Booster Shot

Booster Shot is a perk added to Fallout 3 in the The Pitt DLC.

Medical research from the Pitt has improved your life. Just try not to think of what it may have cost others. Your radiation resistance is improved by 10%.

Booster Shot increases your radiation resistance by 10 points.

This is most likely the reward of Free Labor Quest, the last of the main quest in The Pitt