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Modified three-field technique for breast irradiation
Proceedings of the 33rd Annual ASTRO Meeting
1081 CLINICALPERFORMANCEOF A CT-CAPABLESIMULAT@R R.D. Zwicker, PhD and R. Schmidt-Ullrich, M.D. Medical College of Virgin:.a Purpose: This work reports on the performance characteristics of a radiotherapy simulator with an image intensifier-based CT scanning capability. The study includes measurements to parameterize image quality in terms of spatial resolution, density resolution, and positional accuracy, and an assessment of the usefulness of the modality based on clinical experience with more than 150 patients. Materials and Methods: Test scans on a standard phantom established the effect of technique factors and convolution filter on image quality. Dimensional accuracy and CTnumber precision were evaluated to assess the suitability of the images for treatment Patient scans taken in a variety of treatment geometries were examined and planning. evaluated. Results: Tests indicate a strong dependence of image quality on convolution filter and object position. Spatial resolution is comparable with or better than that published for other nondiagnostic CT systems, while density resolution is generally poor. Linear dimensions were imaged with an accuracy of about 1.0%. The images were found to contain sufficient detail to allow CT-based treatment planning using standard inhomogeneity densities in lieu of accurate electron densities. The CT capability is especially useful for breast treatments since a special modification allowed scans to be taken even with Head and neck setups and lung the patient elevated on a variable-angle breast board. boost planning are also facilitated using CT scans. The relatively small field of a view (32-34 cm) restricts the usefulness of the system for pelvic field planning. The CT scans were adequate for treatment planning even though poor Conclusion: density resolution !.imits the ability to distinguish between similar soft tissues. The system allows patient images to be taken in the treatment position in most cases.
1082 MODIFIED THREE-FIELD
TECHNIQUE
FOR BREAST IRRADIATION
R. D. Zwicker, PhD and K. Radie-Keane,
MD
Medical College of Virginia Purpose: Techniques for therapeutic breast irradiation are under continuing development to accommodate advanc:es in equipment design. This work describes a hybrid isocentric setup featuring simulator-based CT scanning to obtain contours in the treatment position. Materials and Methods: Patients are treated on a special tilt board to improve dose homogeneity in the supraclavicular and matchplane regions. Standard isocentric techniques of half-beam blocking in the supraclavicular field and couch rotation for tangential fields are implemented to optimize field matching. Asymmetric collimation is used in the tangential fields to fix the isocenter at an easily reproducible point. Treatment planning is carried out using CT images obtained with the patient in the treatment position. This is accomplished on a CT-capable simulator which uses the image intensifier for data collection. A quantitative study has been carried out using both phantom and patient images. Results: Asymmetric collimation simplifies daily setup and improves treatment accuracy by allowing direct us.e of the backpointer and distance indicator. An investigation of image quality showed that the CT scans have adequate spatial resolution and oositional accuracv for treatment planning purposes, although so‘ft tissue differentiation is' poor. Our experience with more than 40 patient breast scans confirms the conclusion of others that luna* corrections are critical to the development of optimal treatment plans. Conclusions: The hybrid three-field technique simplifies isocentric setups while allowing optimal matchplane alignment. Simulator-based CT scans are particularly advantageous for breast patients since the typical poor density resolution of these scanners is not critical in th.e planning of these patients, while the simulator allows patients to be scanned in the exact treatment position even when elevated on a tilt board.
233
1081 CLINICALPERFORMANCEOF A CT-CAPABLESIMULAT@R R.D. Zwicker, PhD and R. Schmidt-Ullrich, M.D. Medical College of Virgin:.a Purpose: This work reports on the performance characteristics of a radiotherapy simulator with an image intensifier-based CT scanning capability. The study includes measurements to parameterize image quality in terms of spatial resolution, density resolution, and positional accuracy, and an assessment of the usefulness of the modality based on clinical experience with more than 150 patients. Materials and Methods: Test scans on a standard phantom established the effect of technique factors and convolution filter on image quality. Dimensional accuracy and CTnumber precision were evaluated to assess the suitability of the images for treatment Patient scans taken in a variety of treatment geometries were examined and planning. evaluated. Results: Tests indicate a strong dependence of image quality on convolution filter and object position. Spatial resolution is comparable with or better than that published for other nondiagnostic CT systems, while density resolution is generally poor. Linear dimensions were imaged with an accuracy of about 1.0%. The images were found to contain sufficient detail to allow CT-based treatment planning using standard inhomogeneity densities in lieu of accurate electron densities. The CT capability is especially useful for breast treatments since a special modification allowed scans to be taken even with Head and neck setups and lung the patient elevated on a variable-angle breast board. boost planning are also facilitated using CT scans. The relatively small field of a view (32-34 cm) restricts the usefulness of the system for pelvic field planning. The CT scans were adequate for treatment planning even though poor Conclusion: density resolution !.imits the ability to distinguish between similar soft tissues. The system allows patient images to be taken in the treatment position in most cases.
1082 MODIFIED THREE-FIELD
TECHNIQUE
FOR BREAST IRRADIATION
R. D. Zwicker, PhD and K. Radie-Keane,
MD
Medical College of Virginia Purpose: Techniques for therapeutic breast irradiation are under continuing development to accommodate advanc:es in equipment design. This work describes a hybrid isocentric setup featuring simulator-based CT scanning to obtain contours in the treatment position. Materials and Methods: Patients are treated on a special tilt board to improve dose homogeneity in the supraclavicular and matchplane regions. Standard isocentric techniques of half-beam blocking in the supraclavicular field and couch rotation for tangential fields are implemented to optimize field matching. Asymmetric collimation is used in the tangential fields to fix the isocenter at an easily reproducible point. Treatment planning is carried out using CT images obtained with the patient in the treatment position. This is accomplished on a CT-capable simulator which uses the image intensifier for data collection. A quantitative study has been carried out using both phantom and patient images. Results: Asymmetric collimation simplifies daily setup and improves treatment accuracy by allowing direct us.e of the backpointer and distance indicator. An investigation of image quality showed that the CT scans have adequate spatial resolution and oositional accuracv for treatment planning purposes, although so‘ft tissue differentiation is' poor. Our experience with more than 40 patient breast scans confirms the conclusion of others that luna* corrections are critical to the development of optimal treatment plans. Conclusions: The hybrid three-field technique simplifies isocentric setups while allowing optimal matchplane alignment. Simulator-based CT scans are particularly advantageous for breast patients since the typical poor density resolution of these scanners is not critical in th.e planning of these patients, while the simulator allows patients to be scanned in the exact treatment position even when elevated on a tilt board.
233