Optimization of IMRT Fluence-Map Smoothing can Result in Improved IMRT Plans
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2858 Optimization of IMRT Fluence-Map Smoothing can Result in Improved IMRT Plans B. J. Salter, C. J. Anker, M. Tobler, Y. J. Hitchcock University of Utah-Huntsman Cancer Hospital, Salt Lake City, UT Background: Commercially available IMRT treatment planning systems (TPS) typically include a fluence-map smoothing option designed to decrease irregularities/complexity in delivered beam fluence patterns, thus allowing for decreased monitor units and shorter treatment times. The cost of reducing the complexity of the inverse-planned optimal fluence pattern is typically a reduction in plan quality. Here we study the behavior of 3 different treatment planning systems when smoothing parameters are systemat- ically adjusted. Materials/Methods: We evaluated a case of sinonasal carcinoma treated by IMRT in our clinic. RTOG recommendations for target coverage and object-at-risk (OAR) dose constraints were used for planning. Contours were transferred via DICOM to the Varian Eclipse v6.5, BrainLab Brainscan v5.31, and Nomos Corvus v6.2 TPS’s. Each set of TPS specific plans were optimized identically to each other, except that the TPS-inherent ‘‘smoothing’’ or ‘‘complexity’’ values were varied. For each TPS, plans were optimized with a minimal smoothing level, vendor-defined default smoothing, and double the default smoothing. All plans were normalized for identical target coverage. Key metrics of plan quality and delivery efficiency were gathered for each plan. Results: The various smoothing scenarios studied here can impact significantly on plan quality (see Fig. 1). Results varied widely, by vendor, with regard to both plan quality and delivery efficiency (see Table 1). Conclusions: Appropriate use of the fluence map smoothing functionality inherent to typical IMRT inverse planning systems can result in valuable improvements to plan quality, such as reduced critical structure maximum doses. The behavior of fluence-map smoothing functions varies widely by vendor. It appears important to understand the behavior of the specific TPS in use at each clinic. % Change Relative to Default Smoothing Plan Corvus Corvus Eclipse Eclipse BrainLab BrainLab Smoothing Setting Minimal Maximum/Double Minimal Maximum/Double Minimal Maximum/Double Left Optic Nerve Max. Dose 15.1% 12.6% 0% 1.8% 0% 0% Right Optic Nerve Max. Dose 17.7% 5.5% 1.5% 0.8% 1.4% 2.9% Optic Chiasm Max. Dose 20.3% 2.5% 0.1% 2.0% 1.5% 0% Monitor Units 14.0% 83.6% 37.8% 26.0% 4.2% 6.0% Segments 90.7% 96.2% 13.7% 11.4% 0.5% 1.5% Author Disclosure: B.J. Salter, North American Scientific, F. Consultant/Advisory Board; C.J. Anker, None; M. Tobler, None; Y.J. Hitchcock, None. 2859 Evaluation of Intrafraction Motion in Head and Neck Cancer During Radiotherapy T. H. La, M. Chao, L. Xing, Q. Le Stanford University, Stanford, CA Purpose/Objective(s): To quantify the intrafraction motion of the head, neck, and shoulders during radiotherapy for head and neck cancer. The magnitude and incidence of intrafraction motion, particularly with the increased treatment times required for intensity modulation radiation therapy (IMRT) delivery, may have clinical implications on Planning Target Volume (PTV) margins. Materials/Methods: Twenty-nine patients planned to undergo head and neck radiotherapy were evaluated and all were immobi- lized using a customized Accuform head holder, a thermoplastic mask extending from the cranium to below the mandible, and a customized ‘‘peg board’’ to reproduce the shoulder position. Patients then underwent a positron emission tomography (PET) scan with a computed tomography (CT) scan for attenuation correction as well as a treatment planning contrast enhanced CT scan, both performed in the same setting without moving the patient. The two CT scans were co-registered in the head and upper neck region and separately in the shoulders using our institutional computer software. Both translational and rotational motions were assessed in six dimensions. The motion observed between the two CT scans, which were obtained approximately 20 minutes apart while the patient remained immobilized, serves as a surrogate for intrafraction motion during radiotherapy. Proceedings of the 49th Annual ASTRO Meeting S681
Transcript of Optimization of IMRT Fluence-Map Smoothing can Result in Improved IMRT Plans
Proceedings of the 49th Annual ASTRO Meeting S681
2858 Optimization of IMRT Fluence-Map Smoothing can Result in Improved IMRT Plans
B. J. Salter, C. J. Anker, M. Tobler, Y. J. Hitchcock
University of Utah-Huntsman Cancer Hospital, Salt Lake City, UT
Background: Commercially available IMRT treatment planning systems (TPS) typically include a fluence-map smoothing optiondesigned to decrease irregularities/complexity in delivered beam fluence patterns, thus allowing for decreased monitor units andshorter treatment times. The cost of reducing the complexity of the inverse-planned optimal fluence pattern is typically a reductionin plan quality. Here we study the behavior of 3 different treatment planning systems when smoothing parameters are systemat-ically adjusted.
