On-board Digital Tomosynthesis Research Articles

A software tool of digital tomosynthesis application for patient positioning in radiotherapy.

Digital Tomosynthesis (DTS) is an image modality in reconstructing tomographic images from two‐dimensional kV projections covering a narrow scan angles. Comparing with conventional cone‐beam CT (CBCT), it requires less time and radiation dose in data acquisition. It is feasible to apply this technique in patient positioning in radiotherapy. To facilitate its clinical application, a software tool was developed and the reconstruction processes were accelerated by graphic processing unit (GPU). Two reconstruction and two registration processes are required for DTS application which is different from conventional CBCT application which requires one image reconstruction process and one image registration process. The reconstruction stage consists of productions of two types of DTS. One type of DTS is reconstructed from cone‐beam (CB) projections covering a narrow scan angle and is named onboard DTS (ODTS), which represents the real patient position in treatment room. Another type of DTS is reconstructed from digitally reconstructed radiography (DRR) and is named reference DTS (RDTS), which represents the ideal patient position in treatment room. Prior to the reconstruction of RDTS, The DRRs are reconstructed from planning CT using the same acquisition setting of CB projections. The registration stage consists of two matching processes between ODTS and RDTS. The target shift in lateral and longitudinal axes are obtained from the matching between ODTS and RDTS in coronal view, while the target shift in longitudinal and vertical axes are obtained from the matching between ODTS and RDTS in sagittal view. In this software, both DRR and DTS reconstruction algorithms were implemented on GPU environments for acceleration purpose. The comprehensive evaluation of this software tool was performed including geometric accuracy, image quality, registration accuracy, and reconstruction efficiency. The average correlation coefficient between DRR/DTS generated by GPU‐based algorithm and CPU‐based algorithm is 0.99. Based on the measurements of cube phantom on DTS, the geometric errors are within 0.5 mm in three axes. For both cube phantom and pelvic phantom, the registration errors are within 0.5 mm in three axes. Compared with reconstruction performance of CPU‐based algorithms, the performances of DRR and DTS reconstructions are improved by a factor of 15 to 20. A GPU‐based software tool was developed for DTS application for patient positioning of radiotherapy. The geometric and registration accuracy met the clinical requirement in patient setup of radiotherapy. The high performance of DRR and DTS reconstruction algorithms was achieved by the GPU‐based computation environments. It is a useful software tool for researcher and clinician in evaluating DTS application in patient positioning of radiotherapy.PACS number(s): 87.57.nf

WE-AB-303-01: FEATURED PRESENTATION: A Dual-Detector Phase-Matched Digital Tomosynthesis (DTS) Imaging Scheme Using Aggregated KV and MV Projections for Intra-Treatment Lung Tumor Tracking

Purpose: To develop a dual-detector phase-matched DTS technique for continuous and fast intra-treatment lung tumor localization. Methods: Tumor localization accuracy of limited-angle DTS imaging is affected by low inter-slice resolution. The dual-detector DTS technique aims to overcome this limitation through combining orthogonally acquired beam's eye view MV projections and kV projections for intra-treatment DTS reconstruction and localization. To aggregate the kV and MV projections for reconstruction, the MV projections were linearly converted to synthesize corresponding kV projections. To further address the lung motion induced localization errors, this technique uses respiratory phase-matching to match the motion information between on-board DTS and reference DTS to offset the adverse effects of motion blurriness in tumor localization.A study was performed using the CIRS008A lung phantom to simulate different on-board target variation scenarios for localization. The intra-treatment kV and MV acquisition was achieved through the Varian TrueBeam Developer Mode. Four methods were compared for their localization accuracy: 1. the proposed dual-detector phase-matched DTS technique; 2. the single-detector phase-matched DTS technique; 3. the dual-detector 3D-DTS technique without phase-matching; and 4. the single-detector 3D-DTS technique without phase-matching. Results: For scan angles of 2.5°, 5°, 10°, 20° and 30°, the dual-detector phase-matched DTS technique localized the tumor with average(±standard deviations) errors of 0.4±0.3 mm, 0.5±0.3 mm, 0.6±0.2 mm, 0.9±0.4 mm and 1.0±0.3 mm, respectively. The corresponding values of single-detector phase-matched DTS technique were 4.0±2.5 mm, 2.7±1.1 mm, 1.7±1.2 mm, 2.2±0.9 mm and 1.5±0.8 mm, respectively. The values of dual-detector 3D-DTS technique were 6.2±1.7 mm, 6.3±1.2 mm, 5.3±1.3 mm, 2.0±2.2 mm and 1.5±0.5 mm, respectively. And the values of single-detector 3D-DTS technique were 9.7±8.9 mm, 9.8±8.8 mm, 10.0±9.7 mm, 3.9±2.7 mm and 2.2±1.3 mm, respectively. Conclusion: The dual-detector phase-matched DTS technique substantially improves the tumor localization accuracy, which can be applied to real-time intra-treatment lung tumor localization. The research was funded by the National Institutes of Health Grant No. R01-CA184173 and a grant from Varian Medical Systems.

