SU-E-J-75: Practical Annual Quality Assurance Program for a Real Time Optical Tracking System.

PURPOSE: To verify the accuracy of a real time optical surface tracking system using a practical annual quality assurance program with an anthropomorphic breast phantom. METHODS: An anthropomorphic breast phantom was used to determine the accuracy of registration, shift, source to surface distance (SSD), and live monitoring features of the AlignRT system. Both the two and three camera AlignRT systems were tested. Registration and shift accuracy were evaluated by comparing software output with known phantom displacements and rotations at 0, 90, and 270 couch angles. These tests were performed in static capture and live monitoring modes. SSD accuracy was determined by comparing AlignRT results with expected values from the treatment planning system and optical distance indicator at 0, 90, and 270 degree couch rotations. RESULTS: For the two camera system, registration accuracy at 0, 90, and 270 degree couch angles was within 1.0mm in the lateral, longitudinal, and vertical directions and 0.04 degree. For shifts of +/-10mm and +/-5 degree, static mode shift accuracy was within 1.6mm and 0.23 degree. Registration accuracy of the shifted phantom in live monitoring mode was within 1.7mm and 0.2 degree. For the three camera system, registration accuracy at 0, 90, and 270 degree couch angles was within 1.1 mm in the lateral, longitudinal, and vertical directions and 0.2 degree. For shifts of +/-10mm and +/-5 degree, static mode shift accuracy was within 0.9mm and 0.2 degree. Registration accuracy of the shifted phantom in live monitoring mode was within 1.1mm and 0.2 degree. SSD determination was accurate to within 2mm for both systems and modes. CONCLUSIONS: The AlignRT system accuracy can be easily verified for annual quality assurance using a realistic clinical setup to within 2mm/0.5 degree. System accuracy was comparable for both two and three camera systems in static and live monitoring modes.

Alpha-hydroxybutyrate dehydrogenase activity in intrahepatic cholestasis of pregnancy.

OBJECTIVES: Intrahepatic cholestasis of pregnancy (ICP) is associated with increased perinatal mortality and morbidity. Alpha-hydroxybutyrate dehydrogenase (alpha-HBDH) is an enzyme that originates in the cytoplasm of hepatocytes and can be detected in the serum. The aim of this study was to determine the characteristics of alpha-HBDH activity in ICP. METHODS: The study included 100 women in their third trimester of pregnancy, 58 of whom had ICP (the study group) and 42 were healthy (the control group); another group, 26 nonpregnant women, was also analyzed to follow changes in alpha-HBDH activity during pregnancy. The concentrations or activity of fractionated bilirubin; bile acids; total alkaline phosphatase; alanine and aspartate aminotransferases; total high-density and low-density lipoprotein cholesterol; triglycerides; total protein; and alpha-HBDH were assessed. RESULTS: The activity of serum alpha-HBDH is increased during the third trimester of pregnancies complicated by ICP, and it correlates positively with total and direct bilirubin concentration and total alkaline phosphatase activity. CONCLUSIONS: Alpha-hydroxybutyrate dehydrogenase serum activity seems to be another biochemical parameter useful in the assessment of ICP severity.

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.

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.

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.