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At least 289 records · Page 16Linked to original sources
PubMed2002

Derivation of the expressions for gamma50 and D50 for different individual TCP and NTCP models.

This paper presents a complete set of formulae for the position (D50) and the normalized slope (gamma50) of the dose-response relationship based on the most commonly used radiobiological models for tumours as well as for normal tissues. The functional subunit response models (critical element and critical volume) are used in the derivation of the formulae for the normal tissue. Binomial statistics are used to describe the tumour control probability, the functional subunit response as well as the normal tissue complication probability. The formulae are derived for the single hit and linear quadratic models of cell kill in terms of the number of fractions and dose per fraction. It is shown that the functional subunit models predict very steep, almost step-like, normal tissue individual dose-response relationships. Furthermore, the formulae for the normalized gradient depend on the cellular parameters alpha and beta when written in terms of number of fractions, but not when written in terms of dose per fraction.

Computer Simulation↗
PubMed2006

Bone augmentation in rabbit calvariae: comparative study between Bio-Oss and a novel beta-TCP/DCPD granulate.

AIM: In the present in vivo study, we compare the bone regeneration capacity of a novel brushite cement synthesized in our laboratory (DTG) with Bio-Oss using rabbits as an animal model. METHODS: The study was performed in a group of 14 adult New Zealand rabbits using the bone conduction model. Two titanium cylinders were fixed into perforated slits made on the parietal cortical bone of each rabbit. One cylinder was left empty (negative control) and the other was filled with either Bio-Oss or brushite set-cement granules (test cylinder). Four weeks after the intervention, the animals were sacrificed and biopsies were taken. The following parameters were analysed: bone tissue augmentation, bone mineral density and biomaterial resorption. The comparison of data between the different groups was performed using the Mann-Whitney test with a significance level of p<0.05. RESULTS: The mean bone mineral density and augmented mineral tissue inside the test cylinders were similar but higher than those of negative controls. Material resorption and bone tissue augmentation were significantly higher in the defects treated with the brushite-based set cement (p<0.05). CONCLUSIONS: Brushite cement granules were more resorbable and generated more bone tissue than Bio-Oss inside the titanium cylinders placed in the rabbit calvaria.

Absorbable Implants↗
PubMed2004

TCP isoeffect analysis using a heterogeneous distribution of radiosensitivity.

A formula for the alpha/beta ratio is derived using the heterogeneous (population averaged) tumor control model. This formula is nearly identical to the formula obtained using the homogeneous (individual) tumor control model, but the new formula includes extra terms showing that the alpha/beta ratio, the ratio of the mean value of a divided by the mean value of beta that would be observed in a patient population, explicitly depends on the survival level and heterogeneity. The magnitude of this correction is estimated for prostate cancer, and this appears to raise the mean value of the ratio estimate by about 20%. The method also allows investigation of confidence limits for alpha/beta based on a population distribution of radiosensitivity. For a widely heterogeneous population, the upper 95% confidence interval for the alpha/beta ratio can be as high as 7.3 Gy, even though the population mean is between 2.3 and 2.6 Gy.

Cell Survival↗
PubMed2002

The effects of TCP fabricated with amino acid binders on the proliferation and viability of fibroblast cells.

Calcium phosphate (CaP) biomaterials were produced, by fusing individual crystals together at 1200 degrees C. This ceramic material has the ability to interact with and bond to the surrounding tissue. Therefore, ceramics can serve as scaffolds for tissue growth. The objective of this study was to determine if ceramics formulated with amino acid binders can enhance and support cell growth. A total of 147 tubes containing 1 x 10(5) MRC5 cells were divided into seven equal groups. Group I served as control, Groups II-VI were incubated with ceramics containing amino acid binders (ASP, CYS, HIS, LYS, or SER, respectively) and Group VII served as ceramic without binder control. Equal numbers of tubes were terminated from each group at 24, 48 and 72 hours. Cell numbers, morphology and markers of cell damage were determined at each time point. Results indicated: 1) Total cell numbers at 24 hours were increased in all experimental groups when compared with control. Increased levels of MDA were associated with control cells. 2). At 48 hours the total cell numbers in comparison to the control cells were increased in all groups with the exception of HIS. In addition to cell number, cellular adhesion was also increased in the experimental groups compared with the control. Significant increases in MDA levels were detected at 24 hours in the CYS treated cells. 3). Cellular adhesion in the experimental groups was increased over the control, but the total cell number was only increased in the ceramic material groups containing CYS and LYS. Cells exposed to ceramics with SER as a binder showed decreased cell numbers as well as increased MDA levels at this time point in comparison to control and other binders. Morphological evaluation of the cells showed amino acid binders with acidic side chains caused an increase in the presence of spindled shaped cells. Neutral side chains resulted in cells with elongated appearances, and basic side chains caused the cells to be less elongated. In conclusion, amino acid binders are able to induce the cells to adhere, proliferate and affect their morphological appearance as early as 24 hours.

Amino Acids↗
PubMedDate not supplied

[Adhesive and other properties of Vibrio cholerae tcp+ ctx- isolated from environmental objects in the Rostov region in 2002].

The adhesive, hemolytic and triacylglycerol lipase activity of 4 V. cholerae ctp+ ctx- cultures, sensitive to bacteriophage ctx+, isolated from the Don and sewage water were tested. All these cultures were found to induce hemolysis of sheep red blood cells in the Greig test in 2 hours, possessed triacylglycerol lipase activity, but had no adhesive properties. By these parameters--atoxigenicity and the absence of adhesive properties--the isolated V. cholerae strains were characterized as avirulent and epidemically safe.

Animals↗
PubMedDate not supplied

Tumor control probability (TCP) and normal tissue complication probability (NTCP) in head and neck cancer.

Clinical radiobiology is concerned with the relationship between a given radiation dose and the resulting biological effect on tumors and normal tissues, as well as with all confounding factors related to the delivery of radiation (e.g. dose per fraction, overall treatment time, volume of tumor/normal tissue irradiated, concomitant use of chemotherapy) and/or associated with preexisting conditions of the host (e.g. diabetes, hypertension, genetic syndromes) that may influence this relationship. This article briefly reviews few of the concepts associated with the dose-effect relationships in both normal tissues and tumors of the head and neck area and presents an operational way to integrate all these concepts into the routine radiotherapy planning processes.

Comorbidity↗