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Pre-clinical evaluation of the reliability of a 50 MEV racetrack microtron
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Radiation
Oncology, Biology, Physics Volume 24, Supplement 1
modification of leaf and jaw positions, Dose calculation programs then take into account multileaf Finally, prescription files specifying computation of dose distributions using a pencil beam convolution model. configurations are prepared in treatment machine specific formats and downloaded to the computers driving collimators and other components of the treatment machines.
apertures for leaf and jaw the multileaf
The multileaf collimator configurations Results: Examples will be presented of nasopharynx and prostate treatment plans. Resulting dose distributions for these cases will be shown and the use of the interactive leaf adjustment program illustrated. and a description of actual treatments delivered will also be given. Conclusion: Utilization of multileaf collimation for a heavy patient load of 3D conformal treatments necessitates In order that leaf positions may be interactively adjusted in response of beam aperture definition and delivery. dose distributions. it is also essential that such functions be integrated into a clinical treatment planning system.
automation to resulting
58 3-D PLANNING AND DELIVERY SYSTEM FOR OPTIMIZED CONFORMAL THERAPY Mark P. Carol, M.D., Harris Targovnik, Ph.D., Donald Smith, M.D., David Cahill, M.D University of South Florida, Tampa, Florida Purpose: The aim of radiotherapy is to maximize the difference between dose delivered to the target volume and dose delivered to organs at risk. Current conformal methods may fail to effectively maximize this difference for targets re-entrant in contour and/or where organs at risk exist in the treatment volume. We have developed a 3-D conformal treatment planning and delivery system capable of handling such treatment situations. Materials & Methods: The general approach is a rotational one where field shape and spatial intensity of the beam across the field is continuously varied through the rotation. The parameters driving beam modulation and field shaping are generated by a 3-D planning computer. Plan optimization is accomplished by subjecting a filtered backprojection of the relevant CT or MR data to a simulated annealing algorithm guided by cost functions which quantify prescribed treatment restraints. Resultant isodose data is viewed as lines in orthogonal 2-D images or as volumes in a rotatable 3-D image. A hardware system attached to the accelerator or cobalt unit implements the plan without altering the function of the treatment device. A realtime verification module insures delivery of the prescribed dose. If delivered dose varies from prescribed, an aperture in the implementation system automatically shuts down, protecting the patient from the treatment beam. Results: The system optimizes dose to targets 5 cm to 10 cm in size regardless of shape using one to six 160 degree arcs. Multiple targets can be treated at one time during each rotation. Theoretical measurements have produced results comparable with isodose distributions found in the literature. For single rotational protocols, dose falls to 50% within 1.5 cm. of target margin. Average dose to target is typically >90% with a S.D. on the order of 3.5%; For multiple rotation protocols, falloff has approached 80-90%. lsodose lines 60% or above conform to target contour. Dose-volume histograms vary depending upon the cost function used for optimization. This approach carries with it a price in terms of treatment time. For a four centimeter target, treatment time is doubled when compared to standard rotational protocols; for a ten centimeter target, treatment time is tripled. Conclusion: There is a significant body of literature describing the conformal plans possible when one spatially modulates beam intensity. However, discussions about such approaches have been mostly theoretical as there are limited means available for instituting them. The system with which we have had experience represents a way of creating and delivering spatially modulated conformal therapy plans. Assessing the efficacy of a given plan is problematic due to difficulty quantifying what actually constitutes an optimal plan, since cost functions for optimization can vary depending upon treatment conditions and user. However, this system, designed to be accesible to most treatment facilities regardless of size, has the potential to allow realization of the accepted goal of conformal therapy regardless of target shape: increase the dose to the entire target volume while keeping the dose to critical normal structures within accepted limits. This can only translate into increased efficacy when using radiation therapy as a means of gaining control over localized disease.
Radiation
Oncology, Biology, Physics Volume 24, Supplement 1
modification of leaf and jaw positions, Dose calculation programs then take into account multileaf Finally, prescription files specifying computation of dose distributions using a pencil beam convolution model. configurations are prepared in treatment machine specific formats and downloaded to the computers driving collimators and other components of the treatment machines.
apertures for leaf and jaw the multileaf
The multileaf collimator configurations Results: Examples will be presented of nasopharynx and prostate treatment plans. Resulting dose distributions for these cases will be shown and the use of the interactive leaf adjustment program illustrated. and a description of actual treatments delivered will also be given. Conclusion: Utilization of multileaf collimation for a heavy patient load of 3D conformal treatments necessitates In order that leaf positions may be interactively adjusted in response of beam aperture definition and delivery. dose distributions. it is also essential that such functions be integrated into a clinical treatment planning system.
automation to resulting
58 3-D PLANNING AND DELIVERY SYSTEM FOR OPTIMIZED CONFORMAL THERAPY Mark P. Carol, M.D., Harris Targovnik, Ph.D., Donald Smith, M.D., David Cahill, M.D University of South Florida, Tampa, Florida Purpose: The aim of radiotherapy is to maximize the difference between dose delivered to the target volume and dose delivered to organs at risk. Current conformal methods may fail to effectively maximize this difference for targets re-entrant in contour and/or where organs at risk exist in the treatment volume. We have developed a 3-D conformal treatment planning and delivery system capable of handling such treatment situations. Materials & Methods: The general approach is a rotational one where field shape and spatial intensity of the beam across the field is continuously varied through the rotation. The parameters driving beam modulation and field shaping are generated by a 3-D planning computer. Plan optimization is accomplished by subjecting a filtered backprojection of the relevant CT or MR data to a simulated annealing algorithm guided by cost functions which quantify prescribed treatment restraints. Resultant isodose data is viewed as lines in orthogonal 2-D images or as volumes in a rotatable 3-D image. A hardware system attached to the accelerator or cobalt unit implements the plan without altering the function of the treatment device. A realtime verification module insures delivery of the prescribed dose. If delivered dose varies from prescribed, an aperture in the implementation system automatically shuts down, protecting the patient from the treatment beam. Results: The system optimizes dose to targets 5 cm to 10 cm in size regardless of shape using one to six 160 degree arcs. Multiple targets can be treated at one time during each rotation. Theoretical measurements have produced results comparable with isodose distributions found in the literature. For single rotational protocols, dose falls to 50% within 1.5 cm. of target margin. Average dose to target is typically >90% with a S.D. on the order of 3.5%; For multiple rotation protocols, falloff has approached 80-90%. lsodose lines 60% or above conform to target contour. Dose-volume histograms vary depending upon the cost function used for optimization. This approach carries with it a price in terms of treatment time. For a four centimeter target, treatment time is doubled when compared to standard rotational protocols; for a ten centimeter target, treatment time is tripled. Conclusion: There is a significant body of literature describing the conformal plans possible when one spatially modulates beam intensity. However, discussions about such approaches have been mostly theoretical as there are limited means available for instituting them. The system with which we have had experience represents a way of creating and delivering spatially modulated conformal therapy plans. Assessing the efficacy of a given plan is problematic due to difficulty quantifying what actually constitutes an optimal plan, since cost functions for optimization can vary depending upon treatment conditions and user. However, this system, designed to be accesible to most treatment facilities regardless of size, has the potential to allow realization of the accepted goal of conformal therapy regardless of target shape: increase the dose to the entire target volume while keeping the dose to critical normal structures within accepted limits. This can only translate into increased efficacy when using radiation therapy as a means of gaining control over localized disease.