Lung Tumor Tracking Research Articles

TU-E-BRD-01: Fluoroscopic Lung Tumor Tracking Without Implanted Fiducial Markers

Accurate lung tumor tracking in real time is a crucial for image-guided radiotherapy of lung cancers. Existing lung tumor tracking approaches can be roughly grouped into three categories: (1) deriving tumor position from external surrogates; (2) tracking implanted fiducial markers fluoroscopically or electromagnetically; (3) fluoroscopically tracking lung tumor without implanted fiducial markers. The first approach suffers from insufficient accuracy, while the second may not be widely accepted due to the risk of pneumothorax. We have been developing various algorithms that facilitate the fluoroscopic lung tumor tracking without implanted fiducial markers. The talk will summarize what we have done and then discuss what we plan to do. Learning Objectives: 1. Understand the significance of and difficulty for real-time localization of lung tumor 2. Understand various methods developed for markerless lung tumor tracking Conflict of Interest: The research presented here is partially supported by Varian Medical Systems.

SU‐FF‐J‐59: Adaptive Gating of Radiotherapy Treatment Based On Marker‐Less Tracking of Lung Tumors with KV Fluoroscopy

Purpose: We investigated using kV fluoroscopy for adapting the respiratory gating window prior to each radiation treatment fraction. The gate adaptation was based on marker‐less tracking of the target and correlating the internal motion trace with the external breathing signal. Method and Materials: A phantom study was performed with the on‐board kV imager of the Novalis Tx machine. A dynamic chest phantom with a water‐filled sphere placed inside a movable lung density insert was utilized. Breathing traces from patients that underwent lung SBRT were used to drive the target and external surrogate motion. The Varian RPM gating system was employed to obtain an external breathing signal, while acquiring kV fluoroscopy images. The moving target was tracked and an internal signal was generated. One kV acquisition was used for adapting the gating window based on the correlation of the internal and external signal and another one for verifying the gated position of the target. Gating at end‐exhale is the most commonly used technique in the clinic, while gating at mid‐ventilation makes it more likely that the tolerance window for residual motion includes the tumor during the entire breathing cycle. The two gating windows were investigated and the results were compared. Results: No significant difference in the gated target position errors was observed between the two gating windows. The target was in the expected position about 90% of the time for each one. The maximum deviation outside the tolerance window for residual motion was 1.9mm for the end‐exhale and 2.2mm for the mid‐motion gating windows. Conclusion: The adapt and verify procedure examined in this study, if applied in real‐time, has the potential to improve the accuracy of lung cancer radiotherapy by facilitating the reduction of safety margins used for moving tumors.Conflict of Interest: Varian Medical Systems, Inc.

SU‐FF‐J‐72: Markerless Fluoroscopic Tracking of Lung Tumors Based On 4D CT

Purpose: To develop a markerless fluoroscopic lung tumor tracking algorithm based on 4D CT generated reference templates. Method and Materials: Fluoroscopic images were acquired at a sampling rate of 15Hz using an on‐board X‐ray imaging (OBI) system. Each fluoroscopic image has a resolution of 768 by 1024, where each pixel represents a physical size of 0.26 mm. 4D CT was obtained from phase sorting based on internal anatomic features. DRRs were generated from 10 phases of the 4D CT, of which inhale and exhale DRRs were shifted to cover a greater motion range. These DRRs served as the reference templates for tracking purposes. GTV contours from the 4D CT give the reference tumor positions in the templates. Motion enhancement was applied to both DRR templates and fluoroscopic images. Pearson's correlation was calculated between each fluoroscopic image and each template in a given ROI. The tracking output is the weighted average of the tumor positions in those templates with largest correlation scores, weighted by the corresponding correlation scores. Results: RMS tracking error ranges between 0.65mm and 0.77mm. Absolute error at 95th percentile ranges between 1.41mm and 1.58mm. These values are well within the error bounds obtained from earlier studies, which require human‐marked tumor positions in the fluoroscopic images for training. Conclusion: This work demonstrates the feasibility of tracking lung tumor fluoroscopically based on 4D CT templates. Future work involves more sophisticated image processing and computer vision techniques to obtain more robust tracking results.

