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Technical note: EGSnrc-based dosimetric study of the BEBIG 60Co HDR brachytherapy sources.

PURPOSE
The purpose of this work is to calculate two-dimensional (2D) dose rate distributions around the BEBIG (Eckert & Ziegler, BEBIG GmbH, Germany) models GK60M21 (old) and Co0.A86 (new) 60Co high dose rate brachytherapy sources in an unbounded liquid water phantom. The study includes calculation of absorbed dose to water-kerma ratio D/K around the BEBIG sources and a 60Co point source in water. A comparison is made with previously published data.


METHODS
The EGSnrcMP Monte Carlo code system is used to calculate the absorbed dose and water-kerma in water and air-kerma strength in vacuum. EGSnrcMP-based user codes such as EDKnrc, FLURZnrc, and DOSRZnrc are employed in the work.


RESULTS
The value of D/K reaches a maximum of 1.040 +/- 0.002 for the 60Co point source (constant between 3.6 and 4.5 mm from the source) and 1.076 +/- 0.002 for the BEBIG sources (constant between 2.6 and 3.2 mm along the transverse axis of the sources). Dose rate data for the new and old sources are comparable to published data for radial distances r > 0.5 cm. Differences up to 9% are observed at points close to the source (r = 0.25 cm). In addition for the new source, compared to previously published data, dose rate data are higher by 14% along the longitudinal axis where the source cable is connected. Dose rate differences on the longitudinal axis (8 = 180 degrees) of this source are explained by varying the length of the simulated source cable.


CONCLUSIONS
The 2D rectangular data set calculated in the present work could be considered for quality control on radiotherapy treatment planning systems.