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Biomedical subjects

E C McCullough

Publications and source records attributed to E C McCullough.

At least 19 recordsLinked to original sources
PubMed1995

Intraoperative electron beam radiation therapy: technique, dosimetry, and dose specification: report of task force 48 of the Radiation Therapy Committee, American Association of Physicists in Medicine.

Intraoperative radiation therapy (IORT) is a treatment modality whereby a large single dose of radiation is delivered to a surgically open, exposed cancer site. Typically, a beam of megavoltage electrons is directed at an exposed tumor or tumor bed through a specially designed applicator system. In the last few years, IORT facilities have proliferated around the world. The IORT technique and the applicator systems used at these facilities vary greatly in sophistication and design philosophy. The IORT beam characteristics vary for different designs of applicator systems. It is necessary to document the existing techniques of IORT, to detail the dosimetry data required for accurate delivery of the prescribed dose, and to have a uniform method of dose specification for cooperative clinical trials. The specific charge to the task group includes the following: (a) identify the multidisciplinary IORT team, (b) outline special considerations that must be addressed by an IORT program, (c) review currently available IORT techniques, (d) describe dosimetric measurements necessary for accurate delivery of prescribed dose, (e) describe dosimetric measurements necessary in documenting doses to the surrounding normal tissues, (f) recommend quality assurance procedures for IORT, (g) review methods of treatment documentation and verification, and (h) recommend methods of dose specification and recording for cooperative clinical trials.

Combined Modality Therapy↗
PubMed1990

Selection of techniques for orthovoltage radiation therapy.

Selection of appropriate orthovoltage radiation techniques (peak kilovoltage plus total filtration) may be based on the following factors: (a) central axis percent depth dose, (b) exposure rate, (c) sensitivity of backscatter factor to size of a blocked field, (d) differential bone energy absorption, (e) penumbra characteristics, and (f) field uniformity. An analysis of these factors as a function of beam quality (i.e. half-value layer) has been performed and a recommendation of a minimal number of techniques (consistent with widely available techniques) is presented.

Humans↗
PubMed1990

A needed modification to vendor supplied oversized 45 degree wedges.

A recent change in the source-to-blocking tray distance on at least one new linear accelerator restricts simultaneous use of the vendor supplied oversized (i.e., 20 cm) 45 degree wedge and 7.5 cm or higher custom cerrobend blocks. Truncating the "heel" end of the vendor supplied steel wedge as well as substituting a 45 degree lead wedge (designed and supplied by the vendor) allows simultaneous wedge and 7.5 cm high block usage. Central axis depth dose, transverse dose profile, wedge transmission factor, and surface dose measurements were made for each wedge for 6 through 18 MV x-rays. Dosimetric data for the truncated steel wedge is insignificantly different from that of the untruncated steel wedge, whereas the lead substitute wedge dosimetric data is substantially different and requires remeasurement.

Humans↗
PubMed1988

Evaluation of several film/screen combinations for megavoltage radiation therapy treatment field verification.

The introduction of a lower cost alternative to a film commonly used for megavoltage radiation therapy port films led to a comparison of two films (Kodak X-TL and X-OMAT G) in four metal screen cassette configurations. In addition to determination of H-D curves and point spread functions, images of humanoid phantom sections were obtained and evaluated for clinical "usefulness." The X-OMAT G film-screen combinations compared favorably with the X-TL film combinations with respect to the H-D Curves and point spread functions but there was a slight preference for X-TL film. There were no differences noted whether the film was used in the standard "ready pack" or naked in the cassettes.

Evaluation Studies as Topic↗
PubMed1987

Matching intraoperative electron-beam fields: dosimetric and clinical considerations.

In the setting of a large or irregularly shaped tumor, adjacent or intentionally overlapped intraoperative electron fields may be required to give adequate coverage of the intraoperative target volume. The matching of such intraoperative electron fields present special dosimetric problems because of the divergence of electron isodose curves with depth. In the intraoperative setting, where large, single-fraction doses are delivered, the low- and high dose areas which result from gaps or overlaps between the diverging isodose curves of electron fields matched at depth or the surface may translate into decreased local tumor control or excessive normal tissue toxicity. This study examines the dosimetry of gapped, adjacent, and overlapped 8 X 9 cm2 rectangular intraoperative fields, for 9 to 18 MeV electrons, using film densitometry. "Ideal" methods of matching rectangular intraoperative electron fields are presented, and include: 1) a 2-mm gap plus surface bolus for adjacent fields, and 2) placing a tenth-value layer shaped lead cutout in the overlap region for intentionally overlapped fields.

Combined Modality Therapy↗
PubMed1983

CT-number variability in thoracic geometry.