SU‐EE‐A3‐05: Mutual Information for Beams‐Eye‐View Lung Tumor Tracking Without Radiopaque Markers

Purpose: To keep safety margins in lung stereotactic body radiation therapy (SBRT) small and provide retrospective calculation of the delivered dose, the tumor motion should be monitored. We propose a tumor tracking algorithm that can estimate the tumor location from portal images taken during the treatment without the help of fiducial markers. Method and Materials: An algorithm based on a normalized mutual information technique was developed for tumor tracking. First a tumor template and a search region are identified on a DRR set reconstructed from a 4DCT acquired prior to the treatment. The set consists of 10 images relating to 10 equally sized breathing phase bins. The template is then used to track the tumor over the sequence of portal images. To estimate the tracking precision a dynamic thorax phantom was employed. Results: The phantom study showed a sub millimeter tracking accuracy in the superior‐ inferior direction for anterior‐posterior and lateral fields. In a preliminary retrospective patient study the algorithm was able to track the tumor motion throughout the whole image sequence. Manual verification yielded a tracking magnitude error of xy = (3.4 ± 0.8) mm. Furthermore the algorithm's robustness was tested with portal image sequences from two other patients with different tumor motion amplitude and contrast. The accuaracy was estimated by comparison with manual tracking and yielded xy = (1.7 ± 1.9) mm and xy = (1.2 ± 0.8) mm, respectively. Conclusion: The algorithm has shown great potential for markerless lung tumor tracking. First test results showed that it can perform tumor tracking on portal images and DRRs even if the tracking template was defined in the other modality respectively.Conflict of Interest: Varian Medical Systems, Inc.

Fluoroscopic tumor tracking for image-guided lung cancer radiotherapy

Accurate lung tumor tracking in real time is a keystone to image-guided radiotherapy of lung cancers. Existing lung tumor tracking approaches can be roughly grouped into three categories: (1) deriving tumor position from external surrogates; (2) tracking implanted fiducial markers fluoroscopically or electromagnetically; (3) fluoroscopically tracking lung tumor without implanted fiducial markers. The first approach suffers from insufficient accuracy, while the second may not be widely accepted due to the risk of pneumothorax. Previous studies in fluoroscopic markerless tracking are mainly based on template matching methods, which may fail when the tumor boundary is unclear in fluoroscopic images. In this paper we propose a novel markerless tumor tracking algorithm, which employs the correlation between the tumor position and surrogate anatomic features in the image. The positions of the surrogate features are not directly tracked; instead, we use principal component analysis of regions of interest containing them to obtain parametric representations of their motion patterns. Then, the tumor position can be predicted from the parametric representations of surrogates through regression. Four regression methods were tested in this study: linear and two-degree polynomial regression, artificial neural network (ANN) and support vector machine (SVM). The experimental results based on fluoroscopic sequences of ten lung cancer patients demonstrate a mean tracking error of 2.1 pixels and a maximum error at a 95% confidence level of 4.6 pixels (pixel size is about 0.5 mm) for the proposed tracking algorithm.

Lung tumor tracking in fluoroscopic video based on optical flow.

