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Biomedical subjects

M Goitein

Publications and source records attributed to M Goitein.

At least 109 records · Page 6Linked to original sources
PubMed1976

Review of parameters characterising response of normal connective tissue to radiation.

A comparison is made of the formalisms which have been proposed to characterise the response of normal connective tissue to levels of radiation which may lead to end points other than tissue tolerance; namely, Partial Tolerance, Time-Dose-Fractionation factor, and the Cumulative Radiation Effect. It is shown that, in most situations, conclusions which may be drawn using any one formalism are essentially the same as those which follow from the use of any other.

Connective Tissue↗
PubMed1975

Explorotory study of proton radiation therapy using large field techniques and fractionated dose schedules.

Three patients have been treated with 160-MeV protons combined with high-energy photons to examine the advantages and difficulties associated with the clinical implementation of a program of large-field, fractionated-dose, protonradiation therapy. We havefound it necessary to 1) obtain an accurate three-dimensional determination of the treatment volume including the density of all tissues in the beam path; 2) construct an adequate bolus to compensate for tissue heterogeneities; 3) use much more precise and accurate immobilization and patient positioning devices than used in photon irradiation; 4) treat with both protons and photons so as to keep the skin dose within an acceptable level. IN TISSUES WITHOUT SIGNIFICANT INHOMOGENETIES DUE TO BONE AND AIR SPACES WE HAVE DELIVEREDA WELL-DEFINED DOSE TO INVOLVED TISSUES WHILE SPARING DISTAL SENSITIVE STRUCTURES. However, in those regions where there is much "fine structure" of tissue density, it has been difficult to compensate satisfactorily for the inhomogeneties.

Adult↗
PubMed1975

Immobilization error: some theoretical considerations.

The consequences of immobilization error are explored through a model involving the tumor dose-response characteristics. The quantitative effect of such an error depends upon the field size, the shape of the dose-response function, and the position of the nominal dose being delivered on the dose-response function. Squamous-cell carcinoma of the supraglottis and Hodgkin's disease are discussed and values are calculated for the change in tumor control probability which might accompany immobilization error.

Carcinoma, Squamous Cell↗
PubMedDate not supplied

Mechanism to facilitate the fine adjustment of sidelights.

A simple optical mechanism is presented for the fine adjustment of sidelights. The characteristics of the device are that large angular displacements are required to achieve small lateral motions of a light beam. For this reason, the mounting mechanism may be made to quite coarse tolerances.

Optics and Photonics↗
PubMedDate not supplied

A technique for calculating the influence of thin inhomogeneities on charged particle beams.

A method has been developed for calculating the fluence and dose perturbations which occur in the shadow of inhomogeneous structures exposed to beams of charged particles. It is shown that differences in scattering power in adjacent portions of irradiated material can give rise to fluence perturbations which, in turn, are responsible for dose perturbations. A quantitative analysis of this process is developed which permits calculation of both the perturbed primary fluence and dose distributions. Results of these calculations are given for a square-faced edge discontinuity. The analytic technique, however, can be applied to more complicated interfaces and the general formulae are developed in this paper. They include provisions for the important modifying effects of beam divergence, of overlying or underlying homogeneous material, and of nonuniform beam profiles. In a companion paper, more complex geometries are analyzed and comparisons between calculations and experiments are presented.

Elementary Particles↗
PubMedDate not supplied

Measurements and calculations of the influence of thin inhomogeneities on charged particle beams.

The predictions of an analytic technique for calculating fluence and dose distributions beneath thin inhomogeneities are presented for a number of structures, including a rectangular cavity or bar, a cylinder, a disk, and an angled or diffuse edge. Experiments with both electrons and protons for several geometries are presented and compared with predictions based on this technique. We offer some clinical guidelines for avoiding large perturbations due to scattering effects.

Elementary Particles↗
PubMedDate not supplied

Simulator mounted Moiré topography camera for constructing compensating filters.

