Thinking of the other end of the radiator, beware of just turning the thermostatic valve to the off position and taking the radiator off - if it gets really cold in the room the valve could open and let water out. You need to take the head off the valve and put on a cap in its place which will push down the pin in the valve mechanism to fully seal the valve.

Be aware that once you have isolated both ends of the radiator, it'll be very heavy and full of water, which will need to be drained out - and that the water will probably be horribly dirty and capable of staining your carpets etc