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Characterization of Intrafraction Prostate Deformation and Displacement via Twice Daily MVCT Imaging
Proceedings of the 49th Annual ASTRO Meeting
Author Disclosure: J.D.P. Hoisak, None; S.L. Breen, None; D.A. Jaffray, None.
2802
Video-Coaching as Biofeedback-tool to Improve Gated Treatments: 2 Years Clinical Experience
P. H. Cossmann, A. Stuessi, C. von Briel Radiotherapie Hirslanden, Aarau, Switzerland Purpose/Objective(s): Gated treatments using the Varian RPM-gating TM System include in a standard configuration a coaching tool based on voice commands (‘‘breathe-in’’/’’breathe-out’’) called audio-coaching. As this configuration does not include feedback information like amplitude and breathing period, there are limitations concerning respiration depth and breathing pattern. The aim of this study was to evaluate the impact of video-coaching as biofeedback to achieve more regular breathing and–as a consequence–quality improvements of the 4D CT scans as well as duty cycle reductions. Materials/Methods: Varian RPM-gating system is used for acquisition of the CT-Scan (4D-CT) as well as the treatments; for the latter it manages the controlled switching of the radiation beam during a pre-selected specific phase of the respiratory cycle. 40 patients with gated treatments have been analyzed, whereas 20 were only audio-coached and 20 audio-coached with video-feedback. We evaluated periodicity and amplitude changes as well as compliance with regard to the theoretically calculated duty cycle and determined the dependency of the parameters on the coaching type. Results: For the CT acquisitions several changes has been observed, i.e., fluctuations of the inspiration maxima are significantly smaller (p = 0.005) and the breathing curves are smoother. The compliance during the treatment course was significantly increased: almost all video-coached patients reached in average their theoretical duty cycle, whereas 60% of the patients with audio-coaching only had more than 25% longer treatment times due to inappropriate amplitudes. Periodicity is not dependent on the kind of coaching (p = 0.01). Conclusions: Video-coaching is suitable to significantly improve the quality of 4D scans and allows optimizing the treatment time due to better compliance. In the meantime we also implemented this feedback technology combined with deep inspiration breath hold technique thus allowing the patient to control the treatment themselves in a direct way. These results indicate that this approach could suit the individual patient need in a better way. Author Disclosure: P.H. Cossmann, None; A. Stuessi, None; C. von Briel, None.
2803
Characterization of Intrafraction Prostate Deformation and Displacement via Twice Daily MVCT Imaging
R. C. Susil, T. N. Teslow, T. R. McNutt, J. Wong, T. L. DeWeese, D. Song Department of Radiation Oncology and Molecular Radiation Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD Introduction: As interfraction motion and setup errors are reduced via daily image guidance, intrafraction motion has become increasingly important in defining PTV margins. While previous studies have used intraprostatic fiducial systems to quantify prostate displacement, data on prostate deformation during daily treatment are more limited. By using megavoltage CT (MVCT) images acquired both before and after daily TomoTherapy sessions, this study characterizes daily internal motion and defines margins necessary to account for both intrafraction prostate deformation and displacement. Materials/Methods: The study included 8 patients with clinically localized prostate cancer treated using the TomoTherapy Hi-Art system from 7/2006–9/2006. MVCT imaging was performed immediately before and after treatment on 5 occasions distributed throughout the treatment course (mean treatment time 18.8 minutes). Prostate contours were defined using the Pinnacle3 system
S645
I. J. Radiation Oncology d Biology d Physics
S646
Volume 69, Number 3, Supplement, 2007
(Philips Medical Systems, Inc.) by a single physician on 5–7 images per scan. Data was processed using MATLAB (MathWorks, Inc.). Prostate volumes were expanded in a pair-wise fashion, comparing only pre- and post-treatment images from individual fractions, to determine margins required to cover 95% of the prostate volume on a given day. Results: As shown in Figure 1, while 75% of patients required margin expansions of less than 2.5 mm for 95% coverage of daily intrafraction prostate volumes, two patients (B & F) exhibited greater intrafraction motion (MVCT image review showed prostate deformation caused by changes in rectal distention during these fractions). A single patient (E) showed consistent posterior prostate displacement due to relaxation of the gluteal muscles during each treatment (decreased gluteal thickness and posterior shift was evident on image review). In aggregate, a 4.0 mm margin encompassed 95% of intrafraction prostate motion for 95% of the treatment fractions examined. Conclusions: Radiation dose escalation is an established and important treatment approach in prostate cancer management. Critical to this method are techniques for daily targeting of the prostate and minimization of the rectal toxicity associated with increased dose. Although limited by lower out-of-plane resolution (4 mm) and contrast compared with kVCT & MRI, contouring operator dependence, and low temporal resolution, these data compliment prior reports that utilized implanted fiducial systems by allowing for characterization of not only prostate displacement but also prostate deformation. The continued importance of judicious patient preparation and setup to minimize intrafraction prostate motion is emphasized.
