PubMed · 14402139
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G HOBBS, W HODGKISS. 1960. Modification to an electron microscope grid-holding device.. https://doi.org/10.1128/jb.80.1.140-141.1960
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PURPOSE: In breast radiotherapy, delivery of manually-calculated electron boosts limits retrospective dose-response analyses as dose distribution is unavailable. This work evaluates the feasibility of reconstructing dose distributions from manually planned electron boosts in breast-conserving radiotherapy. METHODS: Only 72 out of 198 breast cancer patients had complete stored dose distributions from sequential electron boosts in the REQUITE study. Arbitrary data from 70/72 patients were used to develop and validate dose reconstruction method. Twenty patients were used to determine optimal parameters for Monte-Carlo-based (MC) electron dose reconstruction on RayStation (v.11B-R), considering CT-calibration curve, MC-history number, andcalculation grid resolution. Remaining 50 patients were used to quantify dose reconstruction accuracy. The similarity between reconstructed and stored dose was evaluated using 3D-gamma index and dosimetric parameters extracted from breast and tumour bed contours. Dose difference location was evaluated using dose-location histogram. RESULTS: Calculation grid resolution significantly impacted electron dose distribution (p < 0.01), where the finest grid (0.15 cm) showed highest similarity to stored doses. CT-calibration curve and MC-history number had a negligible influence on dose reconstruction. Dosimetric difference between reconstructed and stored doses was < 1 Gy for breast and tumour bed. Reconstructed dose was achieved > 90% gamma passing rate in the validation set. However, around 2.5 Gy dose differences were observed at the skin and tissue interface regions. CONCLUSIONS: Retrospective electron boost dose reconstruction is feasible with acceptable accuracy, and could increase data completeness in large cohort studies. Caution is advised when assessing dose near tissue interface and further validation is needed outside the REQUITE dataset.
Resonant inelastic X-ray scattering (RIXS) was used to collect Mn K pre-edge spectra and to study the electronic structure in oxides, molecular coordination complexes, as well as the S1 and S2 states of the oxygen-evolving complex (OEC) of photosystem II (PS II). The RIXS data yield two-dimensional plots that can be interpreted along the incident (absorption) energy or the energy transfer axis. The second energy dimension separates the pre-edge (predominantly 1s to 3d transitions) from the main K-edge, and a detailed analysis is thus possible. The 1s2p RIXS final-state electron configuration along the energy transfer axis is identical to conventional L-edge absorption spectroscopy, and the RIXS spectra are therefore sensitive to the Mn spin state. This new technique thus yields information on the electronic structure that is not accessible in conventional K-edge absorption spectroscopy. The line splittings can be understood within a ligand field multiplet model, i.e., (3d,3d) and (2p,3d) two-electron interactions are crucial to describe the spectral shapes in all systems. We propose to explain the shift of the K pre-edge absorption energy upon Mn oxidation in terms of the effective number of 3d electrons (fractional 3d orbital population). The spectral changes in the Mn 1s2p(3/2) RIXS spectra between the PS II S1 and S2 states are small compared to that of the oxides and two of the coordination complexes (Mn(III)(acac)3 and Mn(IV)(sal)2(bipy)). We conclude that the electron in the step from S1 to S2 is transferred from a strongly delocalized orbital.
PURPOSE: To describe a novel, yet simple, modified segmental boost technique (MSBT) and to compare the dosimetry of our method with that of other traditional methods of treatment for the pelvis and inguinal nodes. METHODS AND MATERIALS: We developed a radiotherapy technique that uses linear accelerators with multileaf collimators to treat the pelvis and sequentially boost the inguinal regions, while minimizing "hot spots" across the match-line. This was achieved by angling the gantry for the inguinal fields so that their medial borders aligned with the divergence of the posterior pelvic field. Film dosimetry was performed to compare the MSBT with the traditional segmental boost technique, partial transmission block, and photon/electron combination techniques. These treatment techniques were scored on the basis of the dose homogeneity index, defined as the ratio of match-line maximum dose to the average dose at a given depth in the groin treatment area. RESULTS: The values of the dose homogeneity index were the same (1.04) for MSBT and partial transmission block, and 1.21, 1.39, and 1.18 for the segmental boost technique, photon pelvis with electron tags, and photon pelvis with electron boost, respectively. CONCLUSION: The MSBT proved to be technically simple while optimizing dose homogeneity compared with the other techniques and allows for maximum use of the features of modern linear accelerators.