Determination of the optimal tolerance for MLC positioning in sliding window and VMAT techniques.

PURPOSE: Several authors have recommended a 2 mm tolerance for multileaf collimator (MLC) positioning in sliding window treatments. In volumetric modulated arc therapy (VMAT) treatments, however, the optimal tolerance for MLC positioning remains unknown. In this paper, the authors present the results of a multicenter study to determine the optimal tolerance for both techniques. METHODS: The procedure used is based on dynalog file analysis. The study was carried out using seven Varian linear accelerators from five different centers. Dynalogs were collected from over 100,000 clinical treatments and in-house software was used to compute the number of tolerance faults as a function of the user-defined tolerance. Thus, the optimal value for this tolerance, defined as the lowest achievable value, was investigated. RESULTS: Dynalog files accurately predict the number of tolerance faults as a function of the tolerance value, especially for low fault incidences. All MLCs behaved similarly and the Millennium120 and the HD120 models yielded comparable results. In sliding window techniques, the number of beams with an incidence of hold-offs >1% rapidly decreases for a tolerance of 1.5 mm. In VMAT techniques, the number of tolerance faults sharply drops for tolerances around 2 mm. For a tolerance of 2.5 mm, less than 0.1% of the VMAT arcs presented tolerance faults. CONCLUSIONS: Dynalog analysis provides a feasible method for investigating the optimal tolerance for MLC positioning in dynamic fields. In sliding window treatments, the tolerance of 2 mm was found to be adequate, although it can be reduced to 1.5 mm. In VMAT treatments, the typically used 5 mm tolerance is excessively high. Instead, a tolerance of 2.5 mm is recommended.

Lead in feathers and delta-aminolevulinic acid dehydratase activity in three raptor species from an unpolluted Mediterranean forest (Southeastern Spain).

This paper presents the levels of lead found in the feathers of adult and blood of nestlings of booted eagle (Hieraaetus pennatus), European buzzard ( Buteo buteo), and goshawk (Accipiter gentilis) sampled in the 1999 and 2000 breeding seasons in a Mediterranean forest of the Province of Murcia (Southeastern Spain) located far from potential sources of metal contamination. Levels of delta-aminolevulinic acid dehydratase activity (delta-ALAD) in blood were also measured in the nestlings. Lead concentrations ranged from 1.1 to 11.21 microg/dl in blood of nestlings and from 0.35 to 1.66 mg/kg d.w. in the feathers of their parents. A significant relationship was found between blood delta-ALAD and lead (rho = -568), showing a negative correlation with blood lead levels even at lead concentrations below 5 microg/dl. This fact suggests the usefulness of this enzymatic biomarker for low lead exposure in forest raptors. There were also positive relationships between the lead concentrations in blood of nestlings and those in feathers of their parents (rho = 0.817), suggesting the usefulness of feathers for biomonitoring environmental exposure to lead.

Pluma de Aguila Calzada (Hieraaetus pennatus) como unidad biomonitora de la exposición de la ambiental a cadmio y plomo / Feather of Booted Eagle (Hieraaetus pennatus) as biomonitor of environmental exposure to cadmium and lead

La determinación de plomo y cadmio en sangre y tejidos de aves rapaces permite obtener información útil sobre el estado de salud de los individuos, de la especie y del medio ambiente en el que viven. Además su medición sistemática en programas de toxicovigilancia facilita la predicción de riesgos y la toma de decisiones de gestión medioambiental. El presente trabajo tiene como objetivo valorar la utilidad de la pluma de aves rapaces como unidad de monitorización de la exposición a metales pesados (cadmio y plomo) en un ambiente considerado a priori como mínimamente contaminado de la Región de Murcia (Sierras de Lavia y Burete, NO de Murcia). Para ello se han tomado muestras de sangre de pollos y plumas de adultos de águila calzada (Hieraaetus pennatus) durante la época de cría de los años 1999 y 2000. Previo al análisis de metales en plumas fue preciso optimizar una técnica de lavado de las muestras capaz de eliminar los metales depositados en su superficie. Todas las muestras de sangre, excepto dos, tenían niveles de cadmio y plomo inferiores a 0,5 y 5 microg/dl, respectivamente, lo que es compatible con situaciones de contaminación ambiental de fondo. Las concentraciones en plumas fueron muy inferiores a las indicativas de efecto, con medias de 16,5 y 750 microg/kg para cadmio y plomo, respectivamente. Las correlaciones entre las concentraciones de ambos metales en sangre y plumas fueron significativas al nivel p< 0,05 para el cadmio y de p <0,01 para el plomo. En conclusión opinamos que la determinación de cadmio y plomo en pluma de águila calzada es útil en los estudios de biomonitorización y toxicovigilancia. (AU)