Rotational X-ray Research Articles

Technical note. Modulation transfer function analysis of a newly revised rotational panoramic machine.

To determine the modulation transfer function (MTF) and noise equivalent passband (NE) values for a newly revised rotational panoramic X-ray machine, the PC-1000 (Panoramic Corp., Fort Wayne, Indiana, USA). Images of a 10 microns test slit were taken at various locations along the X-ray beam projection path using a Lanex Regular/T-Mat G image receptor. Line spread functions were obtained at specific beam paths by scanning slit images with a microdensitometer. MTF values were highest around the central plane of the image layer, with a maximum near the centre of 0.25 at 4 cycles/mm. The NE values near the central plane of image layer were 1.4 cycles/mm. MTF and NE values in the anterior region were low, 0.2 and 1.2, respectively. The width of the image layer was narrower in the anterior and wider in the posterior segments. Rapid decreases in MTF and NE values were found on the X-ray tube side compared with the receptor side of the central plane. Using a spatial frequency of 0.25 MTF the shape of the image layer was coincident with that determined visually. On the basis of the MTF and NE values the image resolution produced by this machine is considered acceptable for panoramic dental radiography.

Total craniofacial photon shell technique for radiotherapy of extensive angiosarcomas of the head

Effective radiotherapy for extensive angiosarcomas of the face and scalp is technically difficult due to the complex shape of the volume at risk, which can consist of the superficial tissues of the entire head. This work reports the details of a rotational X-ray technique used to deliver a large part of the tumour dose. The technique consists of four consecutive 90 degree arcs with changing centre blocks to protect critical midline structures. Multilevel CT based treatment planning is carried out to determine the centre block dimensions and beam weights. As a result the radiation dose is delivered with acceptable uniformity over the entire shell of superficial tissues of the head. The overall treatment combines the rotational fields with large lateral field irradiation and/or local boosts with photons or electrons. Two of three patients treated with this technique had local control of the disease until their deaths at 13 and 18 months. A third patient responded well, with only a small region of stable disease at 9 months.

187.パノラマX線断層装置の品質管理について(第1報) : QCキットの試作について

187.パノラマX線断層装置の品質管理について(第1報) : QCキットの試作について

Growth and Characterization of a New Double Sulfate, AgNH 4SO 4

The double sulfate compound, silver ammonium sulfate (AgNH 4SO 4) has been synthesized and characterized. Powder X-ray diffraction has shown it as a monoclinic system with unit cell dimensions a = 6.49(4), b = 8.47(2), c = 8.71(2) Å and β = 91.913°. A single crystal rotational X-ray photograph also gave the same unit cell dimensions. The infrared spectra exhibit typical NH + 4 and SO 2- 4 vibrational modes. Thermal study using differential scanning calorimetry has shown the existence of a phase transition at 79°C followed by another thermal anomaly at 211°C. The AgNH 4SO 4 crystals also exhibit aging effects, transforming after long storage into Ag 2SO 4. Results are discussed in detail.

Rotational soft x-ray tomography of noncircular tokamak plasmas

A rotational tomography technique for noncircular tokamak plasmas has been developed. Using a linear transformation from an elliptic coordinate system to the circular one, and compensating for the Shafranov shift, the elliptic plasma shape is transformed to the concentric circular shape. Fitting the data of a quarter rotation to the Fourier–Bessel expansions, the tomography is performed. This technique is applied to the snake oscillation, to the slow sawtooth crash, and to the post-cursor oscillations of noncircular plasmas on JET.

