Power balancing the multibeam OMEGA laser.

Multibeam lasers often require an output beam balance that specifies the degree of simultaneity of the laser output energy, instantaneous power, or instantaneous irradiance (power per unit area). This work describes the general problem of balancing a multibeam laser. Specific techniques used to balance the output power of the 60-beam pulsed OMEGA Laser System are discussed along with a measured reduction of beam-to-beam imbalance. In particular, the square-pulse distortion induced by a simple saturating amplifier operating with its output at some fraction of its saturation fluence is derived, and a method to exchange gain between saturated amplifiers in a single beam that have different saturation fluences to adjust balance is described.

Fletcher-Suit-Delclos gynecologic applicator: evaluation of a new instrument.

A new instrument has been added to the Fletcher-Suit-Delclos group of gynecologic applicators. The colpostats can be used as mini-ovoids, but by adding a shielded cap, the instrument has the configuration of the original preload Fletcher colpostat. Dosimetric studies show that this applicator produced transmission ratios (the fraction of radiation transmitted through the tungsten shield) and isodose curves similar to the bladder trigone and anterior rectal wall of 10-25%. With the shield-containing cap removed, the mini-ovoid provides little reduction in dose to those areas and should be used with caution.

Dosimetric comparison of the Fletcher family of gynecologic colpostats 1950-1980.

The Fletcher gynecologic applicator was developed for irradiation of carcinoma of the uterine cervix in the early 1950's. Since that time, numerous modifications and changes have been made in the colpostat construction and in the location of the shields that provide a reduced dose to the bladder trigone anteriorly and to the rectal wall posteriorly. The original applicators include the preload radium double colpostat and the preload radium single colpostat. In the 1960's, afterloading colpostats were manufactured as the Fletcher-Suit and the Fletcher-Green devices. With the introduction of the Delclos mini-colpostat, a new generation of applicators followed in the 1970's. The Fletcher-Suit-Delclos colpostat recently manufactured by two companies can be used as a mini-colpostat. By adding a shield-containing cap, these applicators function as the original Fletcher colpostat. With the development of new applicators over the past 30 years, numerous changes in the position of the shields and, therefore, the dose transmitted to the surrounding tissues have been made. This paper describes dosimetric evaluation of all of these applicators and the various changes that have occurred through the generations of Fletcher colpostats in an attempt to provide information for radiation therapists and gynecologists who are using these instruments in their clinical practice.

The use of a spreadsheet computer program to expedite TLD reporting.

A method has been devised using an electronic spread sheet that will shorten the data processing time and give a printed report of the results. Lithium Fluoride chips are used in pairs so as to produce the same average response. The raw TL readings along with descriptive comments are entered into the computer. The program then computes the single chip dose, the average dose for each chip pair, applies a non-linearity correction factor and prints out a report with comments and patient data. The program offers several advantages: It is much faster than hand calculations, it provides a precise and accurate conversion of raw data to final data, and outputs an organized display of calibration factors, input data, dosimetry data, patient data and listing of involved personnel. The program is easy to use and can be run on any computer that can support a spreadsheet program.

Effect of irradiation on microvasculature: a quantitative study.

In clinical radiation therapy, normal tissues and organs are unavoidably irradiated during the course of treatment of neoplastic diseases. Rubin and Cassaret [Clinical radiation pathology. Philadelphia: W.B. Saunders, 1968; Vols 1, 2] have postulated that microvascular damage may be the major contributing factor to late manifestation of radiation damage. It has been theorized that vascular leakage of the protein-rich fluid leads to fibrosis caused by the accumulation of fibroblasts and macrophages. Vascular changes after irradiation have been demonstrated qualitatively. To quantitate the alteration in permeability characteristics at different doses and time-dose fractionations, we have developed an isotopic technique using 125I, 22Na, and 3H2O that allows us to define vascular, interstitial, and intracellular water spaces. Using these values it is possible to quantitate the vascular changes and membrane integrity. Results show that the permeability of the vascular bed is altered by irradiation.