Norman A. Baily

Fluoroscopic visualization of megavoltage therapeutic x ray beams

Abstract A large flat screen-low light level TV-fluoroscopic system having a 43 cm × 43 cm input screen has been used to monitor patients undergoing radiation therapy with megavoltage treatment beams. This article illustrates some preliminary results obtained for 60 Co and 6 Mv x rays. Portals covering the head, the supraclavicular region, the chest, and pelvic regions have been imaged. The live video images clearly show heart, lung, and diaphragm motion. Except in the pelvis, anatomical structures are clearly demonstrated. Permanent recordings are made either on video tape or video disk. The corresponding verification films are shown in each instance. Improved image quality can easily be obtained with improved hardware. The video images are easily enhanced by special analogue circuitry which is available at reasonable cost.

Computerized Tomography Using Video Recorded Fluoroscopic Images

In this paper we investigate the possibility of constructing computerized tomograms using data collected from a fluoroscopic system. It is shown that through proper handling of these data, useful images can be obtained. The system offers the advantages of eliminating the need for a highly stabilized, linear translating mechanism, and also of requiring relatively low patient dosage. In addition, the data gathering can be done in essentially real time.

Video techniques for x‐ray imaging and data extraction from roentgenographic and fluoroscopic presentations

This review is concerned with the use of video-fluoroscopic images in diagnostic radiology. It particularly emphasizes the potential of such images for performing quantitative procedures such as used in pulmonary and cardiac assessment, evaluation of contrast differentials, and tomographic (including CT) applications. This article also attempts to determine limitations, capabilities, and required developments for both the present and future hardware systems. Most importantly this review attempts to assess the present state of the art and to analyze the reasons for the limited application of such techniques in current radiology operations.

THE LITHIUM-DRIFTED SILICON P-I-N JUNCTION AS AN X-RAY AND GAMMA-RAY DOSIMETER.

The p-i-n junction radiation detector is a solid-state analog of an ionization chamber. A complete review covering the operation of semiconductor junctions as radiation detectors has been given by Brown (1). In general, all types function in the same basic manner and, therefore, are fabricated in the same fashion with minor variations suited to the particular type under discussion. In the case of the p-i-n structure, impurities are introduced in a single crystal of p-type (conduction by holes) silicon, and a highly compensated, or intrinsic, region is thereby established within the bulk. This region, because of its poor conductivity, can act similarly to a dielectric and is capable of sustaining a high electric field. The introduction of the impurity (lithium) requires a high concentration at the surface through which it was diffused. This surface and the volume directly below are overcompensated and are converted to n-type (electron conduction) silicon. When a potential is applied to the device, the field established is uniform across the intrinsic region going to zero at the n-i and i-p boundaries. Energetic charged particles lose energy rapidly in the bulk through interaction with the electrons of the silicon. These collisions may lift electrons from the valence to the conduction band and may also lift electrons from deeper-lying occupied electronic bands to higher-lying unoccupied bands; holes are thereby created in nominally full bands. These electron-hole interactions cause electrons to fall to the bottom of the conduction band and the holes to rise to the top of the valence band. Many more hole-electron pairs are formed during the Auger de-excitation process. Such processes result in a value of approximately 3.5 ev being expended by the incident particle for each hole-electron pair created. These carriers drift in the electric field and give rise to a current. The charge collected is, therefore, a measure of the energy deposited in the counter by the primary particle.

A review of the processes by which ultrasound is generated through the interaction of ionizing radiation and irradiated materials: Some possible applications

The production of acoustic waves following the absorption of energy deposited by ionizing radiation, with a consequent production of localized thermal spikes has been confirmed by a number of papers published in the physics literature. This paper reviews the basic theory and presents most of the supporting experimental data. Some of the experimental methods used and the results obtained are summarized. In addition to the rather straightforward and routine use of acoustic phenomena produced by ionizing radiation for the detection and measurements of such radiation, there are some special applications that appear to be especially attractive for medical physics. Some of these are unique to ionizing radiation in that the amplitude of the ultrasound wave is proportional to the energy deposited in small volumes at localized sites of these interactions, while others derive from methodologies already in use with nonionizing radiations. The detection and measurement of this ultrasonic radiation could possibly lead to methods for the study of such fundamental phenomenon as track structure, precision localization of therapeutic treatment beams, and even the possible imaging of internal anatomic structures to provide on-line portal images.

