Biomedical subjects

G Echner

Publications and source records attributed to G Echner.

3 recordsLinked to original sources

PubMed2006

Comparative efficiency of the multi-leaf collimator and variable-aperture collimator in intensity-modulated radiotherapy.

The potential of the variable-aperture collimator (VAC) in intensity-modulated radiation therapy (IMRT) has been evaluated by comparing its performance with that of the multi-leaf collimator (MLC). This comparison used a decomposition algorithm to find the series of collimator segments that would treat a given intensity-modulated beam (IMB). Collimator performance was measured using both the number of segments required to complete the IMB and the monitor-unit efficiency of the treatment. The VAC was modelled with aperture sizes from 4 x 4 cm to 20 x 20 cm, and these apertures were allowed to be located anywhere within the IMB. To enable a direct comparison, a similar scanning MLC was modelled at the same range of aperture sizes. Using both collimators, decompositions were run on 10 x 10 and 20 x 20 random IMBs with integer bixel values ranging from 1 to 10. Clinical IMBs from lung, head and neck, and pelvic patients were taken from a Pinnacle treatment-planning system and tested in the same manner. It was found that for all treatment sites, a small, scanning MLC performs as well or better than an equivalent sized VAC in both number of segments and monitor-unit efficiency, and would be an efficient choice for centres looking for a simple collimator for IMRT.

Algorithms↗

PubMed2003

Intensity-modulated radiation therapy using a variable-aperture collimator.

This paper extends some earlier concepts of using a tertiary mask plus jaws for delivering IMRT without a multileaf collimator. The new concept is to sweep a variable-aperture collimator (VAC) across the space of the intensity-modulated beam (IMB) to be delivered and to strip this IMB down into multiple-static-field components, each deliverable with the VAC. The stripping algorithm is described and it is shown, for several designs of VAC, that the mean number of field components and mean number of monitor units is less using the VAC than would be required for a jaws-only (JO) decomposition. The VAC would be simpler to construct than several previously suggested jaws-plus-mask (J+M) combinations. As well as describing a simple VAC for the use with jaws, we propose a design concept of a hybrid VAC. We also show that adding the potential to rotate the simple or hybrid VAC for some components relative to the field to be modulated is advantageous.

Algorithms↗

PubMed2000

An integrated head-holder/coil for intraoperative MRI in open neurosurgery.

With the invention of "open" magnetic resonance imaging (MRI) systems, access to the patient is possible during the imaging procedure. An important application of these systems is intraoperative MRI to control the extent of resection during tumor surgery. Up to now flexible surface coils wrapped around, or placed at each side of the head, were used for imaging. These flexible coils have several disadvantages such as unreliability, interindividual problems, difficult handling, poor hygienic properties, and often unsatisfactory or inhomogeneous image quality. To solve most of these problems, an MR-compatible head-holder in combination with an integrated surface coil for use in a 0.2 T C-shaped magnet was developed. Forty-eight patients with known cranial tumors underwent MRI intraoperatively. In 32 patients (67%), residual tumor was found, and additional surgical resection was performed. The integrated head-holder/coil is a safe and practical tool for intraoperative MRI, providing efficient and reliable resection control during neurosurgical procedures.

Brain↗