Depth Dosage Measurements by Means of Goldfish

Abstract

Numerous methods have been employed in approaching a clinical evaluation of the action of roentgen rays. Biological methods permit qualitative as well as quantitative determinations of the effects of radiation. Physical methods enable us to calculate the r units delivered to a certain volume of tissue. One of the outstanding tasks of experimental radiation therapy is the correlation of physical doses with biological effects. In so far as the effects of roentgen and gamma rays on the surface are concerned, this correlation has been achieved fairly satisfactorily. Various reactions with various test objects, such as the skin erythema, the lethal effects on seedlings, ova, tissue cultures, etc., are at our disposal for the study of these surface effetcs. The biological evaluation of the effects of roentgen rays in the depths has, however, encountered certain difficulties. Because of the large percentage of water in the make-up of the human body, the water phantom is commonly used by the physicist for depth dose measurements (3, 13). Two principal obstacles have had to be dealt with in the performance of biological experiments in the depths of this phantom: (1) the difficulty of providing an adequate oxygen supply to the test object; (2) the necessity of wrapping the test object for its protection against water. The deficiency of oxygen affects the vitality of the test object and the wrapping material may change the radiation by absorption. Due to the progressive technical improvements in equipment, with the production of more and more penetrating radiation, interest has been focused on the problem of its biological action in the depths (1–15). Because of the lack of uniformity in existing data (16–25), it appeared worth while to try a biological test object not hitherto used for this purpose, which could be of value in the investigation of the effects of different qualities of radiation both on the surface and in the depths of a water phantom. With the disturbing factors in depth dose measurements mentioned above in mind, the common goldfish (Carassius auratus) was chosen, since water is its natural habitat. In previous investigations we have demonstrated the suitability of the goldfish for the biological evaluation of roentgen radiation on the surface of the water phantom (26). Goldfish are equally suitable for the biological evaluation of the action of different qualities of roentgen rays in the depths of the water phantom, as will be shown. Technic of Irradiation The technic of irradiation in the present experiments was the same as in our previous investigations and may be illustrated by Figure 1. For each exposure 12 fish were placed in an open Petri dish, 15 em. in diameter, covered with a single layer of gauze fixed by an elastic band. In the surface position the dish rested on a layer of gauze suspended flush with the surface of the water in the phantom.