BREATH-HOLD TARGET LOCALIZATION WITH SIMULTANEOUS KILOVOLTAGE/MEGAVOLTAGE CONE-BEAM COMPUTED TOMOGRAPHY AND FAST RECONSTRUCTION

Purpose: Hypofractionated high-dose radiotherapy for small lung tumors has typically been based on stereotaxy. Cone-beam computed tomography and breath-hold techniques have provided a noninvasive basis for precise cranial and extracranial patient positioning. The cone-beam computed tomography acquisition time of 60 s, however, is beyond the breath-hold capacity of patients, resulting in respiratory motion artifacts. By combining megavoltage (MV) and kilovoltage (kV) photon sources (mounted perpendicularly on the linear accelerator) and accelerating the gantry rotation to the allowed limit, the data acquisition time could be reduced to 15 s. Methods and Materials: An Elekta Synergy 6-MV linear accelerator, with iViewGT as the MV- and XVI as the kV-imaging device, was used with a Catphan phantom and an anthropomorphic thorax phantom. Both image sources performed continuous image acquisition, passing an angle interval of 90 within 15 s. For reconstruction, filtered back projection on a graphics processor unit was used. It reconstructed 100 projections acquired to a 512 x 512 x 512 volume within 6 s. Results: The resolution in the Catphan phantom (CTP528 high-resolution module) was 3 lines/cm. The spatial accuracy was within 2-3 mm. The diameters of different tumor shapes in the thorax phantom were determined within an accuracy of 1.6 mm. The signal-to-noise ratio was 68% less than that with a 180 degrees-kV scan. The dose generated to acquire the MV frames accumulated to 82.5 mGy, and the kV contribution was <6 mGy. Conclusion: The present results have shown that fast breath-hold, on-line volume imaging with a linear accelerator using simultaneous kV MV cone-beam computed tomography is promising and can potentially be used for image-guided radiotherapy for lung cancer patients in the near future. (C) 2010 Elsevier Inc

Breath-hold target localization with simultaneous kilovoltage/megavoltage cone-beam CT and fast reconstruction

Hypofractionated high dose radiotherapy of small lung tumors is very effective and was based on stereotaxy until now. It has recently become possible to achieve a high patient positioning precision based on on-line imaging with cone-beam CT (CBCT) and breath-hold techniques. The CBCT acquisition time of roughly 60 seconds, however, is too long for one breath-hold, resulting in image degradation by respiratory motion artifacts. By using megavoltage (MV) an kilovoltage (kV) photon source (mounted perpendicularly on the Linac gantry) for volume reconstruction, we could reduce the acquisition time to 15 seconds. An Elekta Synergy 6MV linear accelerator, iViewGT as an MV- and XVI as a kV-imaging device were used. In 'movie mode' both systems were used for continuous image acquisition passing the angle interval of 90° in 15 seconds. In total, the MV frames needed 8.25 Monitor Units. The kV dose was negligible herein. In order to deduce the missing angle information, a marble with high absorption coefficient was put next to the thorax phantom. After preprocessing the data a GPU was used for the reconstruction of 100 projections generating a 512 x 512 x 512 volume in 6 seconds. The full acquisition and reconstruction workflow was automated. Structures with high contrast interfaces can be recognized easily in the reconstructed volume. These results show that fast on-board imaging based on combined kV-MV CBCT is promising for patient positioning. The scan duration of 15 seconds is short enough to perform single rotation breath-hold imaging for most patients. © 2009 Springer-Verlag

Towards clinical implementation of ultrafast combined kV-MV CBCT for IGRT of lung cancer Evaluation of registration accuracy based on phantom study

Purpose Combined kV-MV cone-beam CT (CBCT) is a promising approach to accelerate imaging for patients with lung tumors treated with deep inspiration breath-hold. During a single breath-hold (15 s), a 3D kV-MV CBCT can be acquired, thus minimizing motion artifacts and increasing patient comfort. Prior to clinical implementation, positioning accuracy was evaluated and compared to clinically established imaging techniques. Methods and materials An inhomogeneous thorax phantom with four tumor-mimicking inlays was imaged in 10 predefined positions and registered to a planning CT. Novel kV-MV CBCT imaging (90 degrees arc) was compared to clinically established kV-chest CBCT (360 degrees) as well as nonclinical kV-CBCT and low-dose MV-CBCT (each 180 degrees). Manual registration, automatic registration provided by the manufacturer and an additional in-house developed manufacturer-independent framework based on the MATLAB registration toolkit were applied. Results Systematic setup error was reduced to 0.05 mm by high-precision phantom positioning with optical tracking. Stochastic mean displacement errors were 0.5 +/- 0.3 mm in right-left, 0.4 +/- 0.4 mm in anteroposterior and 0.0 +/- 0.4 mm in craniocaudal directions for kV-MV CBCT with manual registration (maximum errors of no more than 1.4 mm). Clinical kV-chest CBCT resulted in mean errors of 0.2 mm (other modalities: 0.4-0.8 mm). Similar results were achieved with both automatic registration methods. Conclusion The comparison study of repositioning accuracy between novel kV-MV CBCT and clinically established volume imaging demonstrated that registration accuracy is maintained below 1 mm. Since imaging time is reduced to one breath-hold, kV-MV CBCT is ideal for image guidance, e.g., in lung stereotactic ablative radiotherapy

