The Reference Man in diagnostic radiology dosimetry.

Following the legislation for radiation protection in Europe, increasing interest has been given to patient dosimetry in diagnostic radiology. Dose comparisons between groups of patients have demonstrated considerable discrepancies. The equipment, as well as the procedures used, have been scrutinized in order to find the reasons for the variation and to reduce it. In this work, patient size and shape are considered in patient dose evaluations in diagnostic radiology. The size, shape and constitution of the patients are shown to relate exponentially to the energy imparted during examination of the trunk. The equivalent cylindrical diameter of the patient body is used as the independent variable. Exponential functions are created by linear regression. The ICRP Reference Man with an equivalent diameter of 22.9 cm is used as a body-size standard. A method is suggested by which coordinate transformations reduce data to a base line defined by the Reference Man. It is shown that the method reduces the range of energy imparted by between 30% and 60% for six common X-ray examinations of the trunk. Resulting data constitute a finer instrument for intercomparisons between hospitals for the same examination. Further, it is suggested that adipose tissues should not be included when detrimental effects of radiologic exposure are determined. The Reference Man, stripped of 10 kg subcutaneous adipose tissue, is used as the non-fat standard dimension corresponding to the equivalent cylindrical diameter 21.2 cm. The suggested method is used to estimate the fraction of energy imparted to vital organs only. The results show that the energy imparted is reduced by between 30% and 60% according to this model. Consequently, predicted deaths are reduced by the same amount.

Clinical applications of thermoluminescent dosimetry.

The clinical applications of continuous cylindrical TL dosemeters, readout by linear motion through a heated oven, are presented in this work. The applications extend over high energy electron and photon therapy as well as diagnostic X-ray radiology.

Design of flattening filters based on intracavitary absorbed dose measurements in external radiation therapy.

A method has been developed for the design of flattening filters on the basis of in-vivo oesophagus measurements of absorbed dose distribution in patients given external radiation therapy. The measurements were made by means of LiF-Teflon thermoluminescent dosimeters, read out by an automatic TL-system. A single filter was designed from the resultant dose distribution of parallel opposing fields. The method was checked clinically and was found to be convenient and reliable. The filters reduced the dose variation along the midline of the patients undergoing upper mantle treatments from about +/- 20% to about +/- 5%. The same limits of variation are believed to exist through the entire mid-plane of the body, though it was not possible to prove this by direct measurements.

Tissue heterogeneity in the anterior chest wall and its influence on radiation therapy of the internal mammary lymph nodes.

The density (g cm-3) and electron density (cm-3) of material from the anterior chest wall was determined. On the average, the difference in density between rib bone and intercostal soft tissue amounted to 17 per cent, while the difference in electron density was 7 per cent. The attenuation of high-energy electrons in specimens of rib bone, costal cartilage and sternum was determined by an experimental technique, using dosimeters of TLD material. The results of determinations of attenuation of 10 and 13 MeV electrons in fresh specimens are presented. It is concluded that electron radiation in the energy range of 10 to 13 MeV can be utilized for irradiation of lymph glands along the internal thoracic vessels without risk of underdosage.

Automated thermoluminescence reader. II. Experiments and theory.

A radiothermoluminescence dosimetry system based on an automated reader has been developed. The system utilizes the high sensitivity of the dosimeter material after heating. Thermal treatment is limited to the temperature process in connection with read-out. The measurement values are punched out automatically on paper tape and calculations performed by means of a minicomputer PDP 8/E. The dosimetric system meets the needs of routine use in clinical environment. Recommendations for the practical use of the system are given.

Automated thermoluminescence reader. I. Technical construction and function.

An automated TLD reader has been developed and constructed. The dosimeter material consisting of LiF is permanently enclosed in thin-walled teflon tubes. Dosimeters are identified by numbers, which simplifies individual calibration. A calibration radiation source consisting of a cylinder (90Sr-90Y) is used for the calibrations. The function of the reader and the calibration radiation source is described, and the method of measurement briefly reported.