Selenium substitution during radiotherapy of solid tumours - laboratory data from two observation studies in gynaecological and head and neck cancer patients.

ABSTRACT

OBJECTIVE: Selenium is an essential cofactor of the enzyme glutathione peroxidase (GSH-Px), which is important for the endogenous detoxification of free radicals. A reduced activity of GSH-Px is related to increased toxicities due to radiation therapy during primary cancer treatment. Therefore, selenium substitution may be a new supportive strategy to diminish radiation-associated side effects. PATIENTS AND METHODS: The selenium blood concentrations of 121 radiotherapy patients were measured in two randomized observation studies (81 gynaecological tumours, 40 head and neck tumours). Measurements (atom absorption spectrometry) were performed on serum and whole blood (WB) samples before, in the middle of, at the end, and 6 weeks after radiotherapy. In cases of decreased selenium levels in WB, 63 patients (mean age 63.83+/-9.23 a) received selenium substitution (500 microg sodium selenite at RT days, 300 microg at the weekend) and 64 patients (mean age 63.03+/-10.47 years) were evaluated as control group without any selenium substitution. Both groups were well balanced according to tumour localization and stage. Reference values were 85-162 microg/l WB-selenium, and 65-135 microg/l serum-selenium. RESULTS: We measured the following WB selenium (Se) levels (Se-group vs. control group, U-test) begin RT 64.17+/-13.98 microg/l vs. 64.50+/-14.47 microg/l (p=0.869); mid RT 92.48+/-26.68 microg/l vs. 65.80+/-18.04 microg/l (p<0.001); end RT 93.78+/-25.90 microg/l vs. 64.06+/-17.54 microg/l (p<0.001); 6 weeks after RT 74.01+/-20.06 microg/l vs. 69.66+/-17.83 microg/l (p=0.183). The serum levels were as follows begin RT 59.18+/-13.49 microg/l vs. 61.99+/-15.72 microg/l (p=0.427); mid RT 104.75+/-31.41 microg/l vs. 62.37+/-16.23 microg/l (p<0.001); end RT 100.63+/-31.12 microg/l vs. 62.29+/-16.11 microg/l (p<0.001); 6 weeks after RT 72.73+/-26.53 microg/l vs. 64.17+/-17.22 microg/l (p=0.170). CONCLUSION: The used dosage of 500 microg sodium selenite per day is sufficient to treat selenium deficiency during radiotherapy. After substitution, the patient returns to their individual selenium status.