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Biomedical subjects

C W Coffey

Publications and source records attributed to C W Coffey.

At least 19 recordsLinked to original sources
PubMed2001

AAPM protocol for 40-300 kV x-ray beam dosimetry in radiotherapy and radiobiology.

The American Association of Physicists in Medicine (AAPM) presents a new protocol, developed by the Radiation Therapy Committee Task Group 61, for reference dosimetry of low- and medium-energy x rays for radiotherapy and radiobiology (40 kV < or = tube potential < or = 300 kV). It is based on ionization chambers calibrated in air in terms of air kerma. If the point of interest is at or close to the surface, one unified approach over the entire energy range shall be used to determine absorbed dose to water at the surface of a water phantom based on an in-air measurement (the "in-air" method). If the point of interest is at a depth, an in-water measurement at a depth of 2 cm shall be used for tube potentials > or = 100 kV (the "in-phantom" method). The in-phantom method is not recommended for tube potentials < 100 kV. Guidelines are provided to determine the dose at other points in water and the dose at the surface of other biological materials of interest. The protocol is based on an up-to-date data set of basic dosimetry parameters, which produce consistent dose values for the two methods recommended. Estimates of uncertainties on the final dose values are also presented.

Air↗
PubMed1999

Dose model for a beta-emitting stent in a realistic artery consisting of soft tissue and plaque.

A model for the description of the near-field dose deposition from a 32p impregnated stent in an arterial system consisting of soft tissue and dense plaque is presented. The model is based on the scaling property of the dose-point-kernel (DPK) function which is extended to a heterogeneous medium consisting of a series of layers of different materials. It is shown that, for each point source originating from the stent surface, the DPK function for water can be scaled consistently along the path through the different layers of material to predict the dose at a given point in the heterogeneous medium. Radiochromic film dosimetry on actual 32p stents is used to test the new model. The experimental setup consists of a water-equivalent phantom in which a stent is deployed and on which a thin layer of polytetrafluoroethylene (PTFE) is deposited to simulate the presence of plaque. Layers of radiochromic films stacked over the phantom are used to measure the dose at distances varying from approximately 0.1 mm to approximately 3 mm from the stent surface with and without PTFE. It is shown that the proposed new DPK model for a heterogeneous medium agrees very well with the experimental data and that it compares favorably to the usual homogeneous DPK model. These results indicate that the new model can be used with confidence to predict the dose in a realistic artery in the presence of plaque.

Angioplasty, Balloon, Coronary↗
PubMed1999

Radiochromic film dosimetry of a high dose rate beta source for intravascular brachytherapy.

Good clinical physics practice requires that dose rates of brachytherapy sources be checked by the institution using them, as recommended by American Association of Physicists in Medicine Task Group 56 and The American College of Radiology. For intravascular brachytherapy with catheter-based systems, AAPM Task Group 60 recommends that the dose rate be measured at a reference point located at a radial distance of 2 mm from the center of the catheter axis. AAPM Task Group 60 also recommends that the dose rate along the catheter axis at a radial distance of 2 mm should be uniform to within +/- 10% in the center two-thirds of the treated length, and the relative dose rate in the plane perpendicular to the catheter axis through the center of the source should be measured at distances from 0.5 mm to R90 (the distance from a point source within which 90% of the energy is deposited) at intervals of 0.5 mm. Radiochromic film dosimetry has been used to measure the dose distribution in a plane parallel to and at a radial distance of 2 mm from the axis of a novel, catheter-based, beta source for intravascular brachytherapy. The dose rate was averaged along a line parallel to the catheter axis at a radial distance of 2 mm, in the centered 24.5 mm of the treated length. This average dose rate agreed with the dose rate measured with a well ionization chamber by the replacement method using source trains calibrated with an extrapolation chamber at the National Institute of Standards and Technology. All of the dose rates in the centered 24.5 mm of a line parallel to the axis at a distance of 2 mm were within +/-10% of the average.

Beta Particles↗
PubMed1998

Dose distribution for a 32P-impregnated coronary stent: comparison of theoretical calculations and measurements with radiochromic film.

