A new design of Delclos dome cylinders using standard Cs-137 sources.

Surface dose rates around the currently-marketed Delclos uterine-vaginal afterloading dome (hemispherical) cylinders were calculated and measured for linear standard 3M cesium tube sources. Measurements were carried out using thin thermoluminescent lithium fluoride Chips on the surface of the cylinder and calculations at the same points were generated using a treatment planning computer. Wide surface dose variations were found for 2 to 3.5 cm diameter cylinders, but relatively small variation for 4 to 4.5 cm diameter cylinders. Attempting to achieve a uniform dose distribution around the entire dome surface of the cylinder, we have developed a new ellipsoidal design for the dome component that better conforms to the shape of the isodoses arising from the distal-most source. Thermoluminescent dosimetry indicates that the surface doses for the newly constructed cylinders are quite uniform, with variation within +/- 5%. The effect on surface dose is discussed when the ellipsoidal dome cylinder in combination with vaginal cylinders is used and multiple sources are laid end to end to treat the added areas of the vaginal wall.