1. A single, relatively large quantity of a substance, usually one intended for therapeutic use, such as a bolus dose of a drug injected intravenously.
2. A masticated morsel of food or another substance ready to be swallowed, such as a bolus of barium for radiographic studies.
3. In high-energy radiation therapy, a quantity of tissue-equivalent material placed in the radiation beam, over the surface of the irradiated region, to increase the absorbed dose in the superficial tissues.
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