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P Keall - One of the best experts on this subject based on the ideXlab platform.
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simulated Multileaf Collimator tracking for stereotactic liver radiotherapy guided by kilovoltage intrafraction monitoring dosimetric gain and target overdose trends
Radiotherapy and Oncology, 2020Co-Authors: P R Poulsen, Ricky Obrien, E Worm, Ghulam Murtaza, T Ravkilde, Cai Grau, Morten Hoyer, P KeallAbstract:Abstract Purpose To investigate the potential benefit of Multileaf Collimator (MLC) tracking guided by kilovoltage intrafraction monitoring (KIM) during stereotactic body radiotherapy (SBRT) in the liver, and to understand trends of target overdose with MLC tracking. Methods Six liver SBRT patients with 2–3 implanted gold markers received SBRT delivered with volumetric modulated arc therapy (VMAT) in three fractions using daily cone-beam CT setup. The CTV-to-PTV margins were 5 mm in the axial plane and 10 mm in the cranio-caudal directions, and the plans were designed to give minimum target doses of 95% (CTV) and 67% (PTV). The three-dimensional marker trajectory estimated by post-treatment analysis of kV fluoroscopy images acquired throughout treatment delivery was assumed to represent the tumor motion. MLC tracking guided by real-time KIM was simulated. The reduction in CTV D95 (minimum dose to 95% of the clinical target volume) relative to the planned D95 (ΔD95) was compared between actual non-tracking and simulated MLC tracking treatments. Results MLC tracking maintained a high CTV dose coverage for all 18 fractions with ΔD95 (mean: 0.2 percentage points (pp), range: −1.7 to 1.9 pp) being significantly lower than for the actual non-tracking treatments (mean: 6.3 pp range: 0.6–16.0 pp) (p = 0.002). MLC tracking of large target motion perpendicular to the MLC leaves created dose artifacts with regions of overdose in the CTV. As a result, the mean dose in spherical volumes centered in the middle of the CTV was on average 2.4 pp (5 mm radius sphere) and 1.3 pp (15 mm radius sphere) higher than planned (p = 0.002). Conclusions Intrafraction tumor motion can deteriorate the CTV dose of liver SBRT. The planned CTV dose coverage may be restored with KIM-guided MLC tracking. However, MLC tracking may have a tendency to create hotspots in the CTV.
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Multileaf Collimator tracking improves dose delivery for prostate cancer radiation therapy results of the first clinical trial
International Journal of Radiation Oncology Biology Physics, 2015Co-Authors: P R Poulsen, E Colvill, Jeremy T Booth, Ricky Obrien, Thomas Eade, Andrew Kneebone, P KeallAbstract:Purpose To test the hypothesis that Multileaf Collimator (MLC) tracking improves the consistency between the planned and delivered dose compared with the dose without MLC tracking, in the setting of a prostate cancer volumetric modulated arc therapy trial. Methods and Materials Multileaf Collimator tracking was implemented for 15 patients in a prostate cancer radiation therapy trial; in total, 513 treatment fractions were delivered. During each treatment fraction, the prostate trajectory and treatment MLC positions were collected. These data were used as input for dose reconstruction (multiple isocenter shift method) to calculate the treated dose (with MLC tracking) and the dose that would have been delivered had MLC tracking not been applied (without MLC tracking). The percentage difference from planned for target and normal tissue dose-volume points were calculated. The hypothesis was tested for each dose-volume value via analysis of variance using the F test. Results Of the 513 fractions delivered, 475 (93%) were suitable for analysis. The mean difference and standard deviation between the planned and treated MLC tracking doses and the planned and without-MLC tracking doses for all 475 fractions were, respectively, PTV D 99% −0.8% ± 1.1% versus −2.1% ± 2.7%; CTV D 99% −0.6% ± 0.8% versus −0.6% ± 1.1%; rectum V 65% 1.6% ± 7.9% versus −1.2% ± 18%; and bladder V 65% 0.5% ± 4.4% versus −0.0% ± 9.2% ( P Conclusion This study shows that MLC tracking improves the consistency between the planned and delivered doses compared with the modeled doses without MLC tracking. The implications of this finding are potentially improved patient outcomes, as well as more reliable dose-volume data for radiobiological parameter determination.
