A high speed optical multichannel analyzer.

An optical multichannel analyzer capable of recording spectra at sampling rates up to 100 kHz is described. The instrument, designed to gather data on the kinetic reaction mechanisms of biological preparations such as cytochrome oxidase and bacteriorhodopsin, features a massively parallel approach in which each photosensing element of the detector array has a dedicated amplifier, integrator, analog to digital converter, and sample buffer. The design has 92 such elements divided in two separate arrays, each of which sits at the focal plane of a 1/4 m Ebert spectrometer. The spectrometers may be tuned to cover independent, 130 nm wide, regions of the spectrum from 350 nm to 900 nm with a dispersion of 2.8 nm per element. Each detection channel has 12-bit resolution with an electronic dark count of 1 count and may be sampled 1024 times during a single experiment with dynamically variable sampling intervals from 10 microseconds to several seconds. Time averaging of up to thousands of consecutive laser-initiated kinetic cycles allows analyses of spectral changes < 0.001 optical density units. A personal computer with custom software provides a number of features: entry of experiment parameters; transfer of data from temporary buffers to permanent files; real time display; multiple spectrum averaging; and control and synchronization of associated system hardware. Optical fibers or lenses provide coupling from a parabolic reflector Xenon arc monitoring light source, through the sample chamber, to the entry slit of the monochromator. The instrument has been used for extensive studies on the rapid kinetics and definition of reaction sequences of the energy-transducing enzymes cytochrome oxidase and bacteriorhodopsin. Some results from these studies are discussed.

Dose to lung in primary breast irradiation.

Using anatomic data derived from computerized tomography (CT) scans of the torso, the volume of lung irradiated during primary breast treatment has been measured for a variety of irradiation techniques. Two-field tangential plans which are angled into lung to treat also the internal mammary nodes have been compared to three-field plans which include a separate internal mammary field (IMF). The volume of lung achieving high dose (greater than 3000 rad) is similar in both techniques when photons only are used. Electron beam treatment of the IMF is successful in lowering the lung dose. Additional treatment plans that angle the IMF parallel to the tangential fields may offer some theoretical advantage.