Journal of Psychosomatic Research, Vol. 45, No. 3, pp. 277–293, 1998 Copyright  1998 Elsevier Science Inc. All rights reserved. 0022-3999/98 $–see front matter S0022-3999(97)00286-9 UNDERSTANDING THE LEVEL OF FATIGUE IN CANCER PATIENTS UNDERGOING RADIOTHERAPY E. M. A. SMETS,* M. R. M. VISSER,* B. GARSSEN,† N. H. FRIJDA,‡ P. OOSTERVELD* and J. C. J. M. de HAES* (Received 30 June 1997; accepted 6 October 1997) Abstract—This study tests the hypothesis that a discrepancy between resources and demands explains most of the variance in fatigue in cancer patients undergoing radiotherapy. Patients (n=250) were inter- viewed at pretreatment, posttreatment, and at 9-month follow-up. Resources involved physical condi- tion, neuroticism, optimism, social support, gender, age, and level of education. Demands entailed prog- nosis, radiotherapy dose, the effort associated with actual activity, and the patient’s perception of overall burden. Regression analyses were performed, using interaction terms to operationalize the discrepancy between resources and demands. The hypothesis was not supported. At pretreatment, physical condition explained most of the fatigue, whereas, at posttreatment, both the patients’ physical condition and per- ception of burden contributed to fatigue. At follow-up, demands did not add to the variance already ex- plained by resources, and vice versa. Factors that contribute to the patient’s physical condition before starting radiotherapy and to his/her perception of burden need to be addressed to further our under- standing of their fatigue.  1998 Elsevier Science Inc. Keywords: Fatigue; Radiotherapy; Psychological factors; Resources; Demands. INTRODUCTION Interest in fatigue is increasing, as can be deduced from the growing number of pub- lications on this topic in recent years. This holds in particular for the chronic fatigue syndrome (CFS), or its equivalents, such as neurasthenia, myalgic encephalomyeli- tis, or postviral fatigue syndrome, a condition of persistent and debilitating fatigue lasting at least 6 months and lacking somatic explanation [1]. Interest is also growing for fatigue as a symptom of chronic diseases, including rheumatoid arthritis, renal disease, multiple sclerosis, and cancer. A literature search using Medline on can- cer-related fatigue over the period 1980–1991 yielded nine references in which fa- tigue was mentioned in title, keyword, or abstract [2]. A similar search over the pe- riod 1992–1996 yielded 30 references. A possible reason for this increase in interest *Department of Medical Psychology, Academic Medical Center/University of Amsterdam, Amster- dam, The Netherlands. †Hellen Dowling Institute, Rotterdam, The Netherlands. ‡Department of Psychology, University of Amsterdam, Amsterdam, The Netherlands. Address correspondence to: Ellen Smets, Department of Medical Psychology, Academic Medical Center/University of Amsterdam, P.O. Box 22700, 1100 DE Amsterdam, The Netherlands. Fax: +31- (0)20-5664440; E-mail: e.m.smets@amc.uva.nl 277