Individual variation and dose dependency in the progression rate of skin telangiectasia.

The progression rate of late skin telangiectasia after radiotherapy has been studied prospectively in patients for various fractionation schedules and dose levels. The degree of telangiectasia was scored on an arbitrary scale ranging from no detectable to totally confluent telangiectasia. Skin telangiectasia showed a progressive development at least up to 10 years. The rate of progression was strongly dose dependent. This finding has two important implications: the dose-latency relationship is steep, and the steepness of the dose-response relationship increases with the follow-up time. The most striking finding in this study was that the individual variation in progression rate was very large for the same treatment with a documented small variation in dose. For example, the latency for telangiectasia score 2 ranged between 17 and 90 months after 35 fractions of 1.8 Gy. The reasons for the large individual variation in progression rate are unclear and will be investigated further.