Dose distributions around cylindrical 241Am sources for a clinical intracavitary applicator

Encapsulated, cylindrical sources containing 2, 5, and 8 Ci of 241Am have been designed and fabricated for intracavitary irradiation of uterine cancers. Exposure rates in air and dose rates in water around these sources have been measured using an ionization chamber and a lithium fluoride thermoluminescent dosimetry system. Dose rates in water at a distance of 2.5 cm from the source center along a direction transverse to the source axis were found to be 10.4, 24.3, and 23.3 cGy/h for the 2-, 5-, and 8-Ci sources, respectively, using an ionization chamber. Under the same conditions, the thermoluminescent dosimetry system yielded the values of 10.3, 23.1, and 22.3 cGy/h. It was observed that the ratio of dose-to-water and exposure in air is sensitive to the scattering geometry and source geometry in the case of 241Am photons. This ratio was found to increase substantially as conditions of full scattering were approached. A three-dimensional integration model was employed for the determination of dose distributions around these sources. Results of this dose computation model have been compared against the measured data and were found to be in good agreement with each other. Average deviations of calculated data from measured data were in the range of 0.2 to 0.5 cGy/h and larger deviations were observed in the paraxial region, where the effects of oblique filtration are more severe.(ABSTRACT TRUNCATED AT 250 WORDS)