Puesta en marcha del micro colimador ­ Apex para radiocirugía estereotáctica ­ SRS en la unidad de Radioterapia del Hospital Carlos Andrade Marín / Start up of the micro collimator - Apex for stereotactic radiosurgery - SRS in the Radiotherapy unit of Carlos Andrade Marín Hospital

ABSTRACT

Introduction: Stereotactic radiosurgery allows the treatment of small lesions, giving only one hypo-fractioned, radiation dose, according to the conditions of targeted tissues and other external factor to the patient. In our case, the photon field is generated in a linear electron accelerator. Radiation beams to treat small lesions are formed by a micro collimator (mMLC). Methods: A linear accelerator and a micro collimator were used when implementing the technique. Two ionization chambers, a diode and an electrometer were also used. Data was registered on an IBA Brand water phantom. The dosimetry parameters measured were: radiation transmission through the laminated sheets, absolute dosimetry (water and air) and relative dosimetry (PDD and profiles). These parameters follow the Data recollection guide for Apex and Monaco. Results: The transfer values were set at 0.60% in the CAX, 0.39% and 0.34% in the extremes established by protocol. Data obtained with the output factors adjust, in an optimum way, the curve for each measurement and corresponding field range. After filtering the data in an Omnipro software, the tendency line is now comparable with the references from Elekta. Every PDD with its own field range and every profile obtained were approved by the modelers. Discusion: Setting up the micro collimator system in radiosurgery begins with satisfactory test results and is then ready to offer treatment to patients at this hospital. The documentation delivered by Elekta's modeler physicist includes a simulation algorithm pack, the machine's geometrical parameters, verification and calibration data and measured data.