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Biomedical subjects

B L Werner

Publications and source records attributed to B L Werner.

13 recordsLinked to original sources
PubMed1991

Border separation for adjacent orthogonal fields.

Field border separations for adjacent orthogonal fields can be calculated geometrically, given the validity of some important assumptions such as beam alignment and field uniformity. Thermoluminescent dosimetry (TLD) measurements were used to investigate dose uniformity across field junctions as a function of field separation and, in particular, to review the CCSG recommendation for the treatment of medulloblastoma with separate head and spine fields.

Cerebellar Neoplasms↗
PubMedDate not supplied

The perturbation of electron beam dose distributions at medium interfaces.

The perturbation of electron beam dose distributions in the vicinity of medium interfaces is calculated. Two different solutions to the Boltzmann equation, one an energy averaged solution and the other a diffusion approximation solution, are presented for the calculation of the electron distribution in the vicinity of interfaces. An extension of the energy averaged formalism is presented for media with high atomic number. A new effective depth approximation is introduced to calculate the beam conditions beneath the interface. The transformation from electron distribution to dose distribution is made and dose calculations are compared with published electron beam dose measurements.

Diffusion↗
PubMedDate not supplied

The production of secondary electrons in an electron beam.

Convenient methods for calculating the ratio of restricted to unrestricted collision stopping power in water over a wide range of initial and cutoff energies, the rate of production of secondary electrons, and the primary electron dose distribution in an electron beam, are presented.

Electrons↗
PubMedDate not supplied

Dose perturbations at interfaces in photon beams.

A model based on an approximation called the partial fluence approximation is presented for the calculation of dose distributions in the vicinity of medium interfaces in photon beams. The predictions of the model are compared with dose distributions measured in layered phantoms consisting of aluminum and polystyrene, for photon beams ranging in energy from 60Co to 24 MV.

Humans↗
PubMedDate not supplied

Dose distributions in regions containing beta sources: large spherical source regions in a homogeneous medium.

The energy averaged Boltzmann equation model is applied to the determination of dose distributions in infinite, homogeneous media with uniform, monoenergetic, isotropic source distributions in spherical regions of radius larger than the electron range. The generalization to the case of spherically symmetric source distributions is made. Comparisons with dose distributions calculated by the integration of dose point kernels derived from Monte Carlo calculations are presented.

Beta Particles↗
PubMedDate not supplied

Dose perturbations at interfaces in photon beams: secondary electron transport.

An improved, quantitative version of the partial fluence model [Med. Phys. 14, 585 (1987)] for the calculation of dose perturbations at media interfaces in photon beams is presented and compared with measurements made at interfaces between polystyrene and materials ranging in atomic number from aluminum to lead, for photon beams ranging in energy from 60Co to 24 MV.

Electrons↗
PubMedDate not supplied

Validity of transition-zone dosimetry at high atomic number interfaces in megavoltage photon beams.

Measurement of dose or dose perturbation factors at high atomic number interfaces are usually performed with a thin-window parallel-plate ion chamber. In a transition region, under nonequilibrium conditions, accuracy of ion chamber readings for the dose measurements has often been questioned. This paper critically analyzes the factors (stopping power ratio and charge collection) for the dose measurements at interfaces. Monte Carlo simulations were performed to investigate the secondary electron spectrum produced by photon beams and to calculate the stopping power ratios at the point of measurement. The validity of dose measurements was studied for the photon beams in the range of Co-60 gamma rays to 24-MV x rays at bone and lead interfaces with polystyrene, using thermoluminescent dosimeters, extrapolation chamber and several types of commercially available parallel-plate ion chambers. It is observed that for energies greater than 10 MV most parallel-plate chambers can be used to measure dose accurately. At lower energies, however significant differences between measured doses with different detectors were noticed. It is suggested that at high-Z interfaces and lower energies, the dose measurements should be performed with ultrathin-window parallel-plate ion chambers or extrapolation chambers.

Bone and Bones↗
PubMedDate not supplied

Dose distributions in regions containing beta sources: uniform spherical source regions in homogeneous media.

The energy-averaged transport model for the calculation of dose rate distributions is applied to uniform, spherical source distributions in homogeneous media for radii smaller than the electron range. The model agrees well with Monte Carlo based calculations for source distributions with radii greater than half the continuous slowing down approximation range. The dose rate distributions can be written in the medical internal radiation dose (MIRD) formalism.

Beta Particles↗
PubMedDate not supplied

Dose perturbations at interfaces in photon beams: annihilation radiation.

A model is presented for estimating the contribution of annihilation radiation to the dose perturbation at interfaces between high and low atomic number materials. The contribution is small, but not negligible relative to the total interface dose perturbation. The maximum contribution occurs for photon beams of about 8 MeV in energy. For an 8-MeV beam passing first through lead, then through polystyrene, the annihilation radiation contribution to the interface dose perturbation is about 8%, at a copper/polystyrene interface, the contribution is about 7%, and at an aluminum/polystyrene interface, the contribution is about 3%.

Bone and Bones↗