Respiratory gating and tumor tracking for dynamic multileaf collimator delivery require accurate and real-time localization of the lung tumor position during treatment. Deriving tumor position from external surrogates such as abdominal surface motion may have large uncertainties due to the intra- and interfraction variations of the correlation between the external surrogates and internal tumor motion. Implanted fiducial markers can be used to track tumors fluoroscopically in real time with sufficient accuracy. However, it may not be a practical procedure when implanting fiducials bronchoscopically. In this work, a method is presented to track the lung tumor mass or relevant anatomic features projected in fluoroscopic images without implanted fiducial markers based on an optical flow algorithm. The algorithm generates the centroid position of the tracked target and ignores shape changes of the tumor mass shadow. The tracking starts with a segmented tumor projection in an initial image frame. Then, the optical flow between this and all incoming frames acquired during treatment delivery is computed as initial estimations of tumor centroid displacements. The tumor contour in the initial frame is transferred to the incoming frames based on the average of the motion vectors, and its positions in the incoming frames are determined by fine-tuning the contour positions using a template matching algorithm with a small search range. The tracking results were validated by comparing with clinician determined contours on each frame. The position difference in 95% of the frames was found to be less than 1.4 pixels (approximately 0.7 mm) in the best case and 2.8 pixels (approximately 1.4 mm) in the worst case for the five patients studied.

Fiducial-free Lung Tumor Tracking for CyberKnife Radiosurgery

Fiducial-free Lung Tumor Tracking for CyberKnife Radiosurgery

Development of a Non-migrating Electromagnetic Transponder System for Lung Tumor Tracking

Real-time localization of implanted fiducials for lung cancer is limited by high non-therapeutic imaging radiation, expensive fluoroscopic installations, subjective image interpretation requirements and poor gold fiducial implant stability. A real-time, non-ionizing, objective, electromagnetic localization and tracking system that uses wireless implanted Beacon transponder for use in the prostate (Calypso Medical Technologies, Seattle, WA), initially showed low rates of transponder fixation with bronchoscopic implantation in a canine model.

A deformable lung tumor tracking method in fluoroscopic video using active shape models: a feasibility study

A dynamic multi-leaf collimator (DMLC) can be used to track a moving target during radiotherapy. One of the major benefits for DMLC tumor tracking is that, in addition to the compensation for tumor translational motion, DMLC can also change the aperture shape to conform to a deforming tumor projection in the beam's eye view. This paper presents a method that can track a deforming lung tumor in fluoroscopic video using active shape models (ASM) (Cootes et al 1995 Comput. Vis. Image Underst. 61 38–59). The method was evaluated by comparing tracking results against tumor projection contours manually edited by an expert observer. The evaluation shows the feasibility of using this method for precise tracking of lung tumors with deformation, which is important for DMLC-based real-time tumor tracking.

P3-045: Lung tumor tracking during 4-dimensional stereotactic radiotherapy treatment with the cyberknife: early results

Synchrony, the respiratory tracking system of the CyberKnife requires the insertion of markers in or close to the tumor. However, in this group of inoperable patients, it is associated with high risks like pneumothorax. To reduce the risks, 4 different methods of marker placement were used: 1) intravascular coil placement, 2) percutaneous intrapulmonal, 3) percutaneous extrapulmonal placement (for fixed tumors to the thorax), and 4) the bronchoscopic placement. To evaluate these techniques, we investigated the toxicity of the marker placement and the tumor response of the treatment. Until now 70 tumors are treated, but because the follow up is too short, we report the results of the first 55 patients with 60 tumors. Markers were placed in or around 60 tumors in 55 patients. Forty eight patients were treated with curative intention: 40 patients had a T1-3N0M0 lung cancer and 8 patients had 13 solitary metastases in the lung. Seven patients were treated with palliative intention (5 with recurrent lung cancer, and 2 with metastasis from lung cancer). Platinum fiducials and intravascular embolisation coils were used as markers. In total, 180 markers were placed: 67 intrapulmonal in 26 patients (median: 3 markers per tumor), 84 intravascular in 28 patients (median: 3 makers per tumor), 25 extrapulmonal in 5 patients (median: 5 makers per tumor), and 4 markers in 1 patient with the bronchoscopic method. Seven days after marker placement, a planning CTscan was made and the GTV was contoured on a 4-D CT scan. The PTV equaled the GTV plus 5 mm. For early stage lung cancer, a total dose of 36 to 60 Gy, (median dose: 60 Gy) was given in 3 fractions. Solitary metastasis to the lung were treated with a total dose of 45 to 60 Gy (median dose: 45 Gy) in 3 to 5 fractions. For palliative treatment, a total dose of 30 to 49 Gy was given in 3-7 fractions (median dose: 40 Gy). The dose to the PTV was prescribed to the 70-85% isodose line. The response was evaluated according to the RECIST criteria with a CT scan 6-8 weeks after the last treatment and routinely thereafter. The median follow up with CTscan was 6 months (range: 2-18). Six patients (11%) had a pneumothorax after intrapulmonal placement. One patient had no symptoms. A thorax drain was placed in the 5 other patients. One patient complained of severe intrathoracal pain several hours after intravascular coil placement and 5 patients complained of haemoptoe, one after the intravascular coil placement and 4 after the intrapulmonal placement. The local control was 97%. Seven tumors had a complete response, 38 tumors had a partial response, 13 tumors had stable disease and 2 tumors (both early stage lung cancer) were progressive, one after 8 months and the other after 15 months. Low toxicity of marker placement was seen due to the 4 methods. CyberKnife tumor tracking with markers is feasible and resulted in excellent tumor response.

