Respiration-correlated Cone-beam CT Research Articles

Investigation of gated cone‐beam CT to reduce respiratory motion blurring

Methods of reducing respiratory motion blurring in cone-beam CT (CBCT) have been limited to lung where soft tissue contrast is large. Respiration-correlated cone-beam CT uses slow continuous gantry rotation but image quality is limited by uneven projection spacing. This study investigates the efficacy of a novel gated CBCT technique. In gated CBCT, the linac is programmed such that gantry rotation and kV image acquisition occur within a gate around end expiration and are triggered by an external respiratory monitor. Standard CBCT and gated CBCT scans are performed in 22 patients (11 thoracic, 11 abdominal) and a respiration-correlated CT (RCCT) scan, acquired on a standard CT scanner, from the same day serves as a criterion standard. Image quality is compared by calculating contrast-to-noise ratios (CNR) for tumors in lung, gastroesophageal junction (GEJ) tissue, and pancreas tissue, relative to surrounding background tissue. Congruence between the object in the CBCT images and that in the RCCT is measured by calculating the optimized normalized cross-correlation (NCC) following CBCT-to-RCCT rigid registrations. Gated CBCT results in reduced motion artifacts relative to standard CBCT, with better visualization of tumors in lung, and of abdominal organs including GEJ, pancreas, and organs at risk. CNR of lung tumors is larger in gated CBCT in 6 of 11 cases relative to standard CBCT. A paired two-tailed t-test of lung patient mean CNR shows no statistical significance (p = 0.133). In 4 of 5 cases where CNR is not increased, lung tumor motion observed in RCCT is small (range 1.3-5.2 mm). CNR is increased and becomes statistically significant for 6 out of 7 lung patients with > 5 mm tumor motion (p = 0.044). CNR is larger in gated CBCT in 5 of 7 GEJ cases and 3 of 4 pancreas cases (p = 0.082 and 0.192). Gated CBCT yields improvement with lower NCC relative to standard CBCT in 10 of 11, 7 of 7, and 3 of 4 patients for lung, GEJ, and pancreas images, respectively (p = 0.0014, 0.0030, 0.165). Gated CBCT reduces image blurring caused by respiratory motion. The gated gantry rotation yields uniformly and closely spaced projections resulting in improved reconstructed image quality. The technique is shown to be applicable to abdominal sites, where image contrast of soft tissues is low.

A study of respiration‐correlated cone‐beam CT scans to correct target positioning errors in radiotherapy of thoracic cancer

There is increasingly widespread usage of cone-beam CT (CBCT) for guiding radiation treatment in advanced-stage lung tumors, but difficulties associated with daily CBCT in conventionally fractionated treatments include imaging dose to the patient, increased workload and longer treatment times. Respiration-correlated cone-beam CT (RC-CBCT) can improve localization accuracy in mobile lung tumors, but further increases the time and workload for conventionally fractionated treatments. This study investigates whether RC-CBCT-guided correction of systematic tumor deviations in standard fractionated lung tumor radiation treatments is more effective than 2D image-based correction of skeletal deviations alone. A second study goal compares respiration-correlated vs respiration-averaged images for determining tumor deviations. Eleven stage II-IV nonsmall cell lung cancer patients are enrolled in an IRB-approved prospective off-line protocol using RC-CBCT guidance to correct for systematic errors in GTV position. Patients receive a respiration-correlated planning CT (RCCT) at simulation, daily kilovoltage RC-CBCT scans during the first week of treatment and weekly scans thereafter. Four types of correction methods are compared: (1) systematic error in gross tumor volume (GTV) position, (2) systematic error in skeletal anatomy, (3) daily skeletal corrections, and (4) weekly skeletal corrections. The comparison is in terms of weighted average of the residual GTV deviations measured from the RC-CBCT scans and representing the estimated residual deviation over the treatment course. In the second study goal, GTV deviations computed from matching RCCT and RC-CBCT are compared to deviations computed from matching respiration-averaged images consisting of a CBCT reconstructed using all projections and an average-intensity-projection CT computed from the RCCT. Of the eleven patients in the GTV-based systematic correction protocol, two required no correction, seven required a single correction, one required two corrections, and one required three corrections. Mean residual GTV deviation (3D distance) following GTV-based systematic correction (mean ± 1 standard deviation 4.8 ± 1.5 mm) is significantly lower than for systematic skeletal-based (6.5 ± 2.9 mm, p = 0.015), and weekly skeletal-based correction (7.2 ± 3.0 mm, p = 0.001), but is not significantly lower than daily skeletal-based correction (5.4 ± 2.6 mm, p = 0.34). In two cases, first-day CBCT images reveal tumor changes-one showing tumor growth, the other showing large tumor displacement-that are not readily observed in radiographs. Differences in computed GTV deviations between respiration-correlated and respiration-averaged images are 0.2 ± 1.8 mm in the superior-inferior direction and are of similar magnitude in the other directions. An off-line protocol to correct GTV-based systematic error in locally advanced lung tumor cases can be effective at reducing tumor deviations, although the findings need confirmation with larger patient statistics. In some cases, a single cone-beam CT can be useful for assessing tumor changes early in treatment, if more than a few days elapse between simulation and the start of treatment. Tumor deviations measured with respiration-averaged CT and CBCT images are consistent with those measured with respiration-correlated images; the respiration-averaged method is more easily implemented in the clinic.

