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532 oral A NOVEL CT-BASED CONTRAST ENHANCEMENT TECHNIQUE FOR MARKERLESS LUNG TUMOR TRACKING IN X-RAY PROJECTION IMAGES
W EDNESDAY, M AY 11, 2011
532 oral A NOVEL CT-BASED CONTRAST ENHANCEMENT TECHNIQUE FOR MARKERLESS LUNG TUMOR TRACKING IN X-RAY PROJECTION IMAGES A. Fassi1 , J. Schaerer2 , M. Riboldi1 , D. Sarrut2 , G. Baroni1 1 P OLITECNICO DI M ILANO U NIVERSITY, Bioengineering, Milano, Italy 2 U NIVERSITÉ DE LYON ; CREATIS ; CNRS UMR5220 ; C ENTRE L ÉON B ÉRARD, Lyon, France Purpose: Direct lung tumor tracking using in-room X-ray imaging systems, such as digital radiography or rotational cone-beam CT, provides valuable information for IGRT applications. The superimposition of surrounding radioopaque structures may however result in poor lesion contrast. The aim of this study is to develop and investigate a novel automatic method for contrast enhancement and robust markerless tracking of lung tumors in X-ray images, exploiting anatomical information derived from CT volumes. Materials: The implemented technique was tested on 10 lung cancer patients treated with stereotactic body frame based radiation therapy. Data collected for each patient include 4D CT images acquired using a Philips Brilliance CT scanner and CBCT acquisitions performed with the Elekta Synergy system for patient setup.CT-based contrast enhancement: Lung regions including the tumor are masked in the 4D CT maximum intensity projection (MIP), applying threshold-based segmentation algorithms. Digital reconstructed radiographs (DRRs) are generated from the resulting image, following rigid registration with the reconstructed CBCT volume. Contrast-enhanced tumor ROIs are obtained by subtracting the generated DRRs to the original cone-beam images at corresponding projection angles, after ROI histogram equalization.Tumor tracking: Target identification on enhanced CBCT projections is realized through robust template matching techniques. Reference templates for each cone-beam image are obtained by projecting at different angles the gross tumor volume (GTV) delineated on the reference 4D CT 50% phase image. The position of the projected GTV centroid is identified on CBCT images performing fast normalized cross correlation in the frequency domain. Results: The developed tracking method was evaluated on 10 cone-beam acquisitions (1 for each patient), including about 650 two-dimensional projections provided over a full 360◦ gantry rotation. The rate of target identification in contrast enhanced CBCT images proved to be on average 34% (±6%) higher than in original projections adjusted for intensity. In case of tumor recognition achieved with and without enhancement, the cross-correlation coefficients with the reference templates increased by 11% (±4%) when the contrast enhancement technique was applied. Exemplifying results for three selected studies are reported in figure 1, showing the capability of the proposed method in increasing tumor region visibility and reducing the overlap effect of the surrounding anatomical structures, such as the spine or the rib cage.
P ROFFERED PAPER
S 217
Conclusions: A method for contrast enhancement and robust markerless tracking of lung tumors in X-ray projections is proposed. The developed technique can be applied to improve robust trajectory estimation of moving targets from CBCT projections for intra-fraction motion compensation and to increase the clinical application of image guidance techniques in lung cancer patients based on markerless 2-D X-ray imaging. 533 oral ADAPTIVE RADIOTHERAPY TREATMENT FOR PATIENTS WITH ATELECTASIS BASED ON PORTAL DOSIMETRY AND REPEATED CONEBEAM CT L. Persoon1 , M. Öllers1 , S. Wanders1 , D. De Ruysscher1 , D. Tissen1 , J. Wouters1 , F. Verhaegen1 , S. Nijsten1 1
D EPARTMENT OF R ADIATION O NCOLOGY (MAASTRO), GROW – S CHOOL FOR O NCOLOGY AND D EVELOPMENTAL B IOLOGY, M AASTRICHT U NIVERSITY M EDICAL C ENTRE, Maastricht, Netherlands
Purpose: The amount of atelectasis (lung fluid) in lung cancer patients can change during the course of treatment and may displace tumors or healthy tissue. Consequently, the delivered dose to these patients can be different from the planned dose. To ensure that the correct dose was delivered and to be able to adapt a planned treatment to changes in anatomy, dose verification during treatment is essential. In this study, we describe the implementation of an adaptive clinical protocol for lung cancer patients with atelectasis and a method to determine decision parameters. Materials: An adaptive protocol using weekly conebeam CT (CBCT) scans and 2D portal dosimetry was implemented. In the protocol, a treatment was adapted when either large anatomical changes were visible on CBCT (changes in target positioning >7 mm) or significant dose deviations were detected using 2D portal dosimetry. A dose deviation was classified when for all beams of a treatment fraction >5% of the pixels showed a gamma value (γ ) >1, using gamma criteria of 3%, 3mm. In case of re-planning a second CT was acquired. The dose-volume-histograms (DVHs) for the non-adapted scenario were compared to three adaptive scenarios, which involved dose recalculation and/or re-planning in the second CT. The DVHs were calculated using deformable registration based on demons to accumulate the dose of the different plans on the initially planned patient anatomy and delineations. For this study, we analyzed 6 patients included in the adaptive protocol. Results: From the 6 evaluated patients, 2 patients got a treatment adaptation based on 2D portal dose differences and 2 patients showed target displacements on the CBCT of more than 7 mm, also leading to an adaptation of the treatment. Fig. 1a shows a dose deviation starting to emerge from fraction 11. After fraction 21 a new plan was used for treatment and dose errors diminished considerably. The DVHs showed (Fig. 1b) that when no adaptation was performed the lung dose would have been higher than originally planned.