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image based dynamic Multileaf Collimator tracking of moving targets during intensity modulated arc therapy
International Journal of Radiation Oncology Biology Physics, 2012Co-Authors: P R Poulsen, Walther Fledelius, Byungchul Cho, P KeallAbstract:Purpose Intensity-modulated arc therapy (IMAT) enables efficient and highly conformal dose delivery. However, intrafraction motion may compromise the delivered target dose distribution. Dynamic Multileaf Collimator (DMLC) tracking can potentially mitigate the impact of target motion on the dose. The purpose of this study was to use a single kV imager for DMLC tracking during IMAT and to investigate the ability of this tracking to maintain the dose distribution. Methods A motion phantom carrying a two-dimensional (2D) ion chamber array and buildup material with an embedded gold marker reproduced eight representative tumor trajectories (four lung tumors, four prostate). For each trajectory, a low and high IMAT plan were delivered with and without DMLC tracking. The three-dimensional (3D) real-time target position signal for tracking was provided by fluoroscopic kV images acquired immediately before and during treatment. For each image, the 3D position of the embedded marker was estimated from the imaged 2D position by a probability-based method. The MLC leaves were continuously refitted to the estimated 3D position. For lung, prediction was used to compensate for the tracking latency. The delivered 2D dose distributions were measured with the ion chamber array and compared with a reference dose distribution delivered without target motion using a 3%/3 mm γ-test. Results For lung tumor motion, tracking reduced the mean γ-failure rate from 38% to 0.7% for low-modulation IMAT plans and from 44% to 2.8% for high-modulation plans. For prostate, the γ-failure rate reduction was from 19% to 0% (low modulation) and from 20% to 2.7% (high modulation). The dominant contributor to the residual γ-failures during tracking was target localization errors for most lung cases and leaf fitting errors for most prostate cases. Conclusion Image-based tracking for IMAT was demonstrated for the first time. The tracking greatly improved the dose distributions to moving targets.
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tu c 214 04 prototype of a real time adaptive therapy system integrating automatic soft tissue localization with dynamic Multileaf Collimator dmlc adaptation
Medical Physics, 2011Co-Authors: P Keall, J Rottmann, G Cho, R HillAbstract:Purpose: Develop a prototype real‐time adaptive therapy system integrating automatic soft tissue tumor localization (STTL) with dynamic Multileaf Collimator (DMLC) adaptation of the treatment aperture. The system maintains a dynamic treatment aperture centered on the current tumor location during the entire breathing cycle. The STTL component utilizes portal images and operates without the need for fiducial markers. The proposed system has the potential to improve treatment accuracy, dose conformity and sparing of healthy tissue. Methods: A prototype system was developed. The tumor is located automatically and in real‐time on continuously acquired portal images and the tumor position is forwarded to the DMLC component to adapt the treatment aperture. The functionality is demonstrated with a preliminary setup: portal images are acquired by the treatment control system with a frame rate of 2 fps. The STTL algorithm continuously reads images, locates the target position and forwards it to the DMLC component which moves the treatment field aperture to that location. The preliminary setup was tested with a dynamic chest phantom driving a 1D sinusoidal motion in superior‐inferior direction parallel to the MLC leafs. Results: The individual geometric errors of the STTL algorithm and the DMLC are each smaller than 1mm in this configuration. The latency of the preliminary setup was less than 100 ms for the tracking of 15 landmarks with additional latencies coming from image acquisition, network transfers and DMLC component. The overall latency in the final setup is expected to be better than 550 ms. Conclusions: We have developed a prototype real‐ time adaptive therapy system integrating automatic soft tissue tumor localization with DMLC adaptation of the treatment aperture. The functionality of the combined system was successfully tested in a preliminary setup. The overall geometric accuracy is expected to be better than 2 mm for 1D motion. Varian Medical Systems Inc., NCI grant CA93626
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real time target position estimation using stereoscopic kilovoltage megavoltage imaging and external respiratory monitoring for dynamic Multileaf Collimator tracking
International Journal of Radiation Oncology Biology Physics, 2011Co-Authors: Amit Sawant, P R Poulsen, Dan Ruan, P KeallAbstract:Purpose To develop a real-time target position estimation method using stereoscopic kilovoltage (kV)/megavoltage (MV) imaging and external respiratory monitoring, and to investigate the performance of a dynamic Multileaf Collimator tracking system using this method. Methods and Materials The real-time three-dimensional internal target position estimation was established by creating a time-varying correlation model that connected the external respiratory signals with the internal target motion measured intermittently using kV/MV imaging. The method was integrated into a dynamic Multileaf Collimator tracking system. Tracking experiments were performed for 10 thoracic/abdominal traces. A three-dimensional motion platform carrying a gold marker and a separate one-dimensional motion platform were used to reproduce the target and external respiratory motion, respectively. The target positions were detected by kV (1 Hz) and MV (5.2 Hz) imaging, and external respiratory motion was captured by an optical system (30 Hz). The beam–target alignment error was quantified as the positional difference between the target and circular beam center on the MV images acquired during tracking. The correlation model error was quantified by comparing a model estimate and measured target positions. Results The root-mean-square errors in the beam–target alignment that had ranged from 3.1 to 7.6 mm without tracking were reduced to Conclusion A novel real-time target position estimation method was developed and integrated into a dynamic Multileaf Collimator tracking system and demonstrated an average submillimeter geometric accuracy after initializing the internal/external correlation model. The method used hardware tools available on linear accelerators and therefore shows promise for clinical implementation.
