Fundamental research for dose control during supine dental panoramic radiography.

OBJECTIVE: This study aimed to control radiation doses when using a portable supine dental panoramic radiography system by measured the scattered doses. METHOD: The study used LPX7007 (Asahi Roentgen) for the panoramic radiography system. The subjects comprised a cylinder phantom (QualitA) and a RANDO Phantom (Alderson). The semiconductor dosimeter was an X2 survey sensor (RaySafe). The phantom was set at a height of 1 m from the floor, and the sensor was set at 1 m from the floor at the genital level and 1.5 m at the lens level. Measurements were taken at 30°intervals clockwise from 0°at distances of 0.5 m and 1 m in radius around the phantom. The occupational exposure range was defined as 0 ± 30° and the public exposure range was defined as the occupational exposure range and 30° to 150° and 210° to 330° as the public exposure range. RESULT: The highest doses were observed in the 120° and 240° directions, and the lowest in 0° ± 30° range. The lowest limit number of images taken in the occupational exposure range was 130 images at a distance of 0.5 m, 452 images at 1 m at the lens level for the cylinder phantom, and 320 images at 0.5 m and 1098 images at 1 m for the RANDO Phantom. In the public exposure range at the genital level, there was one image at 0.5 m and six images at 1 m for the cylinder phantom, and two images at 0.5 m and eight images at 1 m for the RANDO Phantom. CONCLUSION: We found that radiation exposure can be reduced by keeping a distance from the subject, avoiding working at 120° and 240° and staying within 0° ± 30° behind the panoramic radiography system.

Stray radiation dose reduction using a backscatter shield and a rectangular collimator for a handheld intraoral X-ray unit.

The objective of this study was to study the dose reduction effect on occupational exposure of operators and public exposure other than operators when a backscatter shield and a rectangular collimator are used in conjunction with a handheld intraoral X-ray unit. The occupational exposure was reduced to 40% when the backscatter shield was attached to the cone-tip, to 13% when the rectangular collimator was attached and to 7.7% when the backscatter shield and rectangular collimator were used together. On the other hand, the public exposure was reduced to 20% when the rectangular collimator was attached, but the backscatter shield was not effective in reducing the public exposure. Attaching a backscatter shield is effective in reducing the occupational exposure, and a rectangular aperture is effective in reducing the occupational exposure, as well as the public exposure.

Effect of cranium structure on dose distribution during intraoral radiography.

OBJECTIVES: This study aimed to evaluate, the effect of the cranium structure on dose distribution by measuring the dose using the RANDO phantom for safe use of an X-ray unit during personal identification work at a large-scale disaster site. METHODS: As the subject, the head and neck of the RANDO Phantom (Alderson) containing a dry skull composed of a tissue-equivalent substance and having a shape similar to that of a living body were studied. With the body in the supine position, the air doses per second of irradiation time were measured for a total of six sections of the anterior, premolar, and molar teeth (molar on the left side) at a tube voltage of 60 kV and tube current of 10 mA during maxilla and mandible intraoral radiography. RESULTS: The region having the highest exposure dose was the main X-ray direction in both the mandible and maxilla. Conversely, the dose tended to be low in the range from the temporal region to the occipital region on both sides of the horizontal plane, from the frontal region to the occipital region of the sagittal plane, and in the parietal region of the frontal plane. CONCLUSIONS: It would be preferable to examine from the top of the body where the dose tends to decrease for all imaging sites.

Comparison of air dose and operator exposure from portable X-ray units.

This study was aimed at investigating and comparing exposure dose of workers and the surrounding workers. In addition, worker's exposure was also measure about lens and finger. Four intraoral portable X-ray units were evaluated. The stray radiations were measured using Pitman 37D and ionization chamber (Pitman). MyDosemini (ALOKA) was used for measurement of the finger exposure dose. Without the shield became high in anterior 0.5 m. Comparing the air dose for the four models used in this study showed a high tendency for the two NOMAD models. And using the shields, the images could be taken 4.6 times of the baseline at a maximum and 3.6 times on average. The finger radiation exposure dose was low with both of the NOMAD models, with no significant difference found. By setting the baseline value without a shield, finger radiation exposure when using a shield was lower than the detection limit for the D3000, and was reduced by approximately 94-96% for other three models. All models can photograph around 100 bodies, so it is considered that it is not necessary to switch out the operator considering the operation limit. But even if it does not reach the operation limit, the stochastic effects of radiation exposure can be increased as well as the deterministic effects of the operation limit. The operator and the surrounding workers seek to protect themselves. It is important to perform exposure management that takes into account the stochastic effects to the operator and the surrounding workers.

Reduction of operator exposure by rectangular collimation in portable intraoral radiography.

Portable intraoral X-ray units are frequently used for home-visit dental treatment and personal dental identification. Therefore, the reduction of operator exposure is crucial. Rectangular collimation is effective at reducing patient exposure and operator exposure; however, its effects are not known. We investigated the reduction of operator exposure through rectangular collimation by measuring the backscattered dose in relation to the operator exposure dose. Using a portable intraoral X-ray unit, a head phantom for CT dose measurement as the object, a dosimeter, and stainless-steel rectangular collimator, a 1-cm ambient dose equivalent was measured in intervals of 15° in horizontal and vertical planes with the radii of 50 and 100 cm. The backscattered dose decreased to approximately one-third when a rectangular collimator was attached to the cone tip. This may have been due to the reduction of the volume of scattered X-rays generated in the phantom by rectangular collimation. We clarified that rectangular collimation is effective at reducing the operator exposure and is useful for protecting the operators of portable intraoral X-ray units during home-visit dental treatment and personal dental identification.

Age estimation based on the volume change in the maxillary premolar crown using micro CT.

Age is often estimated using teeth because numerous external and internal changes appear due to aging. The purpose of this study was to investigate an age estimation method based on the volume ratio of the internal structure of the crown. 61 maxillary first premolars and 50 maxillary second premolars from subjects aged 20-79 years old were used. Micro CT, which can be used to analyze teeth in a non-destructive manner with high sensitivity, was employed in the present study. In consideration of individual differences among subjects, the volume ratio was calculated for the following four items: The pulp chamber was calculated separately based on the presence of enamel.In order to estimate age, regression analysis was conducted with the actual age as the dependent variable and each volume ratio as the independent variable. As a result, the highest correlation was found with PVR (E-) for each measurement item. Therefore, the regression equation using the volume change of the maxillary premolar crown as an index was as follows: Age = -12.43 × 4: PVR (E-) + 69.85. Age = -12.94 × 5: PVR (E-) + 72.54.