[Radiation exposure to patient and radiologist during transcatheter arterial embolization for hepatocellular carcinoma].

PURPOSE: To evaluate radiation exposure to patients and radiologists during transcatheter arterial embolization(TAE) for hepatocellular carcinoma. MATERIALS AND METHODS: In 39 TAE procedures performed at eight institutes, skin doses were evaluated with thermoluminescence dosimeters at the patient's back(entrance surface) and lower abdomen, and at the radiologist's forehead and abdomen. Real-time dosimeters were also used to evaluate patient skin dose. RESULTS: The patients' mean entrance surface dose was 973 +/- 681 mGy(range, 185 to 3543 mGy) with the mean fluoroscopic time of 21 minutes and 6 digital subtraction angiography(DSA) acquisitions. The dose at the patients' lower abdomen was 0.98 +/- 0.77 mGy. Doses for the radiologists were 0.04 +/- 0.04 mGy at the forehead and 0.15 +/- 0.19 mGy and 0.005 +/- 0.01 mGy at the abdomen over and under the apron, respectively. Fifty-six percent of the patients' skin dose was from DSA and 44% from fluoroscopy. CONCLUSIONS: Patient skin dose may occasionally exceed the dose for transient erythema. Because a patient may have repeated TAEs, skin doses or X-ray conditions should be recorded. The exposed doses of radiologists were considered to be acceptable with proper techniques. Further efforts to reduce radiation should be directed toward both DSA and fluoroscopy.

A depth-dose measuring device using a multichannel scintillating fiber array for electron beam therapy.

The development of a new depth-dose measuring device for electron beam therapy is described. The device employs plastic scintillating fiber detectors inserted in a polymethylmethacrylate (PMMA) phantom in line along an incident electron beam. Output photons from a fiber, the number of which is proportional to the absorbed dose at each depth of the phantom, were converted to an electric signal with a photodiode. Each signal from the photodiode was transmitted to a personal computer through a multichannel analog-digital converter, and was processed to draw a depth-dose curve on the computer display. A depth-dose curve could be obtained in a measuring time of 5 s for each incident electron beam with an energy range between 4 and 21 MeV. The mean electron energies estimated using the curves and the depth-scaling factor for PMMA were consistent with those obtained from conventional depth-dose measurements using an ion chamber and a water phantom. The newly developed system, being simple and not time consuming, could be used routinely for quality assurance purposes in electron beam therapy.

[Helical CT for lung-cancer screening: third report: fundamental study for ultralow-dose CT by application of small tube current and filter].

In order to develop ultra-low-dose helical CT for lung cancer screening, the effect of reduction of the tube current to 20mA and application of a 10mm thick aluminium filter upon radiation dose and image quality was evaluated with a phantom. Exposure dose at the center of a gantry and absorbed dose at the center of an acrylic phantom at 20mA with the filter were 15% and 29% of the dose at 50mA without the filter, respectively. For reduction of absorbed dose, reduction of the tube current was more useful than application of the filter. Image noise at 20mA with the filter was double that at 50mA without the filter. Neither reduction of the tube current nor application of the filter changed full width at half maximum on section sensitivity of the Z-axis. Although reduction of the tube current did not affect the difference in CT values between an acrylic sphere and styroform, application of the filter caused a reduction of 4.5% in the difference in CT values. Neither reduction of the tube current nor application of the filter affected the contrast resolution of the high-contrast phantom; however, that of the low-contrast phantom deteriorated. Although improvement of the filter and evaluation of clinical images are necessary, reduction of the tube current to 20mA and application of the aluminium filter appear to be a promising method for ultra-low-dose helical CT of the lung.

[Fundamental study for lung-cancer screening by helical CT. First report: evaluation of radiation dose and image quality using a phantom].

In a fundamental study on the early detection of lung cancer by helical computed tomography (CT), we evaluated the effect of scanning parameters on radiation dose and image quality using a phantom. The exposure dose at the center of the gantry and the absorbed dose at the center of an acrylic phantom changed linearly in proportion to tube current. On the other hand, as the table feed speed increased, the rate of reduction in these doses became smaller. While the change in CT value of an acrylic sphere in the longitudinal axis, the difference in CT value between an acrylic sphere and styrofoam in the horizontal plane and the CT profile curve of an acrylic sphere in the horizontal plane did not change according to tube current, an increase in table feed speed brought about the degradation of these items. In conclusion, reduction of the tube current in helical scanning is able to reduce radiation dose without causing a significant change in image quality, but an excessive increase in table feed speed does not reduce radiation dose effectively and is associated with degradation in image quality.

Selective fallopian tube catheterisation in female infertility: clinical results and absorbed radiation dose.

