B. A. Kihlman

Chromosome aberrations following irradiation with high-energy protons and their secondary radiation: a study of dose distribution and biological efficiency using root-tips of Vicia faba and Allium cepa.

SummarySome radiological properties of a 185 mev proton beam were stuided with root-tips of bean and onion seedlings.The relationship between dose and number of abnormal metaphases was investigated at different depths of penetration in Lucite. The effect, found in the final part of the range of penetration, was higher than expected when the physical depth-dose to surface-dose ratio is considered. The difference is partly attributed to a variation of the relative biological efficiency.The enhancing effect of oxygen was studied at high and low energies. It was found to be nearly constant.The relative biological efficiency of 170 mev protons as compared with 180 kv roentgen rays for producing chromosome aberrations was found to be 0·7.The chromosome-breaking efficiencies of the secondary radiations from proton-irradiated tissue and brass were studied. The results indicate that the effects of secondary radiation may be neglected in therapeutic procedures.

CHROMOSOME BREAKAGE ASSOCIATED WITH VIRUSES AND DNA INHIBITORS

Publisher Summary This chapter discusses some of the observations made utilizing two virus model systems, the Schmidt-Ruppin strain of Rous sarcoma and measles and also two DNA-inhibiting substances, cytosine arabinoside and deoxyadenosine. In the Rous sarcoma studies, the Schmidt-Ruppin strain of the virus was utilized. This virus produces tumors not only in the chicken and fowl but also in a wide variety of mammals in eluding the rat, mouse, guinea pig, hamster, and rabbit. Tumors can be produced in these mammals either by the injection of minced chicken tumor or by cell-free suspensions of the chicken tumor prepared by multiple centrifugations. With both of these methods, the chromosomes of the tumor in the recipient mammal have been analyzed and shown to be those of the recipient mammal rather than the chicken donor, thus establishing new tumor induction rather than a heterotransplant. Once the tumor is established in the mammalian host, it can be successfully passed serially to subsequent generations of the same mammal or in a zigzag fashion back to the chicken and then back to the mammal.

Different effects of 5-fluorodeoxyuridine and 5-bromodeoxuridine on the frequencies of chromatid aberrations obtained in Vicia faba after irradiation with x-rays.

Results of a studi, on the production of chromosomal aberrations in Vicia faba by 5-fluorodeoxyuridine (fUDR) and by 5-bromodeoxyuridine (BUDR) alone, and in combination with x radiation, indicate that the chromosomal damage obtained after x irradiation may be increased by both FUDR and by BUDR, but that the effects are qualitatively different and are probably produced by different mechanisms.

Effect of nitric oxide on the production of chromosomal aberrations by x-rays.

Results are reported from a study of the effects of nitric oxide concentration on the radiosensitivity of root tips of the broad bean, Vicia faba, as demonstrated by chromosomal aberrations. (C.H.)