Quality assurance for a treatment planning system in scanned ion beam therapy

Conformal radiation therapy using dynamic beam delivery systems like scanne d ion beams requires concise quality assurance procedures for the complete treatment planning process. For the heavy ion therapy facility at GSI, Darm stadt, a quality assurance program for the treatment planning system (TPS) has been developed. It covers the development and updating of software, dat a protection and safety, and the application of soft- and hardware. The tes ts also apply to the geometrical precision of imaging devices and the geome trical and dosimetrical verification of dose distributions in different pha ntoms. The quality assurance program addresses acceptance and constancy tes ts of the treatment planning program. Results of the acceptance tests serve d as a basis for its governmental approval. Two main results of the accepta nce tests are representative for the overall performance of the system. (1) The geometrical uncertainty that could be achieved for the target point de finition, setup accuracy, field contouring, and field alignment is typicall y 1.5 mm. The uncertainty for the setup verification using digitally recons tructed radiographs (DRR's) is limited to 2 mm. (2) The mean deviations bet ween measured and planned dose values is 3% for standardized cases in a wat er phantom and up to 6% for more complicated treatment configurations. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)00707-0 ].