Charles G. Amato

IN VIVO RADIATION DOSIMETRY. REVIEW OF A 12-YEAR EXPERIENCE.

Abstract The authors describe the design and development of systems for direct in vivo measurement of dose within the living subject. They have used the method since 1957 for therapy, diagnosis, nuclear medicine, and radio-biology. The systems include home-grown and commercial luminescent solid state dosimeters of various types and geometries, read-out instrumentation, and a methodology for implantation and removal of dosimeters in virtually every body organ and tissue in living patients and animals.

The Use of Radiothermoluminescent Dosimeters in the Field of Diagnostic Radiology

Our investigation deals only with the applicability of synthetic CaF2:Mn, lithium fluoride, calcium sulfate, and preliminary work with lithium borate to medical and radiobiological dosimetry. In order to protect radiothermoluminescent phosphors from ambient atmospheric gases which may cause spurious thermoluminescence and to reduce the possibility of tribothermoluminescence, a protective carrier was developed. In an earlier report (1), radiothermoluminescent dosimeters were employed which were permanently encapsulated, following an out-gassing and flushing procedure with inert gas as specified by Schulman (2, 3). Accordingly, calcium fluoride, lithium fluoride, lithium borate, and calcium sulfate phosphors were encapsulated and outgassed. Some of these dosimeters were stimulated by conduction heating; that is, they were placed upon a platinum heating strip through which direct current was passed for thirty seconds. Due to the varying spectral response of each of the phosphors investigated, several separat...

INHOMOGENEITY OF DOSE DISTRIBUTION IN ANIMALS SUBJECTED TO WHOLE-BODY IRRADIATION WITH 250-KVP X-RAYS.

BS>Even though bi-lateral or more complicated exposure procedures are of considerable importance in total-body exposure of large animals or man, these measures may not result in even approximately the same dose to different tissues. Because of body contour, depth-dose x ray patterns determined in a rice-and-wax phantom contoured to the shape of a dog were appreciably different from the calculated values based on published standard depth-dose tables. In addition to differences due to contour, the tissue traversed by the beam makes considerable difference. Depth-dose patterns in a cadaver dog, compared with the contoured rice-phantom, differed by as much as plus or minus 30%. (auth)

A Critical Survey of Radiation Dosimeters for In-Vivo Dosimetry During Clinical and Experimental Radiotherapy

The principal interest of our investigative group is in the development of effective in-vivo dosimetry systems for use in the living organism during clinical and experimental radiation therapy. Such tools are essential to a better understanding of the impact of therapeutic ionizing radiation upon the structure and function of living human tissues, malignant and benign. Measurements in vivo will be far more meaningful in the management of the individual cancer patient than mass dosage data derived from calculations and from phantoms. Further, treatment planning, time-dose formulae, tissue tolerance guides, bolus technics, inhomogeneity correction values, etc., may be materially improved by in-vivo measurements, enhancing the patients chance for cure and diminishing the risk of serious complications. With this objective, we undertook initially an orderly, systematic, and critical survey of existing dosimeters (Table I). We have prepared a panel of “ideal” criteria or specifications which we consider essent...

In-Vivo Dosimetry with Miniature Glass Rods

A glass rod microdosimeter (1 × 6 mm.), utilizing the concept of radiophotoluminescence (1), is being used for human in vivo measurements in all modes of radiation therapy. Due to its miniature size and integrating ability, it is an ideal dosimeter for medical use (2). The undesirable feature of energy dependence in the range of 200 kev to 1.3 Mev is being corrected by a suitable gold shield designed by the authors (3). A fluorimeter electronic reader, with modifications designed by the U. S. Naval Research Laboratory, assures reproducible and stable results. In human subjects with cancer, the miniature dosimeters were placed with ease in the pharynx, the esophagus, the bladder, and other deep organs. Technics were devised to introduce these units directly into tumors and normal body tissues. In all the clinical experiments, there was a remarkable degree of correlation between the dosimeter reading and the calculated dose when beam irradiation (260 kv, 1000 kv, cobalt 60), radium implants, or isotope ther...

An “Ideal” in Vivo Dosimetry System for Clinical and Experimental Radiation Therapy

This is a progress report on the development of an “ideal” in vivo dosimetry system for both experimental and routine clinical use in radiation therapy of cancer. During rigorous clinical studies this system has thus far proved to be unusually dependable, practical, versatile, and economical to operate. It has been applied in nearly every anatomical structure in living subjects. Further, it is promptly available for general application in clinical practice. The basic dosimeter consists of a tiny photoluminescent glass rod (1 × 6 mm.) encased in a miniature gold cartridge which we designed (1.6 × 10 mm.), with a removable screw-cap. Placed within or upon the body and exposed during radiation therapy, the glass rod may be removed at any time and “read” in a chamber which may be easily constructed or purchased from the commercial source which now supplies the glass rods. Unlike other dosimeters, “reading” does not discharge the unit and it may be replaced in the body for cumulative dose recording as high as ...

A preliminary study of thermoluminescent dosimetry.

A miniature solid state dosimeter based on the phenomenon of thermoluminescence (1) is presently being investigated in our laboratory for introduction into an in vivo dosimetry system, previously described by the authors (1, 3, 4). The radiation-sensitive element is a manganese-activated calcium fluoride phosphor. Development of this phosphor was carried on at the U. S. Naval Research Laboratory by Schulman et al. (2). The dosimeter we are using is in the form of a needle, 10 mm. long and less than 1 mm. in outside diameter. It is sealed within a glass tube and read by heating at a constant rate. Heating liberates electrons which were trapped during irradiation, and these electrons attempt to return to their ground state by emitting energy in the form of blue-green light. A graph of fluorescent intensity vs. time, generated at a constant heating rate, is called a “glow curve.” Either the area under the glow curve, or its peak, may be used to read the dosimeters; we prefer to use the former. This area may ...

Multiple implant dosimetry.

Low-atomic-number, silver-activated radiophotoluminescent glass-needle dosimeters were placed within a four-portal, 10-mil wall gold shield and implanted in a 38-pound dog. Over 150 needles were implanted, by a trocar technic (Fig. 1). Implants were made in three planes, so that most of the vital organs were pierced (Fig. 2). The shielded needles were placed in a PE-320 polyethylene tube. Spacing of 0.25 inch between needles was maintained by inserting plastic cylindrical spacers. An average of 50 needles located in at least three traverses, in the same plane, were exposed at a T.S.D. of 110 cm. to 260-kvp x-rays delivered at 30 ma, with 1 mm. Al and 0.5 mm. Cu filtration. A circular portal 7 cm. in diameter was used. At mid-exposure, the dog was turned over and the total exposure completed. The gold shield designed to achieve energy-independence (1, 2) is shown in the insert in Figure 1. The theory of this dosimeter and its response have been reported by the authors (3–7). Prior to exposure for dosimetri...

A Preliminary Design of a Thermoluminescent Dosimeter Reader

Two types of thermoluminescent dosimeters are currently under investigation in this laboratory. Some of the physical factors encountered in the construction of an electronic reader are being studied, such as the incorporation of an electronic integrator circuit and/or a strip chart recorder. Due to the fact that the powder must be heated for a reading to be obtained, fiber optics may be employed to carry the signal to the photomultiplier tube and thereby reduce thermal noise.