[Quality assurance in stereotactic space. Determination of the accuracy of aim and dose in single dose radiosurgery].

Background: Single dose irradiation techniques require methods of quality assurance of high precision. The complete operational sequence of a treatment from imaging over irradiation planning up to the patient irradiation has to be controlled and verified in a phantom (Figure 2). These demands receive special topicality by the E-DIN 6875-1 [38], which will appear soon.
Material and Methods: A quality assurance package was developed to meet the requirements of the E-DIN 6875-1 [38]. It consists of versatile usable precision phantom (Figure 1), a dose measuring system for the tissue equivalent radiochromic film GAFCHROMIC trade mark type MD 55 II using a high-quality scanner, and a software for standardized test routines (Figures 2 to 4). Correction routines for film fog, darkening, temperature effect as well as for film inhomogeneities (double exposure technology) are implemented.
Results: The measuring system permits routine dosimetry with inaccuracies typically < 5%, for the double exposure procedure typically < 3% with local dissolutions of approx. 1/100 mm in film plane, perpendicularly to it the film stack density and the film thickness (0.3 mm) are determining. The measuring system is designed to simulate the complete three-dimensional treatment of a patient (Figure 4).
Conclusions: The procedure achieves a high quality standard for all steps in radiosurgery. The simple handling permits the employment for the daily routine (according to E-DIN 6875-1 [38]), in addition, for the modelling of complicated 3-d of scattering conditions, e. g. close to risk structures.