P R Poulsen - One of the best experts on this subject based on the ideXlab platform.
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simulated Multileaf Collimator tracking for stereotactic liver radiotherapy guided by kilovoltage intrafraction monitoring dosimetric gain and target overdose trends
Radiotherapy and Oncology, 2020Co-Authors: P R Poulsen, Ricky Obrien, E Worm, Ghulam Murtaza, T Ravkilde, Cai Grau, Morten Hoyer, P KeallAbstract:Abstract Purpose To investigate the potential benefit of Multileaf Collimator (MLC) tracking guided by kilovoltage intrafraction monitoring (KIM) during stereotactic body radiotherapy (SBRT) in the liver, and to understand trends of target overdose with MLC tracking. Methods Six liver SBRT patients with 2–3 implanted gold markers received SBRT delivered with volumetric modulated arc therapy (VMAT) in three fractions using daily cone-beam CT setup. The CTV-to-PTV margins were 5 mm in the axial plane and 10 mm in the cranio-caudal directions, and the plans were designed to give minimum target doses of 95% (CTV) and 67% (PTV). The three-dimensional marker trajectory estimated by post-treatment analysis of kV fluoroscopy images acquired throughout treatment delivery was assumed to represent the tumor motion. MLC tracking guided by real-time KIM was simulated. The reduction in CTV D95 (minimum dose to 95% of the clinical target volume) relative to the planned D95 (ΔD95) was compared between actual non-tracking and simulated MLC tracking treatments. Results MLC tracking maintained a high CTV dose coverage for all 18 fractions with ΔD95 (mean: 0.2 percentage points (pp), range: −1.7 to 1.9 pp) being significantly lower than for the actual non-tracking treatments (mean: 6.3 pp range: 0.6–16.0 pp) (p = 0.002). MLC tracking of large target motion perpendicular to the MLC leaves created dose artifacts with regions of overdose in the CTV. As a result, the mean dose in spherical volumes centered in the middle of the CTV was on average 2.4 pp (5 mm radius sphere) and 1.3 pp (15 mm radius sphere) higher than planned (p = 0.002). Conclusions Intrafraction tumor motion can deteriorate the CTV dose of liver SBRT. The planned CTV dose coverage may be restored with KIM-guided MLC tracking. However, MLC tracking may have a tendency to create hotspots in the CTV.
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Multileaf Collimator tracking improves dose delivery for prostate cancer radiation therapy results of the first clinical trial
International Journal of Radiation Oncology Biology Physics, 2015Co-Authors: P R Poulsen, E Colvill, Jeremy T Booth, Ricky Obrien, Thomas Eade, Andrew Kneebone, P KeallAbstract:Purpose To test the hypothesis that Multileaf Collimator (MLC) tracking improves the consistency between the planned and delivered dose compared with the dose without MLC tracking, in the setting of a prostate cancer volumetric modulated arc therapy trial. Methods and Materials Multileaf Collimator tracking was implemented for 15 patients in a prostate cancer radiation therapy trial; in total, 513 treatment fractions were delivered. During each treatment fraction, the prostate trajectory and treatment MLC positions were collected. These data were used as input for dose reconstruction (multiple isocenter shift method) to calculate the treated dose (with MLC tracking) and the dose that would have been delivered had MLC tracking not been applied (without MLC tracking). The percentage difference from planned for target and normal tissue dose-volume points were calculated. The hypothesis was tested for each dose-volume value via analysis of variance using the F test. Results Of the 513 fractions delivered, 475 (93%) were suitable for analysis. The mean difference and standard deviation between the planned and treated MLC tracking doses and the planned and without-MLC tracking doses for all 475 fractions were, respectively, PTV D 99% −0.8% ± 1.1% versus −2.1% ± 2.7%; CTV D 99% −0.6% ± 0.8% versus −0.6% ± 1.1%; rectum V 65% 1.6% ± 7.9% versus −1.2% ± 18%; and bladder V 65% 0.5% ± 4.4% versus −0.0% ± 9.2% ( P Conclusion This study shows that MLC tracking improves the consistency between the planned and delivered doses compared with the modeled doses without MLC tracking. The implications of this finding are potentially improved patient outcomes, as well as more reliable dose-volume data for radiobiological parameter determination.
