Patient position reproducibility in fractionated stereotactically guided conformal radiotherapy using the BrainLab mask system.

PURPOSE: Dedicated mask systems nowadays allow the use of stereotactic radiotherapy in fractionated regimes, therefore combining the advantages of high precision radiotherapy with the biological benefit of fractionation. Therefore the knowledge of institution specific isocenter accuracy is essential for decision-making about margins to be allowed to form the planning target volume. PATIENTS AND METHOD: Measurements of isocenter deviations during fractionated treatments were performed in 33 patients using the simulator Simulix-xy (Oldelft) in connection with the BrainLab angiographic localizer-box as well as port-films. In both cases repeated images were overlaid by use of anatomical landmarks with a methodical accuracy in the order of 0.5 mm. RESULTS: Both methods yield random isocenter deviations of less then 2 mm (standard deviation) in all three directions and no significant systematic deviations. These values are in the order of the accuracy of the method, obtained by comparison of two independent investigators, as well as they are comparable with the literature. CONCLUSIONS: The accuracy of less than 2 mm indicates safety margins of 3-4 mm as sufficient for clinical routine to cover the target in 95.5% of all set-ups (2 SD).

[The results of radiotherapy in meningiomas with a high risk of recurrence. A retrospective analysis]. / Ergebnisse der Strahlentherapie bei Meningeomen mit hohem Rezidivrisiko. Eine retrospektive Analyse.

AIM: Retrospective assessment of the efficacy of radiation therapy for meningiomas with high risk for local recurrence. PATIENTS AND METHODS: Records of 67 patients with meningiomas treated from 1974 to 1995 at 2 centres were analyzed. Follow-up time ranged from 0.8 to 213 months (median: 61 months). Radiation therapy was given either after local failure or after biopsy or subtotal resection. The ratio between malignant (n = 20) and benign (n = 47) meningioma was 1:2.4. Median age of the patients was 55 years (7 to 77 years). Radiation treatment was given at 1.5 to 2 Gy per fraction to 36 to 79.5 Gy. Survival rates were calculated by the Kaplan-Meier method. Statistical comparisons were performed with the log-rank test and the Cox proportional hazards model. The Bonferroni method was used to correct for multiple comparisons. RESULTS: Five- and 10-year disease-free survival rates were 82% +/- 5% (standard error) and 70% +/- 9%. Local control rates at 5 and 10 years were 78% +/- 5% and 68% +/- 9%. In uni- and multivariate analysis histology, sex, total dose and center showed no significant influence on the results. Patients age was significant for local control (univariate p = 0.02; multivariate p = 0.03) and disease-free survival (univariate/multivariate p = 0.04). The postoperative tumor burden had a significant influence of disease-free survival (multivariate p = 0.04). After Bonferroni correction no significant influence was observed. We did not observe late side effects, especially brain necrosis. CONCLUSIONS: Despite of the negative selection of our patients we observed high survival- and local control rates after radiation therapy. This underscores the role of radiation therapy in the treatment of meningiomas with high risk of local failure.

[The efficacy of radiotherapy in vertebral hemangiomas]. / Effizienz der Strahlentherapie bei Wirbelhämangiomen.

AIM: Assessment of the efficacy of radiation therapy for symptomatic vertebral hemangiomas. PATIENTS AND METHODS: Records of 19 patients who were treated from 1969 to 1988 were retrospectively analyzed. Radiation treatment was given at 2 Gy per fraction to 20 Gy (n = 2), 30 Gy (n = 11), or 40 Gy (n = 6). Improvement of symptoms was chosen to determine the efficacy of the treatment. In addition the lesions were controlled radiographically. RESULTS: Symptomatic improvement was achieved in 17 of 19 patients, remission was complete in 7 patients. No dose-response relationship was observed. The median time to improvement of symptoms was 3 months. The radiographic controls did not correlate with the clinical course. CONCLUSIONS: Radiation therapy is an effective treatment for symptomatic vertebral hemangiomas. The aim of the treatment is to ameliorate clinical symptoms, radiographic improvement is of minor importance.

A quantitative comparison of a percentile rule with a 2-fold rule for assessing mutagenicity in the Ames assay.

Using a model based on the bivariate normal density function, this paper compares the effectiveness of two commonly employed decision rules for assessing mutagenicity in the standard Ames Salmonella assay. The 2-fold method, which considers a compound significantly mutagenic if its mean number of revertants per plate at any dose is equal to or greater than twice the mean number of revertants per plate in the concurrent control, may be a poor indicator of significant mutagenesis. In the percentile method, the frequency of induced mutations for the test compound is tested against the 95th percentile of the accumulated historical data for the spontaneous mutation frequency. As judged by the higher probability of declaring a compound mutagenic that elevates the reversion rate above background, the percentile rule is more reliable than the 2-fold method.

Evaluation of Escherichia coli K-12 343/113 and derived strains for microbial mutagenicity assays.

Several characteristics of the E. coli K-12 mutagenicity tester strains 343/113 and 343/120 have been investigated for their effects on induced mutagenesis using the arg56 and nad113 genes, and resistance to valine. We found, as have earlier authors, that the nad113 marker is relatively specific for detecting frameshift-inducing mutagens and relatively insensitive to agents that cause point mutations. In contrast, both the Arg and Val markers are primarily specific for reversion (or mutation) induction by point mutagens. In all cases tested, the Arg and Val markers respond to mutagens in a qualitatively similar manner. We have enhanced the sensitivity of this tester system to a wide variety of mutagens by permeabilization of the tester cell population using Tris-EDTA treatment. This treatment prior to mutagen exposure enables the detection of mutagenicity of several compounds that are weakly mutagenic or nonmutagenic in untreated cells. We have also increased the mutagenicity of some chemicals by preincubating with rat-liver S9 at pH values other than 7.4. For diethylnitrosamine, for instance, maximal induction occurred at pH 6.5, and for benzo[a]pyrene, maximal induction was at pH 6.8.

Synergistic, additive, and antagonistic mutagenic responses to binary mixtures of benzo(a)pyrene and benzo(e)pyrene as detected by strains TA98 and TA100 in the Salmonella/microsome assay.

Binary mixtures of benzo(a)pyrene (B(a)P) and benzo(e)pyrene (B(e)P) produce synergistic mutagenic (comutagenic) responses in Salmonella typhimurium strain TA98 (a frameshift detector). The optimum enhancement (25 X) was found at B(a)P concentration of 0.3 microgram/plate and B(e)P concentration of 1.5 microgram/plate. The response of strain TA100 (mostly a base-substitution detector) is opposite that of TA98, showing antagonism and additivity in similar concentration ranges.