title: Monte Carlo and analytic calculation of absorbed dose near 137Cs intracavitary sources.
abstract: This paper presents dose-rate tables and treatment planning data needed to accurately implement the Sievert line-source integral, found on most commercial computer-aided treatment planning systems, for two recently introduced 137Cs intracavitary sources. One source uses a high-density active core designed to reproduce the non-elliptical isodose curves characteristic of the traditional radium tube. The other source consists of two or three discrete 137Cs seeds encapsulated in stainless steel. Using Monte Carlo dose-rate calculations as the standard of accuracy, we show that the Sievert model, using conventionally defined filtration corrections, overestimates kerma-rate in free space by as much as 20%. In addition, tissue attenuation and scatter build-up factors, derived from an isotropic point source, do not accurately characterize the distribution of scatter dose about heavily filtered sources. By varying the input parameters of the Sievert line-source integral so as to optimize its agreement with the more rigorous Monte Carlo data, accuracy of 3% can be achieved.
authors.affiliation: Department of Radiation Oncology, University of Arizona, Tucson 85724.
authors.forename: J F
authors.initials: JF
authors.lastname: Williamson
mesh_terms: D001918:Brachytherapy; D002588:Cesium Radioisotopes / Q000627:therapeutic use*; D006801:Humans; D009010:Monte Carlo Method; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011881:Radiotherapy, Computer-Assisted
chemical_list: D002588:Cesium Radioisotopes