A survey of radiation oncologists regarding their radiation physics instruction.

The American Association of Physicists in Medicine, Committee on Training of Radiologists conducted a survey of radiation oncologists requesting information regarding their radiation oncology physics training. General questions were asked of the oncologist regarding their radiation oncology practice such as number of oncologists, number of new patients treated, and the size and type of facility in which the practice is located. The oncologist also responded to questions regarding their educational background. The survey requested the radiation oncologists to answer questions regarding the adequacy and importance of their training in specific areas of radiation physics. The responders indicated that the importance of most physics topics in their clinical practice corresponded to the level of their understanding. The survey indicated that for most radiation oncologists their physics instruction was an important and interesting part of their residency program.

A scanning-slit x-ray videoabsorptiometric technique for bone mineral measurement.

An x-ray videoabsorptiometric technique was developed for measurement of bone mineral content (BMC) in vivo. The principle utility of this technique is the precise measurement of commonly fractured bones, such as the femoral neck, that are difficult to measure by other techniques because of repositioning problems. Scanning slits reduce scattered radiation and improve linearity of measurements. Heavily filtered, high-kVp beams are used to minimize errors from beam hardening, and data renormalization is employed to compensate for spatial nonuniformities of the beam and detector. Linearity of measured BMC over the range 0.8 to 5 g/cm2 is very good (r = 0.998) and compares well to single- and dual-photon absorptiometry. A 1.6% change in measured BMC is observed for a 10% change (approximately 2 cm) in tissue thickness while a 10% change in marrow type causes a 0.6%-0.8% change in BMC. Manual repositioning of a femur phantom revealed a variation of 0.84% over ten measurements when femur values were referenced to standards. A computer repositioning algorithm provides much easier identification of the region for analysis and yields comparable variation (0.9%).

Resonance by rod-shaped reflectors in ultrasound test objects.

Rod-shaped reflectors such as those used in the AIUM test object resonate at medical ultrasound frequencies, producing artifacts posterior to the reflector. Rods of various diameters and materials were examined to determine their resonant properties, and the effect of the Plexiglas scanning surface of the enclosure on image quality was studied. A theory predicting the resonant frequencies of rods is proposed, and methods of eliminating resonance artifacts are discussed.

Transducer beam pattern test object.

A new test object has been developed that generates images of transducer beam patterns on B-mode hardcopy. The extent and depth of the transducer focal zone are measured from these images. The predictions made from test object images were verified in the clinical images obtained from two 3.5-MHz focused transducers. Using the test object images, we have found that we can make a more rational selection of transducer for each clinical situation.