Relationship between Dose and the Latent Period for Radiation Myelopathy in Rats

• Published in: Radiation research Vol. 140; no. 3; pp. 340 - 346
• Main Authors: Geraci, J. P., Mariano, M. S.
• Format: Journal Article
• Language: English
• Published: Oak Brook, Il Radiation Research Society 01-12-1994
• Subjects: Animals; Biological and medical sciences; Dosage; Dose response relationship; Dose-Response Relationship, Radiation; Irradiation; Male; Medical sciences; Miscellaneous; Paralysis; Paraplegia - etiology; Paraplegia - pathology; Radiation dosage; Radiation dose response relationship; Radiation injuries; Radiation Injuries, Experimental; Radiotherapy; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); Rats; Spinal cord; Spinal Cord - pathology; Spinal Cord - radiation effects; Spinal cord diseases; Time Factors; Myelopathy; Latent phase; Vertebrata; Spinal cord; Ionizing radiation; Mammalia; Rat; Animal; Rodentia; Radiation injury; Dose activity relation
• ISSN: 0033-7587; 1938-5404
• DOI: 10.2307/3579111

A 1-cm segment of rat cervical spinal cord was irradiated (16-150 Gy) and the animals were followed for 16 months to determine the dose-response relationship for the latent period for radiation myelopathy. The latent period was found to be dependent on dose in the ${\rm ED}_{0}^{\bullet}$ to ${\rm ED}_{100}$ dose range, independent of dose in the range ${\rm ED}_{100}$ to 1.5 times the ${\rm ED}_{100}$ dose and dependent on dose for doses more than 1.5 times the ${\rm ED}_{100}$ dose. Histologically, some vascular injury and demyelinization were observed in the irradiated cord segment of all paretic animals. In the first dose-dependent region there was a bimodal distribution of latent periods, suggesting two mechanisms for paralysis in this dose region. A hypothesis based on glial and vascular injury is presented which explains the triphasic dose-response relationship for the latent period. The 95% confidence limits for the dose location of both of the dose-dependent regions were less than 10% of the administered dose. Therefore, if used correctly, the latent period as an end point should be able to be used to detect dose-modifying parameters (i.e. RBE and OER) that are greater than 20%.