several answers here,

I had radiation only and did not experience a diminished sex drive.

In searching the web I found only that exposing the unborn to chemo drugs could be a serious problem so a condom is appropriate if you (or your partner) could become or are pregnant. Your immune system is weak so it will likely be easier to contract STD's or other infections (urinary etc.)

If you aren't pregnant, can't get pregnant, are in a monagmous healthy relationship, you should be fine without condoms. (Please verify this with your primary doctor or oncologist.)

Of course if ductape or popsicle sticks are involved I suggest Goodyear 4 ply, steel belted radial models available at most tire stores.