Tumor Motion Monitoring Research Articles

SU-E-J-90: 2D/3D Registration Using KV-MV Image Pairs for Higher Accuracy Image Guided Radiotherapy.

In this work, we investigate the impact of using paired portal mega-voltage (MV) and kilo-voltage (kV) images, on 2D/3D registration accuracy with the purpose of improving tumor motion tracking during radiotherapy. Tumor motion tracking is important as motion remains one of the biggest sources of uncertainty in dose application. 2D/3D registration is successfully used in online tumor motion tracking, nevertheless, one limitation of this technique is the inability to resolve movement along the imaging beam axis using only one projection image. Our evaluation consisted in comparing the accuracy of registration using different 2D image combinations: only one 2D image (1-kV), one kV and one MV image (1kV-1MV) and two kV images (2-kV). For each of the image combinations we evaluated the registration results using 250 starting points as initial displacements from the gold standard. We measured the final mean target registration error (mTRE) and the success rate for each registration. Each of the combinations was evaluated using four different merit functions. When using the MI merit function (a popular choice for this application) the RMS mTRE drops from 6.4 mm when using only one image to 2.1 mm when using image pairs. The success rate increases from 62% to 99.6%. A similar trend was observed for all four merit functions. Typically, the results are slightly better with 2-kV images than with 1kV-1MV. We evaluated the impact of using different image combinations on accuracy of 2D/3D registration for tumor motion monitoring. Our results show that using a kV-MV image pair, leads to improved results as motion can be accurately resolved in six degrees of freedom. Given the possibility to acquire these two images simultaneously, this is not only very workflow efficient but is also shown to be a good approach to improve registration accuracy.

Monitoring tumor motion by real time 2D/3D registration during radiotherapy

Background and purposeIn this paper, we investigate the possibility to use X-ray based real time 2D/3D registration for non-invasive tumor motion monitoring during radiotherapy. Materials and methodsThe 2D/3D registration scheme is implemented using general purpose computation on graphics hardware (GPGPU) programming techniques and several algorithmic refinements in the registration process. Validation is conducted off-line using a phantom and five clinical patient data sets. The registration is performed on a region of interest (ROI) centered around the planned target volume (PTV). ResultsThe phantom motion is measured with an rms error of 2.56mm. For the patient data sets, a sinusoidal movement that clearly correlates to the breathing cycle is shown. Videos show a good match between X-ray and digitally reconstructed radiographs (DRR) displacement. Mean registration time is 0.5s. ConclusionsWe have demonstrated that real-time organ motion monitoring using image based markerless registration is feasible.

An algorithm to extract three‐dimensional motion by marker tracking in the kV projections from an on‐board imager: four‐dimensional cone‐beam CT and tumor tracking implications

The purpose of this work is to extract three‐dimensional (3D) motion trajectories of internal implanted and external skin‐attached markers from kV cone‐beam projections and reduce image artifact from patient motion in cone‐beam computed tomography (CBCT) from on‐board imager. Cone beam radiographic projections were acquired for a mobile phantom and liver patients with internal implanted and external skin‐attached markers. An algorithm was developed to automatically find the positions of the markers in the projections. It uses normalized cross‐correlation between a template image of a metal seed marker and the projections to find the marker position. From these positions and time‐tagged angular views, the marker 3D motion trajectory was obtained over a time interval of nearly one minute, which is the time required for scanning. This marker trajectory was used to remap the pixels of the projections to eliminate motion. Then, the motion‐corrected projections were used to reconstruct CBCT. An algorithm was developed to extract 3D motion trajectories of internal and external markers from cone‐beam projections using a kV monoscopic on‐board imager. This algorithm was tested and validated using a mobile phantom and patients with liver masses that had radio‐markers implanted in the tumor and attached to the skin. The extracted motion trajectories were used to investigate motion correlation between internal and external markers in liver patients. Image artifacts from respiratory motion were reduced in CBCT reconstructed from cone‐beam projections that were preprocessed to remove motion shifts obtained from marker tracking. With this method, motion‐related image artifacts such as blurring and spatial distortion were reduced, and contrast and position resolutions were improved significantly in CBCT reconstructed from motion‐corrected projections. Furthermore, correlated internal and external marker 3D‐motion tracks obtained from the kV projections might be useful for 4DCBCT, beam gating and tumor motion monitoring or tracking.PACS numbers: 87.57.Q, 87.57.C‐

WE-B-BRA-05: Minimizing Radiation Dose in Stereoscopic X-Ray-Based Monitoring of Tumor Motion with the Effective Use of Partial Information

