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Volume 28, Issue 5, May 2001
- PH. D. THESES ABSTRACTS
28(2001); http://dx.doi.org/10.1118/1.1369115View Description Hide Description
In this thesis the design, construction, and installation of a new linac-based stereotactic radiotherapy unit is described. The design requirements were a noninvasive head fixation providing accurate patient repositioning with high reproducibility during multiple fractions. The noninvasive immobilization frame we constructed is used for both localization and for treatments. The immobilization is achieved using three stable locations: the upper dentition, the bridge of the nose, and the back of the neck. This fixation ensures adequate immobilization. The maximum relocation error measured on 22 patients in more than 200 mountings was 1.2 mm. The beam collimation is achieved by eight nondivergent–parallel–circular collimators (diameters between 1–4 cm) and the photon energy used is 6 MV. Concerning dosimetry, a methodology has been developed for dose measurements at the beam central axis. The methodology consists of the irradiation of an ionization chamber with its logitudinal axis parallel to the beam central axis. A correction factor is applied that includes the beam dose profile averaged over the chamber volume. The applied methodology proved to be compatible with film and TLDdosimetry and it has been tested successfully to 4 stereotactic units at different European centers. Furthermore, a new design of head phantom accommodates various dosimeters—ion chambers, TLDs, and films. A three-dimensional treatment planning system, the X-STING, was developed. It is dedicated for stereotactic radiotherapy. In addition to standard features, it includes innovative algorithms for image correlation (between CT and angiographic images with volumetric accuracy of 3%) and a complete model of the treatment machine.