Abstract

PURPOSE
The dosimetric advantages of multiple non-coplanar stationary fields for stereotactic radiotherapy or adiosurgery (SRT/S) are well known. However, this technique is not widely used due to the logistical problems associated with producing and testing customized collimators. We report our experience of SRT/S using multiple non-coplanar stationary fields (conformal SRT/ S). MATERIALS AND METHODS: Between August 1997 and February 2002, we performed frameless SRT/S in 63 patients. We chose conformal SRT/S when the tumor was of a very irregular shape or larger than 4 cm. We obtained three pieces of information: 1) the couch translations required to bring the target point to the isocenter, 2) the distance between the stereotaxic markers in the CT study, and the distance between the markers determined from orthogonal beam films, taken in the anterior- posterior and lateral directions, and 3) the rotational movement of the head position between the CT study and actual treatment position. We evaluated two kinds of data: 1) the precision of the isocenter setup, and 2) the reproducibility of the head position in the a) translational and b) rotational components. RESULTS: Twenty-six of the 63 patients receiving stereotactic treatment received conformal SRT/S. The precision of the isocenter setup for the conformal SRT/S was x=-0.03+/-0.26 mm, y=0.19+/-0.25 mm and z=-0.20+/-0.27 mm. The reproducibilities of the head position with the conformal SRT/S were 0.5 mm and less than 1degrees C, for the translational and rotational components, in any plane. CONCLUSION: We were able to apply conformal stereotactic irradiation, which has a dosimetric advantage, to irregularly shaped intracranial tumors, with precision and reproducibility of head position for the isocenter setup nearly equivalent to that of frame-based SRS or multiple-arc SRT/S.

• Keywords: Intracranial tumors;Conformal stereotactic radiotherapy