PubMed · 13265066
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P ALEXI. 1955-08-20. [Radiotherapy with beta rays].. https://pubmed.ncbi.nlm.nih.gov/13265066/
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Electron backscattering is a prominent secondary effect in beta dosimetry, and is closely correlated with factors such as the geometries of the source and the scattering material, as well as the composition of the scattering material. Previous results were varied depending on the experimental setup and detector resolution, and were generally performed for monoenergetic electron beams, which makes direct application of these factors to beta sources difficult. In this work, backscattering factors were calculated with MCNP 4C for selected beta sources currently in use (32P and 90Sr/90Y) as well as for sources of potential therapeutic use (45Ca, 142Pr and 185W). Specifically, the calculations used beta spectra generated by the SADDE MOD2 code. The factors were calculated as a function of the distance from the interface between water and scatterers. The scatterers include source surroundings, source supporting materials and contrast agents commonly used for imaging purposes in brachytherapy. The results were fit by a simple function for future incorporation into a dose point kernel code. Due to the high-Z material content (iodine, Z = 53) in the contrast agent, a significant dose backscatter was observed near the water interface. Different cross-section algorithms in the MCNP code (inherent and ITS 3.0) affect the factor calculations. The results generated by the ITS 3.0 algorithm closely matched the EGS4 calculations for 32P. The dependence of backscatter factors on log(Z + 1) (Baily 1980 Med. Phys. 7514-9) was observed for all the beta sources with a high correlation coefficient, R (> 0.95). The overall results indicate that the backscattering effect is significant at short distances from the surface of the interface between water and the scattering material. This model can also aid in choosing a source support or mixing materials for beta brachytherapy sources.
During their production, single-walled carbon nanotubes form bundles. Owing to the weak van der Waals interaction that holds them together in the bundle, the tubes can easily slide on each other, resulting in a shear modulus comparable to that of graphite. This low shear modulus is also a major obstacle in the fabrication of macroscopic fibres composed of carbon nanotubes. Here, we have introduced stable links between neighbouring carbon nanotubes within bundles, using moderate electron-beam irradiation inside a transmission electron microscope. Concurrent measurements of the mechanical properties using an atomic force microscope show a 30-fold increase of the bending modulus, due to the formation of stable crosslinks that effectively eliminate sliding between the nanotubes. Crosslinks were modelled using first-principles calculations, showing that interstitial carbon atoms formed during irradiation in addition to carboxyl groups, can independently lead to bridge formation between neighbouring nanotubes.
The aim of this study was to evaluate vessel remodeling after implantation of high-activity (mean, 41.1 +/- 1.2 microCi) beta-emitting ((55)Co) stents. Proton bombarding in cyclotron has brought the radioactivity. Intravascular ultrasound (IVUS) investigation has been completed in 10 patients. The angiographies performed at 6 months revealed restenosis > 50% in five cases (50%). IVUS analysis demonstrated an absence of remodeling behind the stent, with no changes in total vessel volume (TVV; 353.6 +/- 126.3 and 343.9 +/- 90.6 mm(3)) or plaque + media volume (PMV; 171.7 +/- 57.4 and 166.8 +/- 42.6 mm(3)). On the other hand, lumen volume (LV) within the stent decreased significantly from 181.9 +/- 80.2 to 154.6 +/- 45.2 mm(3) (P < 0.02). This was due to presence of neointimal hyperplasia (NIH) at both extremities of implanted stents. No chronic recoil of the implanted stents was found. The analysis of edges (5 mm distally and proximally to the last stent struts) showed no significant changes in TVV (187.3 +/- 62.60 and 176.9 +/- 53.5 mm(3)), but PMV increase significantly from 61.9 +/- 31.2 to 82.2 +/- 43.4 mm(3) (P < 0.04) and LV decreased from 125.2 +/- 40.7 to 94.7 +/- 22.0 mm(3) (P < 0.02). In conclusion, single (55)Co radioactive beta-emitting stents with high initial activity are effective in reducing neointimal hyperplasia only within the stent body, as measured by IVUS, and they do not solve the problem of restenosis at the stent extremities as well as at the stent edges. Edge restenosis in this high radioactive stents was mainly (from 66%) due to neointimal proliferation.