Improving interinstitutional and intertechnology consistency of pulmonary SBRT by dose prescription to the mean internal target volume dose.

PURPOSE: Dose, fractionation, normalization and the dose profile inside the target volume vary substantially in pulmonary stereotactic body radiotherapy (SBRT) between different institutions and SBRT technologies. Published planning studies have shown large variations of the mean dose in planning target volume (PTV) and gross tumor volume (GTV) or internal target volume (ITV) when dose prescription is performed to the PTV covering isodose. This planning study investigated whether dose prescription to the mean dose of the ITV improves consistency in pulmonary SBRT dose distributions. MATERIALS AND METHODS: This was a multi-institutional planning study by the German Society of Radiation Oncology (DEGRO) working group Radiosurgery and Stereotactic Radiotherapy. CT images and structures of ITV, PTV and all relevant organs at risk (OAR) for two patients with early stage non-small cell lung cancer (NSCLC) were distributed to all participating institutions. Each institute created a treatment plan with the technique commonly used in the institute for lung SBRT. The specified dose fractionation was 3â€¯× 21.5 Gy normalized to the mean ITV dose. Additional dose objectives for target volumes and OAR were provided. RESULTS: In all, 52 plans from 25 institutions were included in this analysis: 8 robotic radiosurgery (RRS), 34 intensity-modulated (MOD), and 10 3D-conformal (3D) radiation therapy plans. The distribution of the mean dose in the PTV did not differ significantly between the two patients (median 56.9 Gy vs 56.6 Gy). There was only a small difference between the techniques, with RRS having the lowest mean PTV dose with a median of 55.9 Gy followed by MOD plans with 56.7 Gy and 3D plans with 57.4 Gy having the highest. For the different organs at risk no significant difference between the techniques could be found. CONCLUSIONS: This planning study pointed out that multiparameter dose prescription including normalization on the mean ITV dose in combination with detailed objectives for the PTV and ITV achieve consistent dose distributions for peripheral lung tumors in combination with an ITV concept between different delivery techniques and across institutions.

Structural investigation of GaInP nanowires using X-ray diffraction.

In this work the structure of ternary Ga x In1 - x P nanowires is investigated with respect to the chemical composition and homogeneity. The nanowires were grown by metal-organic vapor-phase epitaxy. For the investigation of ensemble fluctuations on several lateral length scales, X-ray diffraction reciprocal space maps have been analyzed. The data reveal a complicated varying materials composition across the sample and in the nanowires on the order of 20%. The use of modern synchrotron sources, where beam-sizes in the order of several 10 µm are available, enables us to investigate compositional gradients along the sample by recording diffraction patterns at different positions. In addition, compositional variations were found also within single nanowires in X-ray energy dispersive spectroscopy measurements.

Strain relief and shape oscillations in site-controlled coherent SiGe islands.

Strain engineering and the crystalline quality of semiconductor nanostructures are important issues for electronic and optoelectronic devices. We report on defect-free SiGe island arrays resulting from Ge coverages of up to 38 monolayers grown on prepatterned Si(001) substrates. This represents a significant expansion of the parameter space known for the growth of perfect island arrays. A cyclic development of the Ge content and island shape was observed while increasing the Ge coverage. Synchrotron-based x-ray diffraction experiments and finite element method calculations allow us to study the strain behavior of such islands in great detail. In contrast to the oscillatory changes of island shape and average Ge content, the overall strain behavior of these islands exhibits a clear monotonic trend of progressive strain relaxation with increasing Ge coverage.

Particle-assisted Ga(x)In(1-x)P nanowire growth for designed bandgap structures.

Non-tapered vertically straight Ga(x)In(1-x)P nanowires were grown in a compositional range from Ga(0.2)In(0.8)P to pure GaP in particle-assisted mode by controlling the trimethylindium, trimethylgallium and hydrogen chloride flows in metal-organic vapor phase epitaxy. X-ray energy dispersive spectroscopy in transmission electron microscopy revealed homogeneous radial material composition in single nanowires, whereas variations in the material composition were found along the nanowires. High-resolution x-ray diffraction indicates a variation of the material composition on the order of about 19% measuring an entire sample area, i.e., including edge effects during growth. The non-capped nanowires emit room temperature photoluminescence strongly in the energy range of 1.43-2.16 eV, correlated with the bandgap expected from the material composition.