312. QA in Stereotactic Radiosurgery

Procedure of quality assurance and quality control for good alignment of systems for stereotactic radiosurgery technique Pop Madalina Institute of Oncology “Prof. Dr. AL. Trestioreanu”- Bucharest 252 Fundeni Street, 2 Sectors, 72435 cod, Bucharest Town, Romania. The stereotactic radiosurgery technique was performed for the first time in Romania in July 2003 in the Institute of Oncology “Prof. Dr. AL. Trestioreanu” – Bucharest. The aim of this procedure is to assure the best alignment of the systems and accessories to perform a correct administration of prescribed dose in stereotactic radiosurgery teehnique. The procedure provides instructions for checking of the couch alignment with the LINAC isocenter. This alignment is made in 2 steps. In the first step, the lasers system is aligned with LINAC isocenter. For this are used: MEVATRON PRIMUS LINAC, Radionics stereotactic accessories, collimator accessory holding, stereotactic collimators accessory, mechanical isocenter standard, film holder assembly, film test, laser target pointer, radiopaque ball, optical comparator and concentric circle overlay template. After the alignment, it is performed one film test, for different gantry angles (0°, 90° and 270°). The tolerance level accepted is ±0.5 mm. In the second step, the couch is positioned in accordance with intersection lasers point system. To perform this step are additionally used: LINAC couch mount adapter, linac couch stabilizers and rectilinear phantom pointer. To verify all alignments, 2 final film tests are made, one for different gantry angles (0°,90°,270°) and the other for different couch angles (0°,90°,270°). The tolerance level is ≤ 5 1.5mm. General conditions to make the film tests are: dose=9UM, energy=6 MV or 15 MV and LINAC jaws 6×6 cm, with 12.5mm diameter collimator. The results prove this procedure to be a very good system and accessory alignment practice. The deviations are in tolerance criteria of this protocol. Implementation of this protocol for QA\QC for stereotactic radiosurgery, demonstrates a very good alignment of systems i.e. a correct administration of prescribed dose in stereotactic radiosurgery technique.