Directly standardized mortality rates are examples of weighted sums of Poisson rate parameters. If the numbers of events are large then normal approximations can be used to calculate confidence intervals, but these are inadequate if the numbers are small. We present a method for obtaining approximate confidence limits for the weighted sum of Poisson parameters as linear functions of the confidence limits for a single Poisson parameter, the unweighted sum. The location and length of the proposed interval depend on the method used to obtain confidence limits for the single parameter. Therefore several methods for obtaining confidence intervals for a single Poisson parameter are compared. For single parameters and for weighted sums of parameters, simulation suggests that the coverage of the proposed intervals is close to the nominal confidence levels. The method is illustrated using data on rates of myocardial infarction obtained as part of the WHO MONICA Project in Augsburg, Federal Republic of Germany.

To investigate the temporal stability, or progressivity, of neuropsychological (NP) impairment in schizophrenia, 50 patients with first episode (FE) schizophrenia and 50 healthy controls were given a battery of tests at the outset of the study and after a two-year interval. Both patient and control groups were balanced with respect to age, gender, education and parental socioeconomic status. Summary rating scales for semantic memory (SEM), visual memory (VIM), verbal learning (VBL), visual-motor processing and attention (VSM) and abstraction/flexibility (ABS) were constructed. FE schizophrenics showed improvement in VBL, stability of function in SEM, VSM and ABS and absence of improvement in VIM. While performance in VSM and VIM is influenced by medication status, SEM seems to be trait-related and stable; VBL, however, seems to be state-related. Our data suggest that there is no proof for the assumption of progressive deterioration in NP functioning during the first few years of illness.

Purpose: IMRT (intensity modulated radiotherapy) verification techniques are reviewed together with investigations, demonstrating the intrinsic verification problems.

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Progress in the pharmacological treatment of schizophrenia is dependent on the extent of our understanding of the brain as the basis of this disease. Detailed examination of neurobiological data shows that only a systemic approach will integrate this wealth of information. For this reason, the steps involved in model building should be clarified, as further progress will necessitate closer cooperation between neuropsychiatrists, neurobiologists and systems scientists.

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An inhomogeneous anthropomorphic phantom of the human thorax including lungs and spine was developed for verification of three-dimensional (3D) intensity-modulated radiotherapy (IMRT). The phantom and spinal cord were filled with undiluted Fricke gel, whereas the lungs were filled with a special low-density Fricke gel. Based on a computed tomography scan of the phantom, an intensity-modulated stereotactic radiotherapy plan for a bronchial carcinoma was calculated using an inverse planning system (KonRad, DKFZ Heidelberg, Germany). The plan consisted of seven beams delivered in a step and shoot technique out of 67 sub-fields. Immediately after irradiation 3D magnetic resonance (MR) imaging of the phantom was performed using a special pulse sequence for T1 relaxometry. From the MR image data maps of the longitudinal relaxation rate R1 = 1/T1 were calculated. The R1 maps were converted to dose-proportional image data and compared to planning data. Measurement and planning show good agreement in regions of standard Fricke gel with an average deviation below 5%. In regions of the low-density Fricke gel, deviations are higher due to a decreased signal-to-noise ratio in the MR measurement. In these areas also a different sensitivity of the dose response was observed as compared to standard Fricke gel. The inhomogeneous thorax phantom has proven to be a useful pre-clinical tool for 3D methodical verifications.