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image based dynamic Multileaf Collimator tracking of moving targets during intensity modulated arc therapy
International Journal of Radiation Oncology Biology Physics, 2012Co-Authors: P R Poulsen, Walther Fledelius, Byungchul Cho, P KeallAbstract:Purpose Intensity-modulated arc therapy (IMAT) enables efficient and highly conformal dose delivery. However, intrafraction motion may compromise the delivered target dose distribution. Dynamic Multileaf Collimator (DMLC) tracking can potentially mitigate the impact of target motion on the dose. The purpose of this study was to use a single kV imager for DMLC tracking during IMAT and to investigate the ability of this tracking to maintain the dose distribution. Methods A motion phantom carrying a two-dimensional (2D) ion chamber array and buildup material with an embedded gold marker reproduced eight representative tumor trajectories (four lung tumors, four prostate). For each trajectory, a low and high IMAT plan were delivered with and without DMLC tracking. The three-dimensional (3D) real-time target position signal for tracking was provided by fluoroscopic kV images acquired immediately before and during treatment. For each image, the 3D position of the embedded marker was estimated from the imaged 2D position by a probability-based method. The MLC leaves were continuously refitted to the estimated 3D position. For lung, prediction was used to compensate for the tracking latency. The delivered 2D dose distributions were measured with the ion chamber array and compared with a reference dose distribution delivered without target motion using a 3%/3 mm γ-test. Results For lung tumor motion, tracking reduced the mean γ-failure rate from 38% to 0.7% for low-modulation IMAT plans and from 44% to 2.8% for high-modulation plans. For prostate, the γ-failure rate reduction was from 19% to 0% (low modulation) and from 20% to 2.7% (high modulation). The dominant contributor to the residual γ-failures during tracking was target localization errors for most lung cases and leaf fitting errors for most prostate cases. Conclusion Image-based tracking for IMAT was demonstrated for the first time. The tracking greatly improved the dose distributions to moving targets.
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megavoltage image based dynamic Multileaf Collimator tracking of a niti stent in porcine lungs on a linear accelerator
International Journal of Radiation Oncology Biology Physics, 2012Co-Authors: P R Poulsen, Jesper Carl, Jane Nielsen, Martin Skovmos Nielsen, Jakob Borup Thomsen, Henrik Kirstein Jensen, Benedict Kjaergaard, Peter Rose Zepernick, E Worm, Walther FledeliusAbstract:Purpose To investigate the accuracy and potential limitations of MV image-based dynamic Multileaf Collimator (DMLC) tracking in a porcine model on a linear accelerator. Methods and Materials A thermo-expandable NiTi stent designed for kilovoltage (kV) X-ray visualization of lung lesions was inserted into the bronchia of three anaesthetized Gottingen minipigs. A four-dimensional computed tomography scan was used for planning a five-field conformal treatment with circular Multileaf Collimator (MLC) apertures. A 22.5 Gy single fraction treatment was delivered to the pigs. The peak-to-peak stent motion was 3 to 8 mm, with breathing periods of 1.2 to 4 s. Before treatment, X-ray images were used for image-guided setup based on the stent. During treatment delivery, continuous megavoltage (MV) portal images were acquired at 7.5 Hz. The stent was segmented in the images and used for continuous adaptation of the MLC aperture. Offline, the tracking error in beam's eye view of the treatment beam was calculated for each MV image as the difference between the MLC aperture center and the segmented stent position. The standard deviations of the systematic error Σ and the random error σ were determined and compared with the would-be errors for a nontracking treatment with pretreatment image-guided setup. Results Reliable stent segmentation was obtained for 11 of 15 fields. Segmentation failures occurred when image contrast was dominated by overlapping anatomical structures (ribs, diaphragm) rather than by the stent, which was designed for kV rather than MV X-ray visibility. For the 11 fields with reliable segmentation, Σ was 0.5 mm/0.4 mm in the two imager directions, whereas σ was 0.5 mm/1.1 mm. Without tracking, Σ and σ would have been 1.7 mm/1.4 mm and 0.8 mm/1.4 mm, respectively. Conclusion For the first time, in vivo DMLC tracking has been demonstrated on a linear accelerator showing the potential for improved targeting accuracy. The study mimicked the envisioned patient workflow of future patient treatments. Clinical implementation of MV image-based tracking would require markers designed for MV visibility.