Respiration‐phase‐matched digital tomosynthesis imaging for moving target verification: A feasibility study

To develop a respiration-phase-matched digital tomosynthesis (DTS) technique to monitor moving targets, and to evaluate its accuracy for various imaging parameters and anatomical characteristics. Previously developed 3D-DTS techniques, registering onboard DTS (OB-DTS, reconstructed from onboard projections) to reference DTS (R-DTS, reconstructed from DRRs of 3D reference CT), are inadequate to monitor moving targets. The authors' proposed respiration-phase-matched DTS technique registers OB-DTS to R-DTS reconstructed from DRRs generated by the same phase images of 4D reference CT as the corresponding onboard projections. To evaluate the improved accuracy of the author's technique, the authors performed thoracic phantom studies using (1) simulation with the 4D digital extended-cardiac-torso (XCAT) phantom, and (2) experiments with an anthropomorphic motion phantom. The studies were performed for various: respiratory cycle (RC), scan angle, and fraction of RC contained therein. Also, the authors assessed the accuracy of their technique relative to target size/location, and respiration inconsistencies from the R-DTS to OB-DTS. In both simulation and experimental studies, the respiration-phase-matched DTS technique is significantly more accurate in determining moving target positions. For 324 different scenarios simulated by XCAT, the respiration-phase-matched DTS technique localizes the 3D target position to errors of 1.07 ± 0.57 mm (mean ± S.D.), as compared to (a) 2.58 ± 1.37 and (b) 7.37 ± 4.18 mm, for 3D-DTS using 3D reference CT of (a) average intensity projection and (b) free-breathing CT. For 60 scenarios evaluated through experimental study, the uncertainties corresponding to those above are 1.24 ± 0.87, 2.42 ± 1.80, and 5.77 ± 6.45 mm, respectively. For a given scan angle, the accuracy of respiration-phase-matched DTS technique is less dependent on RC and the fraction of RC included in the scan. Increasing scan angle improves its accuracy. For different target locations, the targets near the chest wall or in the middle of lung provide higher registration accuracy compared to those near the mediastinum and diaphragm. Larger targets provide higher registration accuracy than small targets. Different respiratory cycle inconsistencies from R-DTS to OB-DTS minimally affect the registration accuracy. Increasing the respiratory amplitude inconsistencies will decrease the accuracy. The respiration-phase-matched DTS is more accurate and robust in determining moving target positions than 3D-DTS. It has potential application in pretreatment setup, post-treatment analysis, and intrafractional target verification.

Clinical Evaluation of Positioning Verification Using Digital Tomosynthesis and Bony Anatomy and Soft Tissues for Prostate Image-Guided Radiotherapy

To evaluate on-board digital tomosynthesis (DTS) for patient positioning vs. two-dimensional (2D) radiography and three-dimensional cone beam (CBCT).A total of 92 image sessions from 9 prostate cancer patients were analyzed. An on-board image set was registered to a corresponding reference image set. Four pairs of image sets were used: digitally reconstructed radiographs vs. on-board orthogonal paired radiographs for the 2D method, coronal-reference DTS vs. on-board coronal DTS for the coronal-DTS method, sagittal-reference DTS vs. on-board sagittal DTS for the sagittal-DTS method, and planning CT vs. CBCT for the CBCT method. The registration results were compared.The systematic errors in all methods were <1 mm/1 degrees . When registering the bony anatomy, the mean vector difference was 0.21 +/- 0.11 cm between 2D and CBCT, 0.11 +/- 0.08 cm between CBCT and coronal DTS, and 0.14 +/- 0.07 cm between CBCT and sagittal DTS. The correlation between CBCT to DTS was stronger (coefficient = 0.92-0.95) than the correlation between 2D and CBCT or DTS (coefficient = 0.81-0.83). When registering the soft tissue, the mean vector difference was 0.18 +/- 0.11 cm between CBCT and coronal DTS and 0.29 +/- 0.17 cm between CBCT and sagittal DTS. The correlation coefficient of CBCT to sagittal DTS and to coronal DTS was 0.84 and 0.92, respectively.DTS could provide equivalent results to CBCT when the bony anatomy is used as landmarks for prostate image-guided radiotherapy. For soft tissue-based positioning verification, coronal DTS produced equivalent results to CBCT, but sagittal DTS alone was insufficient. DTS could allow for comparable soft tissue-based target localization with faster scanning time and a lower imaging dose compared with CBCT.