Clinical results of fluoroscopic fallopian tube catheterisation and absorbed radiation doses during the procedure were evaluated in 30 infertility patients with unilateral or bilateral tubal obstruction documented on hysterosalpingography. The staged technique consisted of contrast injection through an intrauterine catheter with a vacuum cup device, ostial salpingography with the wedged catheter, and selective salpingography with a coaxial microcatheter. Of 45 fallopian tubes examined, 35 (78%) were demonstrated by the procedure, and at least one tube was newly demonstrated in 26 patients (87%). Six of these patients conceived spontaneously in the follow-up period of 1-11 months. Four pregnancies were intrauterine and 2 were ectopic. This technique provided accurate and detailed information in the diagnosis and treatment of tubal obstruction in infertility patients. The absorbed radiation dose to the ovary in the average standardised procedure was estimated to be 0.9 cGy. Further improvement in the X-ray equipment and technique is required to reduce the radiation dose.

A scintillating fiber beam-energy monitor for electron beam therapy.

A new type of beam-energy monitor is described, which has been developed to check the energies of electron beams from radiotherapy accelerators. The monitor consists of a pair of scintillating fibers and photodiode read-out circuits that measure the energy dependence of electron transmission through a wedge-shaped absorber. A linear energy response and 1% accuracy for energy constancy measurements are attained with the monitor. The monitor having advantages of simple mechanical and electronic constructions, small size, and low cost is suitable for practical use as a portable device.

Thyroidal 125I monitoring system using an NaI (Tl) survey meter.

This paper describes the counting efficiency and detection limit of a thyroidal 125I monitoring system. Two systems were used: (1) M1 was composed simply of one survey meter for 125I (SM) having an NaI (Tl) crystal of 5.08-cm diameter by 5-mm thick, and (2) M2 was composed of the SM having an output terminal for spectroscopy and a multichannel pulse height analyzer. The counting efficiency was determined by using four simulated thyroids of 17, 20.5, 31, and 40 mL containing 125I solution. The simulated thyroids were embedded in an anthropomorphic neck phantom. The counting efficiency between 0 degrees and 45 degrees to the normal of the thyroid (front of the neck) changed by +/-2%. The efficiency of M1 ranged from 1.8 to 7.9% as the distance between the probe and the neck increased from 0 to 5 cm. Similarly, the efficiency of M2 ranged from 2.2 to 8.3%. The detection limit ranged from 7 to 34 Bq for M1 and from 1 to 5.1 Bq for M2. The M2 system was applied to monitoring a worker performing iodination with 74 MBq Na 125I. Both monitoring systems provided the necessary sensitivity to detect thyroidal 125I within the uncertainty of +/-10%.

[Thyroidal 125I monitoring system using a survey meter for 125I].

This paper describes the counting efficiency and detection limit of a thyroidal 125I monitoring system. Two systems were used: (1) M1 was composed of only a survey meter for 125I (SM) having a NaI(T1) crystal of 2 in phi X 5 mmt and (2) M2 was composed of the SM having an output terminal for spectroscopy and a multichannel pulse height analyzer. The counting efficiency was determined by using an anthropomorphic neck phantom embedded four simulated thyroids of 17, 20.5, 31 and 40 ml including 125I solution. The counting efficiency between 0 degrees and 45 degrees to the direction from the center of the thyroid to the front of the neck coincided within -4%. The efficiency of M1 ranged from 7.9 to 1.8% as the distance between the probe and the neck increased from 0 to 5 cm. Similarly the efficiency of M2 ranged from 8.3 to 2.2%. The detection limit of M1 ranged from 7 to 34 Bq, and the limit of M2 ranged from 1 to 5.1 Bq. M2 system was applied to monitoring a worker performing iodination with Na125I of 74 MBq. Both monitoring systems proved to sensitively detect thyroidal 125I within the uncertainty +/- 10%.

Alignment of x-ray tube focal spots for spectral measurement.

A general method to align a diagnostic x-ray machine for x-ray spectrum measurement purpose was theoretically and experimentally investigated by means of the optical alignment of focal pinhole images. Focal pinhole images were obtained by using a multi-pinholed lead plate. the vertical plane, including the central axis and tube axis, was decided upon by observing the symmetry of focal images. the central axis was designated as a line through the center of focus parallel to the target surface lying in the vertical plane. A method to determine the manipulation of the central axis in any direction is presented.

Direct serial magnification angiography applied to cerebral aneurysms.

High-resolution radiographic images may be obtained by using direct serial 4X angiographic magnification with a microfocus 0.05-mm x-ray tube. This technique provides more highly detailed views of cerebral aneurysms than does normal angiography, while lowering the total radiation dosage.