Feasibility and potential advantages using VMAT in SRS metastasis treatments

BackgroundUtilization of stereotactic radiosurgery (SRS) for brain metastases (BM) has become the technique of choice as opposed to whole brain radiation therapy (WBRT). The aim of this work is to evaluate the feasibility and potential benefits in terms of normal tissue (NT) and dose escalation of volumetric modulated arc therapy (VMAT) in SRS metastasis treatment. A VMAT optimization procedure has therefore been developed for internal dose scaling which minimizes planner dependence.Materials and methodsFive patient-plans incorporating treatment with frame-based SRS with dynamic conformal arc technique (DA) were re-planned for VMAT. The lesions selected were between 4–6 cm³. The same geometry used in the DA plans was maintained for the VMAT cases. A VMAT planning procedure was performed attempting to scale the dose in inner auxiliary volumes, and to explore the potential for dose scaling with this technique. Comparison of dose-volume histogram (DVH) parameters were obtained.ResultsVMAT allows a superior NT sparing plus conformity and dose scaling using the auxiliary volumes. The VMAT results were significantly superior in NT sparing, improving both the V₁₀ and V₁₂ values in all cases, with a 2–3 cm³ saving. In addition, VMAT improves the dose coverage D₉₅ by about 0.5 Gy. The objective of dose escalation was achieved with VMAT with an increment of the Dmean and the Dmedian of about 2 Gy.ConclusionsThis work shows a benefit of VMAT in SRS treatment with significant NT sparing. A VMAT optimization procedure, based on auxiliary inner volumes, has been developed, enabling internal dose escalation.     

Survie de Myzus persicae (Aphididae) a un traitement thermique, selon la temperature post-operatoire

Résumé Des pucerons adultes sont exposés à 38,6° pendant une heure, puis placés à diverses températures. Onze jours plus tard, les survivants sont significativement plus nombreux à 13° et 19° qu'aux températures plus élevées (25° et 30°) ou plus basses (7°). On pense que les processus de restauration présentent un optimum thermique, situé entre 13° et 19°.

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Summary After one-hour exposure at 38,6°, the adult Myzus persicae were maintained at 7°, 13°, 19°, 25° and 30°. Eleven days later, the surviving aphids were significantly more numerous at 13° and 19° than at 7° or 25°. At 30° all the insects died. We conclude that the efficiency of the repair processes is increased for temperatures from 13° to 19°, which is the thermic optimum for this physiological function.

     

4. Geographic distribution of freshwater blue-green algae

The analysis of the currently available data for morphologically unambiguously defined freshwater blue-green algae indicates that besides (sub-)cosmopolitan species, taxa with a more restricted distribution also exist. Many of these have a holarctic or pantropic distribution. It is hypothesized that, besides the distribution of ecological niches, temperature is one of the main controlling factors restricting species to particular latitudinal zones. Furthermore, the presence of species with a regional distribution (endemics) can not be ruled out, indicating that other factors must be considered. The possible role of dispersal capacities and of dispersal rates in relation to the earth history and to the speciation of blue-green algae is discussed.