TU‐EE‐A3‐04: Registration of On‐Board Digital Tomosynthesis and Planning CT for Partial Breast Irraadiation Patient Setup Verification with Surgical Clips

Purpose: This study examines the accuracy of On‐Board Digital Tomosynthesis (OB‐DTS) imaging by the localization of individual surgical clips and registration to planning CT instead of a reference‐DTS (RDTS). Using planning CT instead of a RDTS for registration might decrease the uncertainty of the registration resulting from the added edge blurring of DTS and simplify the setup verification process. Method and Materials: A solid water breast phantom containing four surgical clips was imaged with CT and OB‐DTS modalities. The OB‐DTS was acquired for a 40° lateral angle (kV source: 250°–290°). An open‐source GPU based FDK filtered backprojection algorithm was used for reconstruction of DTS image sets. The centroids of all the clips were localized in the DTS image sets and locations were compared with the clip locations in CT image sets. Using a filtered cross‐correlation algorithm, the OB‐DTS was registered with the CT and RDTS image sets and the registration accuracy of OB‐DTS was calculated. Results: Clip centroids were found to be within 1 mm in DTS and CT image sets. The OB‐DTS was registered with the CT within 1 mm ± 2 mm along the x‐axis (direction of projection) and less than 1 mm ± 1 mm along the two orthogonal (y and z) axes with a maximum translation of ±1.4 cm in the orthogonal axes and ±4.7 cm along the x‐axis. The OB‐DTS was registered with the RDTS within 4 mm ± 11.5 mm along the x‐axis, 1.4 mm ± 2.8 mm along the y‐axis and 0.5 mm ± 0.7 mm along the z‐axis, with a maximum translation of ±1.4 cm in the orthogonal axes and ±2.8 cm along the axis of propagation. Conclusion: OB‐DTS can be registered to CT with equal or better accuracy than when registered with RDTS and with greater translations along the propagation axis.

Automatic registration between reference and on-board digital tomosynthesis images for positioning verification

The authors developed a hybrid multiresolution rigid-body registration technique to automatically register reference digital tomosynthesis (DTS) images with on-board DTS images to guide patient positioning in radiation therapy. This hybrid registration technique uses a faster but less accurate static method to achieve an initial registration, followed by a slower but more accurate adaptive method to fine tune the registration. A multiresolution scheme is employed in the registration to further improve the registration accuracy, robustness, and efficiency. Normalized mutual information is selected as the criterion for the similarity measure and the downhill simplex method is used as the search engine. This technique was tested using image data both from an anthropomorphic chest phantom and from eight head-and-neck cancer patients. The effects of the scan angle and the region-of-interest (ROI) size on the registration accuracy and robustness were investigated. The necessity of using the adaptive registration method in the hybrid technique was validated by comparing the results of the static method and the hybrid method. With a 44 degrees scan angle and a large ROI covering the entire DTS volume, the average of the registration capture ranges in single-axis simulations was between -31 and +34 deg for rotations and between -89 and +78 mm for translations in the phantom study, and between -38 and +38 deg for rotations and between -58 and +65 mm for translations in the patient study. Decreasing the DTS scan angle from 44 degrees to 22 degrees mainly degraded the registration accuracy and robustness for the out-of-plane rotations. Decreasing the ROI size from the entire DTS volume to the volume surrounding the spinal cord reduced the capture ranges to between -23 and +18 deg for rotations and between -33 and +43 mm for translations in the phantom study, and between -18 and +25 deg for rotations and between -35 and +39 mm for translations in the patient study. Results also showed that the hybrid registration technique had much larger capture ranges than the static method alone in registering the out-of-plane rotations.

