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PubMed · 1006711

[Therapy simulator for radiotherapy planning].

E Doppelfeld·W Frik
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Abstract

The ideas prevailing so far with regard to therapy simulators are represented and the type of the simulator used is described; after that, the range of problems a simulator is applied to, is being analysed more detailedly. The use of the simulator is necessary within two phases of irradiation planning: Firstly, to trace that cross-sectional view of the body which is best adapted to dosage planning along with a preliminary adjustment informing upon the beam directions and the field sizes needed. Secondly, to accomplish the final fixation of the needed beam directions and field sizes inclusively the marking of cutaneous fields, a definitive schedule of doses having been laid down before. The requirements, therapy simulators have to meet according to these considerations, are discussed.

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RadiotherapyRadiotherapy DosageSkinTechnology, RadiologicEnglish AbstractJournal Article

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E Doppelfeld, W Frik. 1976. [Therapy simulator for radiotherapy planning].. https://pubmed.ncbi.nlm.nih.gov/1006711/

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Field edge smoothing for multileaf collimators.

PURPOSE: To smooth the scalloped dose pattern that occurs for stepped leaves at a treatment field edge defined by a multileaf collimator. METHODS AND MATERIALS: Fields with centers shifted slightly in space were superimposed to blur the staggered dose distribution at the field edge. Film dosimetry was used to monitor changes. The dose distribution for a single field position was compared to the distribution for one and three shifts. Three depths were examined and divergent alloy blocks were included in the comparison. RESULTS: The structure that appears at an edge for a single field when leaves are staggered was nearly eliminated when the field was shifted three times to give a total of four different positions. However, shifting the field one time so that two fields were superimposed gave an intermediate result with only slight improvement in the undulating dose distribution. For the four superimposed fields, the 50% isodose pattern converged to a smoothed line running along the center of the original undulating pattern. The 80 and 20% isodoses did not converge to the center of their scalloped patterns. Instead, these isodose lines were spread leaving a larger penumbra width than a divergent alloy block. CONCLUSIONS: Shifting and adding fields is an effective method for smoothing the staggered dose distribution that results when the leaves of a multileaf collimator are stepped to form an irregular field pattern. However, the width of the penumbra for the combined fields is wider than the penumbra for a cerrobend block.

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