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Biomedical subjects

F C Deibel

Publications and source records attributed to F C Deibel.

11 recordsLinked to original sources
PubMed1989

An afterloading brachytherapy device utilizing thermoplastic material.

An afterloading brachytherapy device for treatment of residual cancer in an enucleated orbit with two cesium-137 sources was designed using a thermoplastic material, Aquaplast. The device consists of a face-mask support held in place with elastic bands around the head and an acrylic afterloading applicator. The device is very easy to make, holds the sources firmly in place, allows full mobility of the patient, and gives excellent dose distribution to the target area. It was easily tolerated by a 7-year-old child during the 50 h of treatment.

Brachytherapy↗
PubMed1989

Total skin electron arc irradiation using a reclined patient position.

Several techniques for the treatment of the total skin of the patient using electron beams have been described in the literature. However, most techniques presuppose that the patient is capable of maintaining a standing position for the duration of the treatment. For patients either weakened by disease or those suffering from a loss of limbs, this is often an unrealistic expectation. We will describe a total skin electron irradiation technique that allows the patient to remain in a reclined position without sacrificing dose uniformity. This technique uses two symmetric +/- 48 degrees arc electron beams to provide a field uniformity of +/- 5% over a range of approximately 250 cm X 45 cm. Six patient positions are used to provide a uniform dose around the periphery of the patient. A description of the treatment technique along with details of the dosimetry are given.

Electrons↗
PubMed1984

The significance of electron binding corrections in Monte Carlo photon transport calculations.

Many Monte Carlo simulations ignore coherent scattering events and utilise the Klein-Nishina free electron distribution, rather than the incoherent differential cross-section, for choosing the trajectories of incoherently scattered photons. We assess the accuracy of this model by comparing its results with those of the complete bound electron model (form factor approach), which simulates coherent scattering events, and uses the appropriate bound electron angular scattering distributions. Both analytic and Monte Carlo calculations demonstrate that use of the free electron scattering distributions significantly underestimates the angular distribution of scattered photon energy resulting from low and medium energy photons incident upon carbon, iron, and platinum barriers. In using the free electron approximations to calculate barrier transmission, significant errors occur only for primary photon energies below 100 keV. Implementation of the complete bound electron model reduces the computational efficiency of our Monte Carlo code by only 10-25%.

Electrons↗
PubMed1982

The relationship between milligram-hours and dose to point A in carcinoma of the cervix.

The relationships between the Fletcher and Manchester methods in dosimetry of cancer of the uterine cervix were explored in order to compare dose prescriptions between the systems, to optimize the best features of both systems, and to establish the necessity for computerized dosimetry. A total of 91 Fletcher-Suit radium applications was analyzed by a linear least-square regression analysis to compare Point A and Point B doses of the Manchester system will milligram-hours of the fletcher system. Although moderately high correlations were found between milligram-hours of radium and doses at Point A and Point B, it was concluded that direct comparisons, particularly between individual patients, are fraught with dose uncertainties of clinical significance. In addition, the correlation between milligram-hours of radium and Point A dose was markedly affected by the position of the colpostats and tandem, thus making it difficult to formulate a simple conversion factor between the two systems.

Brachytherapy↗
PubMedDate not supplied

Lead shielding for electrons.

Using a 13 MeV electron beam as an example, transmission curves for various thicknesses of lead were measured. The data indicated that the choice of shielding thickness depends greatly on the depth at which the measurements are made. The importance of this reference depth and criteria for shield design when shields of minimum thickness are required is discussed.

Electrons↗
PubMedDate not supplied

A model for calculating electron beam scattering in treatment planning.

The Fermi-Eyges theory of electron scattering overestimates the scattering of electron beams used in radiation therapy. The reason for this overestimate is the neglect of the loss of electrons which are scattered into highly oblique paths and removed from the beam at relatively shallow depths. A modification of Eyges' solution to Fermi's equation is presented to take this loss of electrons into account. Equations for the calculation of isodose distributions for any medium using pencil beams are developed. Experimental confirmation is presented for electron beams of 13 and 18 MeV in homogeneous water, polystyrene, Lucite, and aluminum phantoms.

Electrons↗
PubMedDate not supplied

Model for calculating depth dose distributions for broad electron beams.

Central axis electron beam depth dose distributions can be transformed by replacing dose by fluence and depth by a measure of angular dispersion. This transformation was applied to a set of broad beam central axis depth dose distributions calculated by Monte Carlo code for beams with initial energies ranging from 1 to 60 MeV in homogeneous media of water, aluminum, and copper. The resulting fluence distributions belong to a family of curves that can be parametrized by a single-valued function of initial beam energy and medium and can be used to calculate fluence distributions for accelerators. Fluence curves can be easily transformed to depth dose curves.

Models, Theoretical↗
PubMedDate not supplied

Obliquity correction for electron beams.

Uneven air gaps, beam obliquity, or sloping contours create complex dosimetry problems in electron beam treatment planning. We find that the depth dose distribution in an obliquely incident beam can be calculated from the data for a normally incident beam by using inverse square law and obliquity factors. The obliquity factors have been determined for various energy beams in the range of 6-22 MeV and can be used for manual treatment planning.

Electrons↗
PubMedDate not supplied

Dosimetry of asymmetric x-ray collimators.

We have studied the dosimetry of an independent jaw system (provided with the Varian Clinac 2,500) using ionometric measurements performed both in air and in a water phantom. Our study shows that the effect of the independent jaw on the dose distribution is similar to that of secondary blocking except for changes produced in the collimator scatter. A system of dose calculation was developed which takes into account the changes in the collimator scatter as well as in the isodose distribution. A method is described to correctly generate isodose curves for fields shaped by an independent jaw using a modified AECL TP11 treatment planning system. The primary modification in the program consists of correcting the zero-area tissue-maximum ratios for the off-axis variation in beam quality.

Humans↗