An algorithm for generation of implant plans for high-dose-rate irradiators.

An algorithm is described for generating a treatment plan with minimal input from the user for a remote high-dose-rate afterloading irradiator. The algorithm generates a plan after locating all catheters involved and an area of interest on each catheter, and two additional numbers are specified: a radial distance and a target dose. The treatment volume becomes the locus of all points that are within the specified radial distance from any point within the area of interest on any catheter (except for the end points). For a single catheter, the volume may be alternately outlined on an x-ray film of the implant. The routine uses a linear programming formulism to compute which dwell positions are to be used, as well as the dwell time at each position, to irradiate the treatment volume to the target dose while minimizing the total volume integrated dose to the patient.

A dosimetric comparison of three compensator design methods for the mantle field.

The mid-plane dose was measured in an anthropomorphic phantom for parallel opposed mantle fields as typically used in the treatment of Hodgkin's Disease. Doses were measured for four cases: no compensator, a compensator designed by a three-dimensional CT based treatment planning algorithm, a compensator designed from a port film, and a compensator designed from surface topography. The results showed all three compensators gave a significant better dose distribution than using no compensator at all. Without a compensator, doses varied from 92 percent to 131 percent, with a standard deviation of 10.9 percent for 65 measured points. The treatment planning algorithm gave the best performance with a standard deviation of 3.2 percent with all points but three within 5 percent out of the 65 points measured, and no points outside of 10 percent. The port film compensator was next best with a standard deviation of 4.4 percent, with 19 points outside of 5 percent, and doses from 88 to 106 percent. The surface topography compensator had a standard deviation of 6.1 percent with 31 points outside of 5% and doses from 89 to 114 percent.

An algorithm for design of beam compensators.

Beam compensators are optimally designed to give a uniform dose to any plane or midsurface that intersects a single beam, or to give a uniform dose to the volume defined by the intersection of two or more beams. The primary and scatter components are taken into account separately, as well as the patient's shape and internal heterogeneities. The design of the beam compensators is formulated as a linear programming problem and solved with a variation of the Simplex Method. Beam weighting factors are also obtained as part of the solution.

A review of photogrammetry with applications to implant film calibration and seed matching.

The basic concepts of photogrammetry, the science of making geometric measurements from photographs, are reviewed with an emphasis on applications to implant dosimetry. A seed matching algorithm is developed using those concepts.

An algorithm for planning stereotactic brain implants.

A computer software package was developed for the planning and execution of brain biopsy and radioactive implant procedures with the BRW Stereotaxic System. With the application of computer graphics and a zero-one integer variable programming algorithm, an implant plan with accompanying isodose distributions and stereotactic coordinates can be easily accomplished at the time of the operation when the computer imaging terminal and a printer/plotter is placed in the operating room.

A note on designing tissue compensators for parallel opposed fields.

Missing tissue compensators are typically made to correct for the tissue defect separately for each of two parallel opposed radiation fields. Arguments and experimental evidence are provided to show that a more uniform dose distribution is achieved throughout the irradiated volume if the compensator is designed so that each opposed field delivers an equal dose to a surface defining midmass between the opposed body surfaces. An expedient method to approximate this result is to simply divide equally between the two parallel opposed fields the total amount of compensation otherwise required.

An electronic device for digitizing radiotherapy films for the construction of tissue compensators.

An electronic device was designed that measures film optical density and may be attached to the sonic pen of an x,y graphics terminal. Therapy portal films may be digitized by moving the assembly across the film by hand. Data is measured at a rate of 40 data points per second; hence, a large film can be digitized in about 5 min. Supporting computer software constructs a matrix array of optical densities covering the area of the film, converts optical density to dose, and plots tissue compensators. The concept of designing compensators from port films is reviewed. Phantom studies were performed to show that the compensators so designed are satisfactory for clinical application.

Image processing of conventional tomograms.

Previous authors have suggested that high pass spatial filtering of axial transverse and circular tomograms would improve the perceived image. A preliminary study here shows that good signal-to-noise ratio is critical for the success of image processing for the contrasts obtainable in the clinical situation. The successful image processing of a small object on the Philips Polytome is demonstrated, as well as a clinical example. A similar trial with the Toshiba axial transverse tomography machine was not successful due to lower subject contrast with higher kVp techniques. A derivation of the optical transfer function of circular and axial transverse tomograms is given, with emphasis on those features that image processing can improve. To accomplish image processing, two methods employing incoherent light were investigated. Either method may be regarded as an analogue equivalent to the mathematical operations employed by digital computers in the reconstruction of CT images. First, a simple all-purpose image processor is described that makes use of the Herschel effect. Second, a simple film copying technique that simulates a high pass spatial filter is introduced and used to improve tomographic images.

The use of photogrammetry in tissue compensator design. Part I: photogrammetric determination of patient topography.

The surface topography of a patient can be determined by photogrammetry before beginning radiotherapy. The source light of the therapy unit or simulator is used to project a grid pattern onto the patient, and this is then photographed together with control points consisting of miniature light bulbs mounted on a frame suspended from the wedge slot of the therapy machine. When the photograph is projected onto a graphics terminal for data entry into a computer, the three-dimensional topography of the patient's surface can be reconstructed as a two-dimensional matrix of discrete points. A computer algorithm can then design a tissue compensator to fit the individual patient.

The use of photogrammetry in tissue compensator design. Part II: experimental verification of compensator design.

A computer algorithm for designing sheet lead tissue compensators is described. Corrections are made for scatter within the radiation field as well as the shape of the patient for the mantle fields used in treating Hodgkin's disease. The method was tested experimentally with a phantom and found to be clinically acceptable. The advantages of employing this technique with parallel opposed fields are emphasized.