Towards clinical implementation of ultrafast combined kV-MV CBCT for IGRT of lung cancer Evaluation of registration accuracy based on phantom study

Purpose Combined kV-MV cone-beam CT (CBCT) is a promising approach to accelerate imaging for patients with lung tumors treated with deep inspiration breath-hold. During a single breath-hold (15 s), a 3D kV-MV CBCT can be acquired, thus minimizing motion artifacts and increasing patient comfort. Prior to clinical implementation, positioning accuracy was evaluated and compared to clinically established imaging techniques. Methods and materials An inhomogeneous thorax phantom with four tumor-mimicking inlays was imaged in 10 predefined positions and registered to a planning CT. Novel kV-MV CBCT imaging (90 degrees arc) was compared to clinically established kV-chest CBCT (360 degrees) as well as nonclinical kV-CBCT and low-dose MV-CBCT (each 180 degrees). Manual registration, automatic registration provided by the manufacturer and an additional in-house developed manufacturer-independent framework based on the MATLAB registration toolkit were applied. Results Systematic setup error was reduced to 0.05 mm by high-precision phantom positioning with optical tracking. Stochastic mean displacement errors were 0.5 +/- 0.3 mm in right-left, 0.4 +/- 0.4 mm in anteroposterior and 0.0 +/- 0.4 mm in craniocaudal directions for kV-MV CBCT with manual registration (maximum errors of no more than 1.4 mm). Clinical kV-chest CBCT resulted in mean errors of 0.2 mm (other modalities: 0.4-0.8 mm). Similar results were achieved with both automatic registration methods. Conclusion The comparison study of repositioning accuracy between novel kV-MV CBCT and clinically established volume imaging demonstrated that registration accuracy is maintained below 1 mm. Since imaging time is reduced to one breath-hold, kV-MV CBCT is ideal for image guidance, e.g., in lung stereotactic ablative radiotherapy

Fast kilovoltage/megavoltage (kVMV) breathhold cone-beam CT for image-guided radiotherapy of lung cancer

Long image acquisition times of 60-120 s for cone-beam CT (CBCT) limit the number of patients with lung cancer who can undergo volume image guidance under breathhold. We developed a low-dose dual-energy kilovoltage-megavoltage-cone-beam CT (kVMV-CBCT) based on a clinical treatment unit reducing imaging time to <= 15 s. Simultaneous kVMV-imaging was achieved by dedicated synchronization hardware controlling the output of the linear accelerator (linac) based on detector panel readout signals, preventing imaging artifacts from interference of the linac's MV-irradiation and panel readouts. Optimization was performed to minimize the imaging dose. Single MV-projections, reconstructed MV-CBCT images and images of simultaneous 90 degrees kV- and 90 degrees MV-CBCT (180 degrees kVMV-CBCT) were acquired with different parameters. Image quality and imaging dose were evaluated and compared to kV-imaging. Hardware-based kVMV synchronization resulted in artifact-free projections. A combined 180 degrees kVMV-CBCT scan with a total MV-dose of 5 monitor units was acquired in 15 s and with sufficient image quality. The resolution was 5-6 line pairs cm(-1) (Catphan phantom). The combined kVMV-scan dose was equivalent to a kV-radiation scan dose of similar to 33 mGy. kVMV-CBCT based on a standard linac is promising and can provide ultra-fast online volume image guidance with low imaging dose and sufficient image quality for fast and accurate patient positioning for patients with lung cancer under breathhold

Multiple breath-hold CBCT for online image guided radiotherapy of lung tumors: Simulation with a dynamic phantom and first patient data

Background and Purpose: Computer controlled breath-hold effectively reduces organ motion for image-guided precision radiotherapy of lung tumors. However, the acquisition time of 3D cone-beam-CT (CBCT) exceeds maximum breath-hold times. We have developed an approach enabling online verification using CBCT image acquisition with ABC (R)-based breath-hold. Methods: Patient CBCT images were acquired with ABC (R)-based repeat breath-hold. The clinical situation was also simulated with a Motion Phantom. Reconstruction of patient and phantom images with selection of free-breathing and breath-hold projections only was performed. Results: CBCT-imaging in repeat breath-hold resulted in a precisely spherical appearance of a tumor-mimicking structure in the phantom. A faint "ghost" structure (free-breathing phases) can be clearly discriminated. Mean percentage of patient breath-hold time was 66%. Reconstruction based on free-breathing-only shows blurring of both tumor and diaphragm, reconstruction based on breath-hold projections only resulted in sharp contours of the same structures. From the phantom experiments, a maximal repositioning error of 1 mm in each direction can be estimated. Discussion and Conclusion: CBCT during repetitive breath hold provides reliable soft-tissue-based positioning. Fast 3D-imaging during one breath-hold is currently under development and has the potential to accelerate clinical linac-based volume imaging. (C) 2011 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 98 (2011) 309-31