and 3 months later. Eighteen patients were treated with 100 MRC units salmon calcitonin, followed by 500 mg elemental calcium 4 hours after hormone administration. The treatment was administered 10 days a month separated by intervals free of therapy. The other 8 patients were treated without interruption with 500 mg naproxen every 12 hours. In the group treated with calcitonin and calcium, the uptake index declined from 13.3 +/- 8.2 to 4.1 +/- 1.8 (p less than 0.001). The uptake index rose from 2.1.3 +/- 17.7 to 31.1 +/- 23.0 (NS) in the naproxen group. Using the Student t-test for paired samples to evaluate individual changes, a highly significant difference was reached (p less than 0.005) in the calcitonin-calcium group. The difference was also significant (p less than 0.01) in the naproxen group, but it was negative (t = 3.620). These results confirm the efficacy of treating reflex sympathetic dystrophy with calcitonin and calcium and the superiority of this treatment as compared with nonsteroidal anti-inflammatory drugs.

Low-dose autologous in vitro opsonized erythrocytes. Radioimmune method and autologous opsonized erythrocytes for refractory autoimmune thrombocytopenic purpura in adults

Adult patients with chronic autoimmune thrombocytopenic purpura (ATP), which proved refractory to various treatments, received a single dose of autologous in vitro opsonized erythrocytes with 100 micrograms of anti-D IgG. In 1983, 30 of these patients were treated with autologous erythrocytes that had been opsonized and labeled with 25 mCi (740 MBq) of technetium Tc 99m; this treatment was designated as the radioimmune method. Favorable responses were noted in 36% of patients so treated. In 1985, another group of 16 patients with refractory ATP received therapy with autologous opsonized erythrocytes (AOPE) and 55% of these patients showed favorable responses. Five (17%) of the patients treated using the radioimmune method attained a complete, long-term (greater than 35 months) remission of their ATP, and five (31%) of the patients treated using AOPE remained in complete remission over 270 days after cessation of therapy. Major complications were not seen. We concluded that the interaction of macrophages with low-dose AOPE is a successful therapeutic approach in ATP refractory to standard treatment.

Differential glomerular filtration rate in diagnosis of renovascular hypertension and follow-up of balloon angioplasty

Two hundred nine hypertensive patients with high stimulated plasma renin levels were screened for renovascular hypertension using Tc-99m DTPA renal scintigraphy. Differential glomerular filtration rate (Diff-GFR) was obtained by integrating the area under the background-subtracted renogram of each kidney between 1 and 3 minutes. 50 patients who also had undergone selective renal angiography were divided into four groups according to Diff-GFR contribution by one of the kidneys. If one kidney contributed 45-50% of total GFR, this was regarded as normal. A Diff-GFR of less than 45% was very considered to be very suggestive of renovascular hypertension in the appropriate clinical setting, while a Diff-GFR of less than 20% indicated that the renal artery might not be amenable to successful balloon angioplasty. Diff-GFR following balloon angioplasty closely reflected the early clinical response of the patients--and in some cases progressive Diff-GFR improvement was observed several months later. Diff-GFR as a scintigraphic criterion for renovascular hypertension has a sensitivity of 93%, specificity of 74%, and accuracy of 85%.