The Effect of Scan Angle on Target Localization Accuracy Using Digital Tomosynthesis

Purpose/Objective(s): To examine the effect of scan angle on target localization accuracy using on-board digital tomosynthesis (DTS) for breath-hold liver treatment. Material/Methods: 20 CBCT-localized fractions accumulated from liver radiation therapy treatments were studied retrospectively. To remove motion artifacts, image sets were acquired under breath-hold. The effect of scan angle, a key parameter for DTS, on target localization accuracy was evaluated for 10, 20 and 40 degree scan angles in both coronal and sagittal views. Assuming CBCT localization is the gold standard, the accuracy of the DTS technique is evaluated by the relative difference compared to the CBCT positioning. Localization accuracy was compared using two registration methods: bony anatomy based and soft tissue based alignment. Bony matching was performed by aligning the vertebral structures and ribs. Soft tissue matching was performed by aligning the liver boundaries, kidneys, and, when visible, the target. Results: The coronal and sagittal DTS had similar performance in aligning the target. Overall, the means and standard deviations for 40, 20 and 10 degree DTS were 0.2 +0.8 cm (40-cor.), 0.2 +0.8 cm (40-sag.), 0.1 +0.7cm (20-cor.), 0.2 +0.9 cm (20-sag.), 0.2 +0.9 cm (10-cor.), and 0.1 +0.7 cm (10-sag.). Figure 1. shows examples of DTS images at 10, 20, and 40 degree. Figure 2. plots the localization differences for the 10 and 40 degree DTS results in the lateral, vertical and longitudinal directions. Conclusion: The effect of scan angle on bony anatomy is minimal, and 10 degree DTS in either coronal or sagittal view is sufficient for bone based alignment. The visibility of liver boundaries was comparable with corresponding CBCT images on all DTS scans. However, detailed soft tissue contrast suffers when scan angle decreases from 40° to 10°. For BH liver treatment, the entire liver is clearly visible and can be used for soft tissue alignment. Partially supported by a Varian Medical Systems Research Grant

Automatic Registration Between Reference and On-Board Digital Tomosynthesis for Target Localization of Head and Neck Treatment

Digital tomosynthesis (DTS) is being investigated as a new on-board target localization technique. We previously developed an automatic method for registering reference DTS with on-board DTS images. This study is aimed to assess the accuracy and robustness of using this automatic technique for head and neck patient treatment.

On-Board Patient Positioning for Head-and-Neck IMRT: Comparing Digital Tomosynthesis to Kilovoltage Radiography and Cone-Beam Computed Tomography

High-precision intensity-modulated radiotherapy demands high patient positioning accuracy. On-board digital tomosynthesis (DTS) provides three-dimensional (3D) image guidance for daily positioning with a lower imaging dose, faster acquisition, and more geometric flexibility than 3D cone-beam computed tomography (CBCT). This clinical study evaluated DTS as a daily imaging technique for patient positioning and compared the results with 3D CBCT and two-dimensional (2D) radiography. Head and neck cancer patients undergoing intensity-modulated radiotherapy were studied. For each session, the patient was positioned using laser marks. On-board imaging data sets, including 2D kilovoltage radiographs, DTS, and CBCT, were obtained to measure the daily patient positioning variations. The mean and standard deviations of the positioning variations in the translational and rotational directions were calculated. The positioning differences among 2D radiography, DTS, and CBCT were analyzed. Image data sets were collected from 65 treatment fractions for 10 patients. The systematic patient positioning variation was <0.10 cm and 1.0 degrees one dimensionally. The random variations were 0.27-0.34 cm in the translational and 0.93 degrees -1.99 degrees in the rotational direction. The mean vector isocenter variation was 0.48 cm. DTS with 40 degrees and 20 degrees scan angles in the coronal or sagittal directions yielded the same results for patient positioning. DTS performance was comparable to that of CBCT, with positioning differences of <0.1 cm and 0.5 degrees . The positioning difference between 2D radiography and DTS was approximately 0.1 cm and 0.2 cm in the vertical/longitudinal and lateral directions. Our results have demonstrated that DTS is a comparable 3D imaging technique to CBCT for daily patient positioning of head-and-neck patients as determined by manual registration of bony anatomy.

