Skin entrance exposure measurements obtained with a dose-area-product meter and thermoluminescent dosimeters were compared at posteroanterior and lateral chest radiography in 52 adult male patients. In a linear regression analysis of data collected in both views, values of 1.23 +/- 0.02 and 1.26 +/- 0.01 (r = .98 and .99) were found for the ratios of thermoluminescent-dosimeter and dose-are-product exposures, respectively. Skin entrance exposures from 16 mR (4.13 microC/kg) to 150 mR (38.7 microC/kg) in the posteroanterior view and 24 mR (6.19 microC/kg) to 475 mR (123 microC/kg) in the lateral view were found. Dose-area-product meters offer a rapid and accurate means to measure skin entrance exposure when the radiography field size is known.

An artifact simulating aortic dissection has been seen in computed tomography (CT) and reported in numerous journals. The purpose of this study is to determine the origin. A phantom was constructed to simulate the motion of the ascending aorta during the cardiac cycle. Technique factors such as scan time, slice thickness, pitch, and reconstruction algorithms were examined for their effect on the simulated dissection appearance. Change in the angle of the simulated aorta with respect to the scanner axis was also studied. CT images displaying the simulated aortic dissection are obtained reproducibly. The amplitude of the artifact is more pronounced for increased scan time. The artifact amplitude is proportional to the displacement of the phantom. The simulated aortic dissection seems to be more pronounced when the scan time is comparable to the cycling time of aortic motion.

Radiation doses to adult male patients from abdominal aortogram and aorta femoral runoff examinations in a medical center were determined with the help of a dose-area product meter. The abdominal aortogram and aorta femoral runoff examination consisted of scout radiographs, fluoroscopy (to position a catheter near the area of interest), and serial films (to record the flow of contrast media). Measurements were converted to effective doses with the help of published results from Monte Carlo simulation calculations. Data from 19 male adult patients weighing 53 to 86 kg were analyzed. The resulting total effective dose had a value of 14.0 +/- 4A mSv (mean and standard deviation). The percent contribution by fluoroscopy was 18.5 +/- 9.9%. The fluoroscopy effective dose had a stronger correlation with the dose-area product (correlation coefficient of 0.97) than with duration of exposure (correlation coefficient of 0.84). Most of the radiation exposure in the observed abdominal aortogram and aorta femoral runoff examination was attributed to radiography.

Purpose: The 6MV X‐band robot mounted linac in a CyberKnife(CK) system is more compact and maneuverable than conventional S‐band linacs. Long term mechanical and radiation output stability of this linac is crucial for the sub‐millimeter accuracy needed for stereotactic radiosurgery (SRS). The versatility of the CK allows for both extracranial and intracranial SRS use. The synchrony system tracks patient breathing thereby enabling precise irradiation of moving tumors. We evaluate the mechanical and radiation stability of the CK and the targeting error of synchrony with respect to variations in simulated anterior‐posterior(AP) motion using a ball‐cube phantom inside which gafchromic film is orthogonally positioned. Methods and Materials: CK output is monitored by a vented chamber unlike a sealed chamber used in conventional linacs. A daily calibration factor(CF) is obtained to correct for the changes in temperature, pressure and output. Absolute output, flatness, symmetry penumbra, End‐to‐End and Iso‐post tests are done monthly to verify the accuracy of the dose distribution and alignment of the X‐ray tube and detectors respectively. A 2D motion platform was fabricated to simulate respiration. The amplitude of motion ranged between 1cm and 3cm, a dose of 3000cGy from a 3 path fiducially tracked plan were given to the phantom at the 62% iso‐dose line The films were analyzed using End‐to‐End software and the total targeting error in the AP direction was determined. Results: Over two years of clinical use the linac output variation decreased steadily from 2% to below 1% while flatness, symmetry, and penumbra were well within CK specifications. The averaged CF was 1.011±0.008MU/cGy, the static targeting error was 0.8 ± 0.047mm and the synchrony targeting error was 1.63±0.056mm. Conclusion: We conclude that the CK mechanical system delivers the required targeting accuracy in both synchrony and static treatments, while the radiation instability is less than 2 %.

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