[en] Purpose: The design of an appropriate set of multiple fixed fields to achieve a steep dose gradient at the tumor edge, with minimal normal tissue exposure, is a very difficult problem, since a virtually infinite number of possible beam orientations exists. In practice we have selected beams in an iterative and often time-consuming process. This work proposes an optimization method, based on geometric and dose elements, to effectively arrive at a set of beam orientations. Methods and Materials: Beams are selected by minimizing a goal function including an angle function (beam separation for steep dose gradient at target edge) and a length function (related to normal tissue dose volume histogram). The relative importance of these two factors may be adjusted depending on the clinic situation. The model is flexible and can include case specific practical anatomic and physical considerations. Results: In extremely simple situations, the goal function yields results consistent with well-known analytical solutions. When applied to more complex clinical situations, it provides clinically reasonable solutions similar to those empirically developed by the clinician. The optimization process takes approximately 25 min on a UNIX workstation. Conclusion: The optimization scheme provides a practical means for rapidly designing multiple field coplanar or noncoplanar treatments. It overcomes limitations in human three-dimensional visualization such as trying to visualize beam directions and keeping track of the hinge angle between beams while accounting for anatomic/machine constraints. In practice, it has been used as a starting point for physicians to make modifications, based on their clinical judgment

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[en] For Monte Carlo simulated irradiation of any detector having a nonvanishing volume, immersed in a spatially dependent field of radiation, points of incidence or irradiating particles may be determined and then be either accepted or rejected according to the evaluation of a probabilistic model. The model could be based on either the differential arc method or the projected area method discussed in this paper. These two sampling algorithms were developed in order to precisely approximate experimental irradiation conditions for purposes of computer simulated irradiation. In addition, direction cosines describing the paths of travel of particles incident from any spatially dependent source field may be assigned according to a sampling algorithm applicable to any analytically defined isotimic surface where the partial derivatives exist and are continuous. (author)

[en] The dose conversion coefficients for high-energy radiation were reviewed at several SATIF meetings. At the SATIF-6 meeting, the collection of different data sets on dose conversion coefficients was agreed upon and copies of relevant papers and numerical data were gathered. This paper contains summaries of data on: 1) dose conversion coefficients for high-energy radiation, including evaluation using various codes and researchers; and 2) effective dose conversion coefficients for high-energy photons, electrons, positrons, pions, moons, kaons, neutrons, protons and heavy charged particles (up to ⁵⁶Fe ions). (authors)

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[en] The purpose of this study is to develop practical methods for calculating microdosimetric distributions for soft tissue and for lung tissue in which plutonium or other alpha-emitting elements are deposited, particularly when deposited as particulates, to aid in correlating and extrapolating radiation effects measured at different levels of exposure and in different species. The first version of a computer program for particulate microdosimetry and some initial results with it are reported

[en] Proof of necessary relationships between some morphological aspects of survival curves and some characteristics of theoretical models offers obvious interest for the elaboration of these models, regarding their empirical value. The search for such relationships is all the more useful that specialized literature provides with numerous ambiguous or contradictory interpretations regarding such or such aspect of survival curves (shoulders, slope at the origin, asymptotic region, restoration curves, etc...). This is not a surprising situation as, in final outcome, all interpretation results from some theoretical presuppositions. To the extent that such presuppositions are note clearly explicited, there is no reason to presume that all investigators should have exactly the same ones. If this difficult situation is to be remedied, it is therefore indispensable to clearly explicit the underlying theoretical context corresponding to the various types of experiments that are fulfilled. This, of course, has to be done at a relatively general level so that a priori non-justified restrictive hypotheses are not introduced. If such hypotheses sometimes find their place in the elaboration of particular models, they must nevertheless be excluded at the level of a general theory whose essential purpose is to provide a framework for description and thought that is acceptable to all. Specific examples are given regarding the signification of shoulders, slopes at the origin, asymptotes, (either in continuous or fractionated irradiations), signs of concavities, shapes of restoration curves

[en] The possibilities offered by numerical analysis regarding the identification of parameters for the model are outlined. The use of a large number of experimental measurements is made possible by the flexibility of the proposed method. It is shown that the errors of numerical identification over all parameters are proportional to experimental errors, and to a proportionality factor called conditioning of the identification problem which is easily computed. Moreover, it is possible to define and calculate, for each parameter, a factor of sensitivity to experimental errors. The numerical values of conditioning and sensitivity factor depend on all experimental conditions, that is, on the one hand, the specific definition of the experiments, and on the other hand, the number and quality of the undertaken measurements. The identification procedure proposed includes several phases. The preliminary phase consists in a first definition of experimental conditions, in agreement with the experimenter. From the data thus obtained, it is generally possible to evaluate the minimum number of equivalence classes required for an interpretation compatible with the morphology of experimental curves. Possibly, from this point, some additional measurements may prove useful or required. The numerical phase comes afterwards to determine a first approximate model by means of the methods previously described. Next phases again require a close collaboration between experimenters and theoreticians. They consist mainly in refining the first model

[en] The purpose of this investigation was to predict the field size and SSD dependence of wedge factors using simple equations. for internal and external 60 deg. lead wedges a set of wedge factors was measured at various SSDs for several field sizes and for 4, 6 and 25 MV X-rays delivered by three different accelerators. For the internal wedges the relative wedge factor, RWF, increases with field size: from 5*5 to 20*20 cm² this increase amounts 10.4% (25 MV) and 6% (4 MV) for an SSD of 75 cm. This increase reduces for both energies with about 1 or 2% for an SSD of 150 cm or 400 cm, respectively. For the external wedge the variations were much larger: 14.1%, 9.0%, 4.7% and 3.1% for 25 MV with SSDs of 75, 100, 150 and 400 cm, respectively. Similar results were observed for the 6 MV X-ray beam. For the internal wedges, i.e. large wedge-phantom distances, both the field size and SSD dependence of the RWF could be described for both photon beam energies with a single linear relationship of the product, P, of the volume of irradiated wedge visible from the point of measurement, the mass scatter coefficient and an inverse square correction. For external wedges the linear relationship is no longer valid and a higher-order polynomial relationship with P is required. Deviations up to 2% from this relationship have been observed for short SSDs, due to photons scattered from the wedge under large angles. It can be concluded, that a more sophisticated algorithm is required, to describe the variation of the RWF with field size and SSD for the internal and external wedges