Filtration for lowest patient dose in dental radiography

Journal Article · Wed May 01 04:00:00 EDT 1963 · Oral Surgery, Oral Medicine, Oral Pathology

DOI:https://doi.org/10.1016/0030-4220(63)90145-2· OSTI ID:4654734

Wainwright, W. W.

Criticisms are advanced against attempts to avoid unnecessary radiation exposure by adoption of state regulations requiring added filtration in order to absorb the soft x-rays of the beam presumably to spare the patient this part of the radiation exposure. The general adoption of increased filtration is regrettable, it is suggested, since its usefulness applies only to specific conditions and does not reduce radiation exposure in large areas of radiography. This investigation analyzes: the filtration recommendations of the National Bureau of Standards Handbook 76, the measurements on which the recommendations are based, and the results of further measurements in dental radiography. Conflict of the Handbook 76 recommendations with those of the (British) Medical Research Council's Second Report are discussed. Filtration should be increased with increase of kilovoltage, according to the Handbook, but the Report suggests that the gonad dose in dental radiography may be slightly increased by the use of higher penetrating powers. To reconcile these divergent recommendations, a comparison is made of the methods and the criteria of patient dose upon which they are based. A heavily boned adult male skull was impregnated with paraffin and the phantom was mounted with an ionization chamber in the headrest of a dental chair. Measurements in the phantom and in the gonadal position were made at an arbitrary distance of 26 in. from the beam. Measurements were made at total filtrations equal to 1.5, 2.0, 2.5, 3.5, 4.5, and 5.5 mm aluminum for kilovoltages of 90, 65, and 45. Measurements of film dose were also made in a second phantom constructed of aluminum and air. Dental film dose was shown to be constant for a given film, regardless of change in kilovoltage or half-value layer. The results showed that the recommendation that filtration and kilovoltage be increased to reduce patient dose is applicable only to situations in which the gonads lie unprotected in the direct beam. When the gonads lie outside the direct beam, as in dental radiography, an increase in filtration or kilovoltage reduces skin dose and depth dose only up to the depth of 1 in., which is the plane of the film. Beyond this there is a reversal in which the patient dose is increased by an increase in filtration or kilovoltage, and the gonadal dose is unaffected. Increases in filtration or kilovoltage do not decrease the patient dose in dental radiography when an effort is made to keep gonad, skin, and integral doses as low as possible. In vivo gonadal exposures, measured on male subjects without protective aprons in two dental offices, were shown to decrease roughly in proportion to the sitting height, so that exposures in boys as young as 4 or 5 yr of age are two to three times greater than in adult males. In obese persons whose thighs were so large as to completely cover the measuring chamber, gonadal measurements were much lower than in persons of average build. The gonadal doses per set of 20 films varied from 0.3 to 3.7 mr. The in vivo measurements were higher than the measurements on the phantom, presumably because of differences in physical arrangement. (BBB)

• Research Organization: George M. Hollenback Research Associates, Encino, Calif.
• Sponsoring Organization: USDOE
• NSA Number: NSA-17-039334
• OSTI ID: 4654734
• Journal Information: Oral Surgery, Oral Medicine, Oral Pathology, Journal Name: Oral Surgery, Oral Medicine, Oral Pathology Journal Issue: 5 Vol. 16; ISSN 0030-4220
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ABSORPTION
AGE
AIR
ALUMINUM
BEAMS
BODY
BONES
CLOTHING
DOSEMETERS
ENERGY
ENERGY LEVELS
FILTERS
GONADS
HALF-THICKNESS
HEALTH AND SAFETY
IMPREGNATION
IN VIVO
IONIZATION CHAMBERS
MAN
MEASURED VALUES
MOCKUP
PARAFFIN
PHOTOGRAPHIC FILM
RADIATION DOSES
RADIATION PROTECTION
RADIOGRAPHY
SAFETY
SHEETS
SKIN
SKULL
STANDARDS
TEETH
THICKNESS
X RADIATION