A method for obtaining body contours using an ultrasonic scanner and transverse tomograms.
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Anthropometry↗
Biomedical subjects
E S Sternick
Publications and source records attributed to E S Sternick.
Treatment planning with a graphics tablet.
A graphics-tablet treatment planning system is described. The cost effectiveness of this approach is especially attractive where time-sharing use of a central computer facility is available.
Computers↗
Comments on "Noninvasive thermometry with a clinical x-ray CT scanner".
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Temperature↗
UV-induced second readout of LiF thermoluminescent dosimeters in the therapeutic dose range.
A previously developed technique for reading out LiF thermoluminescent dosimeters (TLD) a second and subsequent time by means of ultraviolet (UV)-induced repopulation of dosimetry traps was studied to determine the feasibility of maintaining a second readout capability in a radiotherapy clinical setting. It was found that with grouping of the TLDs according to second readout sensitivity, the UV-induced readout attained a precision comparable to that of the initial readout. However, the UV-induced TL response retained a strong previous dose memory following a standard high-temperature anneal, and routine calibration before each reuse is recommended.
Fluorides↗
Thermal energy deposition from a single-loop rf whole-body applicator.
Whole-body hyperthermia at moderate temperatures (40.0 +/- 0.5 degrees C) is currently being investigated to assess its effectiveness as an adjuvant to other cancer therapies. At our institution, the whole-body heating is achieved by a combination of hot air circulation and rf inductive heating at 27.1 MHz. This paper reports the results of a study of the thermal energy deposition pattern associated with the rf applicator. The applicator consists of a single loop of nearly elliptical shape with dimensions 20 x 46 cm. The loop is embedded in a mattress and is fed by lead wires entering the side of the mattress. Temperature mapping in a heated gelatin phantom placed just above the rf loop showed maximum heating near the lead wires and a cool region above the center of the loop. Calculations of the magnetically induced and capacitive contributions to the electric field near the applicator indicate that the heating near the lead wires is largely capacitive in nature. This feature of the rf heating is of interest because capacitive fields result in preferential heating of fatty tissues. Further calculations showed that the capacitive heating contribution falls away much more rapidly than the induced field contribution with increasing distance from the plane of the rf loop.
Diathermy↗
Dosimetry characteristics of large wedges for 4- and 6-MV x rays.
Two sets of newly designed large wedge filters for field sizes up to 20 X 20 cm2 have become commercially available for use with 4- and 6-MV linear accelerators. Such field sizes are sometimes required to ensure adequate coverage in certain treatment techniques. This work reports base line data resulting from an investigation of the dosimetric properties of these wedges. Measurements of wedge angles, transmission factors, and beam hardening effects are described, and comparisons are made with the smaller standard wedges.
Humans↗
Electron contamination due to Lucite in a 45-MV photon beam.
The presence of the Lucite blocking tray in a 45-MV betatron beam leads to a considerable loss in the skin-sparing properties of this unit. Measurements conducted with a parallel-plate chamber show that the surface dose is approximately doubled (up to 58% of the maximum absorbed dose) and the depth of maximum dose is reduced by as much as 1.5 cm by the Lucite. These results suggest that separate dosimetry data should be kept for blocked and unblocked fields. The penetration of the electron contamination to the open field depth of maximum dose can lead to erroneous results if attenuation measurements are made at that depth. Studies of the effect of the lead sheet and leaded acrylic on the surface dose showed that under normal circumstances the presence of high-Z materials increases the surface dose, hence these materials cannot in general be used as electron filters on very high energy x-ray units. A Luciteless blocking tray with universal triangular corner blocks has been designed for use in special cases requiring a reduced surface dose.
Electrons↗
Implications of adopting the AAPM TG-21 calibration protocol for very high energy photon and electron beams.
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Calibration↗
Reduction of the "horns" observed on the beam profiles of a 6-MV linear accelerator.
The presence of large "horns" was found while plotting beam profiles during acceptance testing of a 6-MV linear accelerator. The in-phantom off-axis ratio (OAR), measured at 22 cm off the central axis along the diagonal of a 40 X 40 cm field at dmax was found to be 1.19, while beam uniformity was within specifications at 10-cm depth. A change in the gun injection voltage and the replacement of the magnet surrounding the magnetron with one of greater strength resulted in a reduction of the OAR to 1.085. The beam uniformity at depth was maintained within specifications. An alternative solution of adding a modifying filter in the primary beam was considered undesirable because of the 20%-25% reduction in dose rate caused by such filters. The relationship between the energy, the intensity distribution of the beam, and the magnitude of the horns is discussed, and the beam profiles, isodoses, and central axis depth doses before and after the changes are compared.
Humans↗
Comments on the method of energy determination for electron beams in the TG-21 protocol.
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Electrons↗
A beam-edge modifier for abutting electron fields.
