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Results: Maximum SUV computed from RT pixel values for the anatomical sites considered (mean 8.2, range 1.7–27.6) corresponded well with those measured on the NM workstation (r20.9985, n90). Kidney maximum SUV only correlated well when the maximum value for the entire organ was considered, due to the dramatic SUV gradient and differences in slice thickness displayed on the two workstations (1 mm - NM, 3.5 mm RT). SUV threshold delineation of CTV was accomplished on 12 of 18 patients whose PET study was within 16 days of the planning CT. Regions were modified to exclude known false-positive areas of uptake (e.g., contralateral tonsil). The volume of SUV 2.5 around CTV1 had a range of 12.7–132.2 cc (mean 59.6). The SUV volume delineated outside of the CTV1 ranged from 0.3–26.8 cc (mean 17. 4cc or 24.4%); the volume of SUV 2.5 outside all CTV regions ranged from 0 –12.6 cc (mean 4.2 cc or 7.7%). The mean SUV in these regions identified outside of CTV1 and all CTVs were 3.1 and 3.4, respectively. The mean minimum expansion of CTV1 and all CTVs required to cover the SUV 2.5 volume were 16.5 and 6.4 mm, respectively. Conclusions: An objective and quantitative tumor delineation approach was developed, using pixel value thresholds for contouring voxels of specified FDG uptake. This methodology was validated for a wide range of SUVs for H&N patients, and when applied to delineate regions around tumors with an SUV 2.5, clinically significant regions outside of both the primary CTV, as well as all CTVs were identified. Author Disclosure: J.E. Bayouth, None; F. Qing, None; M.M. Graham, None; M. Yao, None. 2829 Jaws-Only IMRT Using Direct Aperture Optimization M. K. N. Afghan, M. A. Earl, C. X. Yu, Z. Jiang, D. M. Shepard University of Maryland School of Medicine, Baltimore, MD Purpose/Objective(s): Clinical implementation of intensity modulated radiation therapy (IMRT) is significantly more com- plicated for facilities without a multileaf collimator (MLC). In this study, we have examined the use of Direct Aperture Optimization (DAO) to produce efficient IMRT treatment plans that can be delivered without an MLC. Materials/Methods: This “jaws-only” approach to IMRT uses a series of rectangular field shapes to achieve a modulated intensity pattern from each beam direction. The user specifies the number of allowable jaws-only segments, and the optimizer directly optimizes the jaw positions and the relative weights assigned to each aperture. Because all of the constraints imposed by the jaws are incorporated into the optimization, the need for leaf sequencing is eliminated. The optimization is performed using a simulated annealing algorithm. For fives clinical cases (2 prostates, 1 pancreas, 1 abdomen, and 1 breast), treatment plans were created using 5, 10, 15, 20, and 25 apertures per beam direction. The plans were compared with the benchmark MLC-based DAO plan created for each case using the same treatment objectives. Each plan was delivered to a phantom where absolute dose was measured with an ionization chamber and relative dose was measured with Kodak EDR film. Results: For the jaws-only treatment plans, only minor improvements were observed as the number of segments per beam direction was increased beyond 20. Figure 1 plots a DVH comparison between an MLC plan (5 apertures per direction) versus a jaws-only plan (20 apertures per direction) for a prostate patient. DVH and isodose comparisons for the cases included in this study reveal that jaws-only IMRT is generally able to approach the plan quality provided by MLC-based IMRT using 15 to 20 jaw settings per beam direction. For the most complex cases involving multiple target shapes or multiple prescription levels, jaws-only IMRT is unable to achieve comparable critical structure sparing while maintaining an acceptable number of segments per beam direction. The 5 plans in this study were all delivered in 15 minutes or less and passed our IMRT verification criteria. Conclusions: The ability of DAO to generate efficient jaws-only IMRT plans has been explored. Our results demonstrate that the “jaws-only” approach used in conjunction with DAO provides a feasible IMRT delivery option for clinics without a multileaf collimator. Author Disclosure: M.K.N. Afghan, None; M.A. Earl, None; C.X. Yu, None; Z. Jiang, None; D.M. Shepard, None. S676 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006
Transcript of 2829
Results: Maximum SUV computed from RT pixel values for the anatomical sites considered (mean 8.2, range 1.7–27.6)corresponded well with those measured on the NM workstation (r2�0.9985, n�90). Kidney maximum SUV only correlatedwell when the maximum value for the entire organ was considered, due to the dramatic SUV gradient and differences in slicethickness displayed on the two workstations (1 mm - NM, 3.5 mm RT). SUV threshold delineation of CTV was accomplishedon 12 of 18 patients whose PET study was within 16 days of the planning CT. Regions were modified to exclude knownfalse-positive areas of uptake (e.g., contralateral tonsil). The volume of SUV� 2.5 around CTV1 had a range of 12.7–132.2 cc(mean 59.6). The SUV volume delineated outside of the CTV1 ranged from 0.3–26.8 cc (mean 17. 4cc or 24.4%); the volumeof SUV � 2.5 outside all CTV regions ranged from 0–12.6 cc (mean 4.2 cc or 7.7%). The mean SUV in these regions identifiedoutside of CTV1 and all CTVs were 3.1 and 3.4, respectively. The mean minimum expansion of CTV1 and all CTVs requiredto cover the SUV� 2.5 volume were 16.5 and 6.4 mm, respectively.
