Muscle wasting after radiotherapy in young and adult rats.

The impact of late muscular injury after radiotherapy on the well being of patients, particularly those treated at a relatively young age, is often underestimated. To extend the present knowledge, a detailed comparative study of the radiation response of skeletal muscles was performed. The hind limb of rats was irradiated at the age of 30-60 days (young), at approximately 200 days (adult) or at the age of >360 days (old), with single doses ranging from 15-60 Gy. Muscular wet weight, volume and tibia length was followed up to 12 months post-treatment. Radiation treatment resulted in muscular wasting, which was more severe at higher doses. The radiation response depended strongly on the age of the animal at the time of treatment. Radiation induced muscle wasting and stunted tibia growth were more prominent in young animals than in adult or in old rats. ED50 values based on normalized wet weight were 12.5 (11.5-13.6) Gy for young animals and 22.5 (21.8-23.3) Gy for adult animals. The gastrocnemius muscle of young animals appears to be more radiosensitive than the gastrocnemius muscle of adult or old animals. Furthermore, in young animals, severe wasting of the muscles may already occur after relative low radiation doses (single dose of 15 Gy).