<qa>  What is a double-blind, placebo-controlled trial?This is a double-blind, placebo-controlled trial wherein subjects with breast cancer will be randomized to receive either 20 mg oral melatonin or placebo the night before their first RT, nightly throughout their RT, and for an additional 2 weeks following the completion of their RT. After informed consent is obtained from eligible subjects, they will then be electronically randomized on a 1:1 ratio to melatonin treatment or placebo. The subjects will be stratified according to treatment duration less than 3 weeks; equal to or greater than 3 weeks and prior chemotherapy. 