Sharon A. Glaze

Panoramic dental radiography for mass screening

Dental panoramic radiography has increased in popularity and use since its introduction in the late 1950s and proposals have been made to apply this methodology as a mass screening tool. Ease of examination and the reportedly low radiation exposure to the anterior superficial tissues have been cited as reasons for this application. However, in panoramic radiography the X-ray beam enters posteriorly which results in high doses to posterior and to internal tissues. We have employed LiF thermoluminescent dosimeters to measure the radiation exposure to the superficial tissues of a Rando phantom and of patients during dental panoramic examination. Radiation exposures ranged from an average of 255 mR to the lateral tissues to 22 mR to the symphysis of mandible. Other anterior superficial tissues received exposures of 25-50 mR. On the basis of previous hazards analysis of radiographic procedures, these radiation exposures would seem to be excessive for application as a mass screening tool.

Dosimeter placement in the Rando phantom

Each section of the Alderson Rando phantom contains a tissue-equivalent plastic coating layer approximately 2 mm thick, applied to both faces. This compensates for material removed in the sawing process. Conventional use of thermoluminescent dosimeters positions them totally or partially within the coating layer. Analysis shows that, in the lung region, dosimeters placed in this layer received a dose averaging 39% lower than those placed at midsection. Where bony structures interfere, some dosimeters in the coating layer received an 18% higher dose than those at midsection. Therefore, positioning dosimeters at the center of a section is recommended.

Use of Gypsum Wallboard For Diagnostic X-ray Protective Barriers

Abstract-Type “X” gypsum wallboard, a readily available building material, has been evaluated for its radiation shielding properties for use in low-level medical X-ray applications. Attenuation and transmission curves are presented. Tables for use in barrier calculations are presented in the traditional form of the NCRP Report Nos. 35 and 49. Gypsum wallboard is not suited for use as a primary shielding material except in some dental applications. It is useful as a secondary barrier for facilities with low workloads, for mammography and dental suites, and for well-collimated beams, such as those used in computed tomography.

Patient radiation dose in conventional and xerographic cephalography

A comparison of the radiation doses for xeroradiographic and conventional film screen cephalography was made. Alderson tissue-equivalent phantoms were used for patient stimulation. An optimum technique in terms of patient dose and imaqe quality was established for the xeroradhe data indicated that the dose for the Xerox process ranged from five to eleven times greater than that for the conventional process for entrance and exit exposures, respectively. The most commonly reported dose, the entrance dose, was found to be 206 mrad, which is five Imes that for the conventional cephalogram. This dose, however, falls within an acceptable range for other dental and medical radiation doses. It is recommended that conventional cephalography be used for routine purposes and that xeroradiography be reserved for situations requiring the increased image quality that the process affords.

Patient and personnel exposure during extracorporeal lithotripsy.

Extracorporeal shock wave lithotripsy (ESWL) has provided a nonsurgical approach to treatment of renal stones. The Dornier lithotripter uses dual image intensified x-ray systems to center the stone before treatment. Three imaging modes are offered: a fluoroscopic mode and two video spot filming modes. The average entrance exposure to the stone side of the typical patient at our facility is 2.6 X 10(-3) C kg-1 (10 R) [range: 0.5-7.7 X 10(-3) C kg-1 (2-30 R)] which is comparable and often much less than that reported for percutaneous lithotripsy. Recommendations are made for minimizing patient exposure. Scattered radiation levels in the lithotripter room are presented. We have determined that Pb protective apparel is not required during this procedure provided x-ray operation is temporarily halted should personnel be required to lean directly over the tub to attend to the patient. If the walls of the ESWL room are greater than 1.83 m (6 feet) from the tub, shielding in addition to conventional construction is not required.

Exposure and roentgen-area-product in xeromammography and conventional mammography.

X-ray mammography is assuming increasing importance in the early detection of breast cancer. The principal disadvantage to conventional mammography is high patient dose. Xeromammography offers three advantages over conventional mammography: (a) lower patient dose, (b) better image quality and (c) no special mammography tube required. A transmission ionization chamber and thermoluminescent dosimeters were used to measure the roentgen-area-product and the exposure for three view examinations. Average roentgenarea-product values of 6500 and 4200 R-cm2 were observed for conventional mammography and xeromammography respectively. The medial surface of the breast received the highest radiation exposure for both types of exams and this was shown to be 11.5 and 5.1 R respectively. Omission of the axillary view from the examination reduces the patient dose in both types of approx 60 %.

Computer‐assisted quality assurance for radiographic equipment

A quality assurance procedure which includes a computer program has been implemented to facilitate measurement of some of the parameters normally tested on diagnostic radiographic equipment. These include: reproducibility of output, linearity of mA settings, filtration, kVp calibration, timer error, SID indication, light field--x-ray field coincidence and effective focal spot size. The user may omit those sections which are not applicable to his needs. Full use is made of the data reducing the number of field measurements needed.

CT alignment probe for the dose profile insert

One of the most accepted methods of characterizing the dose in computed tomography (CT) is by measuring the dose profile. Thermoluminescent dosimeters (TLDs) arranged in a stack are scanned in a plexiglass phantom. Unfortunately with this system there is no assurance that the scan properly intercepts the stack. Mispositioning will not be apparent until the TLDs are read, entailing at least a 24 h delay before rescanning. We have designed a simple alignment probe that insures that the scan will be centered on the stack to within 1 mm.

Absence of chromosome damage in the newborn infant following x-ray pelvimetry

Abstract The radiation dose during x-ray pelvimetry to 61 patients was estimated, and the cytogenetic response of peripheral lymphocytes was determined in 25 of their newborn babies. Our calculations resulted in an average midline fetal dose of 1,035 and 1,860 mrads for the patients receiving 2 projections and more than 2 projections, respectively. There was no evidence of radiation induced chromosomal damage in the newborn infants following x-ray exposure in utero.

Radiographic workload and use factors for orthopedic facilities.

Observations of technique factors at 9 radiographic installations dedicated to orthopedic radiography have been made. Monthly area radiation measurements with thermoluminescent dosimeters were made at three of these facilities. The results of these observations and measurements suggest that current NCRP recommended assumptions utilized in protective barrier computations result in considerably more shielding than is necessary. We observed an average workload of 224 mA min/wk and a maximum weekly average of 670 mA min/wk. The use factor for the chest wall averaged 5%. That for all other vertical barriers was less than 1%. The average operating potential was 75 kVp. Room radiation measurements confirm the suggestion that at least two of the walls and the control booth barrier in an orthopedic radiographic facility may be considered secondary barriers.