Image-centred frame of reference in rotational film-based X-ray tomography

Image-centred frame of reference in rotational film-based X-ray tomography

Evaluation of performance of a film-based X-ray tomographic system

The performance of a home-made tomographic system for film-based rotational X-ray tomography is evaluated by comparison of calculated intensity profiles to measured film density profiles within tomograms of aluminium test objects with small implemented defects. The calculated intensity profiles have been obtained using the back-projection and summation method, calculating the linear absorption coefficient by integrating over the entire energy spectrum of the applied microfocus X-ray set. It is shown that the logarithmic response of the X-ray film must be taken into account when relating intensity profiles to film-density units. The resulting calculated film density profiles nicely fits the actually measured profiles, indicating a low total unsharpness. It is concluded that the method is capable of resolving voids down to about 25 µm. However, due to the inherent blurring of the method, image processing techniques must be applied.

The role of electron scattering in the X-ray rotational light curves of Intermediate Polars

The role of electron scattering in explaining the high-energy rotational X-ray modulation of Intermediate Polar binaries is investigated within the framework of the accretion curtain model for such systems. The accreting fractional area at the surface of the white dwarf is shown to be ≲ 1 per cent for a wide range of geometric parameters. This is used, in illustrative calculations, to demonstrate that, for typical accretion rates in Intermediate Polars, provided hydrogen and helium are ionized near the white dwarf, electron scattering can produce high-energy ( > 6 keV) modulation amplitudes similar ( ≳ 10 per cent) to those observed. However, sufficiently large scattering optical depths are only obtained for restricted viewing directions and then the line of sight passes through dense, probably cool, material further from the white dwarf: simple estimates show that the optical depth to photoelectric absorption along these directions is likely to be ≳ 5 at X-ray minimum, compared to an assumed unabsorbed view at X-ray maximum. A simple interpretation of this result is that, when the viewing angle is such that a significant high-energy modulation due to scattering is observed, the low-energy flux should be essentially extinguished at X-ray minimum, resulting in 100 per cent modulated, perhaps flat-bottomed low-energy rotational light curves. Such light curves are not, in general, observed amongst the IPs, despite the fact that the column densities measured from their X-ray spectra are consistent with those derived here. We consider the implications and how the assumptions behind the model might be modified to explain the observations.

Image-centred frame of reference in rotational film-based X-ray tomography

A simplified method of tomographic modelling in rotational film-based X-ray tomography (RFBT) is presented and its ability to generate tomographs of any planar or curved surface within the object is demonstrated.

Image-centred frame of reference in rotational film-based X-ray tomography

Image-centred frame of reference in rotational film-based X-ray tomography

Effects of Finite Angular Steps and Extent of Profile Data on the Calculation of Rotational X-Ray Dose Distributions: Medical Physics, Volum 14, No. 6, November/December 1987, 1053–1055

Computer algorithms for rotational therapy beams, in most cases, perform dose calculations by summing stored fixed beam data at finite angular steps. Such an algorithm, based on the Bentley beam model, was evaluated by comparing calculations with measured data for an 18‐MV x‐ray beam. Measurements were made in a specially constructed cylindrical water phantom of 15‐cm radius using a 0.1‐cm3ionization chamber for an arc of 180° and for a field size of 7.2×7.2 cm2 at 100‐cm source–axis distance. This study revealed that the Bentley beam model, with fixed beams summed every 10°, predicts the dose in the treatment volume, centered about the isocenter, with an accuracy of approximately 2%. However, dose at depths between the phantom surface and the treatment volume could be underestimated by as much as 10% (3% of isocenter). This was shown to be partially due to the truncated tails of the off‐axis profiles in the Bentley model, which extend only 8 mm outside the edge of the radiation field, and the large angular increment of integration (10°). Using beam profiles extending to 4 cm outside the edge of the radiation field and angular steps of 5° or less for summation of fixed beams reduced errors to less than 5%. Therefore, extended beam profiles and smaller angular steps for summing fixed beams are recommended for photon rotation calculation when increased accuracy is required.

