Biomedical subjects

J B Wojcicka

Publications and source records attributed to J B Wojcicka.

3 recordsLinked to original sources

PubMed2000

Cesium-137 source strength verification.

Over the years, the protocol for Cesium-137 source calibration has undergone a number of revisions based on updated data. The 3M Corporation issued product alerts and a revision of the calibration protocol in the early 1980s. We verified the activity of clinically used cesium tubes and found the difference with the activity stated by 3M in the range of 6-13%, which exceeds the recommended by 3M adjustment of 5% for all sources issued before 1979. Therefore, the verification and adjustment of activity should be recommended for each affected tube individually.

Cesium Radioisotopes↗

PubMed1999

Comparison of the transit dose components and source kinematics of three high dose rate afterloading systems.

High dose rate (HDR) afterloading systems are using a high activity Ir-192 source that stops at programmed dwell positions to deliver a prescribed dose. The treatment planning systems are based on the dose calculation model that does not take into account the transit part of a dose resulting from a source while in motion. In this presentation the transit dose components as well as the source kinematics of three commercially available HDR systems were examined using a previously established technique1 based on film dosimetry. The studied systems were: Nucletron-Oldelft, Omnitron 2000 and Gamma Med 12i. The optical density profiles permitted the observation and evaluation of such source kinematics features as velocity, acceleration, deceleration and the source movement between programmed dwell positions. The comparison of the transit dose components for all three HDR systems showed that the largest transit dose can be expected for the Omnitron system with the slowest speed source and the smallest transit dose component is on the Nucletron-Oldelft system with the fastest moving source.

Brachytherapy↗

PubMedDate not supplied

Clinical implementation of stereotaxic brain implant optimization.

This optimization method for stereotaxic brain implants is based on seed/strand configurations of the basic type developed for the National Cancer Institute (NCI) atlas of regular brain implants. Irregular target volume shapes are determined from delineation in a stack of contrast enhanced computed tomography scans. The neurosurgeon may then select up to ten directions, or entry points, of surgical approach of which the program finds the optimal one under the criterion of smallest target volume diameter. Target volume cross sections are then reconstructed in 5-mm-spaced planes perpendicular to the implantation direction defined by the entry point and the target volume center. This information is used to define a closed line in an implant cross section along which peripheral seed strands are positioned and which has now an irregular shape. Optimization points are defined opposite peripheral seeds on the target volume surface to which the treatment dose rate is prescribed. Three different optimization algorithms are available: linear least-squares programming, quadratic programming with constraints, and a simplex method. The optimization routine is implemented into a commercial treatment planning system. It generates coordinate and source strength information of the optimized seed configurations for further dose rate distribution calculation with the treatment planning system, and also the coordinate settings for the stereotaxic Brown-Roberts-Wells (BRW) implantation device.

Algorithms↗