A technique has been developed and implemented by which individualized Ellis compensating filters can be rapidly and accurately produced from Moiré topographic photographs. A novel Moiré camera has been designed such that it has been possible to mount it on a radiotherapy simulator. The camera does not interfere with normal use of the simulator but can be deployed as needed. Depth of missing tissue contours are produced by the camera over the treatment field, accurately registered to the patient's simulated treatment position. An optical enlargement technique is used to transfer the depth of missing tissue contours in the photograph to a lead sheet compensating filter.

Humans↗
PubMedDate not supplied

Limitations of two-dimensional treatment planning programs.

Some limitations of conventional two-dimensional computer programs used to plan radiation therapy are presented. These include: a lack of involvement in defining the clinical problem; deficiencies in the algorithms for computing dose; failure to compute dose throughout the volume of interest; an inability to handle treatments with noncoplanar beams; failure to provide estimates of error; lack of tools for comparing rival plans; inadequate definition of geometric coverage of anatomic structures by external beams; and failure to provide tools for specifying and verifying the accuracy of treatment delivery. Some suggestions are offered for improvements in some of these areas. In particular, subtraction of dose distributions is proposed as a tool for comparing plans, and displays which exhibit the results of error analyses are presented.

Computers↗
PubMedDate not supplied

Planning proton therapy of the eye.

We describe a program for planning treatments of the eye with charged particle beams. Many of its features apply to treatment planning programs in general. These include the three-dimensional definition of the tumor volume and of normal structures, the possibility of delivering the treatment beam from any direction in space, the provision of arbitrary viewpoints including a "beam's eye" point of view, the design and fabrication of the field shaping aperture, the specification of the necessary beam quality (range and modulation), the calculation and display of isodose contours on any plane in space and on relevant surfaces, the identification of the extent to which normal structures are included or excluded from the beam, and the stimulation of the desired alignment film with which patient alignment can be verified.

Choroid Neoplasms↗
PubMedDate not supplied

Nonstandard deviations.

An estimate of uncertainty without a statement as to whether the estimate is a standard deviation or related quantity or an indication of the associated confidence level is meaningless. Nevertheless, the necessary qualification is often omitted. While such omissions are probably most often inadvertent, they may occur because the conventional single standard deviation of a normal distribution is inappropriate. Some unusual uncertainty intervals are therefore suggested. These include noninteger multiples of the standard deviation such as 1.5 standard deviations, asymmetric error bounds, and identification of the possibility of long tails or truncated bounds to the probability density function.

Statistics as Topic↗
PubMedDate not supplied

Beam scanning for heavy charged particle radiotherapy.

An important aspect of heavy charged particle radiotherapy is its ability to localize dose to the target volume. Current techniques generally employ beam delivery schemes which use range modulated beams in which the Bragg peak is spread out over a range of depths. The range modulation is constant over the entire beam cross section. This paper examines the potential gain from the use of variable range modulation over the beam cross section which can be achieved through beam scanning. An analytic technique has been developed to calculate a gain factor, related to integral dose, for a number of different charged particle beams. The dependence of the gain factor on tumor depth, diameter, and size has been examined. These analytic results have been compared with computer calculations of treatment plans simulating beam scanning and fixed modulation delivery techniques for actual clinical cases. The rationale for beam scanning, and its potential impact on tumor control is discussed.

Carbon↗
PubMedDate not supplied

Calculation of the uncertainty in the dose delivered during radiation therapy.

There is, inevitably, uncertainty in our knowledge of the dose at any point within an irradiated patient. A technique is presented for estimating this uncertainty by performing three parallel calculations, one using nominal values and the others extreme values of the parameters upon which the dose depends. Such calculations can be made with almost any algorithm for calculating dose. They result in an estimate, at some specified confidence level which is determined by the data used, of the range of dose likely at any point. Such calculations should help therapists to avert over- or underdosage which might not be evident in conventional calculations of the nominal dose.

Humans↗