Response shift in quality of life measurement in early-stage breast cancerpatients undergoing radiotherapy

In medicine, response shift refers to a change - as a result of an event su ch as a therapy - in the meaning of one's self-evaluation of quality of lif e. Due to response shift, estimates of side effects of radiotherapy may be attenuated if patients adapt to treatment toxicities. The purpose of our st udy was to assess to what extent two components of response shift, scale re calibration and changes in values, occur in early-stage breast cancer patie nts undergoing radiotherapy and to examine what the implications would be f or treatment evaluation. In the week before start of post-operative radioth erapy, 46 patients filled out a questionnaire consisting of quality of life items of the SF-36 and the Rotterdam symptom checklist (RSCL) (pretest). D uring radiotherapy, patients were asked to fill out the questionnaire twice : a posttest (quality of life at that moment) and a thentest (quality of li fe before treatment, retrospectively), supposedly using the same internal s tandard. Changes in values were studied by asking the patients on the two o ccasions to rate the importance of seven attributes representing various do mains of quality of life. Patients were also asked whether their quality of life with respect to the measured aspects had changed since the pretest (s ubjective transition scores). Significant scale recalibration effects were observed in the areas of fatigue and overall quality of life. When the grou ps were divided according to their subjective transition scores, significan t scale recalibration effects were found in case of worsened quality of lif e for fatigue and overall quality of life, and in case of improved quality of life for fatigue and psychological well-being. The mean importance ratin gs remained fairly stable over time, except for 'skin reactions', which obt ained less importance at the end of radiotherapy than before. In conclusion , effects of scale recalibration were observed that would have significantl y affected quality of life evaluations, in that the impact of radiotherapy on fatigue and overall quality of life would have been underestimated. Chan ges in internal values were observed only for 'skin reactions'.