Harold Perry

Automation of Radiation Treatment Planning—IV. Derivation of a Mathematical Expression for the per cent Depth Dose Surface of Cobalt 60 Beams and Visualisation of Multiple Field Dose Distributions

A formula is presented for approximating the per cent depth distribution resulting from any portal size 60Co beam at 80 cm SSD. This equation may be used to obtain computer print-outs of combined multifield dose distributions as described previously (Sterling et al., 1963b), or, in a new programme, can be used to print out the combined isodose curves directly to scale with small error. A distinct geometric property of the per cent depth dose distribution is discovered and described without attempting to explain it.

Automatic variation of field size and dose rate in rotation therapy.

Abstract A technique is presented for changing the field size and dose rate as a function of gantry angle independently or simultaneously during rotation therapy. Two computational methods for calculating the dose distribution using the above technique are described. A comparison of the effectiveness of this new technique relative to conventional approaches is discussed.

A Practical Procedure for Automating Radiation Treatment Planning

A simple method for the translation of isodose graphs into numerical grids is described and the use of these grids for automatic dose computation of multiple field treatments is demonstrated. Details of the preparations of grid values, I.B.M. cards, and programme for one particular computer are given in detail.

Automation of Radiation Treatment Planning. V—Calculation and Visualisation of the Total Treatment Volume

The method for calculating per cent depth doses for all points in the major plane of a 60Co beam has been extended to all points in the treatment volume. An outline for rapid calculation of volumes of co- or multiplanar treatment plans is presented and an application of the system demonstrated.

Automation of Radiation Treatment Planning – VI. A General Field Equation to Calculate Percent Depth Dose in the Irradiated Volume of a Cobalt 60 Beam

Abstract This paper represents the next step forward in the development of a mathematical model that describes the total dose distribution in a field irradiated by a 60Co source at any source-surface distance or angle of entry. To derive this extension the authors collected a large amount of data on dose values throughout a water phantom at different source-surface distances, for different field sizes and for beams entering the phantom at different angles. These data were collected automatically, using a mechanism which drove a Victoreen probe with a 3 mm ionisation chamber through the total volume of a water tank. The basic form of the model which had been derived originally for 80 cm SSD was found to hold quite well in principle for any SSD. The general equation which was derived was found to use two sets of constants, one set for depth less than 2 in and the other for depth of more than 2 in. This division was introduced to adjust for electron build-up over the initial depth. While the relations descri...

Automation of radiation treatment planning. III. A simplified system of digitising isodoses and direct print-out of dose distribution

A system of automated treatment planning is described which enables the radiologist to obtain a direct print-out to scale of dose distribution. This system requires a new and simple method of digitising isodose curves which is also given.

A PROGRAMMABLE CALCULATOR TO ACQUIRE, VERIFY AND RECORD RADIATION TREATMENT PARAMETERS FROM A LINEAR ACCELERATOR?

Abstract A system has been developed for the utilization of a Wang 600-14 programmable calculator to acquire, verify and record treatment parameters from a linear accelerator. The hardware and software components and operation of the system are briefly described. The system is in use daily.

Automation of radiation treatment planning. II. Calculation of non-convergent field dose distributions.

A simple method for the automated computation of dose distributions for non-convergent fixed-field radiation therapy is described. Necessary principles of computation and programming are given.

PLANNING RADIATION TREATMENT ON THE COMPUTER

The abundance of artificially produced sources of ionizing radiation has made radiation therapy increasingly convenient and effective. This method has the obvious advantage of avoiding many of the severe traumas resulting from surgical or chemical extraction of tumors. On the other hand, to be effective, the radiologist must deliver an adequate dose to the tumor without destroying vital tissues. In fact, the dose delivered to the tumor is limited by that amount of radiation the surrounding normal tissues may be expected to tolerate. The total shape and pattern of low and high dose areas within the treatment field will thus determine the efficacy of the treatment. Combining multiple fields in planning a course of therapy so that dose to tumor is high and dose to normal tissues low are the major problems that test the skill of the physician. The preparation and evaluation of individual treatment plans for patients has been one of the most vexing problems in radiation therapy. The usual treatment plan is as follows. A contour is first obtained of the body cross section of interest and is then drawn on transparent paper. From radiographs and physical examinations, the tumor is localized and drawn in its proper location, along with the important normal structures such as the spinal cord. To destroy the tumor it is necessary to deliver a lethal dose to it without, however, damaging adjacent vital tissues. Since the effects of radiation are additive, it is possible to build up a large dose at the tumor and smaller doses at other locations by aiming beams through the body at different angles and having them intersect at the location of the malignancy. FIGURE 1 shows an example of a treatment field for a patient (with carcinoma of the esophagus) who was to be treated with Cobalt 60 teletherapy; 80 em. S.S.D. (skin to source distance) and four 8 X 15 em. fields. The fields were to enter at angles of 40° with the vertical. The total dose at any point in the region of interest is the sum of the contributions from each treatment field at that point. The difficulty in evaluating a treatment plan lies in finding the values of combined doses for a large enough number of points in the treatment field so that the effect of the treatment on the tumor, the surrounding area, and specific vital tissues can be assessed.

X-ray depth-dose characteristics of the Toshiba LMR-16.

The depth-dose characteristics of the Toshiba LMR-16 linear accelerator for 14-MeV x rays have been measured at an SSD of 100 cm using diodes and ion chambers. The surface dose and build-up depth both exhibit a considerable variation with field size. A new central axis model has been developed which takes account of these variations, and the agreement between the measured and computed data using this model is found to be excellent. Formulas are also presented to estimate the surface dose, buildup depth, and output factor as a function of field size.