TU-C-213CD-08: Investigation of Gated Cone-Beam CT to Reduce Respiratory Motion Blurring in Images of Thorax and Abdomen

Purpose: Methods of reducing respiratory motion blurring in cone-beam CT (CBCT) have been limited to lung where soft tissue contrast is large. Respiration-correlated cone-beam CT (RC-CBCT) uses slow continuous gantry rotation but image quality is limited by uneven projection spacing. This study investigates efficacy of a novel gated CBCT technique. Methods: In gated CBCT, the linac (Varian TrueBeam) is programmed such that gantry rotation and kV image acquisition occur within a gate around end expiration (EE) and are triggered by an external respiratory monitor. Standard CBCT and gated CBCT scans are performed in 14 patients (8 thoracic, 6 abdominal) and a respiration correlated CT (RCCT) scan from the same day serves as ground truth. Image quality is compared by calculating contrast-to-noise ratios (CNR) for tumors in lung, gastro-esophageal junction (GEJ) tissue, and liver tissue, relative to surrounding background tissue. Results: Gated CBCT results in reduced motion artifacts relative to standard CBCT, with better visualization of tumors in lung, and of abdominal organs including GEJ, stomach, liver, kidney, and spleen. CNR of lung tumors is larger in gated CBCT in 5 of 8 cases relative to standard CBCT with mean increase 8.8% (range −8.6%–+30.1%). In cases where CNR is not increased, lung tumor motion observed in RCCT is small (range 3.2–5.3 mm). For GEJ images, CNR is larger in gated CBCT in all 3 cases (mean increase 45%, range 24.7%–64.4%). For liver images, CNR is larger in gated CBCT in all 4 cases (mean increase of 73.8%, range 5.4%–119.9%). Conclusions: Gated CBCT reduces image blurring caused by respiratory motion. The gated gantry rotation yields uniformly and closely spaced projections resulting in improved reconstructed image quality. The technique is shown to be applicable to abdominal sites, where image contrast of soft tissues is low. NIH/NCI award R01 CA126993, research grant from Varian Medical Systems

SU‐E‐J‐157: Investigation of Gated Cone‐Beam CT to Reduce Respiratory Motion Blurring

Purpose: Respiration‐correlated cone‐beam CT (RC‐CBCT) using slow continuous gantry rotation is commonly used to reduce respiratory motion blurring but image quality is limited by uneven projection spacing. This study investigates the efficacy of a novel gated CBCT technique (gantry motion and imaging only within gate) in reducing motion blur with improved image quality using a new type of computer‐controlled linac (Varian TrueBeam).Methods: For gated CBCT, the linac is programmed to gate gantry rotation and kV image acquisition with approximately 25% duty cycle around end expiration. The two‐part study examines images in phantom and prospectively in patients with thoracic and abdominal tumors. A motion phantom is programmed to follow a patient respiratory trace (1.4cm mean excursion) and CBCT scans are performed in standard “free‐breathing”, RC‐CBCT, and gated CBCT modes. A standard CBCT of the stationary phantom serves as ground truth. Evaluation of phantom image quality compares contrast‐to‐noise ratios (CNR) of spheres embedded in acrylic, delineated on the static image and aligned to the other images. In patient studies, image fidelity in standard free‐breathing and gated CBCT is compared relative to a respiration‐correlated CT (RCCT) on the same day, by computing a cross‐correlation metric (CCM) in an ROI around the internal target volume following rigid registration.Results: CNR in motion phantom for gated CBCT is nearly that for static phantom (ratio gated/static 0.95) and larger than for RC‐CBCT (ratio 1.64) and standard CBCT (1.22). CCM of the tumor ROI in gated CBCT is larger than standard CBCT in all three thoracic cases thus far (ratio gated/standard mean 1.04 range 1.03–1.06), indicating higher congruence with the ground‐truth RCCT Conclusions: Gated CBCT visibly reduces image blurring caused by respiratory motion. By exploiting recent computer‐controlled linac technology, complete projection sets can be acquired within a gate, yielding improved reconstruction image quality relative to RC‐CBCT.

