Biomedical subjects
R J Barish
Publications and source records attributed to R J Barish.
Patient immobilization with a low-temperature splint/brace material.
The authors describe a low-temperature plastic which is useful for the construction of immobilizing devices where beam orientation is critical.
Autoionography.
A technique has been established for the autoradiography of beta-emitting radionuclides distributed on thin-layer chromatograms. The technique is derived from medical ionography and produces an electrostatic latent image of the distribution of radioactivity by using a planeparallel ionization chamber filled with a suitable gas. The latent image is formed on a highly insulating plastic sheet which covers one electrode of the ionization chamber and is made visible by methods employed in Xerography or related electrophotographic processes. An introduction to the theoretical basis of autoionography is presented and results of application of the technique are shown for prototype imaging chambers operating at pressures of from 1 to 100 atmospheres. The present sensitivity of autoionography compares favorably with that reported in the recent literature for film or film-fluorographic methods. An advantage of ionography is the simplicity and very low cost involved in producing each ionograph.
A new method of beta autoradiography.
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Saturation curve in gases of high atomic number at pressures up to 8 atm. Part II: Freon 13-B1, and mixtures of Freon with xenon and krypton.
The saturation curve has been studied in Freon 13-B1 (CF3Br) and in mixtures of Freon with xenon and krypton up to a pressure of 8 atm. The enhanced initial recombination due to the electron affinity of Freon has been evaluated and an empirical formula constructed that describes the fraction of current which escapes initial recombination over a wide range of voltages, pressures, and electrode spacings. After correction for this initial recombination, the general saturation curve for Freon and for mixtures of this gas with krypton and xenon has been derived and, again, convenient empirical formulae established which allow the current collection efficiency to be calculated for any given parameters within the range investigated. These formulae are of practical value in the design of image-forming ionization chambers.
Extended expression for tissue-maximum ratio fitted to the Varian Clinac-4 and Clinac-6 accelerators.
An expression which generates tissue maximum ratio (TMR) data for the Varian Clinac-4 and Clinac-6 accelerators is presented. This semiempirical expression can be programmed easily for radiotherapy computer systems or the new generation of scientific calculators. Our technique leads to good agreement with the published data, as demonstrated by a total average percent deviation of the measured TMR values of -0.115% for the Clinac-4 and -0.002% for the Clinac-6.
Development of optical process for accessing three-dimensional patient topology.
A commercial optical system developed by Solid Photography, Inc., has been used to generate precise paraffin--polyethylene tissue compensators. A program with the objective of constructing a medical facility has been undertaken to access patient topology for treatment planning, tissue-compensator fabrication, and patient positioning verification on the treatment table. Currently, patients are taken to a specially equipped studio where a series of microprocessor-controlled reticles are projected on the surface to be analyzed and photographs are taken automatically for computer processing. The topology data then drives a machine tool to sculpt the tissue compensators and may be transmitted via acoustic-coupled terminals to a treatment-planning computer at the Medical Center. The tissue compensators have been found to conform accurately to patient contours. At present, data bases can be generated to accommodate volumes of approximately 70,000 cm3.
Long-term use of an isotope check source for verification of ion chamber calibration.
A radioactive check source is recommended for operational and constancy checks of dosimetry systems used for the calibration of therapeutic x-ray generators, including linear accelerators. Eight years of data have been analyzed for two ion chambers (and their associated electrometers) irradiated at fixed geometry in such a device. These dosimetry systems have also been calibrated every 2 years at a single Accredited Dosimetry Calibration Laboratory. Our analysis suggests that when a check source is used, and the results are consistent, the interval between formal calibrations can be lengthened.