ABSTRACT
The purpose of this study was to investigate the application of the Monte Carlo technique to the calculation and analysis of output factors for electron beams used in radiotherapy. The code EGS4/BEAM was used to obtain phase-space files for 6, 12 and 20 MeV clinical electron beams from a scattering-foil linac (Varian Clinac 2100C) for a clinically representative range of applicator and square or rectangular insert combinations. The source-to-surface distance used was 100 cm. The field sizes ranged from 1 x 1 cm2 to 20 x 20 cm2. These phase-space files were analysed to study the intrinsic beam characteristics and used as source input for relative dose and output factor computations in homogeneous water phantoms using the code EGS4/DOSXYZ. The calculated relative central-axis depth-dose and transverse dose profiles at various depths of clinical interest agreed with the corresponding measured dose profiles to within 2% of the maximum dose. Calculated output factors for the fields studied agreed with measured output factors to about 2%. This demonstrated that for the Varian Clinac 2100C linear accelerator, electron beam dose calculations in homogeneous water phantoms can be performed accurately at the 2% level using Monte Carlo simulations.
Subject(s)
Electrons , Monte Carlo Method , Particle Accelerators , Radiotherapy, High-Energy , Computer Simulation , Mathematical Computing , Phantoms, Imaging , Radiotherapy Dosage , WaterABSTRACT
The incidence of secondary cancers in the contralateral breast after primary breast irradiation is several times higher than the incidence of first time breast cancer. Studies have shown that the scatter radiation to the contralateral breast may play a large part in the induction of secondary breast cancers. Factors that may contribute to the contralateral breast dose may include the use of blocks, the orientation of the field, and wedges. Reports have shown that the use of regular wedges, particularly for the medial tangential field, gives a significantly higher dose to the contralateral breast compared to an open field. This paper compares the peripheral dose outside the field using a regular wedge, a dynamic wedge, and an open field technique. The data collected consisted of measurements taken with patients, solid water and a Rando phantom using a Varian 2300CD linear accelerator. Ion chambers, thermoluminescent dosimeters (TLD), diodes, and films were the primary means for collecting the data. The measurements show that the peripheral dose outside the field using a dynamic wedge is close to that of open fields, and significantly lower than that of regular wedges. This information indicates that when using a medial wedge, a dynamic wedge should be used.
Subject(s)
Breast Neoplasms/radiotherapy , Breast/radiation effects , Evaluation Studies as Topic , Female , Fluorides , Humans , Incidence , Lithium Compounds , Models, Structural , Neoplasms, Radiation-Induced/etiology , Neoplasms, Second Primary/etiology , Particle Accelerators , Radiation Protection/instrumentation , Radiotherapy Dosage , Radiotherapy, High-Energy , Scattering, Radiation , Thermoluminescent Dosimetry/instrumentationABSTRACT
The speeds of three computer algorithms suitable for use in three-dimensional radiotherapy planning codes were compared. Two of the algorithms are based on ray-tracing methods, the first algorithm uses a fast ray-tracing procedure directly and the second employs a table lookup procedure; the table was originally calculated by ray tracing. The third algorithm was a convolution procedure using the fast Fourier transform. Benchmark programs were written to compare the fundamental running speeds of the three algorithms operating on three-dimensional arrays of various sizes. The convolution procedure employing the three-dimensional fast Fourier transform had the shortest running times on a VAX/750 (Digital Equipment Corp.) computer. We concluded that this algorithm holds significant potential for practical three-dimensional dose calculations.
Subject(s)
Models, Theoretical , Radiation Dosage , Algorithms , HumansABSTRACT
A formulation of the single energy photon transport problem is cast in the form of a series of convolutions over the primary fluence distribution with invariant kernels. A method is developed for compensating for the variant intervoxel attenuation in the scattered dose distribution by means of an invariant correction kernel. Results of applying the formulation to 60Co distributions in the presence of slab and block inhomogeneities are presented.
Subject(s)
Cobalt Radioisotopes , Radiotherapy Dosage , Humans , Models, Structural , Monte Carlo Method , Radiation , Radiotherapy, High-Energy , Scattering, RadiationABSTRACT
A mathematical procedure is described by which the dose distribution of a seed implant can be calculated employing a Fourier transform. The procedure is described in one-, two-, and three- dimensional representations. Dose distributions calculated using this technique are demonstrated. Mathematical constraints of the procedure are discussed.
Subject(s)
Brachytherapy , Radiotherapy Dosage , Computers , Fourier Analysis , Humans , MathematicsABSTRACT
Frequently it is desirable to digitize patient's external and internal contours from computer-assisted tomography (CAT) scan images and to use them for computer treatment planning. After the contours are digitized, each contour could contain over 1000 points. It is a common practice to reduce the number of contour points by interpolation methods in order to use them in a treatment planning program, and in order to save storage space. This paper describes an alternative method for encoding contours. The x-y coordinates of each contour point are represented as a complex number, x + jy. The discrete Fourier transform (DFT) of the array of complex numbers is then computed. Only the 50 lowest frequency components of the DFT are retained. Each contour is then represented by these 50 complex numbers, known as Fourier descriptors. The original contour is restored by performing the inverse Fourier transform. All the frequency components higher than 50 are assumed to be zero during the inverse Fourier transform. The algorithm is described in detail.
Subject(s)
Computers , Fourier Analysis , Radiotherapy Dosage , Software , HumansABSTRACT
In order for radiotherapy residents to become proficient with physics concepts, a certain amount of reinforcement and repetition is necessary. An assembly of computer programs has been developed for the RSX operating system with the aim of shifting these repetitive tasks from the physics staff to a computer. Three types of interactions are employed: (1) textual summaries of key concepts, (2) numerical problems, and (3) typical board exam questions. A file is maintained which records the resident's performances as they work through the programs.
Subject(s)
Computer-Assisted Instruction , Internship and Residency , Radiology/educationABSTRACT
This paper describes a light, easy to use Moire camera and a computer program written to implement it as part of a clinical compensating filters design system.
