Iranian Journal of Nuclear Medicine
Volume:19 Issue: 1, Winter-Spring 2011

Many radiotracers have been used for sentinel node mapping with acceptable results. The main difference between these radiotracers is the particle size. In the current study, we reported defective labeling of Tc-99m antimony sulfide colloid which resulted in large particle size. Tc-99m-Antimony sulfide colloid was used for axillary sentinel node mapping of 45 breast cancer patients. The prepared kits were turbid and were used for the first 15 patients. For the remaining 30 patients, we used a filter (GyroDisc CA-PC Cellulose Acetate Membrane; 30 mm; Pore size: 0.2 µm) after labeling to remove the possible large particles of the prepared kits. On the lymphoscintigraphy images, at least one sentinel node could be identified in 5 and 29 patients of the unfiltered and filtered groups respectively (p=0.00001). Sentinel node detection by gamma probe was successful in 5 and 30 patients in the unfiltered and filtered groups respectively (p=0.000001). Tc-99-Antimopny sulfide colloid is a suitable radiotracer for sentinel node mapping of the breast cancer patients. In case of any unusual turbidity of the labeled kit, it should not be used or at least be filtered before injection.

Intoduction: Therapeutic radiopharmaceuticals are radiolabeled molecules to deliver sufficient doses of ionizing radiation to specific disease sites such as bone metastases, brain and liver tumors and bone marrows malignancies including multiple myeloma. Among some therapeutic radiopharmaceuticals, 166Ho-1,4,7,10 -tetraazacyclo dodecane-1,4,7,10 tetraethylene phosphonic acid (166Ho-DOTMP) is used for delivering high doses to bone marrow. In this research production, quality control, pharmacokinetics and biodistribution studies of 166Ho-DOTMP with respect to its radiochemical and in vivo biological characteristics have been presented. Holmium-166 was produced by irradiation of holmium oxide (Ho2O3, purity > 99.8%) at a thermal neutron flux. 166Ho-DOTMP complex was obtained in very high yields (radiochemical purity > 99%) under the reaction conditions employed. Radiochemical purity and the stability of the 166Ho-DOTMP complex in human serum were assayed. Wild type rats were used for biodistribution and imaging studies of this agent. 166Ho produced by irradiation of holmium-165 oxide demonstrated high radionuclide purity. 166Ho-DOTMP was obtained in very high yield (radiochemical purity > 99%) and the complex exhibited excellent in vitro stability at pH~7 when stored at room temperature and human serum. Biodistribution studies in rats showed favorable selective skeletal uptake with rapid clearance from blood along with insignificant accumulation of activity in other non-target organs. The scintigraphic image recorded in rat at 3 h after the injection of the 166Ho-DOTMP radiopharmaceutical revealed that 166Ho-DOTMP rapidly accumulated in skeleton especially in the thigh bones. Biodistribution, stability, imaging and pharmacokinetics studies of 166Ho-DOTMP radiopharmaceutical in this research showed favorable features such as; rapid and selective skeletal uptake, fast clearance from blood and almost no uptake in any other major organs. Our research demonstrated that 166Ho-DOTMP has promising features suggesting good potential for efficient use of this radiopharmaceutical for bone marrow ablation in different hematologic malignancies including multiple myeloma.

Monte Carlo (MC) is the most common method for simulating virtual SPECT projections. It is useful for optimizing procedures, evaluating correction algorithms and more recently image reconstruction as a forward projector in iterative algorithms; however, the main drawback of MC is its long run time. We introduced a model based method considering the effect of body attenuation and imaging system response for fast creation of noise free SPECT projections. Collimator detector response (CDR) was modeled by layer by layer blurring of activity phantom using suitable Gaussian functions. Using the attenuation phantom, in each angle, attenuation factor (AF) was calculated for each voxel. This calculated AF is the weight for the emission voxel and states the detection probability of photons that are emitted from that voxel. Finally weighted ray sum of the blurred phantom was driven to create a projection. For the next projection, our phantom was rotated and the procedure was repeated until all projections were acquired. Root Mean Square error (RMS) between all 60 modelled projection and real MC simulated projections was decreased from 0.58 ± 0.15 using simple Radon to 0.19 ± 0.03 using our suggested model. This value was 0.56 ± 0.16 using blurred Radon without attenuation modelling, and 0.21 ± 0.03 using attenuated Radon without CDR modelling. Our suggested model that considers the effect of both attenuation and CDR simultaneously results in more accurate analytical projections compared with conventional Radon model. Creation of 60 primary SPECT projections in less than one minute may make this method as a proper alternative for MC simulation. This model can be used as a forward projector during iterative image reconstruction for correction of CDR and attenuation that is necessary for quantitative SPECT.

Despite presence of a body of evidence in support of high accuracy of cholecystokinin cholescintigraphy (CCK-CS), for diagnosis of chronic cholecystitis(CC), some authors have claimed that gallbladder ejection fraction (GBEF) has poor predictive diagnostic values. The purpose of this study was to determine if there is any difference in GBEF between normal individuals and patients with CC. In a prospective case-control study, we studied 36 subjects as control group who did not have any abdominal symptoms, or history of abdominal disease or gallstone. Patients group were 42 with established choronic calcalous cholecystitis(CCC) who complaining of chronic biliary-like pain and had gallstone on ultrasonography. All subjects underwent gallbladder scintigraphy and GBEF was calculated at 30 and 60 minutes after fatty meal (FM) ingestion. In control group GBEF at 30-minute and at 60-minute after FM ingestion were 69.54%±21.04% and 84.26%±11.41% respectively while in patients group GBEF at 30-minute was 61.21%±16.01% and at 60-minute was 80.22%±12.57%. No significant difference was noticed between control and patient groups. GBEF didnt show significant difference between different groups based on the number of gallbladder stone, severity of chronic inflammatory (lymphoplasma) cell infiltration, wall thickness and evidence of fibrosis in the gallbladder wall. Our data are against the diagnostic value of the GBEF as measured by FM-CS in the workup of patients with CC. Thus, interpretation of GBEF should take the proper clinical context into consideration.