Evaluation of three types of reference image data for external beam radiotherapy target localization using digital tomosynthesis (DTS)

Digital tomosynthesis (DTS) is a fast, low-dose three-dimensional (3D) imaging approach which yields slice images with excellent in-plane resolution, though low plane-to-plane resolution. A stack of DTS slices can be reconstructed from a single limited-angle scan, with typical scan angles ranging from 10 degrees to 40 degrees and acquisition times of less than 10 s. The resulting DTS slices show soft tissue contrast approaching that of full cone-beam CT. External beam radiotherapy target localization using DTS requires the registration of on-board DTS images with corresponding reference image data. This study evaluates three types of reference volume: original reference CT, exact reference DTS (RDTS), and a more computationally efficient approximate reference DTS (RDTSapprox), as well as three different DTS scan angles (22 degrees, 44 degrees, and 65 degrees) for the DTS target localization task. Three-dimensional mutual information (MI) shared between reference and onboard DTS volumes was computed in a region surrounding the spine of a chest phantom, as translations spanning +/-5 mm and rotations spanning +/-5 degrees were simulated along each dimension in the reference volumes. The locations of the MI maxima were used as surrogates for registration accuracy, and the width of the MI peaks were used to characterize the registration robustness. The results show that conventional treatment planning CT volumes are inadequate reference volumes for direct registration with on-board DTS data. The efficient RDTSapprox method also appears insufficient for MI-based registration without further refinement of the technique, though it may be suitable for manual registration performed by a human observer. The exact RDTS volumes, on the other hand, delivered a 3D DTS localization accuracy of 0.5 mm and 0.50 along each axis, using only a single 44 degrees coronal on-board DTS scan of the chest phantom.

1025: Clinical Efficacy of 3D Target Localization Using On-Board Digital Tomosynthesis in Head and Neck Treatment

1025: Clinical Efficacy of 3D Target Localization Using On-Board Digital Tomosynthesis in Head and Neck Treatment

SU-CC-ValA-01: Automatic Comparison Between Reference and On Board Digital Tomosynthesis for Target Localization

Purpose: Digital tomosynthesis (DTS) is a method for reconstructing 3D images from cone-beam projection data acquired with limited angulation (e.g., 40°) of an x-ray source, and is much faster and lower dose than full cone-beam CT (CBCT). We previously developed a method for generating reference DTS images from a planning CT for registration with actual on-board DTS images. This study examines the accuracy of 3D-3D registration of reference and on-board DTS images to assess the potential of DTS for image-guided radiation therapy (IGRT). Method and Materials: We simulated the online positioning of an anthropomorphic chest phantom with 6 noncoplanar reference BBs attached. Planning CT data of the phantom were acquired with a G.E. Lightspeed RT scanner. On-board CBCT projection data were acquired with a Varian 21EX Clinac, equipped with a kV on-board imager. On-board DTS images were reconstructed from a subset of the CBCT projection data (81 projections, 44°). True alignment of planning and on-board image data was achieved according to a 3D point-based registration of the 6 reference BBs in the CT and CBCT images. Single-axis rotations up to +/− 10° and 3-axis translations up to +/− 10 mm were simulated in the planning CT, prior to the generation of reference DTS images. A 67.5mm × 162.5mm × 20.8mm region of interest surrounding the spinal cord was extracted for registration. Mutual information-based 3D-3D registration of reference and on-board DTS images was performed, and residual registration error was recorded. Results: Registration errors are within 0.7mm and 0.1 degree in all cases. The average registration error was 30% less for translations along the dimension of tomographic motion than for the other two dimensions. Conclusions: 3D-3D rigid-body registration of reference and on-board DTS images is highly accurate, suggesting that DTS may be an effective IGRT technique. Partially supported by a Varian research grant.

Digital tomosynthesis with an on-board kilovoltage imaging device

To generate on-board digital tomosynthesis (DTS) and reference DTS images for three-dimensional image-guided radiation therapy (IGRT) as an alternative to conventional portal imaging or on-board cone-beam computed tomography (CBCT). Three clinical cases (prostate, head-and-neck, and liver) were selected to illustrate the capabilities of on-board DTS for IGRT. Corresponding reference DTS images were reconstructed from digitally reconstructed radiographs computed from planning CT image sets. The effect of scan angle on DTS slice thickness was examined by computing the mutual information between coincident CBCT and DTS images, as the DTS scan angle was varied from 0 degrees to 165 degrees . A breath-hold DTS acquisition strategy was implemented to remove respiratory motion artifacts. Digital tomosynthesis slices appeared similar to coincident CBCT planes and yielded substantially more anatomic information than either kilovoltage or megavoltage radiographs. Breath-hold DTS acquisition improved soft-tissue visibility by suppressing respiratory motion. Improved bony and soft-tissue visibility in DTS images is likely to improve target localization compared with radiographic verification techniques and might allow for daily localization of a soft-tissue target. Breath-hold DTS is a potential alternative to on-board CBCT for sites prone to respiratory motion.