Hisashi Maekoshi

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.

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 intraurine 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 perod of 1–11 months. Four pregnancies were intraurine 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.

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.

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%.

Radiation levels of macroradiography. Radiation exposure and image quality.

Macroradiography via 4 to 6 times magnification of a test chart in water phantoms of various thicknesses, using an x-ray tube with 50μ focal spot, is described. Its MTF improves when water depth is reduced. Long exposure of a moving organ in a thick water phantom reduces its image quality. For macroradiography of the human body, the skin dose can be limited to less than 1 rad. Appropriate beam limitation as well as shortening of the focus-film distance, use of the fastest film-screen combination and high-voltage technique are recommended. Clinical macroradiography is described in detail.

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.