Bombesin is a 14-aminoacid peptide isolated from frog skin. The mammalian counterparts of the frog peptide are neuromedin B (NMB) and gastrin-releasing peptide (GRP). Bombesin (BBN) is a peptide showing high affinity for the gastrin releasing peptide receptor (GRPr). Prostate, small cell lung cancer, breast, gastric, and colon cancers are known to over express receptors to bombesin (BBN) and gastrin releasing peptide (GRP). In this study a new 67Ga radiolabeled BBN analogue evaluated based upon the bifunctional chelating ligand DOTA (1, 4, 7, 10-tetraazacyclododecane-1, 4, 7, 10-tetraacetic acid) that can be used as a tool for diagnosis of GRP receptor-positive tumors. DOTA-BBN (7-14) NH2 was synthesized using a standard Fmoc strategy. Labeling with 67Ga was performed at 95°C for 30 minutes in ammonium acetate buffer (pH = 4.8). Radiochemical analysis involved ITLC and HPLC methods. The stability of radiopeptide was examined in the presence of human serum at 37°C up to 24 hours. The receptor-bound internalization and externalization rates were studied in GRP receptor expressing PC-3 cells. Biodistribution of radiopeptide was studied in nude mice bearing PC-3 tumor. Labeling yield of >90% was obtained corresponding to a specific activity of ≈ 2.48 MBq/nmol. Peptide conjugate showed good stability in the presence of human serum. The radioligand showed a good and specific internalization into PC-3 cells (14.13±0.61% at 4 h). In animal biodistribution studies, a receptor-specific uptake of radioactivity was observed in GRP-receptor-positive organs. After 4 h, uptake in mouse pancreas was 1.08 ± 0.29% ID/g (percentage of injected dose per gram of tissue). These data show that [67Ga]-DOTA-Bombesin (7-14) NH2 is a specific radioligand for gastrin-releasing peptide receptor positive tumors.

Almost all malignant tumors have the potential to eventually produce bone metastasis. The aim of the current study was to report the distribution pattern and imaging characteristics of bone metastases detected by conventional whole body bone scintigraphy in patients with different types of malignancies and to assess their relationship with the complaint of bone pain. As a cross-sectional study, 146 consecutive patients with histologically proven cancer who were referred for the assessment of possible bone metastatic involvement were investigated by 99mTc-Methylene Diphosphonate (MDP) whole body scintigraphy. A total of 146 patients (79 male and 67 female; mean age: 59.59±11.95) were enrolled, of which 71 (48.6%) patients had prostate cancer, 61 (41.8%) breast cancer, 6 (4.1%) gastric malignancy, and 8 (5.5%) miscellaneous cancers. The most frequent sites of bone metastases (vertebrae, pelvis and sternum) demonstrated more intense radiotracer uptake. Most of patients (58.5%) with bone metastasis due to breast cancer reported no localized bone pain. Also in the subgroup with prostate cancer, no significant association was noted between the site of bone metastases and location of the pain perception in most of the skeletal zones. Bone scintigraphy (by determining the specific pattern of bone metastases in different tumor types) may help physicians provide better care for patients who suffered from metastatic cancer. On the other hand, in view of the fact that no reliance can be placed on clinical symptoms and the patient's report of bone pain, bone scintigraphic data can be included in the follow-up evaluation of patients suspected to have bone metastasis, even in the absence of bone pain.

In the current study, we evaluated the feasibility of body outlining using Tc-99m filled flood source for lymphoscintigraphy imaging. 80 patients were included in the study. Sentinel node mapping was done using Tc-99m Antimony sulfide colloid. For outlining the body a Tc-99m filled flood source was used which was placed behind or lateral to the patients for Anterior and lateral images respectively. The flood source was filled with 0.5 mCi, 1 mCi, 2 mCi, and 5 mCi for 10, 47, 10, and 3 patients respectively. The quality of outline images was assessed by two nuclear medicine specialists independently. Radiation exposure to the patients was also evaluated using thermoluminescent dosimeter (TLD-100). The quality of body contour images were good in images taken by 1, 2, and 5 mCi filled flood source. However the quality of images was poor in 8 out of 10 lymphoscintigraphies taken by 0.5 mCi filled flood source. The measured dose rate from the Tc-99m flood source was 1.07 ± 0.04 µSv/MBq/hr (39 ± 1.5 µSv/mCi/hr) or 3.25 µSv for 5 min acquisition times. Body outlining is feasible with Tc-99m filled flood source. To assure high quality, at least 1 mCi of Tc-99m pertechnetate should be used for filling the source. This technique can be very useful especially when Co-57 is not available or has decayed. The need to prepare the flood source for each patient and difficulty in handling the source especially for the lateral views are the major limitations.