title: Computation of radiation dose distributions for shielded cervical applicators.
abstract: While cervical applicators with shielded ovoids are used widely in brachytherapy, we know of no system for calculating dose distributions for them. For shielded sources, because of a lack of symmetry and because of a rapid variation of dose as a function of position relative to the source, extensive measured data in three dimensions are required. In the method we have developed, the dose at a given point from a source in a shielded ovoid is calculated by multiplying the dose from an unshielded source by the "effective attenuation factor" of the shields. The latter quantity is obtained by linear-interpolation in a three-dimensional table generated from measurements described in an earlier paper. The unshielded-source dose is calculated as the product of source strength, time of implant, distance-dependent geometry factor and a tabulated quantity called the "relative dose rate factor". Relative dose rate factor is obtained by dividing measured dose rate by the product of geometry factor and source strength. Division by the geometry factor reduces the amount of data required with respect to accuracy in linear-interpolation. Input localization data must include not only the position of the end points defining the source but also a third reference point to define the orientation of the shields.
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation*; D005260:Female; D006801:Humans; D011874:Radiometry; D011879:Radiotherapy Dosage; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*