James M. Galvin

Improved methods for determination of variability in patient positioning for radiation therapy using simulation and serial portal film measurements

Variability in patient positioning was determined by analyzing simulation and portal film measurements for 318 portals in 51 patients treated with external beam radiotherapy to the head and neck. Several indicators of error in patient positioning were examined: random error, a measure of the deviation of all portal films from the average portal film position, systematic error, a measure of the difference between the average portal film and the simulation film, and total uncertainty, a measure of the overall deviation, including both random and systematic uncertainties. The median differences noted were 0.4 cm, 0.6 cm, and 0.7 cm, for Random Error, Systematic Error, and Total Uncertainty, respectively. The treatment fields analyzed in this study show a substantial treatment-to-treatment and simulation-to-treatment variability in patient positioning. The methods described provide an improved means for the systematic analysis of variability in patient positioning.

Three-dimensional treatment planning for lung cancer

The experience of four institutions involved in a three-dimensional treatment planning contract (NCI) for lung cancer is described. It was found that three-dimensional treatment planning has a significant potential for optimization of treatment plans for radiotherapy of lung cancer both for tumor coverage and sparing of critical normal tissues within the complex anatomy of the human thorax. Evaluation tools, such as dose-volume histograms, and three-dimensional isodose displays, such as multiple plane views, surface dose displays, etc., were found to be extremely valuable in evaluation and comparison of these complex plans. It is anticipated that with further developments in three-dimensional simulation and treatment delivery systems, major progress towards uncomplicated local regional control of lung cancer may be forthcoming.

A practical technique for the localization of the tumor volume in definitive irradiation of the breast

In patients being treated with breast conserving surgery and primary irradiation for breast cancer, adequate treatment of the primary tumor bed is associated with improved local control rates. This report presents a practical method for defining the tumor bed. At the time of excisional biopsy, radiopaque surgical clips are placed at the margins of the tumor bed. These clips are used to localize the tumor volume for the simulation of the breast tangents and for planning the boost field. This technique will minimize the potential for a geographic miss during definitive irradiation for breast cancer.

A report of the work party: comparison of total body irradiation techniques for bone marrow transplantation

The report presents a survey of total body irradiation techniques for bone marrow transplantation in nine institutions in North America and England. The survey compares their nominal dose, dose rate, point of dose prescription, type of machine used, patients position during treatment, and use of compensators. This experience has emphasized the need for a system of uniform dose reporting and for uniform dose prescription in total body irradiation.

Three-dimensional photon treatment planning for hodgkin's disease

A multi-institutional study was undertaken using computerized planning systems to develop three-dimensional (3-D) radiotherapy plans for Hodgkins disease (H.D.). Two patients, the first afflicted with bulky stage II disease and another one with early stage I H.D., were studied. Three main categories of plan were produced for each patient: a) a traditional plan which modelled a conventional mantle treatment on the 3-D system, b) a 3-D standard plan where anterior and posterior fields were designed to cover 3-D target volumes, and c) a 3-D unconstrained plan where innovational techniques were employed. Three-dimensional planning provides information about the dose distribution throughout the large volume irradiated in patients with H.D. that is not available with conventional mantle planning. The use of 3-D techniques resulted in improved tumor coverage, but by allowing for uncertainties such as motion, the doses to normal tissues tended to be higher. The use of unorthodox beam arrangements introduced added complexities, and further increased the lung doses. The most even dose distributions were obtained by incorporating compensating filters into anterior fields. Clinicians showed wide variations in their assessment of the plans, possible reasons for which are addressed in this paper. In addition, calculated probabilities from models of tumor control and normal tissue damage are also presented.

