Coplanar Fields Research Articles

Expedient set-up of tangential breast fields with a simple gantry attachment

A novel technique for setting up tangential fields is described. The technique uses a simple device (Breast Aligner) which attaches to the collimator of the treatment unit. The function of the Breast Aligner is similar to conventional front and back pointers except that the beam edge rather than central ray is defined. By delineating beam entrance and exit points at the posterior field edge, the device greatly simplifies and expedites setup, and enhances precision of port alignment. Additional advantageous features include: (a) the ability to compensate for small inadvertent variations from the initial set-up position or for patient movement between the set-up of opposing ports, (b) the ability to visually check port alignment in the treatment position immediately before irradiation, and (c) decreased chance of human and equipment error by eliminating the need for measurements and calculations at the time of treatment. Our method can be used for SSD or SAD techniques and, with minor adjustment, is applicable for establishment of coplanar cephalad field borders as required at the junction of a supraclavicular field.

Steady configurations of a square dipole lattice in an external field

The conditions of existence of the ground and metastable states are obtained for a dipole system on a square lattice in an external co-planar field. The type of transition to the ferroelectric phase is elucidated.

An Approach to Abutting Adjacent Fields

Problems arise in designing treatment techniques involving two pair of adjacent opposing fields where machine limitations require the patient to flip from supine to prone positions. Mantle and para-aortic treatments, in particular, can create challenging problems because of changes in patient position, different SSD’s between adjacent fields, internal anatomical changes from supine to prone position, as well as field size and other treatment machine limitations. A simulator technique has been developed which takes cognizance of these limitations in specifying the gap between adjacent fields. It employs collinearity of the 50% decrement lines of adjacent-opposed field edges and the intersection of all four edges at an internal mid-plane match point. The technique maintains dose homogeneity and eliminates hot and cold triangles in the area of abutment. Simulation radiographs facilitate identification of collinearity with respect to a specific vertebra in the plane of abutment. In summary, this approach: Verifies abutment of coplanar fields by use of match film, improves isodose uniformity at mid-plane, evaluates dose distributions when abutment occurs at a point anterior or posterior to midline, prevents the possibility of spinal cord complications that might occur due to three field overlap.

Three-field technique for breast treatment using a rotatable half-beam block

A new three-field technique for the radiation therapy of breast cancer has been developed. Two opposing tangential fields treat the breast, chest wall, and ipsilateral internal mammary lymph nodes. The third, an anterior field, treats the axilla and supraclavicular area. The objective of the technique is to make the posterior geometric edges of the tangential fields coplanar, and also to make their cephalad geometric edges and the caudad geometric edge of the supraclavicular field coplanar. To effect the matching of fields, the technique utilizes a rotatable half-beam shielding block. To simplify the simulation procedure, an exact mathematical solution is given for the required treatment set-up parameters.

Biological effects evaluated as a function of patient thickness, beam quality, SSD,and treatment schedule.

Continuing efforts are being made by clinical radiotherapists to evaluate radiationcomplications to normal tissue and organs by specific time-dose parameters. Currently,the NSD concept of Ellis is receiving wide application in the literature in the reporting of radiation complications and normal tissue tolerances. To afford an easy and broad application of the NSD concept to the evaluation of physiological, functional, or structural changes, the authors have evolved mathematical expressions for the calculations of NSD as a function of patient thickness, beam energy, SSD, and treatment schedule involving coplanar field arrangements whether the fields are treated alternately or simultaneously. Several interesting aspects evolving form the concepts of treatment planning interms of the NSD or biological effects indicate that 1) for beam energies above 22 MeV, treatment is more ideally performed by treating only one field per day, since the depth of electronic equiliberium provides more effective sparing of superficial organs andtissues; 2) large-field therapy, such as the total nodal irradiation of Hodgkin'sdisease, can be more effectively treated in terms of tissue sparing by higher energy beamsthan cobalt-60 or 4-MeV for practically all patient dimensions; 3) a new concept ofintegral biological dose,the "gram-ret", is proposed, which represents the quantitation of total biological effect; 4) a series of tables with multiplication factors programmed on a digital computeris presented, which very quickly make available the NSD in any fractionated radiation treatment cycle to any plane of the body as a fuction of the beam energy, SSD, patient thickness, and continuous or split-course therapy schedule.

A light analog system for radiotherapy planning.

A LIGHT ANALOG SYSTEM FOR RADIOTHERAPY PLANNINGGERALD S. FREEDMAN, B.M.E., M.D. and PAUL N. GOODWIN, PH.D.Audio Available | Share

The theory of electromagnetic waves in a simple anisotropic medium

A method is given for investigating the behaviour of electromagnetic fields in a homogeneous, anisotropic medium characterized by a dielectric tensor which is diagonal, with two of the three diagonal elements equal. It is shown that each such field is related by a simple scaling procedure to a corresponding vacuum field. The vacuum field is expressed as the superposition of a transverse magnetic field, in which the magnetic vector is everywhere perpendicular to the axis of symmetry of the anisotropic medium, and a coplanar transverse electric field; and different scaling is applied separately to each partial field. The method is illustrated by application to plane-wave and dipole fields. In particular, the field is obtained of a time-harmonic electric dipole of arbitrary orientation situated in the anisotropic medium.