The use of absolute CT numbers for in vivo tissue characterization is compromised by a number of technical and geometrical factors. A phantom simulating thoracic geometry and containing intrapulmonary "features" was scanned on three CT scanners allowing for assessment of CT-number variations with a wide number of scanning and geometric parameters. It was found that, with thoracic geometry, the absolute CT numbers of intrapulmonary features (e.g., solitary pulmonary nodules) can vary significantly due to a number of CT scanning parameters, such as geometry, CT scanner used, and/or time. Such variations must be taken into account when establishing criteria for characterizing tissue types using CT numbers. However, results show that variations in quantitative behavior with reasonable changes in patient geometry do not preclude meaningful characterization of solitary lung nodules (using CT-number averages) using CT scans for the three CT scanners studied, providing CT-number threshold data are derived from the same model scanner and operating conditions. The use of CT-number patterns within high-density intrapulmonary pathology (e.g., solitary pulmonary nodules) is compromised by the fact that high CT-number patterns were found to be a function of the reconstruction filter used and object size as well as being influenced by details of the surrounding medium.

Humans↗
PubMed1982

A measurement of doses to the neck for mantle field treatment of lymphomas with cobalt-60, 4-, and 10-MV photon beams.

Dose distributions within the neck, resulting from equally weighted, parallel, opposed mantle fields, were measured using thermoluminescence dosimetry in using thermoluminescence dosimetry in an anthropomorphic phantom. Results show the similarity and adequacy of the neck dose distribution using photon beams from cobalt 60, a 4-MV linear accelerator with an external filter, and a 10-MV linear accelerator. For equal mid-plane doses, the 4-MV beam without external flattening resulted in superficial dose rates to the lateral neck approximately 10%-15% higher than the other three beams studied.

Cobalt Radioisotopes↗
PubMed1982

The unreliability of CT numbers as absolute values.

The use of CT numbers as absolute values was examined by scanning a standard phantom on five CT scanners under a variety of conditions simulating those encountered in routine body CT scanning. The results show that: (1) There are significant differences in absolute CT numbers between most scanners (only one scanner produced CT numbers that were equal to zero for water); (2) There are significant differences in absolute CT numbers between two scanners of the same manufacturer and model that were examined; (3) There is a significant difference in CT numbers in a single phantom scan, dependent on location in the scan, and the format of this variability is not constant from one scanner to another; and (4) There may be a significant difference in absolute CT numbers depending on various physical factors (e.g., kilovoltage, phantom orientation in scan aperture, and position of the phantom in the scan aperture). The findings suggest that there is a wide range of CT numbers observed for a given tissue type as a result of scanner performance alone, and that if absolute CT numbers are to be used for diagnosis the user must document that these machine-related variations are less than the differences thought to be significant.

Technology, Radiologic↗
PubMed1982

Nuclear magnetic resonance imaging.

Nuclear magnetic resonance scanning provides the potential for measurement of new properties of tissue which may permit better pathologic differentiation. NMR will be less affected by bone, and so neurologic studies in which bone artifacts are a problem in CT may be facilitated. Direct sagittal and coronal imaging are possible. As far as we know, the biologic hazards are expected to be minimal but cannot be definitely ruled out at this time. At present, the relaxation times that are most frequently measured are such that clinically acceptable spatial resolution (2 to 3mm) requires scan times on the order of two minutes or more. Whether chemical cross-sections that are acceptable to clinical demands can be obtained remains to be demonstrated.

Electromagnetic Fields↗
PubMed1981

Fact or artifact: an analysis of artifact in high-resolution computed tomographic scanning of the sella.

Computed tomography (CT) artifacts within the sella turcica, associated with the bones of the skull base, were identified and examined by use of a human skull phantom immersed in water. These artifacts were identified in 63% of 27 clinical high-resolution CT scans performed on patients with suspected sellar or parasellar pathology. Intrasellar artifacts may be minimized or eliminated by careful choice of scanning plane. Identification and elimination of intrasellar CT artifacts are necessary for accurate interpretation of sellar image.

Adult↗
PubMed1981

Dynamic sequential scanning with table incrementation.

Dynamic sequential scanning with table incrementation is a method of rapid computed tomographic head scanning in which a complete 10-section scan can be made in 2 minutes 40 seconds or less. Although some measurable and visible loss of low-contrast resolution occurs, there is no loss of high-contrast resolution. Monthly throughput of patients has been increased by about 30% since this technique was instituted.

Brain↗
PubMed1979

The selection, acceptance testing, and quality control of radiotherapy treatment simulators.

The critical aspects of selection, acceptance testing, and quality control of a radiotherapy treatment simulator are discussed. The selection of a simulator involves consideration of: (a) motions and readouts, (b) safety features, (c) x-ray and imaging systems, and (d) mechanical tolerances (including guarantees). When considering motions, it is important to ascertain the extent of each motion, motorization and speed, control location, and the location accuracy, and type of scale. Important questions in x-ray system selection concern (a) x-ray generator ratings and phase, and (b) details of the x-ray tube and image intensification system.

Humans↗
PubMed1979

The Z2.94 "rule".

Explore the source record for details and available documents.

Biophysical Phenomena↗