Author Disclosure: R.C. Susil, None; T.N. Teslow, None; T.R. McNutt, None; J. Wong, None; T.L. DeWeese, None; D. Song, None.
2804
Deformable Image Registration With Inclusion of Auto-Detected Homologous Tissue Features
1
Y. Xie , L. Xing1, D. Paquin1, D. Levy1, T. Yang2 1 Stanford University, Stanford, CA, 2Northwestern Polytechnical University of China, Xi’an, China Purpose/Objectives(s): Most image registration algorithms ignore the underlying tissue features but simply rely on the similarity of image intensity. As thus, a spatial accuracy better than 35 mm is hardly achievable using any of these techniques. The aim of this work is to develop a tissue feature-based deformable algorithm to substantially improve the performance of registration for various IGRT applications. The novelties of this work include: (1) auto-detection and quantitative characterization of homologous tissue features in the input images; and (2) seamlessly incorporation of the detected tissue feature information for accurate and robust registration. Materials/Methods: The corresponding tissue features in the fixed and moving images are described by the information in the neighborhood of a point of interest. Quantitatively, the local information is characterized by using the Scale Invariance Feature Transformation (SIFT) method (the use of scale-space is to compare different images in the same scale, and is thus referred to as the SIFT), which includes scale-space extrema detection, control point localization, orientation assignment and control point descriptor. Another important feature of SIFT is the orientation histogram technique. In a 2D case, for example, the 8 8 neighborhood around a given point is defined as a volume. The volume is divided into four parts. In each part, the gradient magnitude of each pixel is calculated and sorted into 8 angle bins (the first bin is from 0 degree to 45 degree and so on). To further increase the precision of tissue feature association, a bi-directional mapping strategy is developed based on the intuitive fact that if a feature region in the fixed image is mapped correctly to the moving image, then it will necessarily be mapped back to the original feature region in the fixed image when we apply the inverse map to the corresponding feature region in the moving image. During the bi-directional calculation, the feature region is labeled as a matched region if the displacement vectors match. Otherwise, we consider it a mismatched region and delete it. The obtained homologous tissue features are treated as a priori knowledge in the subsequent deformable registration using thin-plate spline (TPS), or BSpline or finite element (FE) method. Results: A theoretical framework of auto-determining homologous tissue features and incorporating the information into commonly used deformable registration algorithms have been established. Several experiments using both digital phantom and clinical thoracic cases demonstrate the accuracy and efficiency of the proposed method. For each case, the algorithm convergence is confirmed by starting the registration from a large number of initial transformation parameters. It is observed that the convergence
Author Disclosure: J.D.P. Hoisak, None; S.L. Breen, None; D.A. Jaffray, None.
2802
Video-Coaching as Biofeedback-tool to Improve Gated Treatments: 2 Years Clinical Experience
P. H. Cossmann, A. Stuessi, C. von Briel Radiotherapie Hirslanden, Aarau, Switzerland Purpose/Objective(s): Gated treatments using the Varian RPM-gating TM System include in a standard configuration a coaching tool based on voice commands (‘‘breathe-in’’/’’breathe-out’’) called audio-coaching. As this configuration does not include feedback information like amplitude and breathing period, there are limitations concerning respiration depth and breathing pattern. The aim of this study was to evaluate the impact of video-coaching as biofeedback to achieve more regular breathing and–as a consequence–quality improvements of the 4D CT scans as well as duty cycle reductions. Materials/Methods: Varian RPM-gating system is used for acquisition of the CT-Scan (4D-CT) as well as the treatments; for the latter it manages the controlled switching of the radiation beam during a pre-selected specific phase of the respiratory cycle. 40 patients with gated treatments have been analyzed, whereas 20 were only audio-coached and 20 audio-coached with video-feedback. We evaluated periodicity and amplitude changes as well as compliance with regard to the theoretically calculated duty cycle and determined the dependency of the parameters on the coaching type. Results: For the CT acquisitions several changes has been observed, i.e., fluctuations of the inspiration maxima are significantly smaller (p = 0.005) and the breathing curves are smoother. The compliance during the treatment course was significantly increased: almost all video-coached patients reached in average their theoretical duty cycle, whereas 60% of the patients with audio-coaching only had more than 25% longer treatment times due to inappropriate amplitudes. Periodicity is not dependent on the kind of coaching (p = 0.01). Conclusions: Video-coaching is suitable to significantly improve the quality of 4D scans and allows optimizing the treatment time due to better compliance. In the meantime we also implemented this feedback technology combined with deep inspiration breath hold technique thus allowing the patient to control the treatment themselves in a direct way. These results indicate that this approach could suit the individual patient need in a better way. Author Disclosure: P.H. Cossmann, None; A. Stuessi, None; C. von Briel, None.
