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[L. bolus fr Gr. bolos, a lump]

1. A mass of masticated food ready to be swallowed.
2. A rounded preparation of medicine for oral ingestion.
3. A concentrated mass of a diagnostic substance given rapidly intravenously, such as an opaque contrast medium or an intravenous medication.
4. In radiology, a tissue-equivalent material placed on the surface of the body to minimize the effects of an irregularly shaped body surface. The dose at the skin surface tends to increase, minimizing the skin-sparing effect of megavoltage radiation.

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