Spinal cord tolerance to single-session uniform irradiation in pigs: Implications for a dose-volume effect

Abstract: Background and purpose: This study was performed to test the hypothesis that spinal cord radiosensitivity is significantly modified by uniform versus laterally non-uniform dose distributions. Materials and methods: A uniform dose distribution was delivered to a 4.5–7.0cm length of cervical spinal cord in 22 mature Yucatan minipigs for comparison with a companion study in which a laterally non-uniform dose was given [1]. Pigs were allocated into four dose groups with mean maximum spinal cord doses of 17.5±0.1Gy (n =7), 19.5±0.2Gy (n =6), 22.0±0.1Gy (n =5), and 24.1±0.2Gy (n =4). The study endpoint was motor neurologic deficit determined by a change in gait within one year. Spinal cord sections were stained with a Luxol fast blue/periodic acid Schiff combination. Results: Dose–response curves for uniform versus non-uniform spinal cord irradiation were nearly identical with ED50’s (95% confidence interval) of 20.2Gy (19.1–25.8) and 20.0Gy (18.3–21.7), respectively. No neurologic change was observed for either dose distribution when the maximum spinal cord dose was ⩽17.8Gy while all animals experienced deficits at doses ⩾21.8Gy. Conclusion: No dose-volume effect was observed in pigs for the dose distributions studied and the endpoint of motor neurologic deficit; however, partial spinal cord irradiation resulted in less debilitating neurologic morbidity and histopathology. [Copyright &y& Elsevier]