Materials/Methods: We evaluated a case of sinonasal carcinoma treated by IMRT in our clinic. RTOG recommendations fortarget coverage and object-at-risk (OAR) dose constraints were used for planning. Contours were transferred via DICOM to theVarian Eclipse v6.5, BrainLab Brainscan v5.31, and Nomos Corvus v6.2 TPS’s. Each set of TPS specific plans were optimizedidentically to each other, except that the TPS-inherent ‘‘smoothing’’ or ‘‘complexity’’ values were varied. For each TPS, planswere optimized with a minimal smoothing level, vendor-defined default smoothing, and double the default smoothing. Allplans were normalized for identical target coverage. Key metrics of plan quality and delivery efficiency were gathered foreach plan.
Results: The various smoothing scenarios studied here can impact significantly on plan quality (see Fig. 1). Results varied widely,by vendor, with regard to both plan quality and delivery efficiency (see Table 1).
Conclusions: Appropriate use of the fluence map smoothing functionality inherent to typical IMRT inverse planning systems canresult in valuable improvements to plan quality, such as reduced critical structure maximum doses. The behavior of fluence-mapsmoothing functions varies widely by vendor. It appears important to understand the behavior of the specific TPS in use at eachclinic.
% Change Relative to Default Smoothing Plan
Corvus Corvus Eclipse Eclipse BrainLab BrainLab
Smoothing Setting Minimal Maximum/Double Minimal Maximum/Double Minimal Maximum/DoubleLeft Optic Nerve Max. Dose
�15.1% 12.6% 0% 1.8% 0% 0%Right Optic Nerve Max. Dose
�17.7% 5.5% 1.5% 0.8% �1.4% 2.9%Optic Chiasm Max. Dose
�20.3% �2.5% 0.1% 2.0% �1.5% 0%Monitor Units
�14.0% �83.6% 37.8% �26.0% 4.2% �6.0%Segments
90.7% �96.2% 13.7% �11.4% 0.5% �1.5%Author Disclosure: B.J. Salter, North American Scientific, F. Consultant/Advisory Board; C.J. Anker, None; M. Tobler, None;Y.J. Hitchcock, None.
2859 Evaluation of Intrafraction Motion in Head and Neck Cancer During Radiotherapy
T. H. La, M. Chao, L. Xing, Q. Le
Stanford University, Stanford, CA
Purpose/Objective(s): To quantify the intrafraction motion of the head, neck, and shoulders during radiotherapy for head and neckcancer. The magnitude and incidence of intrafraction motion, particularly with the increased treatment times required for intensitymodulation radiation therapy (IMRT) delivery, may have clinical implications on Planning Target Volume (PTV) margins.
Materials/Methods: Twenty-nine patients planned to undergo head and neck radiotherapy were evaluated and all were immobi-lized using a customized Accuform head holder, a thermoplastic mask extending from the cranium to below the mandible, anda customized ‘‘peg board’’ to reproduce the shoulder position. Patients then underwent a positron emission tomography (PET)scan with a computed tomography (CT) scan for attenuation correction as well as a treatment planning contrast enhanced CTscan, both performed in the same setting without moving the patient. The two CT scans were co-registered in the head and upperneck region and separately in the shoulders using our institutional computer software. Both translational and rotational motionswere assessed in six dimensions. The motion observed between the two CT scans, which were obtained approximately 20 minutesapart while the patient remained immobilized, serves as a surrogate for intrafraction motion during radiotherapy.
