PubMed · 14113767
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F BACLESSE. 1964. HYPERFRACTIONATION.. https://pubmed.ncbi.nlm.nih.gov/14113767/
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Practical contemporary radiotherapy dosimetry systems used for dose measurement and verification are ionization chambers (which typically have at least a 0.1 cm3 air cavity volume), thermoluminescent dosimeters (TLDs) and silicon diodes. However, during the last decade, there has been an increased interest in scintillation dosimetry using small water-equivalent plastic scintillators, due to their favourable characteristics when compared with other more commonly used detector systems. Although plastic scintillators have been shown to have many desirable dosimetric properties, as yet there is no successful commercial detector system of this type available for routine clinical use in radiation oncology. The objectives of this study are to identify the factors preventing this new technology from realizing its full potential in commercial applications. A definition of signal to noise ratio (S/N) will be proposed for this category of detectors. In doing so the S/N ratio for an early prototype design has been calculated and/or measured. Criteria to optimize the response and sensitivity of this category of detectors are presented.
Although magnesium fulfills several essential biochemical roles, direct studies on this ion are complicated by its unfavorable spectroscopic characteristics. This contribution explores the possibility of monitoring magnesium-nucleic acid binding via a combination of [Co(NH3)6]3+ as surrogate for [Mg(H2O)6]2+, and of high-resolution solid-state 59Co NMR as a spectroscopic probe. Such strategy quenches fast cationic exchanges between bound and free states, while exploiting the superior NMR properties of the 59Co spin. Experiments on relatively small amounts of tRNA can then discern resonances corresponding to different metal binding environments. These characterizations were assisted by studies on model compounds and by multinuclear 31P-59Co recoupling experiments.
The first investigation and analysis of (59)Co 2D NMR homonuclear chemical shift correlation spectra are reported for the tetrahedral mixed-metal cluster HFeCo(3)(CO)(11)PPh(2)H. For this cluster in solution, the (59)Co 2D COSY and DQF COSY NMR spectra prove the existence of a scalar coupling between (59)Co nuclei. In order to obtain a value of this coupling, the 2D COSY and DQF COSY NMR spectra for a three-spin 7/2 AX(2) system have been simulated by numerical density matrix calculations. The comparison between experimental and theoretical 2D NMR spectra gives a spin-coupling constant |(1)J((59)Co - (59)Co)| = (115 +/- 20) Hz for this cluster. Experimental measurements of T(1) and of the line widths for cobalt 59 as well as theoretical (59)Co 1D NMR spectra are reported and support our findings.