Biomedical subjects

R Vijlbrief

Publications and source records attributed to R Vijlbrief.

3 recordsLinked to original sources

PubMed1995

Electronic portal imaging.

In our institute, we have developed an electronic portal imaging system based on a matrix of 256 x 256 ionisation chambers. By improvements to the electronics, the system produces images with the same quality as the original system but 3-10 times faster. Software for automatic image analysis has been applied to more than 10,000 images over the last two years. Using an off-line correction strategy, the systematic patient set-up error has been limited to 5 mm or less for 98% of the patients treated for prostate cancer.

Equipment Design↗

PubMed1993

Time trend of patient setup deviations during pelvic irradiation using electronic portal imaging.

An electronic portal imaging device (EPID) was used to detect patient setup displacement during the course of a 3-field pelvic irradiation of two groups of patients: 10 rectal and 10 prostate carcinomas. These patients were irradiated with conventional treatment techniques in routine clinical practice. A total of 469 portal images and 60 simulator films were used to determine the values of setup deviations in the X- Y- and Z-directions of a fixed coordinate system, corresponding to the medio-lateral, cranio-caudal and antero-posterior direction, respectively. The absolute displacement averaged over all setups and patients ranged between 0.4 mm and 1.4 mm with a standard deviation (S.D.) of 1.6-3.9 mm. The overall distribution along each direction could be separated into a distribution of random deviations (S.D.s ranging from 1.2 to 2.8 mm) around the mean deviation of each patient and a distribution of the means themselves: the distribution of systematic deviations (S.D.s ranging from 1.0 to 2.6 mm). Significant gradual displacement as a function of time was detected in 5 out of the 20 patients, 2 in the rectum and 3 in the prostate group. This "time trend" was found along each of the 3 directions specified. The magnitude of the time-dependent displacement throughout the course of treatment ranged between 4 and 11 mm. It can be concluded that for treatments requiring a high level of precision, portal images should be made and analyzed during the whole treatment course in order to detect and correct significant time trends.

Carcinoma↗

PubMed1991

Fast evaluation of patient set-up during radiotherapy by aligning features in portal and simulator images.

A new fast method is presented for the quantification of patient set-up errors during radiotherapy with external photon beams. The set-up errors are described as deviations in relative position and orientation of specified anatomical structures relative to specified field shaping devices. These deviations are determined from parameters of the image transformations that make their features in a portal image align with the corresponding features in a simulator image. Knowledge of some set-up parameters during treatment simulation is required. The method does not require accurate knowledge about the position of the portal imaging device as long as the positions of some of the field shaping devices are verified independently during treatment. By applying this method, deviations in a pelvic phantom set-up can be measured with a precision of 2 mm within 1 minute. Theoretical considerations and experiments have shown that the method is not applicable when there are out-of-plane rotations larger than 2 degrees or translations larger than 1 cm. Inter-observer variability proved to be a source of large systematic errors, which could be reduced by offering a precise protocol for the feature alignment.

Computer Simulation↗