The central plane of the image layer determined experimentally in various rotational panoramic x-ray machines

The location of the image layer with respect to how a patient is positioned in a rotational panoramic machine is very critical. At present, no simple method exists for routine testing of panoramic machines to verify that the image layer is where the manufacturer intended it to be. The purpose of this experiment was to locate the central plane of the image layer with respect to a reference point on various machines currently on the market. The data obtained from this study can be used for further evaluations of the consistency in the location of the image layer, first with the existing device and later with a test device that would be adaptable to these machines and serve as a quality-control device in assuring that the machines are functioning properly.

X-ray emission from cataclysmic variables

EXOSAT results on cataclysmic variables are reviewed. The long continuous X-ray observations afforded by this observatory, coupled with the sensitivity of its instruments to medium energy and very low energy X-rays, have enabled the rotational and orbital X-ray light curves of these stars to be measured in unprecedented detail. Examples are given of data on synchronously and asynchronously rotating magnetic systems, and on disc accreting stars. The impact of the new observations on our understanding of cataclysmic variables is discussed.

Method for measuring cardiac dimensions and intramural deformations

Information about the geometry and intramural deformations of the left vertricle of the heart throughout the cardiac cycle is necessary for the analysis of contractile function of the intact heart. In this study a method is developed to measure dimensions and intramural deformations of the left ventricle of a dog heart during the cardiac cycle. Radiopaque markers (platinum spheres of 1mm diameter) were implanted in the wall of the left ventricle. The spatial positions of these markers were determined from pairs of perpendicular X-ray projections, obtained with the aid of rotational X-ray equipment. Preliminary results of venticular deformations are in agreement with measurements by other techniques.

Development of a computed tomographic scanner for radiation therapy treatment planning.

The authors describe a low-cost CT scanner integrated with a radiotherapy simulator and designed for treatment planning. The standard rotational gantry and x-ray tube of the simulator are used with a multiwire xenon lonization chamber and simple current-proportional readout system to measure patient attenuation, avoiding problems associated with diagnostic CT scanners in treatment planning. Although design constraints limit performance, software compensation techniques have reduced artifacts and given satisfactory images.

Rotational x-ray therapy planned to complement radium treatment of carcinoma of the cervix uteri.

A method of treatment of carcinoma of the cervix uteri has been described. It consists of a combined course of radium and are therapy. Only the central part of the pelvic cavity receives an adequate dose from the radium treatment and the moving X-ray fields are designed to build up the dose received by the lateral parts of the pelvis to about 4500 r (X). Details are given of how the treatment is planned and carried out. Two anterior and two posterior moving fields are used. The length of the field is generally 14·4 cm while the width of the field varies from 3·6 to 6 cm depending on the displacement of the uterus and the size of the pelvis. For each patient the dose from are therapy is calculated for six points of importance. The dose thus calculated at point B is added to that received from the radium therapy and used as a control of the lateral pelvic dose to be given by are therapy. Measurements on a model have confirmed the validity of the dose calculations. The method demands accuracy and patience in setting-up. The results so far obtained are gratifying.

Immobilization of the head during rotational x-ray therapy.