Technical Description, Phantom Accuracy, and Clinical Feasibility for Single-Session Lung Radiosurgery Using Robotic Image-Guided Real-time Respiratory Tumor Tracking

To describe the technological background, the accuracy, and clinical feasibility for single session lung radiosurgery using a real-time robotic system with respiratory tracking. The latest version of image-guided real-time respiratory tracking software (Synchrony, Accuray Incorporated, Sunnyvale, CA) was applied and is described. Accuracy measurements were performed using a newly designed moving phantom model. We treated 15 patients with 19 lung tumors with robotic radiosurgery (CyberKnife, Accuray) using the same treatment parameters for all patients. Ten patients had primary tumors and five had metastatic tumors. All patients underwent computed tomography-guided percutaneous placement of one fiducial directly into the tumor, and were all treated with single session radiosurgery to a dose of 24 Gy. Follow up CT scanning was performed every two months. All patients could be treated with the automated robotic technique. The respiratory tracking error was less than 1 mm and the overall shape of the dose profile was not affected by target motion and/or phase shift between fiducial and optical marker motion. Two patients required a chest tube insertion after fiducial implantation because of pneumothorax. One patient experienced nausea after treatment. No other short-term adverse reactions were found. One patient showed imaging signs of pneumonitis without a clinical correlation. Single-session radiosurgery for lung tumor tracking using the described technology is a stable, safe, and feasible concept for respiratory tracking of tumors during robotic lung radiosurgery in selected patients. Longer follow-up is needed for definitive clinical results.

MO‐D‐ValB‐08: Fluoroscopic Tracking of Lung Tumor Mass Without Implanted Fiducial Markers

Purpose: To develop techniques for direct lung tumor tracking in fluoroscopic images without implanted markers. Method and Materials: During the patient setup session, a pair of 15 second orthogonal fluoroscopic images are taken and processed off‐line to generate reference templates. Each breathing cycle is divided into 12 phase bins. Setup image frames falling in a specific bin are motion‐enhanced and averaged, and an ROI that contains the tumor is selected to be the reference template for that phase bin. Each reference template corresponds to a tumor position in the image. During the treatment, as soon as a fluoroscopic image is acquired, the cross‐correlation score between each reference template and this image is maximized by allowing small shifts of the template in both X and Y directions. Then the tumor position is derived by averaging the tumor centroid coordinates in those templates of high scores (above 85% of the maximum score). For comparison, tumor position in each image frame was also marked by a clinician. Results: We tested our algorithm on six sequences of fluoroscopic images from six lung cancer patients. The automatically detected tumor centroid coordinates agree well with the manually marked results, with an average error of 1 mm. Conclusion: This study demonstrates the feasibility of tracking lung tumor mass in fluoroscopic images without implanted fiducial markers. Future research will concentrate on further improvement of the accuracy and robustness, and reducing the computational cost.The project is partially supported by NCI grant (1 R21 CA110177 A 01A1) and NSF Grant No. IIS‐0347532.

