Conformal therapy planned by three-dimensional dose-optimizing algorithms holds promise to reduce the incidence and severity of normal tissue complications and perhaps provide a means for increased local control by dose escalation. The project proposed here will develop three treatment planning tools needed to implement advanced and effective variants of clinical conformal radiotherapy. Conformal Therapy Optimization Tools. Two conformal therapy dose optimization procedures will be developed and compared. A Discrete Beam optimization approach will be developed that employs the fast Fourier transform beam model. Optimization will be achieved by simulated annealing of """"""""pencil beams"""""""" using dose-volume histograms as the means to control and evaluate the procedure. This method of Discrete Beam optimization will be compared with a Beam Ensemble optimization procedure proposed by Brahme. In addition a comparison will be made of the use of a biological objective function with a physical objective function for each technique. Dynamic MLC Compensation Tools. The optimized treatment planning procedures will specify the delivery of a number of fixed fields each requiring in-field compensation as well as beam shaping. Tools will be developed to irradiate patients with the required compensated beams with a multileaf collimator. These techniques will be developed first as a sequence of radiation exposures made with stationary leaf positions. The accuracy of the method will be assessed using film and ferrous-sulfate gel MRI dosimetry. As more advanced hardware becomes available, the technique will be refined to adapt to continuous leaf motion during the irradiation. EPID Field Verification Tools. Once dose is delivered to a patient using these complex, computer-controlled methods, some means must be provided to verify correct dose delivery. A set of tools will be developed to use electronic portal imaging devices (EPIDs) to provide the checks. Patient positioning as well as the MLC treatment sequence will be verified by comparing EPID-measured images of the transmitted x-ray field with digitally reconstructed radiographs. The comparisons will be made using methods employing image moments and correlation using fast Fourier transforms.
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