THE IMPORTANCE of maintaining a tumor in a fixed position during rotation th erapy after accurate beam local ization is well recognized. With tumors of the trunk this is ordinarily accomplished without difficulty, bu t with th e equipment currently available for treatment of tumors of th e head and neck, the problem is less simple. The usual rotation apparatus is provided with two flat wooden piece s to maintain th e position of the head during treatment. These slats, somet imes reinforced with straps, are placed one on each side of the face. While th ese are suitable for keeping the head from swaying from side to side, th ey do not prevent its flexion on the ches t. The disastrous result of such an unintentional change of position, especially where an x-ray beam of small dimensions is used, is readily apparent. This deficiency of equipment can be obviated by th e use of a head-holder which maintain s th e head in a fixed position by mean s of a chin rest and a vert ex support (Figs. I and 2). The chin rest consists of a small Lucite cup attached to an adjust abl e horizontal rod, which in turn is connected to a vertical rod supported on a metal block. Both rods are capable of movement to permit adjustment of th e chin cup verticallyand/ or horizontally. The size and shape of the cup can be modified on an individual basis to fit a particular face and give additional support where necessary. The metal block can be slid along a metal bar fixed to the underarm supports . The chin rest can thus be properly centered in the coronal plane. This metal bar is attached to one of th e underarm supports by a hinge and is locked to th e other by a bolt and nut through a groove. The underarm supports can be adjusted by sliding them along the grooves in the metal bars, thus facilitating the centering of the patient. There are several methods for constructing a suitable vertex support. In the devic e described here a head rest from a dental chair was adapte d for attachment to th e upright pole of the rotation apparatu s. A head pad was employed to apply pressure against the vertex to hold the head in a fixed position. Figure 3 illustrates th e use of th e head -holder in two different positions (neutral and forward flexion ), indicating the way the head might be placed during rotation. Although the co-operation of the patient is still essential, the possibility of the tumor moving “off-cent er” is ext remely remote with this device . This headholder has been of material assistance where physical weakness or postural unsteadiness might otherwise make the patient unsuitable for rotation therapy. Another advantage of the head-holder is the small amount of foreign material used about the head, giving the radiation therapist a wider latitude in adjusting the head to a desired plane of rotation. Summary A head-immobilizing device for rotational x-ray therapy is described.

回転照射中の頭部の固定

回転照射中の頭部の固定

Rotation therapy technic applicable to standard deep-x-ray machines.

Rotational x-ray therapy permits the delivery of a large tissue dose of radiation to a deep-seated tumor, with relatively small doses to adjacent structures and to the skin. This method of treatment may be considered an extreme utilization of the technic of cross-firing, since by rotation of the patient relative to the x-ray beam there are an infinite number of portals of entry. Since Pohl (5) first suggested rotational therapy in 1906, many radiologists have recognized its advantages. In recent years de Rochemont (6), J. Nielsen (4), Hawley (3), Hare and Trump (2), and Greene (1) have applied the basic method, usually with a particular refinement in equipment or technic. This report sets forth some experiences in the use of a standard deep-therapy machine in conjunction with a unit which rotates the patient in his vertical axis. Rotational therapy with x-rays of any quality has been shown to have advantages over the use of multiple fixed ports in the treatment of deep-seated lesions. The ratio of tumor dose to skin dose becomes increasingly favorable as the half-value layer increases. Futhermore, radiations of higher energies provide a more homogeneous dosage distribution in any plane perpendicular to the central ray. This can be seen by examination of isodose curves; at higher energies, the curves are flatter. It is, however, practicable to employ x-rays generated at 200–250 kv. The half-value layer of the beam utilized in the work to be reported is 1.5 mm. of copper. Selection of Target-to-Axis-of-Rotation Distance: For any quality of radiation, the target-axis distance will have to be short enough to give a reasonable dosage rate, but as long as possible for better depth dose distribution. Most of the European work appears to have been done with x-rays generated at 180–200 kv., half-value layer 1.0 mm. of copper, and target-axis distance 50 cm. Although improvement is slight with increased distance, a target-axis distance of 85 cm., which is practicable with the 250-kv. equipment, does afford better depth dose distribution. Since the cross section of the human body is not circular, the target-skin distance varies constantly, but with a target-axis distance of 85 cm. the target-skin distance is seldom less than 65 cm. Applicability of Conventional Isodose Charts to Determination of Dose in Rotation Therapy with Radiation of Half-Value Layer 1.5 mm. Copper: Figure 1 shows a centrally located tumor 10 cm. in diameter, lying in the isodose chart for a 10 × 15 cm. field at 70 cm. target-skin distance, half-value layer 1.5 mm. copper. As the body turns on an axis at A, the tumor will always be completely within a region defined by WXYZ, which can be called the “effective beam.” All other parts of the body are sometimes in this beam and sometimes outside it. It is not, however, self-evident that doses throughout the tumor are uniform. Part of the mass is always at the center of the beam, and parts are near the edge.