Lung tumor tracking during stereotactic radiotherapy treatment with the CyberKnife: Marker placement and early results

Lung tumor tracking during stereotactic radiotherapy with the CyberKnife requires the insertion of markers in or close to the tumor. To reduce the risk of pneumothorax, three methods of marker placement were used: 1) intravascular coil placement, 2) percutaneous intrathoracal, and 3) percutaneous extrathoracal placement. We investigated the toxicity of marker placement and the tumor response of the lung tumor tracking treatment. Markers were placed in 20 patients with 22 tumors: 13 patients received a curative treatment, seven a palliative. The median Charlson Comorbidity Score was 4 (range: 1–8). Platinum fiducials and intravascular embolisation coils were used as markers. In total, 78 markers were placed: 34 intrathoracal, 23 intravascular and 21 extrathoracal. The PTV equaled the GTV + 5 mm. A median dose of 45 Gy (range: 30–60 Gy, in 3 fractions) was prescribed to the 70–85% isodose. The response was evaluated with a CTscan performed 6–8 weeks after the last treatment and routinely thereafter. The median follow-up was 4 months (range: 2–11). No severe toxicity due to the marker placement was seen. Pneumothorax was not seen. The local control was 100%. Four tumors in four patients showed a complete response, 15 tumors in 14 patients a partial response, and three tumors in two patients with metastatic disease had stable disease. No severe toxicity of marker placement was seen due to the appropriate choice of one of the three methods. CyberKnife tumor tracking with markers is feasible and resulted in excellent tumor response. Longer follow-up is needed to validate the local control.

Insertion and fixation of fiducial markers for setup and tracking of lung tumors in radiotherapy

Internal 1.5-mm fiducial markers were used in real-time tumor-tracking radiotherapy (RT) for lung cancer. The fixation rate of the markers using the bronchial insertion technique, reliability of the setup using markers around the target volume, dislocation of the markers after real-time tumor-tracking RT, and long-term toxicity of marker insertion were investigated. Between July 2000 and April 2004, 154 gold markers were inserted into 57 patients with peripheral lung cancer. The distances between the implanted markers in 198 measurements in 71 set-ups in 11 patients were measured using two sets of orthogonal diagnostic X-ray images of the real-time tumor-tracking RT system. The distance between the markers and the chest wall was also measured in a transaxial CT image on 186 occasions in 48 patients during treatment planning and during follow-up. The median treatment time was 6 days (range, 4-14 days). In 115 (75%) of the 154 inserted markers, the gold marker was detected throughout the treatment period. In 122 markers detected at CT planning, 115 (94%) were detected until the end of treatment. The variation in the distances between the implanted markers was within +/-2 mm in 95% and +/-1 mm in 80% during treatment. The variation in the distances between the implanted markers was >2 mm in at least one direction in 9% of the setups for which reexamination with a CT scan was indicated. The fixation rate in the left upper lobe was lower than in the other lobes. A statistically significant relationship was found between a shorter distance between the markers and the chest wall and the fixation rate, suggesting that the markers in the smaller bronchial lumens fixed better than those in the larger lumens. A learning curve among the endoscopists was suggested in the fixation rate. The distance between the markers and the chest wall changed significantly within a median of 44 days (range, 16-181 days) after treatment. The fixation of markers into the bronchial tree was useful for the setup for peripheral lung cancer and had an accuracy of +/-2 mm during the 1-2-week treatment period. The relationship between the markers and tumor can change significantly after 2 weeks, suggesting that adaptive four-dimensional RT is required.