The Goldfish as a New Biologic Test Object in Experimental Radiation Therapy

Abstract

THE problem of clinical evaluation of the action of x-rays has been approached by different means: Biologic methods permit us to express qualitatively as well as quantitatively the effects of radiation; Physical methods enable us to calculate in r units the total dose of x- or gamma radiation delivered to a certain volume of tissue. The task of experimental radiation therapy consists in the correlation of physical doses with biologic effects. Scientists in all parts of the world have contributed considerably to the solution of this problem. Interest has been focussed anew on this problem recently, since, in the development of supervoltage x-ray therapy, some disagreement between biologic observations and measurements by means of ionization chambers has been discovered (1, 3, 4, 8, 10, 15). To evaluate the action of x-rays of different wave lengths, it appeared worth while to try a biologic test object not hitherto used for this purpose, and in the paper to follow our experience with its use has been reported.3 Because depth dose measurements are important and since the water phantom is commonly used for such measurements, the use of fish whose habitat is water seemed logical, and the goldfish (Carassius auratus)4 was chosen. The use of goldfish offers the following advantages: No covering material is necessary, which may influence the effects of radiation. The difficulty of providing sufficient oxygen for respiration in the depths is overcome. Goldfish of small size permit the simultaneous irradiation of large numbers of individuals, thus avoiding the danger of error in instances in which too few individuals are used. In spite of small size, their rate of growth is very slow. This makes them especially suitable for study of the time-intensity factor. They permit an approach to the problem of “volume dose” on adult individuals of the same kind varying in size 1:100 and more. Goldfish are available the year around; they are cheap and their care is easy. Technics. The radiation factors were: 200 kv., 30 ma. (mechanical rectification); filter (a) zero, H.V.L. 6 mm. A1, corresponding to 0.233 mm. Cu (intensity, 230–172 r/min.); (b) 0.5 mm. co and 1 mm. A1, H.V.L. 1 mm. Cu (intensity, 48 r/min.). The distance was always 50 cm. (target—surface of the water), and the field size 15 × 15 cm. The doses, ranging from 500 to 10,000 r (measured in air), have been given in one session. A total of more than 2,000 goldfish were used in these experiments, 500 of which served as unirradiated controls For each exposure 12 fish were placed in an open Petri dish, 15 cm. in diameter, covered with a single layer of gauze fixed by an elastic. In the surface position, as shown in Figure I-A (zero position of the experiments), the dish (1) rested on a layer of gauze, suspended flush with the surface of the water in the phantom.