Purpose: Patients treated with identical radiotherapy schedules show a substantial variation in the degree of acute and late normal tissue reactions. To identify any possible contributing factors to this phenomenon, we have analyzed the treatments of 402 breast cancer patients.
Methods and materials: The patients received adjuvant postoperative radiotherapy between 1972 and 1985 and have been followed up since then. Multivariate analyses were performed with peak reflectance erythema and peak acute reaction score as endpoints for the acute reactions, and with progression rate of telangiectasia as well as telangiectasia score as endpoints for the late reactions. Twenty patient- and treatment-related factors were tested such as age, menopausal status, hemoglobin level, serum calcium, smoking habits, hypothyroidism, diabetes, hypertension, blood pressure, cardiovascular and autoimmune disease, the influence of hormone therapy and chemotherapy, pretreatment reflectance value, acute skin reactions, radiation quality, individual dose, bilateral fields, and the total effect (TE) for the dose schedule applied.
Results: The TE was a strong prognostic factor for all endpoints. In addition to TE, blood pressure was prognostic for the peak erythema measured by reflectance spectrophotometry, and the pretreatment reflectance value was prognostic for the acute score. The only independent prognostic factors found for the progression of skin telangiectasia and telangiectasia score except for TE were the individual dose and the acute skin reactions.
Conclusions: These factors explained at most about 30% of the variance describing the total patient-to-patient variability for each endpoint. The remaining variability is still unexplained but may be related to individual differences in cellular radiosensitivity, partly determined by genetic variations and partly by unknown epigenetic factors.