PURPOSE: Restenosis, caused by proliferation of smooth-muscle cells, limits the efficacy of catheter-based revascularization of coronary arteries. Irradiation has been shown to inhibit growth of smooth-muscle cells in vitro and to prevent restenosis in animal models following stent placement. An intraarterial source of 32P, a pure beta emitter with a half-life of 14.28 days and a 90% range in water of 3.6 mm, is almost ideal for irradiating just arterial wall without exposing any other part of the patient's heart or any other organs, while posing minimal hazards to medical personnel. Two types of previously developed coronary stent impregnated with 32P were investigated. This study aimed to calculate and measure the dose outside of two types of 32P-impregnated beta-emitting coronary stents under conditions closely simulating clinical use. METHODS AND MATERIALS: The dose distributions in water surrounding these stents were calculated using a convolution method and measured by exposing radiochromic film in a solid-water phantom. RESULTS: Experimental results were in excellent agreement with theoretical calculations. CONCLUSIONS: Radiochromic dosimetry can be used to measure the dose distribution around a beta-emitting intraarterial stent at distances as small as 0.1 mm from the stent surface. A simple cylindrical shell model is adequate for calculating the dose at points farther than 0.5 mm from the stent surface.

Angioplasty, Balloon, Coronary↗
PubMed1998

Small photon field dosimetry for stereotactic radiosurgery.

Performing and assuring the quality of the planning and delivery of stereotactic radiosurgery with photon beams requires accurate evaluation of beam parameters, usually including output factors, tissue-phantom ratios and off-axis ratios, and measurement of actual dose distributions from simulated treatments. For the small photon fields used in radiosurgery, these measurements require special equipment and techniques, which are described in this review.

Humans↗
PubMed1997

Radiation dose from a phosphorous-32 impregnated wire mesh vascular stent.

The near field dose distribution of a realistic vascular stent impregnated with radioactive 32P is calculated employing the dose-point-kernel (DPK) method in a homogeneous and uniform medium. The cylindrical wire mesh geometry for the Palmaz-Schatz [Palmaz-Schatz is a tradename of Cordis (a Johnson & Johnson company)] stent is incorporated in the model calculation, and the dose distribution generated by the beta particles emitted from the decayed radioactive 32P is computed at distances ranging from 0.1 to 2 mm exterior to the stent surface. Dose measurements were obtained using radiochromic film dosimetry media on an actual Palmaz-Schatz half-stent impregnated with 32P using ion implantation, and compared to the DPK model predictions. The close agreement between the model calculation and the film dosimetry data confirms the validity of the model which can be adapted to a variety of different stent designs.

Angioplasty, Balloon, Coronary↗
PubMed1996

Use of a micro-ionization chamber and an anthropomorphic head phantom in a quality assurance program for stereotactic radiosurgery.

Quality assurance methods used in association with radiosurgery must include all aspects of the radiosurgery process: visualization and localization of the target, treatment and dose planning and dose delivery. Presented here is a quality assurance method that utilizes an anthromorphic head phantom and a micro-ionization chamber to demonstrate precise target localization and accurate dose delivery. This micro-ionization chamber method offers an immediate readout which is both accurate and reproducible. Additionally, this method allows unlimited repetition of the dose measurement process without repeated radiographic localization studies as is necessary with the conventional methods of TLD, film, and Fricke gels. The method and techniques presented can be used in the acceptance testing and routine quality assurance of both linac-based and Gamma Knife radiosurgery units.

Anthropometry↗
PubMed1994

Low-dose, beta-particle emission from 'stent' wire results in complete, localized inhibition of smooth muscle cell proliferation.

BACKGROUND: Restenosis after catheter-based revascularization has been demonstrated to be primarily caused by medial and/or intimal smooth muscle cell (SMC) proliferation. The objective of this study was investigate the ability of local emission of beta-particles from a 32P-impregnated titanium "stent" wire source to inhibit vascular SMC and endothelial cell proliferation in cell culture and to determine the dose-response characteristics of this inhibition. METHODS AND RESULTS: A series of experiments were performed using 0.20-mm-diameter titanium wires that were impregnated with varying low concentrations of 32P (activity range, 0.002 to 0.06 microCi/cm wire, n = 47) or 31P (nonradioactive control, n = 28) in cultures of rat and human aortic SMCs and in cultured bovine aortic endothelial cells. The zone of complete cell growth inhibition (in millimeters from stent wire) was measured using light microscopy in the cultures exposed to the radioactive (32P) or control (31P) wires at 6 and 12 days after plating. In both rat and human SMC cultures there was a distinct 5.5- to 10.6-mm zone of complete SMC inhibition at wire activity levels > or = 0.006 microCi/cm. In contrast, there was no zone of inhibition surrounding the control (31P impregnated) wires (P < .001 versus 32P wires at all wire activities > or = 0.006 microCi/cm for human and rat SMCs). Proliferating bovine endothelial cells were more radioresistant than SMCs, with no zone of inhibition observed at wire activity levels up to 0.019 microCi/cm (P < .001 versus SMCs at 0.006 microCi/cm and 0.019 microCi/cm). CONCLUSIONS: We conclude that very low doses of beta-particle emission from a 32P-impregnated stent wire (activity levels as low as 0.006 microCi/cm of wire) completely inhibit the growth and migration of both rat and human SMCs within a range of 5.5 to 10.6 mm from the wire. Endothelial cells appear to be much more radioresistant than SMCs. These data suggest that an intra-arterial stent impregnated with a low concentration of 32P may have a salutary effect on the restenosis process. Whether this approach can be used successfully and safely to inhibit restenosis in vivo and in the clinical setting is under investigation.

