It is known that slight variations in total dose delivered to the patient in external beam photon radiotherapy can significantly alter the probability of tumour control. For this reason, ICRU has recommended a goal of $ pm$5% precision in the dose delivery to the target volume. Several investigators have analyzed the degree of precision routinely achieved and have come to the conclusion that ICRU's goal can be attained, but in practice this is just barely so. / We have measured the degree of precision which exists in our institution by examining each step of the radiotherapy process on a cobalt unit and a 10 MV linear accelerator. Our study finds beam intensity uncertainties of $ pm$3.8% (one standard deviation) and beam positional uncertainties of $ pm$5.5 mm (one standard deviation). The effect of these uncertainties on the dose to the patient is illustrated for a typical case.

The effect of disturbed flows on mass transfer to and from an arterial wall was studied both theoretically and experimentally using an idealized model of arterial stenoses in which an annular ring vortex was formed. It was found that the transport of macromolecules, including low density lipoproteins, from flowing blood to a semi-permeable vessel wall is greatly enhanced in regions of disturbed flow with a local maximum locating around the reattachment (stagnation) point. The surface concentration of macromolecules increases with increasing the filtration velocity and decreasing the flow rate. The disturbed flows also facilitated the transport of low molecular weight substances such as biochemicals but not macromolecules from arterial walls to flowing blood. These results strongly suggest that disturbed flows with slow recirculation flow provide favorable conditions for the genesis and development of atherosclerotic lesions by affecting local mass transport phenomena at the blood-vessel wall boundary.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6251. Adviser: Richard F. Nelson. Includes bibliographical references (leaves 81-82) Available on microfilm from Pro Quest Information and Learning.

The A2780s is a cisplatin and radiation-sensitive human ovarian carcinoma cell line from which the more resistant variant, A2780cp, was derived. In vitro experiments on the radiosensitivity of these cells with different treatments may be representative of the in vivo radiosensitivity, and maybe of use to patients receiving radiotherapy. Therefore, many studies have been directed at evaluation of the inhibition of DNA repair in order to improve radiotherapy. Previous studies showed that drugs and hyperthermia are repair inhibitors increasing the effectiveness of radiation. Cisplatin can also radiosensitize the A2780s and A2780cp and inhibit the sublethal damage repair (SLDR) (Raaphorst et al., 1995a). In this study we found no radiosensitization in the A2780s and A2780cp cells when cisplatin is added immediately before or after radiation. When cisplatin was added 24 hours prior to radiation, no increase in cellular resistance (adaptive response) to radiation treatment was observed. On the other hand cisplatin induced resistance when added during a pulse dose rate (PDR of 1 Gy/h) radiation treatment.

This dissertation is a report on a study of the elastic properties of the human mandible. Using a pulse transmission technique, it was determined that the elastic stiffness 76 specimens, from various locations in the ramus and corpus of four mandibles material exhibited symmetry properties which were characteristics of anisotropic material In order to facilitate an understanding of the coordinate system used in determining the elastic stiffnesses of the specimens, a simplistic model can be employed. Assume that a section of the human mandible is projected point-by-point on to a straight line with the left wisdom tooth at one extreme, and the right wisdom tooth at the other Now consider this projection of the mandible to approximate a right circular cylinder. The x$\sb3$-direction is defined to be along the length of the cylinder, axial direction. The circumferential direction is designated by x$\sb2$ and the radial by x$\sb1$ The similarity between mandibular and femoral bone is quite remarkable. Femoral bone is slightly more dense and stiff, but the similarities far outweigh the differences. The average density of mandibular bone is 1799 kg/m$\sp3$ 95% of that of femoral bone. The average stiffness coefficient for mandibular bone is 96% of that of femoral bone. It would appear from this comparison that the mandible is in its elastic properties very much like a long bone bent in the shape of a parabola. The average technical constants for mandibular and femoral bone show a distinct parallelism It was determined from a study of the human mandible by region that the lingual region, surface in the proximity of the tongue, is most dense and stiff while the buccal, surface nearest the cheek, is the least stiff. Similarly, it was found that average specimens from mandibles with teeth were denser and stiffer than those from mandibles without teeth. (Abstract shortened with permission of author.) / acase@tulane.edu

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