Relative Biological Effectiveness of Various Qualities of Radiation as Determined by the Electroretinogram

The acute and irreversible effects on the electroretinogram were used to determine the relative biological effectiveness of 100-kvp, 250-kvp, and 2000-kvp x-rays on the rabbits visual cells. The results obtained by this method are similar to those obtained by histologi- cal determination of cell death. In this system, the relative biological efficiency was found to increase with decreasing linear energy transfer. The average values determined were 0.722 plus or minus 0.011 for 100 kvp x rays, 1.00 for 250-kvp x rays, and 1.30 plus or minus 0.02 and 1.31 plus or minus 0.08 for x rays generated at 2000 kvp when the radiation was presented to the eye anterior-posteriorly and posterioranteriorly, respectively. (auth)

Patient exposure to ionizing radiation in dental radiography.

The use of ionizing radiations and exposure of the individual are increasing. As larger segments of the population are being exposed, two important requirements become apparent. The first is that exposures to various radiations be accurately evaluated; the second, that all possible means be taken to reduce exposures in necessary medical and dental procedures. In dental radiography, patient exposure may be reduced by the use of faster films, increased focal skin distance, and more penetrating radiation. The effects of these factors have been considered by various authors. Trout, Kelley and Cathey (1) and Seeman and Cleare (2) have shown that with increased filtration substantial reduction in the dosage to the skin and the first few millimeters of underlying tissue is possible without affecting the diagnostic value of the resulting roentgenograms. The use of such filtration results in a roentgen beam having greater penetration and thereby reduces the ratio of skin to bone dosage. This reduction in skin dose...

The Relative Stopping Powers of Pure Gases to That of Air

Preliminary reports giving some experimentally determined stopping powers of pure gases relative to air have been published (1, 2). These were published prior to completion of the experimental work. It is the purpose of this paper to present complete experimental results for the gases H2, He, N2, 02, Ne, A, Kr, and Xe using the /-ray spectra emitted by thick sources of S35, p32, and Y90 and to compare these with theoretically computed values. The experimental method and the apparatus used have been completely described in an earlier report (2). Theoretical values were computed in the following manner. First, it must be realized that the electron spectrum which is being considered is not that emitted by the radioactive material being utilized. The spectrum which is of interest is one which includes the primary spectrum emitted but which has been degraded by the passage of the electrons through the material (polystyrene) and secondary electrons generated in the material and in the gas. Since the experimental conditions met all requirements of the Bragg-Gray relationship (3, 4), the electron spectrum is the same in the solid electrode as it is in each gas studied. On the basis of the computed spectrum, the energy delivered per gram of each gas was then calculated. The relative stopping power per gram of gas to that of a gram of air was then obtained by taking the ratio of the energy delivered to a gram of each of these gases to that delivered to a gram of air.

IODINE EXCHANGE IN ASCOPHYLLUM

1. Through the use of radioactive iodine the following information concerning the removal of iodine from sea water by Ascophyllum has been established: the removal occurs as an exchange process between iodine in the sea water and iodine already present in the cells; the iodine is exchanged in the form of iodides, not iodates; the exchange takes place in living cells only and in entire plants as well as the isolated segments studied in detail.2. The exchange rate is dependent upon concentration of iodine available. Two different exchange rates may exist, suggesting that a two-step process is involved.3. The iodine concentration within the alga is about 220 times that of sea water and the absolute iodine content of the alga examined was 0.19 mg./g. fresh weight.

Surface Charging of Triglycine Sulfate

Virgin crystals of triglycine sulfate were found to emit light when heated through the ferroelectric Curie temperature. This light comes from electrical discharges into the surrounding atmosphere, and both the first negative and the second positive band spectra of nitrogen have been observed. The crystal will repeat the phenomenon only if it is exposed to a humid environment. The moisture layer responsible for the sparking phenomenon does not exceed 50 A in thickness.