Possible association of dose rate and the development of late visual toxicity for patients with intracranial tumours treated with pencil beam scanned proton therapy.

BACKGROUND AND PURPOSE: Rare but severe toxicities of the optic apparatus have been observed after treatment of intracranial tumours with proton therapy. Some adverse events have occurred at unusually low dose levels and are thus difficult to understand considering dose metrics only. When transitioning from double scattering to pencil beam scanning, little consideration was given to increased dose rates observed with the latter delivery paradigm. We explored if dose rate related metrics could provide additional predicting factors for the development of late visual toxicities. MATERIALS AND METHODS: Radiation-induced intracranial visual pathway lesions were delineated on MRI for all index cases. Voxel-wise maximum dose rate (MDR) was calculated for 2 patients with observed optic nerve toxicities (CTCAE grade 3 and 4), and 6 similar control cases. Additionally, linear energy transfer (LET) related dose enhancing metrics were investigated. RESULTS: For the index cases, which developed toxicities at low dose levels (mean, 50 GyRBE), some dose was delivered at higher instantaneous dose rates. While optic structures of non-toxicity cases were exposed to dose rates of up to 1 to 3.2 GyRBE/s, the pre-chiasmatic optic nerves of the 2 toxicity cases were exposed to dose rates above 3.7 GyRBE/s. LET-related metrics were not substantially different between the index and non-toxicity cases. CONCLUSIONS: Our observations reveal large variations in instantaneous dose rates experienced by different volumes within our patient cohort, even when considering the same indications and beam arrangement. High dose rate regions are spatially overlapping with the radiation induced toxicity areas in the follow up images. At this point, it is not feasible to establish causality between exposure to high dose rates and the development of late optic apparatus toxicities due to the low incidence of injury.

Rituximab intravítreo como tratamiento de la recidiva de un linfoma no Hodgkin a nivel intraocular / Intravitreal rituximab for the treatment of intraocular relapse of non-Hodgkin's lymphoma

Caso clínico: Mujer de 58 años que presenta una recidiva de un linfoma difuso de células B grandes a nivel intraocular. Inicia tratamiento con rituximab intravítreo (1 mg/0,1 ml) con pauta semanal durante 4 semanas. Tras 12 meses de la última administración de rituximab intravítreo no se observan lesiones compatibles con linfoma ni reacciones adversas asociadas a su administración. Discusión: El rituximab intravítreo ha resultado efectivo y seguro para el tratamiento de la recaída del linfoma no Hodgkin a nivel intraocular, induciendo su remisión completa y resultando ser una buena alternativa respecto a otras opciones terapéuticas con mayor número de reacciones adversas graves (AU)

Clinical case: A 58-year-old woman with intraocular relapse of a diffuse large B cell lymphoma. Weekly intravitreal rituximab (1 mg/0.1 ml) for 4 weeks were administered. 12 months after the last intravitreal rituximab dose, signs and symptoms of lymphomas or adverse reactions associated with intravitreal Rituximab administration were not observed. Discussion: Intravitreal rituximab is an effective and safe treatment of intravitreal lymphoma, by inducing complete remission; it could be a good alternative to other therapeutic options with greater number of serious complications (AU)

Estudio estructural de la mielina del nervio óptico humano por difracción de rayos X / Structural study of the human optic nerve myelin by x-ray diffraction

Se obtuvieron muestras de pacientes que ingresaron al servicio de oftalmología del hospital Universitario de Caracas y se les realizó enunciación por presentar heridas irreparables del globo ocular post-trauma ocular severo. Sin antecedentes de patología ocular y/o sistémica; se utilizó técnica de difracción de rayos X y los algoritmos matemáticos de Luzzati y Mateu (1-6) para cuantificación de los parámetros estructurales de la mielina. se determinaron así, por primera vez que para un adulto jóven normal dichos parámetros estructurales: La distancia promedio de la separación entre lamelas (D) es de 154 a 156 A. La varianza de esta distancia (OD) es de 1.3 a 3.3 A. El número promedio de vueltas de mielina por axón () es de 4.1 a 6.5. La técnica de difracción de rayos X es un método rápido preciso, no invasivo, puede realizarse en tejido fisiológicamente intacto, como in vivo, y puede utilizarse en el estudio de la patología tumoral y/o de mielina del nervio óptico