Using Respiration-correlated Cone Beam CT (RC-CBCT) Scans to Correct Target Positioning Errors in Radiotherapy of Thoracic Cancer

Using Respiration-correlated Cone Beam CT (RC-CBCT) Scans to Correct Target Positioning Errors in Radiotherapy of Thoracic Cancer

Evaluation of respiration‐correlated digital tomosynthesis in lunga)

Digital tomosynthesis (DTS) with a linear accelerator-mounted imaging system provides a means of reconstructing tomographic images from radiographic projections over a limited gantry arc, thus requiring only a few seconds to acquire. Its application in the thorax, however, often results in blurred images from respiration-induced motion. This work evaluates the feasibility of respiration-correlated (RC) DTS for soft-tissue visualization and patient positioning. Image data acquired with a gantry-mounted kilovoltage imaging system while recording respiration were retrospectively analyzed from patients receiving radiotherapy for non-small-cell lung carcinoma. Projection images spanning an approximately 30 degrees gantry arc were sorted into four respiration phase bins prior to DTS reconstruction, which uses a backprojection, followed by a procedure to suppress structures above and below the reconstruction plane of interest. The DTS images were reconstructed in planes at different depths through the patient and normal to a user-selected angle close to the center of the arc. The localization accuracy of RC-DTS was assessed via a comparison with CBCT. Evaluation of RC-DTS in eight tumors shows visible reduction in image blur caused by the respiratory motion. It also allows the visualization of tumor motion extent. The best image quality is achieved at the end-exhalation phase of the respiratory motion. Comparison of RC-DTS with respiration-correlated cone-beam CT in determining tumor position, motion extent and displacement between treatment sessions shows agreement in most cases within 2-3 mm, comparable in magnitude to the intraobserver repeatability of the measurement. These results suggest the method's applicability for soft-tissue image guidance in lung, but must be confirmed with further studies in larger numbers of patients.

On-Line Target Position Localization in the Presence of Respiration: A Comparison of two Methods

To compare two "four-dimensional" methods for image-guided target localization in the presence of respiration. Four-dimensional image guidance was performed with two methods. A respiration-correlated computed tomography (RCCT) was acquired on a CT simulator, and an average CT (AVG-CT) image was generated from the RCCT. A respiration-correlated cone-beam CT (RC-CBCT) and a free-breathing cone-beam CT (FB-CBCT) were acquired. The "RCCT method" consisted of calculating the mean target position on both the RCCT and RC-CBCT, registering the RCCT to the RC-CBCT, and determining the shift in the mean target position from the planned mean position. The "AVG-CT method" consisted of registering the AVG-CT to the FB-CBCT. The ability of each to measure the shift in the mean target position was compared, both in a respiratory phantom and in 8 patients. In phantom, the RCCT and AVG-CT methods were able to measure the true mean target position to within 0.15 cm and 0.10 cm, respectively. In the patient study, the mean error between the methods was 0.13 cm (left-right), 0.14 cm (anterior-posterior), and 0.10 cm (cranio-caudal). The error was not observed to vary with tumor position or magnitude of tumor motion. Respiration may impact the on-line image guidance process. The RCCT method enables localization of the mean tumor position and measurement of changes in the motion pattern, whereas the AVG-CT method is simple, fast, and easily implemented. We found the methods to be nearly equivalent in detecting shifts in the mean tumor position.

Quantifying Inter and Intra-Fraction Tumor Motion using Respiration-Correlated Cone Beam CT in Lung Stereotactic Body Radiotherapy (SBRT)

Quantifying Inter and Intra-Fraction Tumor Motion using Respiration-Correlated Cone Beam CT in Lung Stereotactic Body Radiotherapy (SBRT)

400 oral Matching the average position of moving lung tumours to the PTV, using respiration correlated cone beam CT data

400 oral Matching the average position of moving lung tumours to the PTV, using respiration correlated cone beam CT data

Image-guided radiotherapy for lung cancer: Respiration-correlated (cone-beam) CT to verify tumor position and motion characteristics during treatment delivery

In radiotherapy of lung cancer it is essential that the average position and motion characteristics of the tumor during treatment delivery are identical to those during treatment preparation. In this work we present a method to verify the tumor position and motion characteristics by comparing respiration-correlated cone-beam CT scans (RC-CBCT) made on the treatment machine with respiration-correlated CT scans (RC-CT) made for treatment preparation.

Image-guided radiotherapy for lung cancer: Respiration-correlated (cone-beam) CT to verify tumor position and motion characteristics during treatment delivery

Image-guided radiotherapy for lung cancer: Respiration-correlated (cone-beam) CT to verify tumor position and motion characteristics during treatment delivery