Dose consumption for quality assurance and maintenance at a dedicated IORT accelerator.

Dedicated accelerators for intra-operative radiation therapy (IORT) are operated at high dose rates in order to achieve short treatment times within which the anaesthetisized patient must be remotely monitored (e.g. via video cameras and telemetric anesthesia instruments). Due to these high dose rates, large doses accumulate from the irradiations necessary for quality assurance (QA) and maintenance. In practice, the dose load for QA, maintenance and repairs will probably far exceed the patient dose. The total dose consumption for all of these actions must be considered in facility licensing, in radiation protection assessments, and in the shielding calculations. Dose consumption for QA and maintenance was assessed for the dedicated IORT facility at Heidelberg University for the operation period between June 1991 and December 2007 (15.5 years). Average doses per year of 5847 Gy for maintenance and repairs and 3686 Gy for QA were needed during this period. The causes and composition of these high doses are analyzed and discussed separately for irradiations that need to be performed in the operation room and which, with a mobile accelerator, may be performed in a separate QA vault.