Dosimetric evaluation of the Leksell GammaPlan™ Convolution dose calculation algorithm.

The dosimetric accuracy of the Leksell GammaPlan Convolution calculation algorithm was evaluated through comparison with corresponding Monte Carlo (MC) dosimetric results. MC simulations were based on generated sector phase space files for the 4 mm, 8 mm and 16 mm collimator sizes, using a previous comprehensive Gamma Knife Perfexion™ source model and validated using film dosimetry. Test cases were designed for the evaluation of the Convolution algorithm involving irradiation of homogeneous and inhomogeneous phantom geometries mimicking clinical cases, with radiation fields created using one sector (single sector), all sectors with the same (single shot) or different (composite shot) collimator sizes. Dose calculations using the Convolution algorithm were found to be in excellent agreement (gamma pass rate greater than 98%, applying 1%/1 mm local dose difference and distance agreement criteria), with corresponding MC calculations, indicating the accuracy of the Convolution algorithm in homogeneous and heterogeneous model geometries. While of minor clinical importance, large deviations were observed for the voxels laying inside air media. The calculated beam on times using the Convolution algorithm were found to increase (up to 7%) relative to the TMR 10 algorithm currently used in clinical practice, especially in a test case mimicking a brain metastasis close to the skull, in excellent agreement with corresponding MC calculations.

Poor endoscopic findings in children with non variceal upper gastrointestinal bleeding: is biopsy necessary?

BACKGROUND: Gastrointestinal bleeding in infants and children is a potentially serious condition in the practice of general pediatrics that requires investigation. The objective of this study is to describe the endoscopic and histopathological findings in children with upper gastrointestinal (UGI) bleeding of non variceal origin. PATIENTS AND METHODS: We performed a retrospective study of the medical records of 181 children, aged 1 month to 15.2 years, with non variceal UGI bleeding, who were admitted in our department over the period 1988-2008 and underwent upper GI endoscopy accompanied by histology. Patients were divided in 4 groups according to their age (=0-1 years, = 1-6 years, C=6-12 years, D= 12-16 years). RESULTS: An endoscopically evident bleeding source was detected in only 5% of all patients. Histological examination revealed increased incidence of eosinophilic infiltration in infants, in contrast to all other age groups, where non-specific or H. pylori related inflammation predominated. Peptic ulcer was found in 4.4% of all patients. CONCLUSION: Although an evident bleeding source was detected in only a small percentage of patients, the accompanying histological examination provided additional information regarding possible underlying diseases and contributed to the subsequent therapeutic management.