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real time target position estimation using stereoscopic kilovoltage megavoltage imaging and external respiratory monitoring for dynamic Multileaf Collimator tracking
International Journal of Radiation Oncology Biology Physics, 2011Co-Authors: Amit Sawant, P R Poulsen, Dan Ruan, P KeallAbstract:Purpose To develop a real-time target position estimation method using stereoscopic kilovoltage (kV)/megavoltage (MV) imaging and external respiratory monitoring, and to investigate the performance of a dynamic Multileaf Collimator tracking system using this method. Methods and Materials The real-time three-dimensional internal target position estimation was established by creating a time-varying correlation model that connected the external respiratory signals with the internal target motion measured intermittently using kV/MV imaging. The method was integrated into a dynamic Multileaf Collimator tracking system. Tracking experiments were performed for 10 thoracic/abdominal traces. A three-dimensional motion platform carrying a gold marker and a separate one-dimensional motion platform were used to reproduce the target and external respiratory motion, respectively. The target positions were detected by kV (1 Hz) and MV (5.2 Hz) imaging, and external respiratory motion was captured by an optical system (30 Hz). The beam–target alignment error was quantified as the positional difference between the target and circular beam center on the MV images acquired during tracking. The correlation model error was quantified by comparing a model estimate and measured target positions. Results The root-mean-square errors in the beam–target alignment that had ranged from 3.1 to 7.6 mm without tracking were reduced to Conclusion A novel real-time target position estimation method was developed and integrated into a dynamic Multileaf Collimator tracking system and demonstrated an average submillimeter geometric accuracy after initializing the internal/external correlation model. The method used hardware tools available on linear accelerators and therefore shows promise for clinical implementation.
S Webb - One of the best experts on this subject based on the ideXlab platform.
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the effect on imrt conformality of elastic tissue movement and a practical suggestion for movement compensation via the modified dynamic Multileaf Collimator dmlc technique
Physics in Medicine and Biology, 2005Co-Authors: S WebbAbstract:A major remaining problem in delivering radiotherapy, specifically intensity-modulated radiation therapy (IMRT), is the need to accommodate and correct for intrafraction movement. The developing availability of 4D computed tomographic images can potentially form the basis of the new field of image-guided IMRT. It is important to understand the effects on delivered dose of the patient breathing during IMRT and this paper models the effect which applies whether there is or is not a time component to the IMRT delivery method. It then goes on to suggest a practical correction strategy. The 'stretch-and-shift-the-planned-modulations' strategy is proposed and a practical method to deliver this is explained. This practical strategy is based on a modification of the dynamic Multileaf Collimator IMRT method whereby the leaves are arranged to 'breath' in tandem with the breathing of the patient. Some examples are also given from a study of mismatching the patient and leaf-correction motions.
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configuration options for intensity modulated radiation therapy using multiple static fields shaped by a Multileaf Collimator ii constraints and limitations on 2d modulation
Physics in Medicine and Biology, 1998Co-Authors: S WebbAbstract:This paper addresses the technique of using multiple static Multileaf-Collimator-shaped field components to create a two-dimensional intensity-modulated beam (2D IMB). It addresses the physical constraints on the problem of determining the optimum field-component leaf configurations under the circumstances that (i) the static field components are shaped by leaves alone and (ii) the 2D intensity distribution is delivered by exactly N field components when there are N rising-intensity equal-fluence increments in the 1D channel containing the maximum fluence in the 2D IMB. This corresponds to the least inefficient delivery. In general it is noted that an optimum solution (set of field-component leaf configurations) with zero tongue-and-groove underdose may not exist (depending on the distribution) and an exhaustive search for the set of leaf configurations with the minimum tongue-and-groove underdose is impossible for realistically sized problems. Against this background iterative methods to examine a limited search space are shown to yield an optimum solution with zero tongue-and-groove underdose for certain intensity distributions. These searches are not robust and can be defeated. The problem of finding an optimum solution may be generally insoluble for some 2D IMBs under the conditions (i) and (ii). If, however, a larger number of field components is permitted and/or the accelerator jaws may also be used, in addition to the multileaves, then an optimum solution with zero tongue-and-groove underdose can always be found with lower efficiency.
