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Biomedical subjects

P H McGinley

Publications and source records attributed to P H McGinley.

At least 19 recordsLinked to original sources
PubMed2001

Dose rate outside primary barriers.

The author has investigated the use of the inverse square function to predict the photon dose rate outside primary barriers for medical accelerators. Measurements of the dose rate as a function of distance outside the barriers were made at five medical accelerator facilities. An analysis of the data showed that the radiation field appears to diverge from a point between the x-ray target and primary barrier. This behavior of the x-ray beam was attributed to scattering of photons in the shield barrier. It was concluded that the dose outside the barrier will be overestimated if the distance from the x-ray target to the point of calculation is utilized to carry out an inverse square correction.

Health Physics↗
PubMed2000

A quality control method for detecting energy changes of medical accelerators.

A description is presented of a simple and sensitive method for detecting a change in the energy of the electrons bombarding the target of medical accelerators. This technique is useful for x-ray beams with end point energy in the range of 15.7 to 25 MeV. The method is based on the photoactivation of 160 and 14N in a small sample of ammonium nitrate. It was found that the ratio of the activity induced in the oxygen divided by that produced in the nitrogen can be used as a quality control technique to detect a change in the energy of the electrons that bombard the target of the accelerator. An electron energy change of the order of 0.2 MeV can be determined using this method.

Electrons↗
PubMed2000

Evaluation of the contribution of capture gamma rays, x-ray leakage, and scatter to the photon dose at the maze door for a high energy medical electron accelerator using a Monte Carlo particle transport code.

A Monte Carlo simulation of the photon dose due to scattered x rays, head leakage photons, and capture gamma rays in the maze of an 18 MeV accelerator facility was carried out. The results of the Monte Carlo simulation were compared with dose measurements made in the maze and also with values calculated using an empirical equation. Agreement within +/-26% was found among the three techniques used to evaluate the capture gamma ray dose. It was found that the empirical equation overestimated the scattered x ray plus head leakage photon dose by a factor as large as 2.9 as compared to the other methods. It was concluded that the photon dose, for mazes greater than 3 m in length, is produced predominately by capture gamma rays.

Biophysical Phenomena↗
PubMed1999

Room scattered neutrons.

A method of evaluating the photoneutron fluence in the maze of accelerator facilities due to room scattered neutrons is presented. Measurements were made to demonstrate that the room scattered fluence is reduced by a factor of 2pi in going from the treatment room to the inner maze entrance.

Gamma Rays↗
PubMed1995

A method for calculating the dose due to capture gamma rays in accelerator mazes.

An empirical technique for calculation of the capture gamma ray dose in the maze of high-energy medical accelerators is described. The total photon dose was measured along the maze centre line and by use of a graphical technique the capture gamma dose and the low-energy photon dose component were determined. Tenth-value lengths for both photon dose components are reported for four medical accelerators operating with megavoltages in the range 16.8-22.0 MV. The capture gamma dose and the low-energy photon dose in the maze were related to the following parameters: the room surface area, the distance from the isocentre to the inner maze entrance, and the neutron head leakage at a fixed distance from the target.

Gamma Rays↗
PubMed1995

A history of radiation shielding of x-ray therapy rooms.

In this report the history of shielding for radiation treatment rooms is traced from the time of the discovery of x-rays to the present. During the early part of the twentieth century the hazards from ionizing radiation were recognized and the use of lead and other materials became commonplace for shielding against x-rays. Techniques for the calculation of the shield thickness needed for x-ray protection were developed in the 1920's and shielding materials were characterized in terms of the half value layer or simple exponential factors. At the same time, better knowledge of the interaction between radiation and matter was acquired. With the development of high energy medical accelerators after 1940, new and more complex shielding problems had to be addressed. Recently, shielding requirements have become more stringent as standards for exposure of personnel and the general public have been reduced. The art of shielding of radiation treatment facilities is still being developed and the need for a revision of the reports on shielding of medical accelerators from the National Council on Radiation Protection and Measurements is emphasized in this article.

History, 19th Century↗
PubMed1994

Laminated primary ceiling barriers for medical accelerator rooms.

In this work the performance of a number of laminated shields used as the primary ceiling barrier for high-energy accelerator rooms was investigated. The neutron and photon dose equivalent rates were measured outside each shield. Based on the measured photon level and the calculated x-ray leakage level the dose equivalent rate due to photons produced by neutron interactions with the shield materials was estimated. Shielding parameters for polyethylene were established for photons and neutrons. It was found that the barriers designed using the techniques given in an NCRP Report suffered from excessive radiation leakage.

Algorithms↗
PubMed1992

An adjustable collimator for stereotactic radiosurgery.

