Comparison of the transit dose components and source kinematics of three high dose rate afterloading systems.

High dose rate (HDR) afterloading systems are using a high activity Ir-192 source that stops at programmed dwell positions to deliver a prescribed dose. The treatment planning systems are based on the dose calculation model that does not take into account the transit part of a dose resulting from a source while in motion. In this presentation the transit dose components as well as the source kinematics of three commercially available HDR systems were examined using a previously established technique1 based on film dosimetry. The studied systems were: Nucletron-Oldelft, Omnitron 2000 and Gamma Med 12i. The optical density profiles permitted the observation and evaluation of such source kinematics features as velocity, acceleration, deceleration and the source movement between programmed dwell positions. The comparison of the transit dose components for all three HDR systems showed that the largest transit dose can be expected for the Omnitron system with the slowest speed source and the smallest transit dose component is on the Nucletron-Oldelft system with the fastest moving source.