PubMed · 5983469
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L Zintl. 1966-06-11. [Thorotrast damage].. https://pubmed.ncbi.nlm.nih.gov/5983469/
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This work was directed towards an assessment of alpha/beta separation, alpha detection efficiency, energy resolution, quench sensitivity, and background count rate for four commercially available liquid scintillation cocktails using a Wallac 1415 liquid scintillation counter. The four cocktails were Wallac Oy OptiPhase HiSafe 3 and HiSafe 2, and Packard Ultima Gold AB and Ultima Gold XR. Aqueous radioactive solutions were prepared in 0.1 N HCl and contained 241Am (5.49 MeV alpha) and 90Sr/90Y (0.46/2.28 MeV beta-). The radioactive solutions were loaded into the cocktails at a ratio of 1 mL of aqueous solution to 10 mL of cocktail in 20 mL high-density polyethylene (HDPE) liquid scintillation vials. The effect of three levels of chemical quench on the various properties of interest was assessed for each of the LS cocktails. Alpha/beta discrimination was quantified by the fraction of beta interactions that "spillover" into the alpha window and vice versa, at the working discriminator setting. The working discriminator setting was defined as the point where the spillover of beta interactions into the alpha window and alpha interactions into the beta window were equal. For the low-quench samples, Ultima Gold AB had the lowest spillover (0.25%) and Ultima Gold XR had the highest spillover (0.8%). For the high-quench samples, the spillover ranged from 4% (HiSafe 3) to 10.5% (Ultima Gold XR). The detection efficiency for 241Am was nearly 100% and decreased with increased quench because of loss from spillover. HiSafe 2 gave the best energy resolution, 500 keV (FWHM), for the low-quench sample. The lowest background count rate was achieved with Ultima Gold AB, 0.056 cpm in the 241Am window, for a low-quench blank.
PURPOSE: Microdosimetric expectations of Boron contents are extracted from a CRAY-Monte Carlo simulation of the nuclear reaction 10B(n, alpha)7Li as it occurs on a boronated membrane of a model cell and as the reaction fragments (alpha and Li) traverse into the cellular nucleus. METHODS AND MATERIALS: The present microdosimetry calculation is based upon the assumption that the therapeutic advantage of boron neutron capture therapy (BNCT), while depending upon the RBE and LET of the reaction particles, is equally dependent on the boron carrier preferential localization to tumor tissue, and the boron selectivity to cancerous cells and its specificity within subcellular compartments. In particular, boron fixes to cell membrane as it ought to, using monoclonal antibodies. The present Monte Carlo simulation computes stochastic expectations of alpha/Li energy depositions to the nucleus in a uniformly boronated membrane shell of a spherical cell. Differential energy gain was deduced from the stochastic energy depositions in events of neutron reactions with membrane boron compared against those with natural elements (O, H, N) in the cell. RESULTS: Microdosimetry data are presented in terms of specific energy (keV/micron3) and lineal energy (keV/micron) functions of the nucleus-to-cell volume ratios (NCVR). When folded with the geometric boron content and accounting for background reaction energies, the distributions yield effective energy gain to the cell nucleus per neutron capture event. Boron amount required to yield these energy gains are found to be of the order of picograms of boron per gram of cell mass. CONCLUSION: The boron content as inferred by the present Monte Carlo microdosimetry compares well with that deliverable by present pharmacokinetic means, but are orders of magnitude (mu-grams) less than those deduced previously from anthropomorphic macrodosimetry.
We have studied the radiation responses of a human mammary epithelial cell line, H184B5 F5-1 M/10. This cell line was derived from primary mammary cells after treatment with chemicals and heavy ions. The F5-1 M/10 cells are immortal, density-inhibited in growth, and non-tumorigenic in athymic nude mice and represent an in vitro model of the human epithelium for radiation studies. Because epithelial cells are the target of alpha-particles emitted from radon daughters, we concentrated our studies on the efficiency of alpha-particles. Confluent cultures of M/10 cells were exposed to accelerated alpha-particles [beam energy incident at the cell monolayer = 3.85 MeV, incident linear energy transfer (LET) in cell = 109 keV/microns] and, for comparison, to 80 kVp x-rays. The following endpoints were studied: (1) survival, (2) chromosome aberrations at the first postirradiation mitosis, and (3) chromosome alterations at later passages following irradiation. The survival curve was exponential for alpha-particles (D0 = 0.73 +/- 0.04 Gy), while a shoulder was observed for x-rays (alpha/beta = 2.9 Gy; D0 = 2.5 Gy, extrapolation number 1.6). The relative biological effectiveness (RBE) of high-LET alpha-particles for human epithelial cell killing was 3.3 at 37% survival. Dose-response curves for the induction of chromosome aberrations were linear for alpha-particles and linearquadratic for x-rays. The RBE for the induction of chromosome aberrations varied with the type of aberration scored and was high (about 5) for chromosome breaks and low (about 2) for chromosome exchanges.(ABSTRACT TRUNCATED AT 250 WORDS)