Biomedical subjects
Publications and source records attributed to C W Coffey.
Software packages for a programmable pocket calculator have been developed for use in dosimetry. Using a field equation and a mathematical model of the beam profile, one can find the dose delivered to any point within the irradiated volume. Use of these programs for simple field calculations allows the radiologist to concentrate on more complex treatment plans.
An alternative to the Clarkson technique for calculating total scattered radiation is presented. Resultant TAR values are compared with those obtained by the Clarkson technique for the same field. The new scatter technique is always more than 2.8 times faster than the Clarkson technique and more than 4 times faster on a large number of fields. The new approach appears to offer a simple and expedient alternative to the more traditional methods for iiregular field dose calculations.
Beam characteristics and dosimetry measurements of the 6 MV x-ray beam from a Varian Associates Clinac 6-100 linear accelerator are presented. Percentage depth dose tables are given as a function of field size for square fields. Tissue-maximum ratios and scatter-maximum ratios are tabulated as a function of depth and field size. Investigation of surface dose and depth of maximum dose reveal a dependence on field size. Other beam parameters measured are presented include field flatness, symmetry, SSD dependence, and penumbra. Treatment planning parameters including field size output factors and wedge factors are discussed.
An alternative to the Clarkson technique for calculating total scattered radiation is presented for use with 10 MV photon beams. When compared to the same field size and depth parameters, the resultant TMR values are in good agreement with results utilizing the Clarkson technique. Lengthy iterative procedures are avoided in this new scatter technique in favor of a more efficient SMR algorithm, thereby reducing the amount of required computation time. The speed and simplicity of this method make it especially amenable to use with small desk top computers and even programmable pocket calculators.
This investigation presents the design and fabrication of a magnetic resonance imaging (MRI) test phantom for determining slice thickness, slice adjacency, slice offset, and slice angulation. This test phantom is a three-dimensional conic section of MRI image producing material; proper orientation allows analysis in each of the major imaging planes. The phantom design (geometrical configuration) incorporates both theoretical and quantitative methodologies. The necessary mathematical analyses are both simple and rapid. In addition, this phantom has been successfully used to assess the image slice parameters for computed tomography (CT) scanners and single photon emission computed tomography (SPECT) imaging systems. Slice profile parameter results, full width at half maximum (FWHM), from this phantom design are compared with conventional methods.
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We present a patient with unresectable bronchogenic carcinoma who underwent irradiation, then had four consecutive bone imaging studies in a 26-month period. Apparent photopenia of the upper thoracic vertebrae developed within six months after irradiation and became more apparent in the images thereafter. At autopsy a section of the corresponding bone marrow showed extensive fatty changes with very few residual blood vessels. Radiation damage of the vascular networks may significantly reduce the blood supply, when integrity of the blood supply is essential for delivery of a normal bone image by the bone-imaging agent. Interruption of blood supply may cause photopenia, and this interruption plus irradiation to marrow elements may also affect the hematopoietic activity of the corresponding bone marrow. The occurrence of radiation-induced photopenia on a bone-imaging study may indicate fatty changes of the corresponding marrow.
A quality control program for magnetic resonance imaging is necessary to evaluate the major imaging characteristics and to monitor image performance constancy. The methods used to evaluate and monitor imaging quality characteristics and image quality variables are discussed. These imaging characteristics and methods may be utilized by the trained radiology technologist to assist in the continuation of a quality control program for magnetic resonance imaging.