Quantifying the setup uncertainty of a stereotactic murine micro-image guided radiation therapy system.

OBJECTIVE:: Investigate the reproducibility of murine cranial positioning using solely a stereotactic stage, and quantify the potential improvements from the on-board image guidance of the X-RAD SmART irradiator. METHODS:: For intermouse reproducibility, athymic nude mice (N = 5, ×4 groups) were cranially fixed on a stereotactic stage. Each mouse was imaged via cone-beam CT (CBCT). A virtual isocenter target was placed in the brain, the stage shifted to that target, and the couch positions recorded. The mouse was removed from the stage and this process repeated twice (N=60 measurements). The first acquired CBCT coordinates (within each group of five mice) were used to define "stereotactic couch coordinates." CBCT shifts were calculated to quantify the accuracy of setup based on couch coordinates alone. For intramouse reproducibility, C57BL/6 mice (N=4) were imaged daily for 7 days. Each mouse had individual stereotactic coordinates defined from their first day of CBCT localization, and positional shifts required on the six subsequent days of imaging were quantified (N = 24 measurements). RESULTS:: The mean vector shift between stereotactic setup and CBCT alignment for inter and intramouse analysis was 0.78 ± 0.27 mm and 0.82 ± 0.34 mm, respectively. CONCLUSION:: Cranial irradiation that can permit positional uncertainties on the order of a millimeter can rely solely on stereotactic coordinates derived from a single daily CBCT. Irradiations of subregions requiring submillimeter accuracy require daily image guidance for each mouse. ADVANCES IN KNOWLEDGE:: This is the first investigation of stereotactic reproducibility using the X-RAD SmART and it suggests a method for increased efficiency in high-throughput experiments.

Neuroprotective effect of dexamethasone on the morphology of the Irradiated post natal developing cerebellum of wistar rat (Rattus norvegicus)

RESUMEN: Se estudió el efecto neuroprotector de la dexametasona, sobre el cerebelo post-natal en desarrollo irradiado de ratas Wistar. 75 neonatos de 1 día de edad fueron separados en 3 grupos; el grupo control no recibió ni drogas ni irradiación, un grupo irradiado y el otro irradiado con aplicación de dexametasona. Esta droga fue administrada una hora antes de la exposición de 5Gray (5Gy) de rayos gamma. El tejido cerebelar de cada grupo con 5, 9, 14, 21 y 25 días fueron procesados para estudios histológicos e histomorfométricos. El resultado del estudio demostró que la sola irradiación redujo significativamente el grosor de la capa granular externa, en los grupos con 5 y 14 día,s con un p0,05; la capa molecular en los ejemplares de 5, 9, 14 y 21 días con un p0,05 y la capa granular en las ratas de 5,9,14 y 25 días, con un p0,05. Cuando se combinó la dexametasona con irradiación, se observó un grosor significativamente diferente en la capa granular externa, en especímenes con 5, 9 y 14 días; en la capa molecular en los animales de 5, 14 y 21 días y en la capa granular en los que tenían 5 y 14 días, al compararlos con el grupo irradiado, con un p>0,05. El diámetro de las células de Purkinje (capa de Purkinje) aunque fue significativamente reducido en el grupo irradiado de 14 y 21 días, no fue significativamente diferente cuandos se administró dexametasona a los animales irradiados de 5, 9, 14, 21 y 25 días con un p0,05. Histológicamente, las células de la capa molecular, en el grupo irradiado de 9 y 14 días, fueron marcadamente gliosadas comparadas con las medianamente marcadas en los grupos control e irradiados-dexametasona. Hubo distorsión de la monocapa de Purkinje, con algunas células encontradas en la capa molecular o en la capa de Purkinje, en el grupo irradiado de 5, 9, 14 y 25 días. De los resultados de este estudio, se puede afirmar que la administración de 0,005 ml de dexametasona intraperitonealmente, una hora antes de una exposición a una irradiación, parece proteger el desarrollo del cerebelo de la rata, de lesiones producidas por irradiación.

A comparison of normal tissue complication probability of brain for proton and photon therapy of canine nasal tumors.

This study compared the calculated normal tissue complication probability of brain in dogs with a nasal tumor, which had both photon and proton treatment planning. Nine dogs diagnosed with a variety of histologies, but all with large, caudally located nasal tumors were studied. Three-dimensional (3-D) photon dose distribution, and a proton dose distribution was calculated for each dog. To calculate the normal tissue complication probability (NTCP) for brain, the partial brain volume irradiated with the prescribed dose was determined, then a mathematic model relating complications to partial volume and radiation dose was used. The NTCP was always smaller for proton plans as compared to photon plans, indicating conformation of the dose to the target allows a higher dose to be given. If a 5% NTCP were accepted, the mean applicable dose for this group of dogs was 50.2 Gy for photons, but 58.3 Gy for protons. Not all dogs would benefit the same from proton irradiation. If a large partial brain volume has to be irradiated, the advantage becomes minimal. There is also a minimal advantage if the planning target volume (PTV) includes a small, superficial brain volume. However, for a complex PTV shape the degree of conformation is clearly superior for protons and results in smaller calculated NTCPs.