Nonisocentric

In our institution we have introduced the variable angle reconstruction method with a nonisocentric C-arm as brachytherapy localizer in gynecological treatments. The main advantage of this method is that on the posterior oblique images the ovoids of the Fletcher-Suit-Delclos (FSD) applicator are clearly separated. The main problem with the nonisocentric machine is that the magnification factor is not known exactly and varies with the C-arm angle. For generation of treatment plans with a commercial brachytherapy planning system the magnification factors of the reconstruction images have to be determined previously...

In this paper a novel technique is proposed and validated for radiosurgery treatment planning of arteriovenous malformations (AVMs). The technique was developed for frameless radiosurgery by means of the CyberKnife, a nonisocentric, linac-based system which allows highly conformed isodose surfaces to be obtained, while also being valid for other treatment strategies. The technique is based on registration between computed tomography (CT) and three-dimensional rotational angiography (3DRA). Tests were initially performed on the effectiveness of the correction method for distortion offered by the angiographic system...

The field of stereotactic radiosurgery is rapidly advancing as a result of both improvements in radiosurgical equipment and better physician understanding of the clinical applications of stereotactic radiosurgery. This article will review recent developments in the field of radiosurgery, including advances in our understanding of the treatment of brain metastases and arteriovenous malformations, as well as the use of stereotactic radiosurgery as a boost following conventional radiation for nasopharyngeal carcinoma to minimize the rate of local recurrence...

The most commonly used technique for matching two adjoining parallel opposed fields has been geometric matching with a skin gap calculation. Many modifications have been suggested in order to minimize the shortcomings of this technique. Most of these, however, are more complex and time consuming in clinical practice, with little dosimetric improvement. We propose a simple new method for adjacent field abutment that eliminates hot and cold spots due to different beam divergences. This method is based upon the use of a single match plane for both the cephalad and caudad parallel opposed beams...

Dose calculations for radioactive seed implants require knowledge of the three-dimensional source coordinates. These are usually determined from a pair of orthogonal radiographs. However, occasionally localization films are taken with portable, and/or nonisocentric x-ray units, and no assurances can be made as to whether or not the films were truly exposed in an orthogonal geometry. A three-dimensional magnification ring is described (consisting of three mutually orthogonal rings) which permits the treatment planner to accurately establish the exact source rotation angle used when exposing the films...