Purpose: A number of stereoscopic X‐ray imaging techniques based on kV, hybrid kV/MV X‐ray systems (with or without other auxiliary external surrogate devices such as RPM) have been proposed for real‐time therapeutic guidance. The patient radiation exposure during the X‐ray image guided procedure is a major concern. We propose a general strategy of minimizing the patient imagingdose by effective use of the partial system information and demonstrate its potential clinical utility. Methods: While the nature of partial information depends on the specific stereoscopic imagingsystem and application, in this work we use the information from the primary imagers to estimate the tumor position during IMRT and/or VMAT and switch on the second imager only when an over‐threshold abnormal motion is observed. For a kV/MV system for example, the intrafraction tumor motion is monitored by two separate but related steps: (i) detect potential target motion beyond a pre‐defined threshold by using MV images and (ii) confirm the displacement and determine whether an intervention is needed through combined MV‐kV imaging. A Trilogy IX and a newly available Varian Trilogy MX linac with onboard kV imager were used to evaluate the performance of the strategy. The performance of the algorithm was evaluated for the case of prostate motion using computer simulation and 4D phantom measurements for 536 Calypso‐measured tracks from 17 patients, and for the case of thoracic motion using Cyberknife lung data from 5 patients. Mean position tracking algorithms were used on the latter case. Results: Over‐threshold displacement was detected for more than 98% of the time. The use of kV imaging was significantly reduced compared to continuous or periodic stereoscopic x‐ray imaging.Conclusions: A “failure” detection strategy for prostrate and thoracic motion has been presented that achieves high targeting accuracy while minimizing radiationdose.

SU‐EE‐A3‐05: Real Time Tumor Motion Monitoring during IGRT Based on Manifold Learning and Dynamic Registration between 4DCT and Fluoroscopy

Purpose: To develop a real time tumor respiratory motion monitoring methodology for thoracic cancer IGRT by integrating manifold learning and dynamical registration of 4DCT and fluoroscopy technique during the radiation treatment.Method and Materials: 10‐phases retrospective 4DCT have been acquired from 6 patients (5 lung, 1 pancreas) with audio coaching. During their gated radiation treatment, fluoroscopy videos were collected with the same audio coaching. A radiation oncologist delineated the contours including the GTV in the 50% phase 4DCT. The methodology is divided into three steps. First an object‐constrained registration has been used to register 4DCT at other phases to the reference 50% phase in order to build a spatial‐temporal tumor motion model. Then the 4D motion model has been used as the constraint in the spatial registration and temporal matching of the 4DCT with the fluoroscopy. An Isomap based manifold learning has been used to establish a global matching scheme between the 4DCT phases and fluoroscopy frames. In the last step, the GTV in newly acquired fluoroscopy frames were monitored in real time based on the fast registration between the frame and the DRR of the corresponding 4DCT phase using the global constraint and local image information.Results: The registration between 4DCT phases is within 30 minutes. The 4DCT to fluoroscopy registration and tumor motion monitoring are close to real time. After registration and training, for all 6 patients, the tumor (GTV) in an arbitrary fluoroscopy frame can be tracked with motion error less than 2mm, based on comparison between manually delineated contours in the fluoroscopy and the deformed GTV. Conclusion: The proposed tumor monitoring approach can achieve real time efficiency as well as satisfactory accuracy and precision and has the potential to be used in IGRT to improve setup and tumor tracking accuracy to achieve desired dose coverage.

Dynamic MR Based Analysis of Tumor Movement in Upper and Mid Lobe Localized Lung Cancer

Tumor motion is a very important factor in the radiotherapy of lung cancer. Uncertainty resulting from tumor movement must be considered in 3D therapy planning especially in case of IMRT or stereotactic therapy. The aim of our dynamic MR based study was to detect tumor movements in upper and mid lobe lung tumors. Twenty-four patients with newly diagnosed stage II-IV lung cancer were enrolled into the study. According to tumor localization in the right S1-S3 segments 9, in the right S4-S6 segments 2, in the left S1-S3 segments 9 and in the left S4-S6 segments 4 lesions were detected. In normal treatment position individual dynamic MR examinations were performed in axial, sagittal and coronal planes (100 slices/30 sec). For tumor motion analysis E-RAD PAC's software was used. Movements of the tumor under normal breathing conditions were registered in the three main directions. The mean antero-posterior deviation was 0,109 cm (range: 0,063 cm-0,204 cm), the mean medio-lateral deviation was 0,114 cm (range: 0,06 cm- 0,244 cm). The greatest deviation was measured in cranio-caudal direction (mean: 0,27 cm, range: 0,079 cm- 0,815 cm). The mean direction independent deviation was 0,18 cm (range: 0,09 cm- 0,48 cm). Dynamic MR is a sensitive and well tolerated method for tumor motion monitoring in high precision 3D therapy planning of lung cancer patients. Our results demonstrate that tumors located in the upper and mid lobes have moderate breath synchronous movements. The greatest deviation occur in cranio-caudal direction.