Stereotactic radiosurgery utilizing a linear accelerator is now carried out using small non-coplanar beams to produce a high-dose volume that is approximately spherical in shape. It is desirable to shape the high-dose region so that it is similar to the target volume thereby reducing the amount of healthy tissue irradiated by a high dose. An adjustable collimator has been developed that can be employed to control the target volume height and diameter. Based on film dosimetry and measurements made with a small parallel-plate ionization chamber it was determined that the beams produced by the collimator have properties that make them suitable for radiosurgery. The basic dosimetry parameters (output factors and tissue maximum ratios, TMR) needed for patient treatment were evaluated. It was found that the diameter and length of the high-dose region produced by the patient rotation method are related to the light-field size at 100 cm from the x-ray target. A more favourable dose distribution was found for the adjustable collimator as compared to treating the same volume by use of the two-target method.

Humans↗
PubMed1992

Photoneutron production in the primary barriers of medical accelerator rooms.

Several radiation surveys, at medical linear accelerator facilities where lead or steel had been used with concrete to fabricate the primary barriers, revealed the existence of a sizable neutron field outside the shielding. This neutron field is produced by photoneutrons generated in the metal portion of the shield when the primary x-ray beam is aimed at the barrier. A method was developed to calculate the neutron dose-equivalent rate expected outside a primary shield when it is irradiated by a high-energy x-ray beam. It was found that the minimum photoneutron dose was produced when the metal part of the shield was positioned inside the treatment room in front of the concrete and also by using steel in place of lead. A thickness of less than or equal to 17 cm of metal on the inner surface of the shield produced only a slight increase in the neutron dose equivalent outside the barrier.

Health Facility Environment↗
PubMed1992

Photoneutron fields in medical accelerator rooms with primary barriers constructed of concrete and metals.

This study investigates the photoneutron field found in medical accelerator rooms with primary barriers constructed of metal slabs plus concrete. An increased neutron dose equivalent was observed for barriers containing lead or steel as compared to barriers fabricated entirely of concrete. The effect of the beam's size and distance from the primary barriers on the neutron dose was evaluated and the portion of the neutron dose due to the metal slabs was determined.

Construction Materials↗
PubMed1990

A patient rotator for stereotactic radiosurgery.

A new technique for stereotactic radiosurgery by use of a patient rotator is described. Using the rotator with a small collimated beam of 6 MV x-rays, a small well-defined region of the brain can be irradiated to a high dose with rapid fall off of the dose outside the target volume. Since the linear accelerator gantry does not move during therapy the possibility of a collision between the gantry and the patient or stereotactic equipment is eliminated. The system is also independent of the rotational stability of the linear accelerator gantry axis and turntable axis. Dose distributions measured in a Lucite head phantom with film exhibited properties well suited for radiotherapy. Tests carried out to evaluate the ability to irradiate a selected target point within the brain with the rotator system showed a maximum positional error of 1.0 and 2.0 mm for angiography and CT localisation respectively.

Brain Diseases↗
PubMed1983

Combination of internal radiation therapy and hyperthermia to treat liver cancer.

Sixteen patients were treated for liver cancer (primary and metastatic) by a combination of internal radiation therapy with intra-arterial yttrium 90 microspheres and regional hyperthermia with electromagnetic radiation. Four patients have their liver disease apparently controlled; two had a partial regression of more than 50%; and two had a partial regression of less than 50%. The complications consisted of one case of radiation hepatitis and one of peptic ulcer.

Adolescent↗
PubMed1981

The influence of bone on temperature patterns produced by 434-MHz electromagnetic radiation.

The temperature pattern produced in phantoms containing simulated bone and muscle components was determined for 434-MHz electromagnetic radiation. A parallelepiped phantom was employed in this study and heating was conducted for 15 minutes using a commercially available diathermy unit. Both slab and cylindrical bone geometries were investigated, as well as the influence of depth in muscle of the bone component on the resulting temperature pattern. The temperature perturbation produced by bone irradiated by 434-MHz radiation was found to vary drastically with the bone geometry, as well as with the depth of the bone in muscle.

Body Temperature↗
PubMed1980

Dosimetry of a silicone breast prosthesis.

Dose measurements were conducted in a phantom which simulates breast tissue and in another phantom which simulates a breast containing a silicone prosthesis. No detectable difference was found when the irradiations were carried out with tangential beams of 60Co radiation. The degree of backscatter and absorption of radiation by the prosthesis and phantom were also similar. A slight decrease in dose of approximately 8% was found at the interface between the prosthesis and muscle-equivalent material.

Breast Neoplasms↗
PubMed1979

Small electron beams in radiation therapy.

The use of lead cutouts to produce small beams in electron therapy results in a reduced dose to the patient. The authors investigated this effect for beams with energies less than 8 MeV and diameters of 3 cm or less. Dose measurements were obtained using film and an ionization chamber. Based on these values, corrections were established to account for dose reduction due to cutout spaces and air spaces between the end of the electron cone and the skin surface. Data were also obtained on the dose increase due to backscattering from internal eyeshields.

Electrons↗