Biomedical subjects

Josef Scherer

Publications and source records attributed to Josef Scherer.

5 recordsLinked to original sources

PubMed2004

Verification of IMRT: techniques and problems.

PURPOSE: IMRT (intensity-modulated radiotherapy) verification techniques are reviewed together with investigations demonstrating the intrinsic verification problems. MATERIAL AND METHODS: Different IMRT verification procedures for either class solutions or individual patients are demonstrated. Among the latter are techniques like fluence or three-dimensional (3-D) dose distribution verification within a transfer phantom. Different radiographic films and absolute dose probes are investigated for their suitability. Finally, Monte Carlo techniques (XVMC/VEF) are used for error detection and IMRT verification. RESULTS: During introduction of clinical IMRT for head and neck (H and N) tumors, we concurrently applied fluence, relative, and absolute dose measurement. While fluence and relative dose are in rather good agreement with calculations, absolute dose is always low when compared to the TPS (TMS 6.1A, Nucletron B.V.) by 5-7%. This deviation seems to depend not on the number of segments, but can strongly depend on MLC misalignment. Further investigations have revealed the importance of a detailed commissioning of the TPS down to the small-field range using diamond or diode probes and its detailed verification. In addition, simple tests have shown that dose calculation approximations in the IMRT option of TMS are one major source of the dose deviation. XVMC/VEF does not use such approximations. CONCLUSION: The procedure starts with a detailed TPS commissioning and verification process. Different verification methods are recommended during clinical IMRT implementation phase, in order to locate sources of error. Later on, a minimal program could consist of a fluence or relative dose verification procedure with few films and absolute dose measurement, followed by an intensive MLC quality assurance (QA). Inverse Monte Carlo systems, like IMCO(++)/IKO or Hyperion, seem to be able to reduce the effort.

Head and Neck Neoplasms↗

PubMed2004

[Incidence of rigor during treatment with flupentixol decanoate in comparison to risperidone].

STUDY OBJECTIVE: We investigated as to whether dosedependent extrapyramidal tolerance of Flupentixol decanoate is inferior to that of Risperidone. METHOD: 143 Risperidone and 177 Flupentixol decanoate treated patients were consecutively entered into this non - randomized open study and assessed with the Simpson-Angus-Scale regarding presence of rigor. Treatment comparisons of rigor frequency was done by Kaplan-Meier analysis. RESULTS: The risk of rigor increased with dose on both treatments. EPMS-risk was not increased under treatment with Flupentixol decanoate (mean dose 35.06 +/- 19.7 mg/2 weeks) compared to Risperidone (mean daily dose: 5.2 +/- 2.5 mg/kg) when comparable weight standardized Haloperidol equivalence doses (WHE) were used. CONCLUSION: This study offers limited evidence for methodological reasons. Yet, results do not support the view that EPS are more frequent on Flupentixol decanoate than on Risperidone when doses are comparable.

Adult↗

PubMed2003

Neurological soft signs and neuropsychological performance in patients with first episode schizophrenia.

Neurological soft signs and neuropsychological (NP) impairments are prevalent in schizophrenic patients. However, the relationship of these deficits is rarely studied, and it remains controversial in what way soft signs influence NP performance. The Neurological Evaluation Scale (NES) and a comprehensive neuropsychological test battery were used to assess soft signs and cognitive functions in 61 first-episode schizophrenic patients. The NP test battery included tests such as the California Verbal Learning Test, the Continuous Performance Test, the Span of Apprehension Test, the Stroop Color-Word Test, the Trail-Making Test and the Wisconsin Card Sorting Test. The NP tests were also administered to 87 healthy controls. The first-episode schizophrenic patients were split along the median of their NES total score (SS- vs. SS+). The level of NP performance and the differences in relative performance (shape of the NP profile) on NP functions between the two groups were assessed. The two groups (SS- vs. SS+) did not differ in any demographic or clinical variable. However, they differed in the level of their NP performance (profile mean) but did not show differential deficits in NP performance (profile shape). Neurologic soft signs influence NP performance and are correlated to a generalized NP deficit rather than to any specific NP functions.

Adult↗

PubMed2002

A prospective 2-year follow-up study of neurocognitive functioning in patients with first-episode schizophrenia.

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.

Adult↗

PubMed2002

[IMCO(++)--a Monte Carlo based IMRT system].

The application of intensity modulated radiotherapy (IMRT) to dose escalation in the target volume sets particular demands in terms of accuracy of dose calculation. Dose calculation errors due to approximations are compensated by the optimization algorithm, a procedure that ultimately leads to incorrect fluence modulation. Such inaccuracies affect particularly the dose distribution in areas with secondary electron disequilibrium. In case tissues heterogeneity predominates, conventional dose calculation methods (such as Pencil Beam) can produce relative errors up to more than 10%. The accuracy can be significantly improved by the application of a Monte-Carlo (MC) algorithm. This paper describes a MC-based inverse treatment planning algorithm (IMCO++), based on a non-iterative approach with a feedback-controlling process. The convergence behavior of IMCO++ was investigated and the used MC dose-calculation codes MMms and XVMC were compared by means of a heterogeneous phantom. IMCO++ plans were optimized in various phantoms. All plans showed conformity in terms of dose distribution of the target volume and dose reduction in risk organs (according to the requirements of the target parameter), as well as a very fast convergence of the algorithm (in less than 10 optimization steps).

Humans↗