Biomedical subjects
M Lassen
Publications and source records attributed to M Lassen.
[Retained glass fragments in the hand].
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Dermatologic radiotherapy and thyroid cancer. Dose measurements and risk quantification.
Thyroid doses for various dermatologic radiation techniques were measured with thermoluminescent dosimeters and ionization rate meters in an Alderson-Rando anthropomorphic phantom. The effects of changes in radiation quality and of the use or nonuse of treatment cones and thyroid shields were evaluated in detail. The results indicate that the potential risk of radiogenic thyroid cancer is very small when proper radiation protection measures are used. The probability of radiogenic thyroid cancer developing and the potential mortality risk were assessed quantitatively for each measurement. The quantification of radiation risks allows comparisons with risks of other therapeutic modalities and the common hazards of daily life.
Dermatologic radiotherapy and breast cancer. Dose measurements and risk quantification.
This study was set up to provide quantitative data to evaluate unsubstantiated claims that improper dermatologic radiation techniques may cause breast cancer. A thin mylar window ionization rate meter placed at the location of the right breast of an Alderson-RANDO anthropomorphic phantom was used to measure direct and scatter radiation reaching the female breast during radiotherapy of the facial region (as given for acne). The results indicate that scatter doses are very small; they are influenced by radiation quality and the use or nonuse of a treatment cone. Quantitative risk estimates show that the very small risk of breast cancer induction can be reduced even further by the use of proper radiation protection measures.
Theoretical considerations of effects of x-ray film-screen characteristics on threshold detectability of small low-contrast objects.
An expression is derived for visual contrast of a radiographed small object that takes into account the proportion of scattered radiation as well as the shape of the sensitometric curve of the film-screen combination. Based on this expression for visual contrast applied to two different film-screen systems, predictions are made for threshold perceptability of low-contrast objects radiographed with the two imaging systems in the presence of scattered radiation and at different points on the sensitometric curves.
Measurements of the effects of x-ray film--screen characteristics on threshold detectability of small low-contrast objects.
Experiments were performed to test threshold detectability of a small nylon bead radiographed with two different image receptors and under different scattering conditions. In another paper, the present authors predicted, on theoretical grounds, the visibility of small low-contrast objects radiographed in the presence of scattered radiation. The experiments discussed in this paper tested these predictions using an observer-testing method resulting in Receiver Operating Characteristic (ROC) curves. In addition to the rigidly controlled experiments from which the ROC curves were obtained, another experiment was performed in which a human phantom was used and the radiographs rated as to the visibility of small artificial lesions. By and large, the experiments confirmed the predictions made from the theoretical analysis, using visual contrast as a measure of detectability.
Change relationships, resolve conflict.
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