2803
Characterization of Intrafraction Prostate Deformation and Displacement via Twice Daily MVCT Imaging
R. C. Susil, T. N. Teslow, T. R. McNutt, J. Wong, T. L. DeWeese, D. Song Department of Radiation Oncology and Molecular Radiation Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD Introduction: As interfraction motion and setup errors are reduced via daily image guidance, intrafraction motion has become increasingly important in defining PTV margins. While previous studies have used intraprostatic fiducial systems to quantify prostate displacement, data on prostate deformation during daily treatment are more limited. By using megavoltage CT (MVCT) images acquired both before and after daily TomoTherapy sessions, this study characterizes daily internal motion and defines margins necessary to account for both intrafraction prostate deformation and displacement. Materials/Methods: The study included 8 patients with clinically localized prostate cancer treated using the TomoTherapy Hi-Art system from 7/2006–9/2006. MVCT imaging was performed immediately before and after treatment on 5 occasions distributed throughout the treatment course (mean treatment time 18.8 minutes). Prostate contours were defined using the Pinnacle3 system
S645
I. J. Radiation Oncology d Biology d Physics
S646
Volume 69, Number 3, Supplement, 2007
(Philips Medical Systems, Inc.) by a single physician on 5–7 images per scan. Data was processed using MATLAB (MathWorks, Inc.). Prostate volumes were expanded in a pair-wise fashion, comparing only pre- and post-treatment images from individual fractions, to determine margins required to cover 95% of the prostate volume on a given day. Results: As shown in Figure 1, while 75% of patients required margin expansions of less than 2.5 mm for 95% coverage of daily intrafraction prostate volumes, two patients (B & F) exhibited greater intrafraction motion (MVCT image review showed prostate deformation caused by changes in rectal distention during these fractions). A single patient (E) showed consistent posterior prostate displacement due to relaxation of the gluteal muscles during each treatment (decreased gluteal thickness and posterior shift was evident on image review). In aggregate, a 4.0 mm margin encompassed 95% of intrafraction prostate motion for 95% of the treatment fractions examined. Conclusions: Radiation dose escalation is an established and important treatment approach in prostate cancer management. Critical to this method are techniques for daily targeting of the prostate and minimization of the rectal toxicity associated with increased dose. Although limited by lower out-of-plane resolution (4 mm) and contrast compared with kVCT & MRI, contouring operator dependence, and low temporal resolution, these data compliment prior reports that utilized implanted fiducial systems by allowing for characterization of not only prostate displacement but also prostate deformation. The continued importance of judicious patient preparation and setup to minimize intrafraction prostate motion is emphasized.
Author Disclosure: R.C. Susil, None; T.N. Teslow, None; T.R. McNutt, None; J. Wong, None; T.L. DeWeese, None; D. Song, None.
2804
Deformable Image Registration With Inclusion of Auto-Detected Homologous Tissue Features
1
Y. Xie , L. Xing1, D. Paquin1, D. Levy1, T. Yang2 1 Stanford University, Stanford, CA, 2Northwestern Polytechnical University of China, Xi’an, China Purpose/Objectives(s): Most image registration algorithms ignore the underlying tissue features but simply rely on the similarity of image intensity. As thus, a spatial accuracy better than 35 mm is hardly achievable using any of these techniques. The aim of this work is to develop a tissue feature-based deformable algorithm to substantially improve the performance of registration for various IGRT applications. The novelties of this work include: (1) auto-detection and quantitative characterization of homologous tissue features in the input images; and (2) seamlessly incorporation of the detected tissue feature information for accurate and robust registration. Materials/Methods: The corresponding tissue features in the fixed and moving images are described by the information in the neighborhood of a point of interest. Quantitatively, the local information is characterized by using the Scale Invariance Feature Transformation (SIFT) method (the use of scale-space is to compare different images in the same scale, and is thus referred to as the SIFT), which includes scale-space extrema detection, control point localization, orientation assignment and control point descriptor. Another important feature of SIFT is the orientation histogram technique. In a 2D case, for example, the 8 8 neighborhood around a given point is defined as a volume. The volume is divided into four parts. In each part, the gradient magnitude of each pixel is calculated and sorted into 8 angle bins (the first bin is from 0 degree to 45 degree and so on). To further increase the precision of tissue feature association, a bi-directional mapping strategy is developed based on the intuitive fact that if a feature region in the fixed image is mapped correctly to the moving image, then it will necessarily be mapped back to the original feature region in the fixed image when we apply the inverse map to the corresponding feature region in the moving image. During the bi-directional calculation, the feature region is labeled as a matched region if the displacement vectors match. Otherwise, we consider it a mismatched region and delete it. The obtained homologous tissue features are treated as a priori knowledge in the subsequent deformable registration using thin-plate spline (TPS), or BSpline or finite element (FE) method. Results: A theoretical framework of auto-determining homologous tissue features and incorporating the information into commonly used deformable registration algorithms have been established. Several experiments using both digital phantom and clinical thoracic cases demonstrate the accuracy and efficiency of the proposed method. For each case, the algorithm convergence is confirmed by starting the registration from a large number of initial transformation parameters. It is observed that the convergence