Margin re-excision and local recurrence in invasive breast cancer: A cost analysis using a decision tree model.

BACKGROUND: SSO-ASTRO recently published guidelines defining adequate margins in breast conservation therapy (BCT) as no tumor on ink based on studies demonstrating little difference in local recurrence (LR) with wider margins. We hypothesize that not routinely re-excising close margins results in decreased costs without compromising care. METHODS: A decision tree model was developed for the management of margins after BCT for invasive cancer. Patients were compared among three margin status groups: positive, close (≤2 mm) and negative (>2 mm). Ten publications provided re-excision rates (RER) and LR rates. The model assumed 140,000 BCT/year. Sensitivity analyses determined the most cost-effective strategy. Surgical costs were estimated using 2013 Medicare reimbursement rates. RESULTS: Re-excising close margins was significantly more costly than the alternative, $233.1 million versus $214.3 million, per year in the United States. Total surgical cost was most sensitive to re-excision of close margins-increasing the RER from 0% to 100% resulted in an $18.8 million cost difference. CONCLUSIONS: The strategy of re-excising close margins resulted in a predicted cost of $18.8 million per year. This does not include hospital costs, the cost of surgical complications after re-excision, and underestimates the potential savings by using Medicare reimbursement rates.

Temperature dependence of alkali-metal rattling dynamics in the ß-pyrochlores, AOs2O6 (A = K, Rb, Cs), from MD simulation.

We investigate the temperature response of the alkali-metal rattling modes in ß-pyrochlores, AOs2O6 (A = K, Rb, Cs), from the results of ab initio molecular dynamics (MD) simulations performed at 20 K, 100 K and 300 K. Our results show that the temperature response of the T1u mode is clearly different from that of the T2g mode for all three pyrochlores. In this regard, two features are of particular note for both K and Rb; (1) the T1u mode exhibits a distinctly stronger softening response with decreasing temperature compared to the T2g mode, and (2) the T1u mode becomes stronger and sharper with decreasing temperature. These two findings suggest that the T1u mode is significantly more anharmonic and sensitive to the cage dynamics than the T2g mode. Examination of the local potentials around the alkali-metal atoms reveals that K has the flattest and most anharmonic potential at all temperatures while Cs exhibits the narrowest potential. The temperature dependence of the local potentials reveals that, for K, the potential at a higher temperature is not a simple extrapolation to higher energy of that at a lower temperature. Instead, we find significant reconstruction of the potential at different temperatures. Finally, we explore the temperature response of the coupling between the alkali metals and find a complex temperature dependence which suggests that the origin of the coupling may be more complex than a pure Coulomb interaction. We also find an unexpected increase in the static disorder of the system at low temperatures for the K and Rb pyrochlores.

Molecular dynamics evidence for alkali-metal rattling in the ß-pyrochlores, AOs2O6 (A = K, Rb, Cs).

We have used ab initio molecular dynamics simulations validated against inelastic neutron scattering data to study alkali-metal dynamics in the ß-pyrochlore osmates AOs2O6 (A=K, Rb, Cs) at 300 K to gain insight into the microscopic nature of rattling dynamics in these materials. Our results provide new evidence at the microscopic level for rattling dynamics: (1) the elemental magnitude spectra calculated from the MD show a striking dominance by the alkali metals at low energies indicating weak coupling to the cage, (2) the atomic root-mean-square displacements for the alkali metals are significantly larger than for the other atoms, e.g., 25% and 150% larger than O and Os, respectively, in KOs2O6, and (3) motions of the alkali metals are weakly correlated to the dynamics in their immediate environment, e.g. K in KOs2O6 is 6 times less sensitive to its local environment than Os, indicating weak bonding of the K. There is broadening of the elemental spectra of the alkali metals from Cs to K corresponding to a similar broadening of the local potential around these atoms as determined from potential of mean-force calculations. This feature of the spectra is partly explained by the well-known increase in the relative cage volume with decreasing atomic size of the alkali metal. We find that for the smallest rattler in this series (K) the larger relative cage volume allows this atom freedom to explore a large space inside the cage leading to vibration at a broader range of frequencies, hence a broader spectrum. Thus, since K is considered the best rattler in this series, these findings suggest that a significant feature of a good rattler is the ability to vibrate at several different but closely spaced frequencies.

Charge distribution near bulk oxygen vacancies in cerium oxides.

Understanding the electronic charge distribution around oxygen vacancies in transition metal and rare earth oxides is a scientific challenge of considerable technological importance. We show how significant information about the charge distribution around vacancies in cerium oxide can be gained from a study of high resolution crystal structures of higher order oxides which exhibit ordering of oxygen vacancies. Specifically, we consider the implications of a bond valence sum analysis of Ce7O12 and Ce11O20. To illuminate our analysis we show alternative representations of the crystal structures in terms of orderly arrays of coordination defects and in terms of fluorite-type modules. We found that in Ce7O12, the excess charge resulting from removal of an oxygen atom delocalizes among all three triclinic Ce sites closest to the O vacancy. In Ce11O20, the charge localizes on the next nearest neighbour Ce atoms. Our main result is that the charge prefers to distribute itself so that it is farthest away from the O vacancies. This contradicts the standard picture of charge localization which assumes that each of the two excess electrons localizes on one of the cerium ions nearest to the vacancy. This standard picture is assumed in most calculations based on density functional theory (DFT). Based on the known crystal structure of Pr6O11, we also predict that the charge in Ce6O11 will be found in the second coordination shell of the O vacancy. We also extend the analysis to the Magnéli phases of titanium and vanadium oxides (M(n)O(2n₋1), where M = Ti, V) and consider the problem of metal-insulator transitions (MIT) in these oxides. We found that the bond valence analysis may provide a useful predictive tool in structures where the MIT is accompanied by significant changes in the metal-oxygen bond lengths. Although this review focuses mainly on bulk cerium oxides with some extension to the Magnéli phases of titanium and vanadium, our approach to characterizing electronic properties of oxygen vacancies and the physical insights gained should also be relevant to surface defects and to other rare earth and transition metal oxides.