Accurate estimation of dose distributions inside an eye irradiated with 106Ru plaques.

BACKGROUND: Irradiation of intraocular tumors requires dedicated techniques, such as brachytherapy with (106)Ru plaques. The currently available treatment planning system relies on the assumption that the eye is a homogeneous water sphere and on simplified radiation transport physics. However, accurate dose distributions and their assessment demand better models for both the eye and the physics. METHODS: The Monte Carlo code PENELOPE, conveniently adapted to simulate the beta decay of (106)Ru over (106)Rh into (106)Pd, was used to simulate radiation transport based on a computerized tomography scan of a patient's eye. A detailed geometrical description of two plaques (models CCA and CCB) from the manufacturer BEBIG was embedded in the computerized tomography scan. RESULTS: The simulations were firstly validated by comparison with experimental results in a water phantom. Dose maps were computed for three plaque locations on the eyeball. From these maps, isodose curves and cumulative dose-volume histograms in the eye and for the structures at risk were assessed. For example, it was observed that a 4-mm anterior displacement with respect to a posterior placement of a CCA plaque for treating a posterior tumor would reduce from 40 to 0% the volume of the optic disc receiving more than 80 Gy. Such a small difference in anatomical position leads to a change in the dose that is crucial for side effects, especially with respect to visual acuity. The radiation oncologist has to bring these large changes in absorbed dose in the structures at risk to the attention of the surgeon, especially when the plaque has to be positioned close to relevant tissues. CONCLUSION: The detailed geometry of an eye plaque in computerized and segmented tomography of a realistic patient phantom was simulated accurately. Dose-volume histograms for relevant anatomical structures of the eye and the orbit were obtained with unprecedented accuracy. This represents an important step toward an optimized brachytherapy treatment of ocular tumors.

[Sensitivity and specificity of mouse peritoneal macrophages in the diagnosis of Chlamydia trachomatis infections]. / Sensibilidad y especificidad de los macrófagos peritoneales de ratón en el diagnóstico de infecciones por Chlamydia trachomatis.

We analyzed the sensitivity and specificity of mouse peritoneal macrophages (MPM) for the diagnosis of infection by Chlamydia trachomatis. Fifty seven samples were studied, 25 of them were from cervix and 32 were from bronchial aspiration, resulting 29 positive by immunofluorescence in McCoy cells and only 16 in MPM. The sensitivity and specificity for MPM were 55% and 96% respectively. We concluded that McCoy cells are the election cells for the diagnosis of Chlamydia infection. However, the MPM can be useful in the recuperation of this microorganism, if no other method is available.