Using a mattress after Chemo and Radiation

Is it safe to sleep on a mattress after a radiation and chemo patient?  There is a small stain that happened while she was having chemo and radiation.  She hasn't slept on it for over a month.  

[Cleveland Clinic]

Dear cancerquestions, A difficult question to answer specifically as we don't know alot of information such as timing of the stain, radiation implants vs. external beam radiation, how long ago this occurred, type of mattress etc.).  In general it is safe, of course laundering bedding etc. is necessary.  

[cancerquestions]

It was external beam radiation.  I'm not sure of the last treatment before the stain.  Should I get a plastic cover as a precaution?  Thank your for help.