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Background: Chlorotoxin is a 36-amino acid peptide found in the venom of the Leiurus quinquestriatus which blocks small-conductance chloride channels. Chlorotoxin binds preferentially to glioma cells that allow development of new methods for the treatment and diagnosis of several types of cancer. Thus chlorotoxin derivative was labeled with ¹³¹I for further investigation. Materials and Methods: A chlorotoxin derivative was synthesized on a solid phase using a standard Fmoc strategy. Labeling with iodine-131 was performed through chloramine-T method and radiochemical analysis involved sephadex G-25 and HPLC methods. The stability of radiopeptide was checked in the presence of PBS and human serum at 37 °C up to 24 h. The biodistribution was studied in mice. Results: The chemical purity of synthesized peptide as assessed by analytical RP-HPLC was 95%. Labeling of peptide resulted in a radiochemical yield of 80% with radiochemical purity of > 95% with specific activity of 0.740 GBq/μmol. Result of in vitro studies demonstrated acceptable stability of compound in human serum and PBS solution. Biodistribution data showed moderate blood clearance, with concentration of radioactivity in the kidneys, liver, intestine and stomach. Conclusion: Results indicates that the labeled Chlorotoxin derivative might be useful in determining tumor extent and also, tumor therapy of gliomas or possibily other cancers. Iran. J. Radiat. Res., 2011 8(4): 243-248

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Background: Hadron therapy for malignant tumor is becoming increasingly popular. There are many factors which effect on implementation of a proper treatment planning. The purpose of this work is to investigate the inhomogeneity effects as affecting factor on proton range, Full width at half maximum (FWHM) and 20% position of penumbra (P20) by MCNPX code. Materials and Methods: An inhomogeneous tissue (Bone or Adipose) with a variable thickness (0.1 cm, 0.5cm and 1.0 cm) was inserted into a phantom. Then this phantom was irradiated by 108.8 MeV proton beam located at 10 cm away from it. Particle energy deposition (PEDEP) in mesh tally card was used for simulation of Bragg curve and obtaining the proton range, FWHM and 20% position of penumbra (P20). Finally, the MCNPX results were compared with GEANT4. Results: The results of MCNPX for water phantom including 1cm adipose for range and P20 were 8.87 and 9.10 cm respectively, and for 1cm bone, range and P20 were 8.52 and 8.58 cm. By increasing the adipose thickness, range and P20 were reduced but it was vice versa for increasing the bone thickness. Also FWHM does not show a regular variation in both bone and adipose tissues. Conclusion: The results show that the location of the inhomogeneous tissues does not affect the variation of the whole shape of the Bragg curve, while it radically affects the dose in the Bragg curve. The comparison between MCNPX and GEANT4 results showed that the MCNPX results have the closer values than GEANT4 to references.