Fractionation sensitivity and latency of telangiectasia after postmastectomy radiotherapy: a graded-response analysis.

Latent time and dose-fractionation characteristics for telangiectasia are estimated in a series of 401 treatment fields in 335 patients treated with postoperative radiotherapy at the Department of Oncology in Gothenburg. To this end an extension of the mixture model to include graded-response data is proposed. In addition, a method for non-parametric estimation of median latent time is presented. Severity of telangiectasia was scored on an arbitrary 4-point scale ranging from no reaction to severe telangiectasia. The estimated number of tissue-rescuing units for the three grades of telangiectasia increased with increasing grade of reaction. The average length of time to expression of 90% of the ultimately expected damage was estimated at 6.6 years, 9.1 years and 14.8 years for grades greater than or equal to 1, greater than or equal to 2 and equal to 3, respectively. Thus increasing grades of telangiectasia occurred at progressively longer follow-up times. A statistically significant correlation was found between the level of tissue injury and the latent period. Patients with a high probability of ultimately expressing a specific grade of telangiectasia had a shorter latent period the higher the level of injury.