Technical note: Correlation between TQA data trends and TomoHD functional status.

TomoTherapy Quality Assurance (TQA) is a software package developed to monitor certain aspects of machine performance. In this study, the TQA quantities or data trends most effective in monitoring energy drifts and magnetron stability were determined respectively. This retrospective study used data collected from three TomoHD units. The TQA modules investigated were Step-Wedge Helical, Step-Wedge Static, and Basic Dosimetry. First, the TQA quantities correlated with energy changes (|r| > 0.85, where r is the Pearson's correlation coefficient) were found. The corresponding sensitivities to percentage depth dose (PDD) ratio changes were then calculated and compared. Second, the pulse-by-pulse dose stability was compared before and after each magnetron replacement using a nonparametric comparison test (Welch's t-test), and the raw dose profiles were surveyed. In this study, exit detector flatness obtained in Basic Dosimetry was shown to be the most sensitive (r = 0.945) to energy changes, followed by the energy differences in Step-Wedge Static (r = 0.942) and Step-Wedge Helical (r = 0.898). The three quantities could detect a PDD ratio change of 5.1 × 10⁻4, 5.4 × 10⁻4, and 7.1× 10⁻4, respectively. Pulse-by-Pulse Dose1 from Basic Dosimetry over a one-week period before and after a magnetron replacement showed a significant difference (p < 0.05) in only three of the nine instances. On the other hand, a raw output profile free from discontinuities, frequent dropped pulses and abnormal spikes was found to indicate that the magnetron would continue to function normally for a week 89% of the time.

The attachment of catalase and poly-l-lysine to plasma immersion ion implantation-treated polyethylene.

Plasma immersion ion implantation (PIII) treatment of polyethylene increased the functional attachment of catalase and increased the retention of enzyme activity in comparison to untreated controls. The attached protein was not removed by SDS or NaOH, while that on the untreated surfaces was easily removed. Poly-l-lysine was found to attach in a similar way to the treated surface and could not be removed by NaOH, while it did not attach to the untreated surface. This indicates that a new binding mechanism, covalent in nature, is introduced by the plasma treatment. Surfaces treated with PIII maintained the catalase activity more effectively than surfaces plasma treated without PIII. The PIII-treated surface was hydrophilic compared to the untreated surface and retained its hydrophilic character better than surfaces subjected to a conventional plasma treatment process. The strong modification of a deeper region of the polymer than for conventional plasma treatments is believed to be responsible for both the enhanced hydrophilic character and for the increase in functional lifetime of the attached protein. The results show that PIII treatment of polymers increases their usefulness for protein microarrays.

Plasma-treated nanostructured TiO(2) surface supporting biomimetic growth of apatite.

Although some types of TiO(2) powders and gel-derived films can exhibit bioactivity, plasma-sprayed TiO(2) coatings are always bioinert, thereby hampering wider applications in bone implants. We have successfully produced a bioactive nanostructured TiO(2) surface with grain size smaller than 50 nm using nanoparticle plasma spraying followed by hydrogen plasma immersion ion implantation (PIII). The hydrogen PIII nano-TiO(2) coating can induce bone-like apatite formation on its surface after immersion in a simulated body fluid. In contrast, apatite cannot form on either the as-sprayed TiO(2) surfaces (both <50 nm grain size and >50 nm grain size) or hydrogen-implanted TiO(2) with grain size larger than 50 nm. Hence, both a hydrogenated surface that gives rise to negatively charged functional groups on the surface and small grain size (<50 nm) that enhances surface adsorption are crucial to the growth of apatite. Introduction of surface bioactivity to plasma-sprayed TiO(2) coatings, which are generally recognized to have excellent biocompatibility and corrosion resistance as well as high bonding to titanium alloys, makes them more superior than many current biomedical coatings.