where D is the dose absorbed by the tissue

where D is the dose absorbed by the tissue irradiated with the given type of radiation; is the dose required to achieve the same effect with reference radiation. Radiation types whose effect is well-studied can be chosen as reference, for example, hard X-ray radiation (200 − 250kV) or the 60Со radionuclide gamma radiation. Figs. 2 and 3 show the experimental data for the RBE values of protons, obtained by in vitro and in vivo methods [8]. It follows from these data that the experiments conducted do not allow to unambiguously determine the proton RBEs. In clinical practice of proton therapy, the RBE value equal to 1.1, averaged from the results of in vivo studies, is customarily used as the biological dose instead of the absorbed dose (independent of proton energy). However, numerous experiments point to an increase in RBE with a decrease in proton energy [9], and, respectively, with an increase in LET protons. To date, several theoretical models have been developed to take into account the dependence of RBE ions on the magnitude of their LET.
Results and discussion Fig. 4 shows the results of our computations of dose distributions during the transport of protons with a maximum energy of 60MeV in water (water phantom):
It can be seen from the data in Fig. 4 that factoring in the dependence of RBE on LET leads to a significant change in the shape of the modified Bragg curve in the region of the absorbed dose plateau. A particularly significant increase in the biological effect is observed in the distal part of this curve, which can lead to overexposure of the critical structures located behind the irradiated volume. It also follows from Fig. 4 that refining the RBE can reduce the required absorbed dose (and the proton fluence) by about 20%.
Conclusion
Introduction The interest in studying the structure and properties of nanogel films of bacterial alkaline phosphatase inhibitor Gluconacetobacter Xylinus (BC NGFs) is due to its potential applications in medicine and in the emerging industrial technologies [1–7]. The morphological structure of a native BC NGF synthesized by static cultivation is known to be complex and has not been received sufficient attention in research [8–10]. NMR spectroscopy was used to establish that BC NGFs typically have a three-dimensional ordered structure including nanosized crystallites from fragments of cellulose chains [11]. Fig. 1a shows a fragment of the cellulose structure with chain ordering due to intra- and intermolecular hydrogen bonds; Fig. 1b shows polycrystalline structures in dried BC gel films. Disintegrated BC NGF proved to be the most effective for solving certain problems in medicine and technology, necessitating the study of its macroscopic properties [12–14]. The dielectric method is a useful tool in correlating the molecular structure and the macroscopic properties of polar systems [15]. For example, the studies involving static dielectric polarization of dilute aqueous solutions of modified cellulose (polymethylcellulose) have revealed that its macromolecules tend to associate, so as a result, the solution is transformed to gel under certain thermodynamic conditions [16].
Experimental procedure Biosynthesis of BC NGF was described earlier in Ref. [17]. After removal of bacteria by the conventional method of boiling in a 1% NaOH solution and thorough washing with distilled water, the obtained BC gel film was dried to constant weight. The dry BC film was dissolved in purified cadoxene (cadmium ethylenediamine complex) to obtain a molecularly dispersed solution, so that the molecular weight of the BC could then be determined by viscometry. The value of the molecular weight obtained by this method amounted to 3.89·105Da The BC gel film was disintegrated with the addition of distilled water in a blender (JTC, Omniblend 1, model TM-767) at two blade rotation rates: 1.5·104 and 2.0·104rpm; the procedure was carried out in three stages lasting 5 minutes each (15 minutes overall), with 30-minute breaks to cool the colloidal suspension to room temperature.