Selenium supplementation during radiation therapy for solid tumours—Laboratory findings of a phase III trial on gynaecological and ENT tumours

Abstract

Background Selenium is an essential cofactor of glutathione peroxidase and is responsible for the body's metabolism of free radicals. Reduced activity of this enzyme system is associated with increased toxicity of radiation therapy (RT) for tumours. Materials and methods In a randomized phase III trial, whole-blood and serum selenium levels in 127 patients with confirmed selenium deficiency (81 gynaecological tumours and 42 ENT tumours) were measured before, during, and after RT by means of atomic absorption spectroscopy. A total of 63 patients (median age: 63.83±9.23 years) received oral selenium supplementation in the form of 500 μg sodium selenite on RT days and 300 μg on non-RT days (weekends, public holidays, and equipment failure). Sixty-four patients (median age: 63.03±10.47 years) served as the control group. Both groups were comparable with regard to tumour entity and tumour stage. The following ranges, which are recommended for Germany, were defined as normal: whole-blood selenium 85–162 μg/l; serum selenium: 65–135 μg/l. Results The following levels were measured in whole blood (selenium group vs. control group, U test): start RT 64.17±13.98 μg/l vs. 64.50±14.47 μg/l ( p =0.869); mid-RT 92.48±26.68 μg/l vs. 65.80±18.04 μg/l ( p p p =0.183). The follow levels were measured in serum: start RT 59.18±13.49 μg/l vs. 61.99±15.72 μg/l ( p =0.427); mid-RT 104.75±31.41 μg/l vs. 62.37±16.23 μg/l ( p p p =0.170). Conclusion Selenium supplementation using 500-μg doses of sodium selenite was sufficient to compensate for an existing selenium deficiency during RT for solid tumours. However, this does not guarantee a durable correction of selenium status in the absence of continued supplementation.