PRECISION AND ACCURACY OF STEREOTAXIC CONVERGENT-BEAM IRRADIATIONS FROM A LINEAR-ACCELERATOR

Purpose: The accuracy and the precision for radiosurgery procedures at linear accelerator facilities were investigated. Methods and Material s: The technique of convergent beam irradiation, that is a series of s uccessive isocentric are irradiations, is specifically considered in t his paper. Accuracy and precision depend on a sequence of methods and equipment among which localization of the target, patient alignment, a nd the dose delivery are the most critical steps. The purpose of the i nvestigation was to quantitatively assess their contribution to the ov erall accuracy. The definitions and methods used to quantify and contr ol accuracy are described. Measurements were carried out at a phantom to analyze the localization and positioning errors. Errors which may o ccur with the dose delivery technique were studied by a computer simul ation. Results: The calculations showed that these errors are not the main contributors to the overall accuracy as long as the linac inaccur acies are in the order or less than 1 mm. The accuracy found in the lo calization and positioning methods was less than 1 mm. Conclusion: It was concluded that an overall accuracy in the order of 1 mm can be obt ained also under routine conditions. The great importance of adequate quality control is emphasized.