Can Cough Syrup Be Taken While Udergoing Tomotherapy?

my father is 62 yrs old and has been operated for brain tumour(CP angle,schwannoma)in the month of dec2010.Now he is undergoing tomotherapy,16 fractions of radiations have been given.At present he is having cough with no fever.and is taking cofdex cough syrup.Will the cough syrup have any effect on his health and radiation.please advice.