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configuration options for intensity modulated radiation therapy using multiple static fields shaped by a Multileaf Collimator
Physics in Medicine and Biology, 1998Co-Authors: S WebbAbstract:One-dimensional (1D) intensity-modulated beams (IMBs) can be generated by multiple static fields (MSFs) created by a Multileaf Collimator (MLC) with the radiation switched off between field re-settings (Bortfeld-Boyer method). Each component irradiation is of equal fluence. This paper presents and analyses the formulae for the number of physically allowed combinations of leaf settings which generate any given IMB. The formulae are general to an IMB with any number of local minima and extend from the well-known formula for a single-peaked IMB with N left-leaf (L-leaf) and N right-leaf (R-leaf) positions. A `combination' is a set of N L-leaf and R-leaf pairings. A `physically allowed combination' is one in which no L-leaf is paired with an R-leaf to its left. The physically allowed combinations are grouped by specific properties into classes in which the well-known techniques of `leaf-sweep' and `close-in' are just two members. Consideration of these properties leads to a new suggestion of the `forced-baseline' configuration in which the first intensity increment is delivered for the full field width and there remain choices concerning the delivery of the rest of the IMB within which two different possibilities are `one-out-of-sync leaf-sweep' and `minimum leaf travel'. The extension to 2D is briefly introduced.
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the effect of stair step leaf transmission on the tongue and groove problem in dynamic radiotherapy with a Multileaf Collimator
Physics in Medicine and Biology, 1997Co-Authors: S Webb, Thomas Bortfeld, Jorg Stein, D ConveryAbstract:When intensity-modulated fields are created using a Multileaf Collimator with dynamic leaf movement the potential problem for underdoseage beneath the tongue-and-groove interleaf regions has been identified and a solution based on leaf-movement synchronization has been provided by Van Santvoort and Heijmen. Their first-order analysis ignored the transmission through an exposed stair-step. In this brief Note we provide the extended analysis including this contribution and show the effect on irradiation with synchronization. The result is that the synchronization approach of Van Santvoort and Heijmen solves the tongue-and-groove problem even when the transmission through the stair-step is considered, but partial synchronization is generally sufficient.
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optimization by simulated annealing of three dimensional conformal treatment planning for radiation fields defined by a Multileaf Collimator ii inclusion of two dimensional modulation of the x ray intensity
Physics in Medicine and Biology, 1992Co-Authors: S WebbAbstract:For pt.I see ibid., vol.36, p.1201-26 (1991). Interest is rapidly growing in using multiple X-radiation fields defined by a Multileaf Collimator to achieve conformal radiotherapy. Three-dimensional treatment planning in such situations is in its infancy and most 3D planning systems provide no tools for optimizing therapy. A previous paper addressed how to calculate optimum beamweights when both the target volume and all or some parts of organs at risk were in the fields-of-view. The present work extends this technique to allow each radiation port to be spatially modulated across the geometrically shape field. An optimization method based on simulated annealing is presented. It is shown that including spatial modulation leads to a wider separation between the dose-volume histograms of the target volume and organs at risk. The improvement is quantified in terms of the tumour control probability at constant normal tissue complication probability. Possible limitations of a posteriori applied biological model are discussed in detail.
Amit Sawant - One of the best experts on this subject based on the ideXlab platform.
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real time target position estimation using stereoscopic kilovoltage megavoltage imaging and external respiratory monitoring for dynamic Multileaf Collimator tracking
International Journal of Radiation Oncology Biology Physics, 2011Co-Authors: Amit Sawant, P R Poulsen, Dan Ruan, P KeallAbstract:Purpose To develop a real-time target position estimation method using stereoscopic kilovoltage (kV)/megavoltage (MV) imaging and external respiratory monitoring, and to investigate the performance of a dynamic Multileaf Collimator tracking system using this method. Methods and Materials The real-time three-dimensional internal target position estimation was established by creating a time-varying correlation model that connected the external respiratory signals with the internal target motion measured intermittently using kV/MV imaging. The method was integrated into a dynamic Multileaf Collimator tracking system. Tracking experiments were performed for 10 thoracic/abdominal traces. A three-dimensional motion platform carrying a gold marker and a separate one-dimensional motion platform were used to reproduce the target and external respiratory motion, respectively. The target positions were detected by kV (1 Hz) and MV (5.2 Hz) imaging, and external respiratory motion was captured by an optical system (30 Hz). The beam–target alignment error was quantified as the positional difference between the target and circular beam center on the MV images acquired during tracking. The correlation model error was quantified by comparing a model estimate and measured target positions. Results The root-mean-square errors in the beam–target alignment that had ranged from 3.1 to 7.6 mm without tracking were reduced to Conclusion A novel real-time target position estimation method was developed and integrated into a dynamic Multileaf Collimator tracking system and demonstrated an average submillimeter geometric accuracy after initializing the internal/external correlation model. The method used hardware tools available on linear accelerators and therefore shows promise for clinical implementation.
