QUANTIFICATION OF PATIENT TO PATIENT VARIATION OF SKIN ERYTHEMA DEVELOPING AS A RESPONSE TO RADIOTHERAPY

A method is described to determine accurately skin redness during a co urse of radiotherapy using reflectance spectroscopy utilizing informat ion from across the visible spectrum according to the La*b* color coo rdinate system. The method was used to quantify the development of ski n erythema during and after electron beam irradiation of the chest wal l following mastectomy. A number of factors were identified which coul d influence the wide variation in response seen between patients. Thes e were: intra- and inter-observer variation; intra- and inter-patient variation and variation in the actual dose delivered. Statistical anal ysis, including an analysis of variance of inter- and intra-patient va riation, revealed that the major factor that accounts for the observed difference between patients is a true inter-patient variation, with a coefficient of variation, corrected for intra-patient variation, of 4 3%. Within the narrow dose range administered in this study, there was no demonstrable dose-effect relationship, raising questions about the role of cell death in the basal layer of the epidermis in the pathoge nesis of radiation induced erythema.