The Use of 60Co-sources for Afterloading alternate to 192Ir-sources

Abstract

Up to now the production of small sources for HDR afterloading was for technological reasons possible only for 192Ir sources. This causes a dominant prominence for 192Ir sources in HDR afterloading. Since a fairly long time 60Co sources became available with geometrical dimensions identical to those of 192Ir sources. The 60Co sources have the advantage of a longer half time. Therefore, a source change is required in a notably longer interval only. Therewith the problems concerning transport, change and disposal of the sources and quality assurance are reduced. Consequently the introduction of small 60Co sources appears of high interest. For the introduction of 60Co sources the equivalence to 192Ir sources has to be demonstrated. For the same air kerma rate for 60Co an activity is required, which is lower by a factor 2.8 in comparison to 192Ir. For the same dose in water the differences in tissues are so small that 60Co sources can be used alternate to 192Ir sources. Monte-Carlo calculations demonstrate that the radial dose function for the 192Ir source provides higher values than for the 60Co source. Contrary to the 60Co source the anisotropy factor for the 192Ir source deviates entirely at the top of the source and in the region of source mounting from the value 1.00. The comparison is completed by three representative clinical irradiations: The afterloading of carcinoma of bronchus, oesophagus and cervix are examples for linear sources. The combination of ring shaped and linear applicator is used for the cervix carcinoma. The temporary implantation of needles for afterloading of prostate carcinoma represents a more complicated situation. Identical dose distributions result from the investigated 60Co- und 192Ir-sources for these typical situations in brachytherapy. The verification of the alternate usage of 60Co sources to 192Ir sources for HDR afterloading is successfully.