PubMed · 4430616
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J R Carr, R R Rich. 1974. A gamma dose integration system using miniature ionization chambers.. https://pubmed.ncbi.nlm.nih.gov/4430616/
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Gamma irradiation is a widely adopted method for terminal sterilization of medical devices; however, its application to collagen-based extracellular matrix (ECM) materials remains limited due to radiation-induced degradation of structural integrity and mechanical performance. Here, we present an engineered terminal-processing strategy that combines oxygen controlled gamma irradiation (25-30 kGy) with post-irradiation dry-heat annealing to preserve ECM functionality while achieving effective sterilization. By modulating oxygen availability during irradiation, this approach alters radical reaction pathways, suppresses oxygen-mediated oxidative degradation, and generates a metastable radical-containing intermediate, which is subsequently converted into a structurally stabilized collagen network through thermal annealing. As a result, the treated matrices preserved ECM integrity and recovered clinically relevant mechanical properties. Furthermore, the process achieved cumulative viral reductions exceeding 6 log10 across a representative panel including enveloped and non-enveloped DNA and RNA viruses, demonstrating compatibility with sterility assurance and viral safety requirements for biologically derived medical devices. Notably, preliminary observations indicate that mechanical integrity can be partially preserved even at elevated irradiation doses up to 50 kGy, suggesting potential applicability to sterilization validation frameworks requiring higher assurance levels. Overall, this work establishes a mechanistically grounded terminal-processing paradigm that enables control of radical fate, decouples sterilization efficacy from material degradation, and integrates sterilization, viral safety, and functional preservation into a unified and scalable framework for collagen-based biomaterials. This concept repositions gamma-irradiation from a purely degradative process to a controllable tool for tuning collagen structure and performance.
This paper investigates the displacement effect corrections for ionization chambers calibrated in air in terms of air kerma and used at a depth in a phantom irradiated by medium-energy x-rat beams for tube potentials between 100 kV and 300 kV. The EGS4 (electron gamma shower version 4) Monte Carlo code system has been used to simulate the coupled transport of photons and electrons. The chamber displacement correction factor, pdis, has been calculated both using a simple photon attenuation and scattering method and by direct Monte Carlo calculation of the ration of the water kerma at a depth in a phantom to the water kerma in a low-density (the same density as that of air) water cavity with its centre placed at the same depth in the phantom irradiated by medium-energy x-ray beams. Good agreement has been achieved between the pdis factors obtained using the simple method and those obtained by the direct Monte Carlo simulation. In contrast to the values recommended by the IAEA code of practice, which exceed unity by up to 10%, our pdis values for a stemless NE2571 chamber vary between 0.994 and 1.001 for the same energy range and for a stemless NE2561 chamber between 0.974 and 0.993. The beam quality correction factor and stem correction factor have been investigated in separate works. The ratios of the overall correction factors calculated in this work for an NE2571 chamber to that for an NE2561 chamber are consistent with the recent experimental results.
The spatial resolution of positron emission tomography (PET) improves when positron annihilation takes place in a strong magnetic field. In a magnetic field, the Lorentz force restricts positron range perpendicular to the field. Since positron annihilation occurs closer to its point of origin, the positron annihilation point spread function decreases. This was verified experimentally by measuring the spread function of positron annihilation from a 500 mm 68Ge bead imbedded in tissue-equivalent wax. At 5 T the spread function full width at half maximum (FWHM) and the full width at tenth maximum (FWTM) decrease by a factor of 1.42 and 2.09, respectively. Two NaI(Tl) scintillation crystals that interface to a pair of photomultiplier tubes (PMTS) through long lightguides detect positron annihilation at zero field and 5.0 T. Photomultiplier tubes, inoperable in strong magnetic fields, are functional if lightguides bring the photons produced by scintillators within the field to a minimal magnetic field. These tests also demonstrate techniques necessary for combining magnetic resonance imaging (MRI) and PET into one scanner.