Three-dimensional photon treatment planning in carcinoma of the larynx

The role of three-dimensional (3-D) treatment planning in the definitive treatment of carcinoma of the larynx with radiation was evaluated at four institutions as part of an NCI contract. A total of 30 different treatment approaches were devised for two patients with larynx cancer. CT scans were obtained for both patients and various treatment planning tools were employed to optimize beam arrangements and to evaluate the resulting dose distribution. The effect on dose distribution of a number of factors was also examined: 1) the use of dose calculation algorithms which correct for tissue inhomogeneities, 2) the variation of the CT numbers used for inhomogeneity corrections to simulate inaccuracies in the knowledge of the CT numbers, and 3) the modification of beam energy. A multitude of data was used in plan evaluation and a numerical score was given to each plan to estimate the tumor control probability and the normal tissue complication probability. We found 3-D treatment planning to be of potential value in optimizing treatment plans in larynx cancer. Improved target coverage was achieved when complete information describing 3-D geometry of the anatomy was utilized. In some cases, the treatment planning tools employed, such as the beams eye view, helped devise novel beam arrangements which were useful alternatives to standard techniques. We found little effect of change in CT number on dose distributions. A comparison between dose distributions calculated with tissue inhomogeneity corrections to those calculated without this correction showed little difference. We did find some improvement in the dose to the primary tumor volume at lower beam energies, but with an increased larynx volume potentially receiving doses above tolerance.

Determination of depth for electron breast boosts

A technique has been developed to determine the depth for the electron boost treatments for patients undergoing definitive irradiation for early stage breast cancer. A series of parallel link chains are placed on the breast over the clinically determined site of the boost. Using fluoroscopy, the physician confirms that the chains overlie the tumor bed which is outlined by radiopaque surgical clips placed at the time of the breast biopsy. A pair of orthogonal films and/or rotational stereo shift films are obtained with a standard simulator unit. Using the image of the chains to define the surface contour, the depth of each surgical clip is measured directly from the orthogonal films or calculated from the rotational stereo shift films. With this information, the physician can determine the appropriate electron energy to cover the target volume. This method was tested by comparison with depths measured from CT scan, and close agreement was demonstrated.

Contouring structures for 3-dimensional treatment planning

Three-dimensional (3-D) treatment planning is a labor-intensive process with contouring of the target volume and critical normal tissues being a significant time-consuming component. The use of 3-D treatment planning on a routine basis may be limited by the time required to complete treatment plans. Despite the need to increase the efficiency of the process, there is little literature addressing the speed and accuracy of contouring systems. In an attempt to initiate systematic analysis of the contouring process, data sets consisting of 10 CT images each were developed on two patients with esophageal carcinoma. Nine different operators manually contoured structures (target volume, spinal canal, lungs) on the data sets using four different contouring systems present in our department. These included both commercially available systems and those developed by the authors. There was a wide variation in the hardware and software characteristics of these systems. The time required to contour the CT data sets was recorded and analyzed. The contouring accuracy was assessed by comparison with a standard template derived from the CT data set for each image. The contouring time was found to be dependent on the system design, previous contouring experience, and the type of drawing instrument (lightpen vs mouse). The mean contouring time ranged from 26 minutes per patient for the fastest system to 41 minutes for the slowest. Potential clinically significant errors in contouring were rare for the spinal canal and lungs but present at a greater rate for the target volume (30.3%). The implications of this finding are discussed.

Calculation and prescription of dose for total body irradiation.

The use of large total body fields creates a unique set of problems that stress the accuracy of techniques routinely used for dose calculation. This paper discusses an approach suggested by the Childrens Cancer Study Group (CCSG) for both prescribing the total body irradiation (TBI) dose and calculating the beam-on time or meter set needed to deliver it. It is aimed at guaranteeing the accuracy of the calculations, while at the same time ensuring a high degree of compliance for the various CCSG protocols using TBI. Data supporting the various CCSG recommendations are presented.

A SIMPLE DOSE CALCULATION METHOD FOR TOTAL BODY PHOTON IRRADIATION

A simple technique for calculation of the prescribed dose for total body irradiation (TBI) is presented. The technique uses a standard calibration procedure and applies standard correction methods to account for variations in the field size, depth, and treatment distance. Since the scattering volume (the entire body) is smaller than the X ray field for this treatment, the change in output with field size is handled separately from changes due to scatter within the phantom. The latter is shown to be a function of the phantom size (corresponding to the frontal area of the trunk of the body for patient irradiation) rather than the size of the field opening. Dosimetric tests of this technique have been conducted and the errors determined. For these tests, three different phantom sizes were used to represent the upper body sizes of a 2-year old child, an 8-year old, and an adult, and three linear accelerator energies (6, 10, and 15 MV) were included. Calculations were performed using the technique and compared to measurements for the same phantom sizes. Differences of less than 1.3 were found.