Varying lengths of the cervical spinal cord of rats were irradiated with single doses of X rays. Dose-related changes in the latency for the development of paralysis, or for the presence of histological lesions in the spinal cord, indicated a dependency on the length of spine irradiated. The dose associated with a specified latency increased as the field size was reduced from 16 mm to 4 mm. A more precise indication of the importance of field size came from a determination of the ED50 values for rats developing paralysis in less than 30 weeks of irradiation or from those that showed neurological signs, or histological evidence, of irradiation damage, occurring after latent periods of greater than 30 weeks. These end-points were primarily related to white-matter necrosis and gross vascular damage respectively. For paralysis in greater than 30 weeks the ED50 increased markedly from 21.5 +/- 0.3 Gy for a 16 mm field to 50.98 +/- 2.28 Gy when a 4 mm length of cord was irradiated. For vascular lesions only a small change in ED50 value was found, from 20.0 +/- 0.5 Gy to 25.58 +/- 2.78 Gy for 16 mm and 4 mm fields respectively. At less than or equal to ED25 no evidence for a field-size effect was seen for this late lesion. These results were examined in the light of some old and some more recently analysed clinical data for radiation myelopathy. It is hoped that this will initiate other investigations in this important area of radiotherapy practice.

No abstract

A number of European laboratories studying the late effects of ionizing radiation in animals have established an effective cooperation within the European Late Effects Project Group (EULEP) since 1970. To facilitate the exchange of biological results several techniques, including quality control of the experimental animals, pathology and dosimetry, have to be standardized. The most important aspects of the procedures for X-irradiation and dosimetry of small animals are summarized. These include recommendations on irradiation conditions, dosimetry methods, characteristics of phantoms and factors affecting X-ray dosimetry. X-irradiation procedures employed by the participating institutes are described and the results of five X-ray dosimetry intercomparisons are reported. The introduction of a common dosimetry protocol has resulted in improvements in exposure arrangements and absolute dosimetry.

No abstract