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electromagnetic guided dynamic Multileaf Collimator tracking enables motion management for intensity modulated arc therapy
International Journal of Radiation Oncology Biology Physics, 2011Co-Authors: P Keall, Amit Sawant, P R Poulsen, Dan Ruan, Byungchul Cho, Herbert Cattell, Laurence J Newell, J Petersen, S KorremanAbstract:Purpose Intensity-modulated arc therapy (IMAT) is attractive because of high-dose conformality and efficient delivery. However, managing intrafraction motion is challenging for IMAT. The purpose of this research was to develop and investigate electromagnetically guided dynamic Multileaf Collimator (DMLC) tracking as an enabling technology to treat moving targets during IMAT. Methods and Materials A real-time three-dimensional DMLC-based target tracking system was developed and integrated with a linear accelerator. The DMLC tracking software inputs a real-time electromagnetically measured target position and the IMAT plan, and dynamically creates new leaf positions directed at the moving target. Low- and high-modulation IMAT plans were created for lung and prostate cancer cases. The IMAT plans were delivered to a three-axis motion platform programmed with measured patient motion. Dosimetric measurements were acquired by placing an ion chamber array on the moving platform. Measurements were acquired with tracking, without tracking (current clinical practice), and with the phantom in a static position (reference). Analysis of dose distribution differences from the static reference used a γ-test. Results On average, 1.6% of dose points for the lung plans and 1.2% of points for the prostate plans failed the 3-mm/3% γ-test with tracking; without tracking, 34% and 14% (respectively) of points failed the γ-test. The delivery time was the same with and without tracking. Conclusions Electromagnetic-guided DMLC target tracking with IMAT has been investigated for the first time. Dose distributions to moving targets with DMLC tracking were significantly superior to those without tracking. There was no loss of treatment efficiency with DMLC tracking.
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dynamic Multileaf Collimator tracking of respiratory target motion based on a single kilovoltage imager during arc radiotherapy
International Journal of Radiation Oncology Biology Physics, 2010Co-Authors: Amit Sawant, P R Poulsen, Dan Ruan, Byungchul Cho, P KeallAbstract:Purpose To demonstrate and characterize dynamic Multileaf Collimator (DMLC) tracking of respiratory moving targets that are spatially localized with a single kV X-ray imager during arc radiotherapy. Methods and Materials During delivery of an arc field (358° gantry rotation, 72-sec duration, circular field shape), the three-dimensional (3D) position of a fiducial marker in a phantom was estimated in real time from fluoroscopic kV X-ray images acquired orthogonally to the treatment beam axis. A prediction algorithm was applied to account for system latency (570 ms) before the estimated marker position was used for DMLC aperture adaptation. Experiments were performed with 12 patient-measured tumor trajectories that were selected from 160 trajectories (46 patients) and reproduced by a programmable phantom. Offline, the 3D deviation of the estimated phantom position from the actual position was quantified. The two-dimensional (2D) beam-target deviation was quantified as the positional difference between the MLC aperture center and the marker in portal images acquired continuously during experiments. Simulations of imaging and treatment delivery extended the study to all 160 tumor trajectories and to arc treatments of 3-min and 5-min duration. Results In the experiments, the mean root-mean-square deviation was 1.8 mm for the 3D target position and 1.5 mm for the 2D aperture position. Simulations agreed with this to within 0.1 mm and resulted in mean 2D root-mean-square beam-target deviations of 1.1 mm for all 160 trajectories for all treatment durations. The deviations were mainly caused by system latency (570 ms). Conclusions Single-imager DMLC tracking of respiratory target motion during arc radiotherapy was implemented, providing less than 2-mm geometric uncertainty for most trajectories.
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implementation of a new method for dynamic Multileaf Collimator tracking of prostate motion in arc radiotherapy using a single kv imager
International Journal of Radiation Oncology Biology Physics, 2010Co-Authors: Amit Sawant, P R Poulsen, Byungchul Cho, P KeallAbstract:Purpose To implement a method for real-time prostate motion estimation with a single kV imager during arc radiotherapy and to integrate it with dynamic Multileaf Collimator (DMLC) target tracking. Methods and Materials An arc field with a circular aperture and 358° gantry rotation was delivered to a motion phantom with a fiducial marker under continuous kV X-ray imaging at 5 Hz, perpendicular to the treatment beam. A pretreatment gantry rotation of 120° in 20 sec with continuous imaging preceded the treatment. During treatment, each kV image was first used together with all previous images to estimate the three-dimensional (3D) target probability density function and then used together with this probability density function to estimate the 3D target position. The MLC aperture was then adapted to the estimated 3D target position. Tracking was performed with five patient-measured prostate trajectories that represented characteristic prostate motion patterns. Two data sets were recorded during tracking: (1) the estimated 3D target positions, for off-line comparison with the actual phantom motion; and (2) continuous portal images, for independent off-line calculation of the 2D tracking error as the positional difference between the marker and the MLC aperture center in each portal image. All experiments were also made with 1- Hz kV imaging. Results The mean 3D root-mean-square error of the trajectory estimation was 0.6 mm. The mean root-mean-square tracking error was 0.7 mm, both parallel and perpendicular to the MLC. The accuracy degraded slightly for 1- Hz imaging. Conclusions Single-imager DMLC prostate tracking that allows arbitrary beam modulation during arc radiotherapy was implemented. It has submillimeter accuracy for most prostate motion types.
