DOSIMETRY OF INTRALUMINAL BRACHYTHERAPY

Dose specification in intraluminal brachytherapy varies considerably in the literature. A terminology is proposed, inspired from the Paris System of interstitial brachytherapy, to define some dosimetric guidelines. The dose is specified in the central plane which is a plane perpendicular to the source and passing through its centre. The reference dose rate is calculated in this plane. The treated volume is the volume encompassed by the reference isodose. The hyperdose sleeve is the volume receiving a dose equal to or greater than twice the reference dose. A study of the dose distribution along a linear source of iridium-192 was undertaken. Results obtained, also valid for caesium-137 and cobalt-60, show that the radius of the hyperdose sleeve is relatively independent of the length of the source. It is approximately 0.6 times the distance between the source axis and the point of dose specification when the active length varies from 3 to 20 cm. Reporting not only the dose, but also the thickness of tissue covered by the reference isodose and the thickness of tissue included in the hyperdose sleeve, is recommended to assist in evaluation of the results of treatment and to facilitate the exchange of clinical information in intraluminal brachytherapy. Practical examples are given.