Biomedical subjects

R L Gerber

Publications and source records attributed to R L Gerber.

4 recordsLinked to original sources

PubMed1991

Study of treatment variation in the radiotherapy of head and neck tumors using a fiber-optic on-line radiotherapy imaging system.

On-line radiotherapy imaging systems allow convenient daily acquisition of portal images for treatment verification. The information can also be used to study treatment variability. Using a prototype fiber-optic imaging system, we have measured the treatment variation of 17 head and neck patients. Daily digital portal images were acquired for the on-cord left and right lateral fields. Treatment variations were quantified using the Cumulative Verification Image Analysis (CVIA) method developed at our institute. In the CVIA method, daily portal images were aligned according to three anatomical points predefined on a digitized simulation, or prescription, image. After each image alignment, the block position was cumulated in a bit-map and superimposed on the prescription image to give a cumulative verification summary image. Iso-frequency distributions, or contours, of the block overlap were calculated and examined with respect to the prescription treatment area. The range of the treatment variation was large for the 17 patients. On average, separation of the 0% to 100% block overlap contours was about 10 mm, and the 20% to 80%, 5 mm. The block overlap contours were also used to calculate the frequency with which the prescription area as defined on the simulation film had been treated. The fraction of the prescription area treated depended on the accuracy of the treatment setup and patient repositioning, as expected. At best, approximately 95% of the prescribed area was irradiated 100% of the time during the entire course of radiotherapy. At worst, approximately 70% of the prescribed area was irradiated 100% of the time. These results demonstrate that despite immobilization, large setup variation can still occur. Presenting treatment variation data as population averages does not reflect on the large variation that may be observed in the individual patient.

Adolescent↗

PubMed1987

Dosimetry considerations for a Lipowitz metal tissue compensator system.

The present report describes the fabrication technique and the dosimetry aspects of a new compensator system that uses the low melting point allow Lipowitz metal. Compensating ratios (CR, mm of tissue compensated per mm of cerrobend) were determined for various field sizes and depths for 60Co, and X ray energies of 4, 6, 18, and 25 MV. Typical CR for 10 cm X 10 cm field and 10 cm depth were: 60Co, 4 MV, and 6 MV, 1:15; 18 and 25 MV, 1:20. Verification of these CR were performed at 6 MV using polystyrene phantoms. Ionization measurements were made for various field sizes and depths and normalized to central axis full-phantom readings for both compensated and non-compensated fields. Without compensation, percent differences ranged as high as 40% for a tissue deficit of 10 cm. With the compensating filters (CF) in place, this difference was reduced to 2-4%. Overall, the CF system was capable of producing dose uniformity to within +/- 10% for a wide range of depths and field sizes.

Metals↗

PubMed1977

Cardiovascular responses of men and women to lower body negative pressure.

Changes in blood flow and blood redistribution were measured by impedance plethysmography in the pelvic and leg regions of six male and four female subjects during three 5-min exposures to -20, -40, and -60 mm Hg lower body negative pressure (LBNP). Female subjects demonstrated significantly higher mean heart rate and lower leg blood flow indices than the male subjects during the recumbent control periods. Men had slightly higher mean resting systolic and diastolic blood pressures and higher mean control pelvic blood flow indices. Women demonstrated significantly less blood pooling in the legs and slightly less in the pelvic region than the men. All of the 18 tests with male subjects at -60 mm Hg were completed without initial signs of syncope, while only two of the tests with women were completed successfully without the subject exhibiting presyncopal conditions. The results of this study indicate that impedance plethysmography can be used to measure segmental cardiovascular responses during LBNP and that females may be less tolerant to -60 mm Hg LBNP than males.

Atmospheric Pressure↗

PubMedDate not supplied

Verification data for electron beam dose algorithms.

The Collaborative Working Group (CWG) of the National Cancer Institute (NCI) electron beam treatment planning contract has performed a set of 14 experiments that measured dose distributions for 28 unique beam-phantom configurations that simulated various patient anatomic structures and beam geometries. Multiple dose distributions were measured with film or diode detectors for each configuration, resulting in 78, 2-D planar dose distributions and one, 1-D depth-dose distribution. Measurements were made for 9- and 20-MeV electron beams, using primarily 6 x 6- and 15 x 15-cm applicators at several SSDs. Dose distributions were measured for shaped fields, irregular surfaces, and inhomogeneities (1-D, 2-D, and 3-D), which were designed to simulate many clinical electron treatments. The data were corrected for asymmetries, and normalized in an absolute manner. This set of measured data can be used for verification of electron beam dose algorithms and is available to others for that purpose.

Algorithms↗