Toward Submillimeter Accuracy in the Management of Intrafraction Motion: The Integration of Real-Time Internal Position Monitoring and Multileaf Collimator Target Tracking

Multileaf collimator (MLC) tracking represents a promising technique for motion management in radiotherapy. However, the conflict between limited leaf speed/acceleration and the demand for tracking fast target motion is now a prominent issue. Conventional MLCs typically have a maximum leaf speed of 3–4 cm/s and a maximum leaf acceleration of 50–70 cm/s2, which are inadequate to track fast target motion. To cope with this problem, we have recently developed a high‐speed multileaf collimator (HS‐MLC) prototype, which employs linear motors instead of rotary motors to drive leaves. Consequently, it inherits various benefits of linear motors, including direct drive and high dynamics. The primary aim of this paper was to introduce the development and performance evaluation of the HS‐MLC. The evaluation includes Monte Carlo simulations of the basic dosimetric properties, camera‐based measurements of the mechanical properties and tracking experiments for 25 sets of patient‐measured motion data. The Monte Carlo simulation results show that the maximum leakage at 6MV is 1.29% and the average is 0.61%. The end‐to‐end leakage is 3.96% for 5 cm offset and is 1.75% for 10 cm offset. The penumbra for a standard 10 × 10 cm2 field ranges from 4.8 mm to 5.4 mm across the full range of leaf motion. The mechanical property measurements demonstrate that the maximum leaf speed is 40 cm/s, the maximum leaf acceleration is 1000 cm/s2, and the geometric accuracy can be kept within 0.5 mm. Regarding the tracking experiments for a wide range of motion patterns (fast breathing, irregular breathing, etc.), a root‐mean‐square error (RMSE) of less than 0.19 mm was achieved. In conclusion, the HS‐MLC is able to well track fast target motion that is beyond the capability of conventional MLCs due to its superior mechanical properties. The new MLC design provides a feasible solution to make high‐accuracy and high‐efficiency motion management possible.

Only target motion parallel to the leaf motion direction is considered in this paper.

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Section: Resultsmentioning

confidence: 99%

Development and performance evaluation of a high‐speed multileaf collimator

Zhang

2016

“…( 16 – 20 ) This correlation was reported to be poor or nonexistent unless the external surrogate measuring the skin surface was near the target volume. ( 21 ) Furthermore, there is no guarantee that these correlations are constant throughout the course of radiotherapy, ( 22 ) and these correlations provide the clinician little quantitative information as to the position or location of the radiation target in question. Alternative methods for tracking internal markers have focused on kilovoltage imaging.…”

Section: Technological Advances For Electromagnetic Trackingmentioning

confidence: 99%

“…This will give clinicians another technique that accounts for respiratory motion but with higher delivery efficiency than a gated treatment. ( 22 ) Several investigators have published on dynamic MLC tracking of varying target motion. ( 28 – 31 ) Electromagnetic tracking can be a key component in this effort.…”

Section: Technological Advances For Electromagnetic Trackingmentioning

confidence: 99%

“…3). ( 22 ) With the industrial collaborations between linac suppliers and electromagnetic tracking system developers, real‐time tracking with dynamic MLCs may be a viable option in the near future. Electromagnetic tracking systems provide translational position data, as well as reporting rotational information during the localization process.…”

Section: Technological Advances For Electromagnetic Trackingmentioning

confidence: 99%

“…This type of information can theoretically be implemented with dynamic MLC tracking to account for more complex motion such as in‐plane rigid rotation and target deformation. ( 22 ) The combination of the MLC tracking and couch robotics integrated with an electromagnetic tracking system could potentially lead to increased conformal dose distributions and reduced dosimetric uncertainties, all with the possibility to improve treatment outcome by reducing the effects of intrafraction motion.…”

Section: Technological Advances For Electromagnetic Trackingmentioning

confidence: 99%

See 2 more Smart Citations

Expanding the use of real‐time electromagnetic tracking in radiation oncology

Shah

Kupelian

Willoughby

et al. 2011

In the past 10 years, techniques to improve radiotherapy delivery, such as intensity‐modulated radiation therapy (IMRT), image‐guided radiation therapy (IGRT) for both inter‐ and intrafraction tumor localization, and hypofractionated delivery techniques such as stereotactic body radiation therapy (SBRT), have evolved tremendously. This review article focuses on only one part of that evolution, electromagnetic tracking in radiation therapy. Electromagnetic tracking is still a growing technology in radiation oncology and, as such, the clinical applications are limited, the expense is high, and the reimbursement is insufficient to cover these costs. At the same time, current experience with electromagnetic tracking applied to various clinical tumor sites indicates that the potential benefits of electromagnetic tracking could be significant for patients receiving radiation therapy. Daily use of these tracking systems is minimally invasive and delivers no additional ionizing radiation to the patient, and these systems can provide explicit tumor motion data. Although there are a number of technical and fiscal issues that need to be addressed, electromagnetic tracking systems are expected to play a continued role in improving the precision of radiation delivery.PACS number: 87.63.‐d

Patient specific methods for room‐mounted x‐ray imagers for monoscopic/stereoscopic prostate motion monitoring

Stevens

Parsons

Robar

2017

PurposeTo investigate the improvement of combined monoscopic/stereoscopic prostate motion monitoring with room‐mounted dual x‐ray systems by adopting patient specific methods.MethodsThe linac couch was used as a motion stage to simulate 40 highly dynamic real patient prostate trajectories. For each trajectory, 40 s pretreatment and 120 s treatment periods were extracted to represent a typical treatment fraction. Motion was monitored via continuous stereoscopic x‐ray imaging of a single gold fiducial and images were retrospectively divided into periods of stereoscopic and monoscopic imaging to simulate periodic blocking of the room‐mounted system by the gantry during arc‐based therapy. The accuracy of the combined motion monitoring was assessed by comparison with the linac couch log files. To estimate 3‐D marker position during monoscopic imaging, the use of population statistics was compared to both maximum likelihood estimation and stereoscopic localization based estimation of individualized prostate probability density functions (PDFs) from the pretreatment period. The inclusion of intrafraction updating was compared to pretreatment initialization alone.ResultsCombined mono/stereoscopic localization was successfully implemented. During the transitions from stereoscopic to monoscopic imaging, fiducial localization exhibits sharp discontinuities when population PDFs were employed. Patient specific PDFs successfully reduced the localization error when estimated from stereoscopic localizations, whereas maximum likelihood estimation (MLE) was too unstable in the room‐mounted geometry. Intrafraction stereoscopic updating provided further increases in accuracy. Residual error tended to decrease throughout the treatment fraction, as the patient‐specific PDFs became more refined.ConclusionsThis is the first demonstration of toggled monoscopic/stereoscopic localization using room‐mounted dual x‐ray imagers, enabling continuous intrafraction motion monitoring for these systems. We showed that both pretreatment individualization and intrafraction updating should be used to provide the most accurate motion monitoring.