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Increased Radiosensitivity Following Simultaneous Ultrasonic and Gamma–ray Irradiation

1969; Radiological Society of North America; Volume: 93; Issue: 1 Linguagem: Inglês

10.1148/23.1.175

1527-1315

E. Spring,

Radiation Effects and Dosimetry

It is well known that sound affects the functional activity of cells. This aroused the author's interest in seeing whether ultrasonic radiation could increase the radiosensitivity of a biological material. if it were applied simultaneously with ionization radiation. If an increase could be observed, this could be of great importance in radiotherapy, as simultaneous irradiation with ultrasonic and ionization radiation would be easy to apply. Grass seeds (Lalium italicum) were irradiated with gamma radiation of 60CO, with and without simultaneous 2 megahertz ultrasonic radiation, as is indicated in Figure 1.2 It was expected that a difference, if observed, would be discerned in the growth rates. Measuring showed that the ratio of the growth rates of irradiated and unirradiated seeds remained approximately constant during the fifth to nin th days after the seeds had begun to germinate. Both dry and wet seeds were irradiated. It was not expected that the dry seeds would be affected by the ultrasonic radiation. The wet seeds were prepared by keeping them on a wet bed for one day before irradiation; the weight of the seeds was approximately doubled. No difference was observable in the growth rates with and without simultaneous ultrasonic radiation. The findings, valid for both types of irradiation, are indicated in Figure 2. The delay in the growth can be described by the 37 per cent dose (D37) , the dose needed to induce a diminution in the growth rate to 37 per cent of the growth rate of unirradiated seeds. For dry seeds the 37 per cent dose was 19,500 rads. The results obtained with wet seeds could be resolved into two components, the first with a 37 per cent dose of 1,030 rads, and the second with a corresponding dose of 21,900 rads, or almost the same as that for dry seeds. The first component included about 90 per cent of the seeds. The most interesting results were obtained in observation of the germinative capacity. The results in respect to the wet seeds are given in Figure 3. In this case the single–hit, multitarget model is well applicable, with the seed taken as a biological unity. The results of measurements do not exhibit any difference in the extrapolation number; they approximately equal one. The difference is indicated in the 37 per cent doses (Fig. 3). Simultaneous 2 megahertz ultrasonic radiation increases the radiosensitivity by a factor of about 2.6. The seeds were also irradiated with ultrasonic radiation alone, but no effect on the germinative capacity was observed. Further studies are in progress at this clinic with similar examinations of cancer cells. Summary This study shows that the radiosensitivity of biological material may be increased by simultaneous ultrasonic and gamma–ray radiation.