Studies of radiation interactions with tissue equivalent material find importance in efforts that seek to avoid unjustifiable dose to patients, also in ensuring quality control of for instance nuclear medicine imaging equipment. Use of the Monte Carlo (MC) simulation tool in such characterization processes allows for the avoidance of costly experiments involving transmitted X- and γ-ray spectrometry. Present work investigates MC simulations of γ-ray transmission through tissue equivalent solid phantoms. Use has been made of a range of radionuclide gamma ray sources, 99mTc, 131I, 137Cs, 60Co (offering photons in the energy range from a few keV up to low MeV), popularly applied in medicine and in some cases for gauging in industry, obtaining the transmission spectra following their interaction with various phantom materials and thicknesses. In validation of the model, the simulated values of mass attenuation coefficients (μ/ρ) for different phantom materials and thicknesses were found to be in good agreement with reference values (NIST, 2004) to within 1.1% for all material compositions. For all of the primary photon energies and medium thicknesses of interest herein, results show that multiple scattering peaks are generally located at energies lower than 100 keV, although for the larger phantom thicknesses it is more difficult to distinguish single, double and multiple scattering in the gamma spectra. Transmitted photon spectra investigated for water, soft tissue, breast, brain and lung tissue slab phantoms are demonstrated to be practically independent of the phantom material, while a significant difference is observed for the spectra transmitted through bone that was proved to be due to the density effect and not material composition.
During bone allograft processing, despite stringent donor screening and use of aseptic techniques, microbial invasion may occur due to the porous nature of the graft and cause potentially fatal infections. The aim of the present study was to prepare bone allograft with and without gentamicin and to compare bioburden and sterility in the obtained grafts to evaluate the role of antibiotic in enhancing graft safety. Fifty samples of demineralized freeze-dried bone allograft were prepared from suitable donors according to international standards. Randomly selected 25 samples were placed in 8 mg gentamicin/gram bone solution for 1 h. Packaging and sealing was done to ensure no microbial ingress during transportation. 40 samples were selected for bioburden testing. Remaining 10 were subjected to 25 kGy gamma radiation and tested for sterility. Microbiological evaluation revealed no evidence of colony forming units in all the samples of both the groups (Bioburden = 0). Post-radiation sterility testing also revealed no bacterial colony in the tested samples from both the groups. Favorable results validate the processing protocol while comparable results in both groups indicate no additive benefit of gentamicin addition. Nil bioburden may be used in further studies to determine a lower radiation dose to achieve adequate sterility and minimize the disadvantages of radiation like collagen cross-linking and decreased osteoinductive capacity.