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first demonstration of combined kv mv image guided real time dynamic Multileaf Collimator target tracking
International Journal of Radiation Oncology Biology Physics, 2009Co-Authors: Amit Sawant, P R Poulsen, Alexander Sloutsky, P KeallAbstract:Purpose For intrafraction motion management, a real-time tracking system was developed by combining fiducial marker-based tracking via simultaneous kilovoltage (kV) and megavoltage (MV) imaging and a dynamic Multileaf Collimator (DMLC) beam-tracking system. Methods and Materials The integrated tracking system employed a Varian Trilogy system equipped with kV/MV imaging systems and a Millennium 120-leaf MLC. A gold marker in elliptical motion (2-cm superior–inferior, 1-cm left–right, 10 cycles/min) was simultaneously imaged by the kV and MV imagers at 6.7 Hz and segmented in real time. With these two-dimensional projections, the tracking software triangulated the three-dimensional marker position and repositioned the MLC leaves to follow the motion. Phantom studies were performed to evaluate time delay from image acquisition to MLC adjustment, tracking error, and dosimetric impact of target motion with and without tracking. Results The time delay of the integrated tracking system was ∼450 ms. The tracking error using a prediction algorithm was 0.9 ± 0.5 mm for the elliptical motion. The dose distribution with tracking showed better target coverage and less dose to surrounding region over no tracking. The failure rate of the gamma test (3%/3-mm criteria) was 22.5% without tracking but was reduced to 0.2% with tracking. Conclusion For the first time, a complete tracking system combining kV/MV image-guided target tracking and DMLC beam tracking was demonstrated. The average geometric error was less than 1 mm, and the dosimetric error was negligible. This system is a promising method for intrafraction motion management.
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impact of the high definition Multileaf Collimator on linear accelerator based intracranial stereotactic radiosurgery
British Journal of Radiology, 2011Co-Authors: J Tanyi, Yiyi Chen, C M Kato, Z Chen, M FussAbstract:Objectives: The impact of two Multileaf Collimator (MLC) systems for linear accelerator-based intracranial stereotactic radiosurgery (SRS) was assessed. Methods: 68 lesions formed the basis of this study. 2.5mm leaf width plans served as reference. Comparative plans, with identical planning parameters, were based on a 5mm leaf width MLC system. Two collimation strategies, with collimation fixed at 0u or 90u and optimised per arc or beam, were also assessed. Dose computation was based on the pencil beam algorithm with allowance for tissue heterogeneity. Plan normalisation was such that 100% of the prescription dose covered 95% of the planning target volume. Plan evaluation was based on target coverage and normal tissue avoidance criteria. Results: The median conformity index difference between the MLC systems ranged between 0.8% and 14.2%; the 2.5mm MLC exhibited better dose conformation. The median reduction of normal tissue exposed to >100%, >50% and >25% of the prescription dose ranged from 13.4% to 29.7%, favouring the 2.5mm MLC system. Dose fall-off was steeper for the 2.5mm MLC system with an overall median absolute difference ranging from 0.4 to 1.2 mm. The use of collimation optimisation resulted in a decrease in differences between the MLC systems. The results demonstrated the dosimetric merit of the 2.5mm leaf width MLC system over the 5mm leaf width system, albeit small, for the investigated range of intracranial SRS targets. Conclusion: The clinical significance of these results warrants further investigation to determine whether the observed dosimetric advantages translate into outcome improvements.
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implications of a high definition Multileaf Collimator hd mlc on treatment planning techniques for stereotactic body radiation therapy sbrt a planning study
Radiation Oncology, 2009Co-Authors: James A Tanyi, Paige A Summers, Charles L Mccracken, Yiyi Chen, M FussAbstract:Purpose To assess the impact of two Multileaf Collimator (MLC) systems (2.5 and 5 mm leaf widths) on three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, and dynamic conformal arc techniques for stereotactic body radiation therapy (SBRT) of liver and lung lesions.