Simulation and comparison of radiology X-ray spectra by MCNP and GEANT4 codes

Monte Carlo method is a very accurate method to optimize medical diagnostic radiology spectra and simulation of radiation transportation. Using MCNP code, radiology and mammography attenuated x-rayspectraweresimulated.The IPEM report number 78 was used as a reference to compare with the GEANT4 and MCNP simulations because of its popularity and wide availability. The results of GEANT4 in 40keV showed a good homogeneity with IPEM report in terms of intensity, whilst the MCNP code in tube voltage 150kVp showed a very good agreement. Whereas theGEANT4outputintensityinallcases was less than the IPEM report, MCNP code showed higher characteristic peak intensity. The MCNP results were obtained with a less error percentage in comparison with IPEM reportexceptatlowenergies. The comparison shows a good agreement between these two codes. MCNP shows a very goodagreement in high tube voltage whereas GEANT4 showsvery goodagreement in low tube voltage

[131]I-Chlorotoxin dosimetry in liver using MCNP simulation code

Chlorotoxin is a 36 amino acids peptide, which is able to block chloride channels isolated from mouse brain. A derivative of chlorotoxin is synthesized and it is labeled by iodine 131; then animal experiments carry out on rats. Multiple organ doses may be calculated with biological distribution results in rats with labeled compounds using simulated MCNP4C code. Human dose can be calculated using the dose distribution in rats with a conversion ratio for dose distribution. Chloramine T is our method for marking, and electrophilic substitution reactions are methods for iodize of peptides. Simulation of a human phantom to evaluate dose distribution was done using simulation code MCNP4C. To evaluate the dose distribution in the human body, using this code and the accumulated activity in each organ tissue dose is calculated. To study the biological distribution of the radiotracer 131I, 0.37 MBq radiotracer was injected into rat via the tail vein. The accumulated activity in each organ with the agent "ID / g" is determined. Biological distribution of 131I-chlorotoxine in the normal rats is obtained. Its Decay constant in the liver is 0.07h and the effective half-life of the radiotracer is 10h in rat liver. The total number of particles found in the leak from liver tissue was reported 67600. Liver tissue dosimetries originating from other sources [thyroid tissue, stomach, kidney, right and left lung, spleen, and pancreas] were examined. Then, the overall dose to the target tissue will be calculated. Leaked beta particles in liver itself [self-dose] are the most delivered dose to the liver [98%]; it is for gamma rays 1.1%, while its source is adjacent tissues in addition to liver [cross-dose]; Because of low atomic number of the tissue, delivered dose originated from Bremsstrahlung [braking radiation] is low [0.9%]. Radiation dose to the liver in intravenous injection of 0.37 MBq [131]I-chlorotoxine radiotracer is 3.44 [asterisk] 10-6

Measuring natural radioactivity of bricks used in the constructions of Tehran

Naturally occurring radionuclides have different amount of activity concentration for [226] Ra, [232]Th and [40]K in building materials. In this study, natural radioactivity has been measured for bricks used in Tehran. For this work, 9 samples of three types of bricks, clay brick [CB], making the facade brick [MFB] and firebrick [FB] has been selected from different regions and factories in Tehran. Gamma rays analyzed by high purity germanium [HPGe] detector and spectroscopy system. As the results show, the maximum value of the mean [226] Ra, [232]Th and [40]K for clay brick has been 17, 9 and 422Bq/kg respectively. Maximum of radium equivalent activities [Ra[eq]] were calculated 62.81Bq/kg that less than the level has been determined 370Bq/kg for building materials. Other type of bricks had low amounts compared to clay bricks. The calculation results show that the bricks are safe for inhabitants because hazard indexes for gamma were below the standard was been introduced. The results of this research compared with other studies in different countries

Preparation and evaluation of 67Ga-DOTA-Bombesin [7-14] as a tumor scintigraphic agent

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

Preparation and biodistribution study of a [99m]Tc-labeled toxic fraction of Iranian mesobuthus eupeus scorption venom

Iranian scorpion species are classified in Buthidae and Scorpionidae with 16 genera and 25 species. In Iran, similar to other parts of the world, there are a few known species of scorpions responsible for severe envenoming. Mesobuthus eupeus is the most common species in Iran. Its venom contains several toxin fractions which can affect the ion channel. In this study purification, labeling and biological evaluation of Mesobuthus eupeus scorpion venom are described. To separate different venom fractions, soluble venom was loaded on a chromatography column packed with sephadex G50 gel then the fractions were collected according to UV absorption at 280 nm wavelength. Toxic fraction [F3] was loaded on anionic ion exchanger resin [DEAE] and then on a cationic resins [CM]. Finally toxic fraction F319 was labeled with [99m]Tc and radiochemical analysis was determined by paper chromatography. The biodistribution was studied after injection into normal mice. Toxic fraction of venom was successfully obtained in purified form. Radiolabeling of venom was performed at high specific activity with radiochemical purity more than 95% which was stable for more than 4 h. Biodistribution studies in normal mice showed rapid clearance of compound from blood [2.64% ID at 4 h] and tissues except the kidneys [27% ID at 4 h]. As tissue distribution studies are very important for clinical use, results of this study suggest that [99m]Tc labeling of venom can be a useful tool for in vivo studies and is an excellent approach to follow the process of biodistribution and kinetics of toxins

New freeze-dried kit for diagnosis of bombesin receptor expressing tumors

It has been shown that some primary human tumors and their metastases, including prostate and breast tumors, over-express gastrin-releasing peptide [GRP] receptors. Bombesin is a neuropeptide with a high affinity for these GRP receptors. The purpose of this study was to prepare and evaluate the characteristics of a new Freeze-dried kit, [6-hydrazinopyridine-3-carboxylic acid [HYNIC]]-GABA-Bombesin [7-14] NH[2] designed for the labeling with 99mTc using tricine and EDDA as coligand. Synthesis was performed on a solid phase using a standard Fmoc strategy and HYNIC precursor coupled at the N-terminus. Purified peptide conjugate was labeled with [99m]Tc at 100°C for 10 min. Radiochemical analysis involved ITLC and high-performance liquid chromatography methods. Peptide conjugate stability and affinity to human serum was challenged for 24 hours. The internalization rate was studied in GRP receptor expressing PC-3 cells. Biodistribution of radiopeptide was studied in rats. Radiolabeling was performed at high specific activities, and radiochemical purity was >98%. The stability of radiolabeled peptide in human serum was excellent. In vitro studies showed >14% of activity was specific internalized into PC-3 cells up to 4 h. After injection into rat biodistribution data showed a rapid blood clearance, with renal excretion and specific binding towards GRP receptor-positive tissues such as pancreas [1.15 +/- 0.19% ID/g after 4 h]. [[99m]Tc-HYNIC]-GABA-Bombesin [7-14] NH[2] showed favorable radiochemical and biological characteristics which make our new designed labeled peptide conjugate as a very suitable agent for diagnostic purposes in malignant tumors