SU‐GG‐J‐191: Use of Megavoltage Fluoroscopy and Cone‐Beam CT for On‐Line Verification During 4D/gated Delivery

Purpose: On‐line real‐time monitoring of tumor motion is essential for 4D/gated radiation delivery based a surrogate signal because the correlation between the surrogate signal and tumor locations on the treatment day may change from that on the simulation day. The purpose of this study is to develop tools to establish a real‐time correlation between the surrogate signal and tumor motion by registering on‐line megavoltage fluoroscopy (MVF) and/or cone‐beam CT with the planning images. Method and Materials: Both MVF and cone‐beam CT were acquired using a flat panel detector installed on a Siemens Linac using 6MV photon beams for phantoms with moving structures and for thoracic cancer patients. A frame‐grabber of 7 frames per minute was used to capture the MVF movie. The cone‐beam projection images consist of 200 frames corresponding to 200 gantry angles. The acquired images were synchronized with the breathing signal from a pressure sensor (Anzai Inc.). A previously developed software, RTReg4D, was used to register acquired images with planning DRRs from 4DCT. Results: The software can effectively and accurately register MVF images with time‐sequenced DRRs. For the registration with the cone beam projection images, the software fails at some gantry angles and manual registration is needed to correct these false registrations. These registration results can establish a real‐time correlation between the Anzai surrogate signals and tumor motion. This correlation would update the correlation established during the planning process for subsequent treatment delivery using either gating or 4D tracking. If gated delivery is used, the gating window may be adjusted based on the real‐time correlation. Conclusion: MV fluoroscopy and/or cone‐beam CT acquired before treatment delivery can be used to establish a real‐time correlation between surrogate signal and tumor location for 4D/gated treatment delivery. Conflict of Interest: This work is sponsored in part by Siemens OCS.

Geometric uncertainty of 2D projection imaging in monitoring 3D tumor motion

The purpose of this study was to investigate the accuracy of two-dimensional (2D) projection imaging methods in three-dimensional (3D) tumor motion monitoring. Many commercial linear accelerator types have projection imaging capabilities, and tumor motion monitoring is useful for motion inclusive, respiratory gated or tumor tracking strategies. Since 2D projection imaging is limited in its ability to resolve the motion along the imaging beam axis, there is unresolved motion when monitoring 3D tumor motion. From the 3D tumor motion data of 160 treatment fractions for 46 thoracic and abdominal cancer patients, the unresolved motion due to the geometric limitation of 2D projection imaging was calculated as displacement in the imaging beam axis for different beam angles and time intervals. The geometric uncertainty to monitor 3D motion caused by the unresolved motion of 2D imaging was quantified using the root-mean-square (rms) metric. Geometric uncertainty showed interfractional and intrafractional variation. Patient-to-patient variation was much more significant than variation for different time intervals. For the patient cohort studied, as the time intervals increase, the rms, minimum and maximum values of the rms uncertainty show decreasing tendencies for the lung patients but increasing for the liver and retroperitoneal patients, which could be attributed to patient relaxation. Geometric uncertainty was smaller for coplanar treatments than non-coplanar treatments, as superior–inferior (SI) tumor motion, the predominant motion from patient respiration, could be always resolved for coplanar treatments. Overall rms of the rms uncertainty was 0.13 cm for all treatment fractions and 0.18 cm for the treatment fractions whose average breathing peak–trough ranges were more than 0.5 cm. The geometric uncertainty for 2D imaging varies depending on the tumor site, tumor motion range, time interval and beam angle as well as between patients, between fractions and within a fraction.

Fluoroscopic study of tumor motion due to breathing: facilitating precise radiation therapy for lung cancer patients.

Target motion due to breathing is one of the major obstacles in dose escalation of radiation therapy to some tumors in the thoracoabdominal region. The development of beam gating or target motion tracking techniques provides a possibility to reduce normal tissue volume in a treatment field. Tumor motion monitoring in those techniques plays a crucial role, but has not yet been adequately explored. This paper reports our preliminary investigation on breath introduced tumor motion. Tumor locations and motion properties were determined from digitized fluoroscopic videos acquired during patient simulation. Image distortion due to irregularities in the imaging chain, such as the pincushion distortion, was corrected with a polynomial unwarping method. Temporal Fourier transformation of the fluoroscopic video was introduced to convert the motion information over time to a static view of a motion field, in which regions with different motion ranges can be directly measured. Patient breathing patterns vary from patient to patient and so does the kinematic behavior of individual tumors. In order to evaluate the feasibility for tracking internal target motion with nonionizing-radiation techniques, motion patterns between internal targets and external radio opaque markers placed on patient's chest during fluoroscopic video acquisition were compared. For some patients, significant motion phase discrepancies between an internal target and an external marker have been observed. Quantitative measurements are reported. These results will be useful in the design of a motion tracking or gated radiotherapy system.