Animals↗
PubMed1993

A tissue equivalent phantom for stereotactic radiosurgery localization and dose verification.

A tissue equivalent head phantom was utilized in the stereotactic localization and dose verification of radiosurgery procedures with the Leksell Gamma Knife Unit at the University of Kentucky Medical Center. A radiation dose-dependent color-doped gel target was positioned within the head phantom and stereotactically localized using either angiography, CT, or MR techniques. Utilizing standard Gamma Knife treatment procedures, the head phantom was irradiated, which resulted in a color change of the gel tumor at the position of the treatment isocenter and thereby confirmed the localization procedure. Additionally, a radiation dosimeter (thermoluminescent dosimetry--TLD) was positioned within the head phantom and localized using an angiography frame and a standard radiation therapy simulator. The phantom skull measurements and the dosimeter coordinates were entered into the Leksell Gamma Knife dose planning computer (KULA) and an irradiation time for 40 Gy using the 18-mm collimator was determined. The TLD dose evaluations were relatively determined using a cobalt-60 calibration curve. The experimental dose verification results agreed well (+/- 4%) with computer dose estimates.

Algorithms↗
PubMed1991

Radiation induced acute tumor lysis syndrome in the bone marrow transplant setting.

Patients with highly chemo-responsive malignancies have for some time been known to be at risk for life threatening acute tumor lysis syndrome (TLS). This report describes two cases involving acute TLS in patients with malignant diseases which had become refractory to therapy and received initial total body irradiation as a part of the preparative regimen for allogeneic bone marrow transplantation.

Acute Disease↗
PubMed1989

Dosimetric evaluation of a variable energy superficial X-ray machine with applications for endocavitary radiotherapy techniques.

This investigation presents the beam characteristics of a newly-marketed variable energy superficial X ray machine for radiotherapy. The X ray system hardware, including a high voltage generator, and console software allow for nine independent operator-selected X ray beams from 10-150 kVp. Filament current values are also independently variable; 1.0-13.0 mA for 90-150 kVp, and 1.0-30.0 mA for 10-90 kVp. The HVL's, effective energies, and radiation outputs for the nine combinations of kVp and mA are presented. In addition, percentage depth dose and beam uniformity results are presented as a function of cone size. Radiation output stability and reproducibility results are included. Discussion of adaptation of this X ray system to the Papillon technique for the treatment of rectal cancers is presented.

Brachytherapy↗
PubMed1984

Five-year cure of cervical cancer treated using californium-252 neutron brachytherapy.

Female pelvic carcinoma is one of the common malignancies seen at the University of Kentucky Medical Center and often presents in an advanced stage. In 1976, we began to test californium-252 neutron brachytherapy (NT) for its efficacy for control of primary and recurrent advanced uterine, cervix, and vaginal cancers. The first protocol used was 5000-5500 rad of whole pelvis irradiation followed by 1-2 Cf-252 insertions using a single tandem placed in the utero-cervico-vaginal region. Of 27 patients with primary carcinomas treated, 10 are alive and well 5 years later (37%). Two of two recurrent tumors were locally controlled but failed later. These patients had advanced cervical, vaginal, or endometrial carcinomas. In 1977, a transitional year, treatment of only unfavorable stages and presentations with NT was initiated. Similar results were obtained with NT as compared to conventional photon therapy (PT). Further improvement in treatment results can be anticipated as NT brachytherapy is used for advanced cancer therapy by more effective treatment schedules and radiation doses. Cf-252 can be used as a radium substitute and achieved similar rates of tumor control and 5-year survivals.

Adenocarcinoma↗
PubMed1980

Radiation pneumonitis following electron beam radiotherapy.

A case of radiation pneumonitis is reported. The problem presented in a postmastectomy breast patient after completion of 5000 rads of high-energy electron beam radiotherapy. Within 7 months the lungs showed almost complete clearing and clinical symptoms had disappeared.

Adenocarcinoma↗