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Dose reduction by field size trimming in rotational panoramic radiography.

A substantial dose reduction may be obtained for patients in need of frequent retakes with rotational panoramic radiography by reducing the width and height of the film area irradiated. An electronic timer was connected to the circuit of an Orthopantomograph 5 (Siemens) whereby exposure times could easily be selected in the range 5-15 s. Vertical extracollimation was provided. With the field size reduced to encompass the developing dentition only, about 60% reduction in integral absorbed dose was obtained using standard (Siemens special) screens. With rare earth (Titan HS) screens a reduction of 85% was obtained in integral absorbed dose and absorbed doses to the thyroid gland and eye lens were reduced by 70-79% and 80-89%, respectively. The doses thus obtained were equal to or less than those reported with a single dental film in speed Group D.