532 oral A NOVEL CT-BASED CONTRAST ENHANCEMENT TECHNIQUE FOR MARKERLESS LUNG TUMOR TRACKING IN X-RAY PROJECTION IMAGES A. Fassi1 , J. Schaerer2 , M. Riboldi1 , D. Sarrut2 , G. Baroni1 1 P OLITECNICO DI M ILANO U NIVERSITY, Bioengineering, Milano, Italy 2 U NIVERSITÉ DE LYON ; CREATIS ; CNRS UMR5220 ; C ENTRE L ÉON B ÉRARD, Lyon, France Purpose: Direct lung tumor tracking using in-room X-ray imaging systems, such as digital radiography or rotational cone-beam CT, provides valuable information for IGRT applications. The superimposition of surrounding radioopaque structures may however result in poor lesion contrast. The aim of this study is to develop and investigate a novel automatic method for contrast enhancement and robust markerless tracking of lung tumors in X-ray images, exploiting anatomical information derived from CT volumes. Materials: The implemented technique was tested on 10 lung cancer patients treated with stereotactic body frame based radiation therapy. Data collected for each patient include 4D CT images acquired using a Philips Brilliance CT scanner and CBCT acquisitions performed with the Elekta Synergy system for patient setup.CT-based contrast enhancement: Lung regions including the tumor are masked in the 4D CT maximum intensity projection (MIP), applying threshold-based segmentation algorithms. Digital reconstructed radiographs (DRRs) are generated from the resulting image, following rigid registration with the reconstructed CBCT volume. Contrast-enhanced tumor ROIs are obtained by subtracting the generated DRRs to the original cone-beam images at corresponding projection angles, after ROI histogram equalization.Tumor tracking: Target identification on enhanced CBCT projections is realized through robust template matching techniques. Reference templates for each cone-beam image are obtained by projecting at different angles the gross tumor volume (GTV) delineated on the reference 4D CT 50% phase image. The position of the projected GTV centroid is identified on CBCT images performing fast normalized cross correlation in the frequency domain. Results: The developed tracking method was evaluated on 10 cone-beam acquisitions (1 for each patient), including about 650 two-dimensional projections provided over a full 360◦ gantry rotation. The rate of target identification in contrast enhanced CBCT images proved to be on average 34% (±6%) higher than in original projections adjusted for intensity. In case of tumor recognition achieved with and without enhancement, the cross-correlation coefficients with the reference templates increased by 11% (±4%) when the contrast enhancement technique was applied. Exemplifying results for three selected studies are reported in figure 1, showing the capability of the proposed method in increasing tumor region visibility and reducing the overlap effect of the surrounding anatomical structures, such as the spine or the rib cage.
P ROFFERED PAPER
S 217
Conclusions: A method for contrast enhancement and robust markerless tracking of lung tumors in X-ray projections is proposed. The developed technique can be applied to improve robust trajectory estimation of moving targets from CBCT projections for intra-fraction motion compensation and to increase the clinical application of image guidance techniques in lung cancer patients based on markerless 2-D X-ray imaging. 533 oral ADAPTIVE RADIOTHERAPY TREATMENT FOR PATIENTS WITH ATELECTASIS BASED ON PORTAL DOSIMETRY AND REPEATED CONEBEAM CT L. Persoon1 , M. Öllers1 , S. Wanders1 , D. De Ruysscher1 , D. Tissen1 , J. Wouters1 , F. Verhaegen1 , S. Nijsten1 1
D EPARTMENT OF R ADIATION O NCOLOGY (MAASTRO), GROW – S CHOOL FOR O NCOLOGY AND D EVELOPMENTAL B IOLOGY, M AASTRICHT U NIVERSITY M EDICAL C ENTRE, Maastricht, Netherlands
Purpose: The amount of atelectasis (lung fluid) in lung cancer patients can change during the course of treatment and may displace tumors or healthy tissue. Consequently, the delivered dose to these patients can be different from the planned dose. To ensure that the correct dose was delivered and to be able to adapt a planned treatment to changes in anatomy, dose verification during treatment is essential. In this study, we describe the implementation of an adaptive clinical protocol for lung cancer patients with atelectasis and a method to determine decision parameters. Materials: An adaptive protocol using weekly conebeam CT (CBCT) scans and 2D portal dosimetry was implemented. In the protocol, a treatment was adapted when either large anatomical changes were visible on CBCT (changes in target positioning >7 mm) or significant dose deviations were detected using 2D portal dosimetry. A dose deviation was classified when for all beams of a treatment fraction >5% of the pixels showed a gamma value (γ ) >1, using gamma criteria of 3%, 3mm. In case of re-planning a second CT was acquired. The dose-volume-histograms (DVHs) for the non-adapted scenario were compared to three adaptive scenarios, which involved dose recalculation and/or re-planning in the second CT. The DVHs were calculated using deformable registration based on demons to accumulate the dose of the different plans on the initially planned patient anatomy and delineations. For this study, we analyzed 6 patients included in the adaptive protocol. Results: From the 6 evaluated patients, 2 patients got a treatment adaptation based on 2D portal dose differences and 2 patients showed target displacements on the CBCT of more than 7 mm, also leading to an adaptation of the treatment. Fig. 1a shows a dose deviation starting to emerge from fraction 11. After fraction 21 a new plan was used for treatment and dose errors diminished considerably. The DVHs showed (Fig. 1b) that when no adaptation was performed the lung dose would have been higher than originally planned.