Several treatments have been researched as ways to minimize hair loss or speed regrowth, but none of them are 100% effective. Hair-restoration "experts" and products may make big promises; as a general rule, if it sounds too good to be true, it probably is.
Applying Rogaine directly to your scalp won't entirely prevent hair loss, but it's been shown to speed hair regrowth in breast cancer patients who have lost their hair, and it may even delay the loss. A small 1996 study found that while minoxidil did not prevent hair loss in women undergoing chemotherapy for breast cancer, it took longer for hair to fall out, and hair eventually grew back faster.
Depending on the type of chemo you're receiving, wearing a frozen gel cap or ice pack during treatment may help reduce hair loss. By chilling the scalp during intravenous chemo, blood flow to hair follicles is reduced. This, in turn, reduces the amount of the chemo drug absorbed by the follicles, which minimizes follicle damage and potential hair loss.