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Pediatric dose study supports rectangular collimation

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 Pediatric dose study supports rectangular collimation



December 18, 2012 -- Digital imaging and rectangular collimation should be used to ensure that the ALARA (as low as reasonably achievable) principle can be maximized when taking bitewing radiographs in pediatric patients, according to a poster presentation at the American Academy of Oral and Maxillofacial Radiology (AAOMR) annual meeting last month.

An epidemiological study published earlier this year in the journal Cancer prompted a flurry of media coverage and public concern because it claimed to have found a link between frequent bitewing x-ray exposure and increased risk of developing meningioma.

However, the study relied on patients' recall of past dental radiographic history, which is not an accurate means of assessing data accurately, noted Iryna Branets, DDS, an instructor in the department of cariology and comprehensive care at New York University (NYU) College of Dentistry, who presented the poster at the AAOMR meeting.

"We must admit that there could be a slim possibility linking dental x-rays to meningioma, since prior to ALARA there was no rectangular collimation, faster speed films, or digital radiography," she said. "Unfortunately, the study [in Cancer] lacked valid statistical data on the actual patient exposure dosimetry."

In addition, a literature review revealed that there is no valid data on bitewing dosimetry to the head and neck organs of pediatric patients.

First pediatric dose study

Dr. Branets and colleagues from NYU College of Dentistry, Stony Brook University School of Dental Medicine, and Memorial Sloan-Kettering Cancer Center used two anthropomorphic CIRS juvenile phantoms (5 years old and 10 years old) to gather dosimetric measurements on the x-ray exposures from bitewing radiographs using round and rectangular collimation for both film and digital radiography.

The phantoms were exposed for the radiographs using a Gendex Dental Systems 765 x-ray machine at the manufacturer's preset film and digital pediatric settings for both rectangular and round collimation. Optically stimulated luminescence (OSL) dosimeters were placed in 21 head and neck premanufactured slots in each phantom. All exposures were repeated 15 times, and the results were divided by 15 to evaluate the average dose per view. Average organ dose was calculated in micrograys (µGy) based on four bitewing views. Organ fractions irradiated were determined from International Commission on Radiological Protection Publication 89 (ICRP-89). Organ equivalent doses and overall effective doses in microsieverts (µSv) were based on four bitewing views and the ICRP-103 tissue-weighting factors.

For the 5-year-old phantom, the dose to the brain with round collimation/film was 6.93E-01 µGy, while with round collimation/digital the organ dose was 5.73E-01 µGy. With the exposure for rectangular collimation/film versus rectangular collimation/digital, the organ dose was reduced to 1.24E+00 µGy and to 6.73E-01 µGy.

With the 10-year-old phantom, the organ doses to the brain were 3.05E-01 µGy for round/film, 3.18E-01 µGy for round/digital, 6.42E-01 µGy for rectangular/film, and 2.77E-03 µGy for rectangular/digital.

Overall, the radiation exposures using rectangular and round collimators were about the same for both phantoms. The effective dose in microsieverts for the 5-year-old ranged from a low of 1.8 (rectangular/digital) to a high of 3.1 (round/film). The 10-year-old ranged from a low of 1.5 µSv (rectangular/digital) to a high of 2.8 (rectangular/film) and 2.7 (round/film).

Doses to the thyroid and other organs were low, the researchers found. The highest doses were seen in the glands, extrathoracic airway, and oral mucosa.

This was the first study utilizing juvenile CIRS phantoms in conjunction with OSL to provide organ dose data from pediatric bitewing radiographs, Dr. Branets noted.

"Our findings confirmed that digital imaging in conjunction with rectangular collimation must be used so that the ALARA concept in relation to children's head and neck exposure may be maximized," she and her colleagues concluded.

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