Abutment of unmodified electron fields to irradiate large areas can lead to significant dose inhomogeneities in the region of junction of the fields. In this paper we describe the design and dosimetric characteristics of a device developed to broaden the electron beam penumbra and thereby to improve the dose uniformity in the overlap region. The device is a high-density triangular-toothed comb capable of reducing the beam intensity without seriously degrading the beam energy. The effect of the comb is such that a single device will generate a beam penumbra which is broad and very nearly linear at all depths for all clinically used beam energies. Results are shown for various field configurations and energies. With a gap of 5.0 cm between the treatment cone and phantom surface the dose "ripple" in the region beneath the teeth was found not to exceed +/- 5% at 0.5-cm depth.
Electrons↗
Effective wedge angles for 6-MV wedges.
Measurements were undertaken with 30 degrees and 45 degrees large wedges on a 6-MV linac to determine the effective wedge angle for various combinations of open and wedged fields. The validity of Tatcher's equation, relating effective wedge angle to maximum dose weightings, was examined over a range of field sizes from 5 X 5 to 20 X 20 cm. An alternative equation involving only central axis quantities was also investigated. The results obtained from an analysis of point dose measurements indicate that, for these wedges, either equation yields sufficient accuracy for clinical purposes.
Animals↗
Tumor dose specification of I-125 seed implants.
A new calculation procedure for interstitial implants with I-125 seeds is presented. The total activity of I-125 seeds required to deliver a net minimum dose of 1 Gy is also given as a function of implant volume for various seed spacings. This will permit clinicians to prescribe a specific dose for patients as a primary or boost treatment. Elongation and shape corrections are studied. Discussions and comparisons with other dosimetric calculations such as "matched" peripheral dose, average minimum dose, and minimum peripheral dose are made. The results indicate that for a fixed total activity the net minimum dose is relatively insensitive to variations in seed spacing and individual seed activity.
Brachytherapy↗
Performance characteristics of a helical microwave interstitial antenna for local hyperthermia.
A helical microwave antenna has been designed to improve heat deposition by interstitial applicators used for clinical hyperthermia. Iso-specific-absorption-rate (SAR) curves of the helical antenna as well as a conventional monopole antenna were measured and compared in both muscle and brain tissue phantoms. The heating pattern of the helical antenna is more uniform along the length of the antenna which has important implications for multiarray implant configurations.
Humans↗
A dose homogeneity index for evaluating 192Ir interstitial breast implants.
To evaluate and optimize dose homogeneity of 192Ir interstitial breast implants, we define a quantity, the dose homogeneity index (DHI), as follows: DHI = [V(TDR)--V(HDR)]/V(TDR), where V(TDR) denotes the total treatment volume enclosed by the prescribed treatment dose rate (TDR) and V(HDR) denotes the volume enclosed by high-dose rate (HDR), which is 1.5 X TDR or greater. We have used the DHI to examine and compare 192Ir double-plane implants of various sizes planned by the Memorial system or the Tufts system. Criteria have been suggested for the number of planes required for implants in a given treatment volume. Anderson's volume-dose histogram with inverse square suppression is adopted for illustration.
Brachytherapy↗
Effect of gold shielding on the dosimetry of an 125I seed at close range.
Radioactive 125I plaques with gold shields have been used for the treatment of choroidal melanoma. The effect of the gold shield on the dosimetry of a single 125I seed (model 6711) has been investigated in this paper. Increases in dose at close range due to the presence of the shield are observed. Such enhancement is in agreement with Williamson's Monte Carlo calculations.
Brachytherapy↗
An isodose shift technique for obliquely incident electron beams.
It is well known that when an electron beam is incident obliquely on the surface of a phantom, the depth dose curve measured normal to the surface is shifted toward the surface. Based on geometrical arguments alone, the depth of the nth isodose line for an electron beam incident at an angle theta should be equal to the product of cos theta and the depth of the nth isodose line at normal incidence. This method, however, ignores the effects of scatter and can lead to significant errors in isodose placement for beams at large angles of incidence. A semi-empirical functional relationship and a table of isodose shift factors have been developed with which one may easily calculate the depth of any isodose line for beams at incident angles of 0 degrees to 60 degrees. The isodose shift factors are tabulated in terms of beam energy (6-22 MeV) and isodose line (10%-90%) and are shown to be relatively independent of beam size and incident angle for angles less than 60 degrees. Extensive measurements have been made on a Varian Clinac 2500 linear accelerator with a parallel-plate chamber and polystyrene phantom. The dependence of the chamber response on beam angulation has been checked, and the scaling factor of the polystyrene phantom has been determined to be equal to 1.00.
Electrons↗
Spatial resolution measurements for passive microwave radiometry using a tissue-equivalent phantom.
A tissue-equivalent "hot" line source phantom is described for assessing spatial resolution in passive microwave radiometry systems. LSFs were measured for two rectangular waveguide antennas connected to a 4.7-GHz radiometer. The normalized LSFs and corresponding modulation transfer functions were found to be independent of line source temperature, but dependent upon antenna size, orientation, and line source depth.
Biophysical Phenomena↗