Stewart C. Bushong

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.

Single‐step calculation of the MTF from the ERF

A method is presented whereby the modulation transfer function can be calculated directly from the edge response function without having to find the line spread function as an intermediate step.

Effect of nuclear magnetic resonance on chromosomes of mouse bone marrow cells

Three groups of six male Balb/c mice, subjected to 30 MHz continuous wave NMR exposure in a static magnetic field of 7.05 K Gauss for one hour, were each compared to another group of ten unexposed mice with respect to chromatid and chromosomal aberrations. The exposed groups were sacrificed at two hours, 24 hours and 48 hours following NMR exposure respectively. Control mice were sacrificed 24 hours after sham-exposure. All groups had approximately 0.02 apparent aberrations per cell. These apparent aberrations were in the form of metacentric chromosomes, possibly resulting from a union of chromosomes at their centromeres or possibly simply chromosomes in association. The results are consistent with earlier in vitro findings that NMR exposure causes no adverse cytogenetic effects.

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.

Gonadal dose in male radiotherapy patients.

Abstract Lithium fluoride thermoluminescent dosimeters were used to measure the gonadal dose in male patients undergoing radiotherapy on a 2-MV Van de Graaff accelerator. The patients were selected from two treatment groups, and the gonadal dose was measured and expressed as a function of the tumor dose. The gonadal dose was 0.0112 and 0.045% of the tumor dose for radiation therapy to the head and thorax, respectively. Phantom measurements showed that most of the radiation reaching the gonads was transmitted axially through the body, and therefore it is not possible to reduce this dose measurably with simple shielding.

Radiocytogenetic Determination of the Oxygen Enhancement Ratio of Californium 252

Abstract Californium 252 was studied as a possible replacement for radium 226 in radiation therapy. Irradiation of Chinese hamster cells with 252Cf produced an aerobic and anaerobic aberration frequency of 0.0135 and 0.0077 single-hit chromosome aberrations per cell per rad, respectively. The oxygen enhancement ratio was 1.75. This study suggests that 252Cf may be more effective than 226Ra in the treatment of malignant disease.

The Relative Biological Effectiveness of Californium 252 on Acute Mammalian Lethality

The relative biological effectiveness of 252Cf was compared with radium on the basis of lethality over a 30-day period. Mice were irradiated with 252Cf, radium, and 60Co. Probit analysis of the number of deaths showed an LD50∕30 of 537 rads for 252Cf, 1,286 rads for 240 mg radium, 1,609 rads for 120 mg radium, and 663 rads following high-dose 60Co. The RBE estimate for 252Cf compared to radium over a comparable time interval is 3.01. These findings are consistent with other recently reported RBE values. The 60Co values were not compared due to differences in dose distribution and dose-rate.

Computer assisted MTF determination in CT.

A series of computer programs have been written to analyze a scan of the AAPM CT performance phantom resolution insert with little operator assistance. A representative analysis is done on a scan from an AS&E scanner as an example. Its point spread function, edge response function and modulation transfer function are presented.

Analysis of errors in spectral reconstruction with a Laplace transform pair model

The sensitivity of a Laplace transform pair model for spectral reconstruction to random errors in attenuation measurements has been investigated. No spectral deformation or significant alteration resulted from the simulated attenuation errors. It is concluded that the range of spectral uncertainties to be expected from the application of this model is acceptable for most scientific applications.

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.