Conclusions: An objective and quantitative tumor delineation approach was developed, using pixel value thresholds forcontouring voxels of specified FDG uptake. This methodology was validated for a wide range of SUVs for H&N patients, andwhen applied to delineate regions around tumors with an SUV� 2.5, clinically significant regions outside of both the primaryCTV, as well as all CTVs were identified.
Author Disclosure: J.E. Bayouth, None; F. Qing, None; M.M. Graham, None; M. Yao, None.
2829 Jaws-Only IMRT Using Direct Aperture Optimization
M. K. N. Afghan, M. A. Earl, C. X. Yu, Z. Jiang, D. M. Shepard
University of Maryland School of Medicine, Baltimore, MD
Purpose/Objective(s): Clinical implementation of intensity modulated radiation therapy (IMRT) is significantly more com-plicated for facilities without a multileaf collimator (MLC). In this study, we have examined the use of Direct ApertureOptimization (DAO) to produce efficient IMRT treatment plans that can be delivered without an MLC.
Materials/Methods: This “jaws-only” approach to IMRT uses a series of rectangular field shapes to achieve a modulatedintensity pattern from each beam direction. The user specifies the number of allowable jaws-only segments, and theoptimizer directly optimizes the jaw positions and the relative weights assigned to each aperture. Because all of theconstraints imposed by the jaws are incorporated into the optimization, the need for leaf sequencing is eliminated. Theoptimization is performed using a simulated annealing algorithm. For fives clinical cases (2 prostates, 1 pancreas, 1abdomen, and 1 breast), treatment plans were created using 5, 10, 15, 20, and 25 apertures per beam direction. The planswere compared with the benchmark MLC-based DAO plan created for each case using the same treatment objectives. Eachplan was delivered to a phantom where absolute dose was measured with an ionization chamber and relative dose wasmeasured with Kodak EDR film.
Results: For the jaws-only treatment plans, only minor improvements were observed as the number of segments per beamdirection was increased beyond 20. Figure 1 plots a DVH comparison between an MLC plan (5 apertures per direction) versusa jaws-only plan (20 apertures per direction) for a prostate patient. DVH and isodose comparisons for the cases included in thisstudy reveal that jaws-only IMRT is generally able to approach the plan quality provided by MLC-based IMRT using 15 to 20jaw settings per beam direction. For the most complex cases involving multiple target shapes or multiple prescription levels,jaws-only IMRT is unable to achieve comparable critical structure sparing while maintaining an acceptable number of segmentsper beam direction. The 5 plans in this study were all delivered in 15 minutes or less and passed our IMRT verification criteria.
Conclusions: The ability of DAO to generate efficient jaws-only IMRT plans has been explored. Our results demonstrate thatthe “jaws-only” approach used in conjunction with DAO provides a feasible IMRT delivery option for clinics without amultileaf collimator.
Author Disclosure: M.K.N. Afghan, None; M.A. Earl, None; C.X. Yu, None; Z. Jiang, None; D.M. Shepard, None.
S676 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006
