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Radiation doses of collimated vs non-collimated cephalometric exposures

¹ Oral Imaging Centre, Department of Periodontology, School for Dentistry, Oral Pathology and Maxillofacial Surgery, Katholieke Universiteit Leuven, Leuven, Belgium; ² Department of Oral Radiology, Academic Centre for Dentistry, Amsterdam, The Netherlands; ³ Department of Radiotherapy, Katholieke Universiteit Leuven, Leuven, Belgium

*Correspondence to: Reinhilde Jacobs, Oral Imaging Centre, Department of Periodontology, School for Dentistry, Oral Pathology and Maxillofacial Surgery, Katholieke Universiteit Leuven, Kapucijnenvoer 7, B-3000 Leuven, Belgium; E-mail:; Email: reinhilde.jacobs{at}uz.kuleuven.ac.be

Received 11 July 2002; revised 14 March 2003; accepted 24 March 2003

Objectives: The aim of the study was to compare organ and effective radiation doses for collimated and non-collimated cephalometric radiographs made by a multipurpose extraoral radiation unit.

Methods: Cephalometric exposures were made from a Rando head phantom representing an average man with the Cranex Tome multipurpose radiation unit. A collimator was fabricated from a 3-mm thick piece of lead. The collimator was designed so that structures relevant for orthodontic diagnosis were not shielded, whereas the thyroid gland and the major part of the skull were shielded. Absorbed organ doses were measured using thermoluminescent dosimeters. The effective dose was calculated both with (E_sal) and without (E) inclusion of the salivary glands.

Results: Use of a wedge-shaped lead collimator yielded a reduction in field size of 55% and a reduction in E from 3.0 µSv to 1.6 µSv (47%) and in E_sal from 3.7 µSv to 2.2 µSv (41%).

Conclusions: Use of a wedge-shaped collimator should be advocated in all cases where depiction of the thyroid gland and the neurocranium is not required. The resulting reduction in effective dose using our collimator was 47% (41% when the salivary glands are included), which is of clinical importance, especially in children.

Keywords: radiography, dental; radiation dosage; radiography, cephalometric; collimation

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