BACKGROUND
Stereotactic body radiation therapy (SBRT) is a technique used to deliver high, ablative doses of radiation in a limited number of fractions to one or more extracranial target(s). The prevalence of SBRT use among radiation oncologists in the United States is unknown.

A survey of stereotactic body radiotherapy use in the United States.

Geometric accuracy of a novel gimbals based radiation therapy tumor tracking system.

Embodiments provide method and systems for determining alignment of a patient's body part, such as an eye, in an external coordinate system of a treatment or diagnostic device, such as a radiotherapy device, so as to define a reference axis for guiding device operation. Additional embodiments provide image-based methods and systems for aligning, tracking and monitoring motion of a body part and a treatment target in relation to a radiation beam axis. Particular ophthalmic embodiments provide method and systems including an eye-contact guide device and imaging system for aligning and tracking motion of an eye and ocular treatment target in relation to an orthovoltage X-ray beam axis, so as to monitor application of radiation to a lesion, such as a macular lesion of the retina. Particular methods for controlling radiation in response to motion of the target during treatment are described, such as algorithms for gating or interrupting radiation emission, both to ensure treatment goals and to avoid exposure to sensitive structures.

Methods and devices for detecting, controlling, and predicting radiation delivery

Purpose: We report on the clinical process, quality assurance, and geometric and dosimetric results of the first clinical implementation of electromagnetic transponder-guided MLC tracking which occurred on 28 November 2013 at the Northern Sydney Cancer Centre.

Methods: An electromagnetic transponder-based positioning system (Calypso) was modified to send the target position output to in-house-developed MLC tracking code, which adjusts the leaf positions to optimally align the treatment beam with the real-time target position. Clinical process and quality assurance procedures were developed and performed. The first clinical implementation of electromagnetic transponder-guided MLC tracking was for a prostate cancer patient being treated with dual-arc VMAT (RapidArc). For the first fraction of the first patient treatment of electromagnetic transponder-guided MLC tracking we recorded the in-room time and transponder positions, and performed dose reconstruction to estimate the delivered dose and also the dose received had MLC tracking not been used.

Results: The total in-room time was 21 min with 2 min of beam delivery. No additional time was needed for MLC tracking and there were no beam holds. The average prostate position from the initial setup was 1.2 mm, mostly an anterior shift. Dose reconstruction analysis of the delivered dose with MLC tracking showed similar isodose and target dose volume histograms to the planned treatment and a 4.6% increase in the fractional rectal V60. Dose reconstruction without motion compensation showed a 30% increase in the fractional rectal V60 from that planned, even for the small motion.

Conclusions: The real-time beam-target correction method, electromagnetic transponder-guided MLC tracking, has been translated to the clinic. This achievement represents a milestone in improving geometric and dosimetric accuracy, and by inference treatment outcomes, in cancer radiotherapy.

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The first clinical implementation of electromagnetic transponder-guided MLC tracking.

Development and optimization of methods for adequately accounting for respiratory motion in radiation therapy of thoracic tumors require detailed knowledge of respiratory dynamics and its impact on corresponding dose distributions. Thus, computer aided modeling and simulation of respiratory motion have become increasingly important. In this article a biophysical approach for modeling respiratory lung motion is described: Major aspects of the process of lung ventilation are formulated as a contact problem of elasticity theory which is solved by finite element methods; lung tissue is assumed to be isotropic, homogeneous, and linearly elastic. A main focus of the article is to assess the impact of biomechanical parameters (values of elastic constants) on the modeling process and to evaluate modeling accuracy. Patient-specific models are generated based on 4D CT data of 12 lung tumor patients. Simulated motion patterns of inner lung landmarks are compared with corresponding motion patterns observed in the 4D CT data. Mean absolute differences between model-based predicted landmark motion and corresponding breathing-induced landmark displacements as observed in the CT data sets are in the order of 3 mm (end expiration to end inspiration) and 2 mm (end expiration to midrespiration). Modeling accuracy decreases with increasing tumor size both locally (landmarks close to tumor) and globally (landmarks in other parts of the lung). The impact of the values of the elastic constants appears to be small. Outcomes show that the modeling approach is an adequate strategy in predicting lung dynamics due to lung ventilation. Nevertheless, the decreased prediction quality in cases of large tumors demands further study of the influence of lung tumors on global and local lung elasticity properties.

Patient-specific finite element modeling of respiratory lung motion using 4D CT image data.

Tumor tracking using a dynamic multileaf collimator (DMLC) represents a promising approach for intrafraction motion management in thoracic and abdominal cancer radiotherapy. In this work, we develop, empirically demonstrate, and characterize a novel 3D tracking algorithm for real-time, conformal, intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT)-based radiation delivery to targets moving in three dimensions. The algorithm obtains real-time information of target location from an independent position monitoring system and dynamically calculates MLC leaf positions to account for changes in target position. Initial studies were performed to evaluate the geometric accuracy of DMLC tracking of 3D target motion. In addition, dosimetric studies were performed on a clinical linac to evaluate the impact of real-time DMLC tracking for conformal, step-and-shoot (S-IMRT), dynamic (D-IMRT), and VMAT deliveries to a moving target. The efficiency of conformal and IMRT delivery in the presence of tracking was determined. Results show that submillimeter geometric accuracy in all three dimensions is achievable with DMLC tracking. Significant dosimetric improvements were observed in the presence of tracking for conformal and IMRT deliveries to moving targets. A gamma index evaluation with a 3%–3 mm criterion showed that deliveries without DMLC tracking exhibit between 1.7 (S-IMRT) and 4.8 (D-IMRT) times more dose points that fail the evaluation compared to corresponding deliveries with tracking. The efficiency of IMRT delivery, as measured in the lab, was observed to be significantly lower in case of tracking target motion perpendicular to MLC leaf travel compared to motion parallel to leaf travel. Nevertheless, these early results indicate that accurate, real-time DMLC tracking of 3D tumor motion is feasible and can potentially result in significant geometric and dosimetric advantages leading to more effective management of intrafraction motion. In order to visually illustrate the algorithm, a movie of MLC tracking for a conformal field has been added to the submission as EPAPS.

/pdf/management-of-three-dimensional-intrafraction-motion-through-4703tpdbh3.pdf

Management of three-dimensional intrafraction motion through real-time DMLC tracking

A method of continuous real-time monitoring and positioning of multi-leaf collimators during on and off radiation exposure conditions of radiation therapy to account for target motion relative to a radiation beam is provided. A prediction algorithm estimates future positions of a target relative to the radiation source. Target geometry and orientation are determined relative to the radiation source. Target, treatment plan, and leaf width data, and temporal interpolations of radiation doses are sent to the controller. Coordinates having an origin at an isocenter of the isocentric plane establish initial aperture end positions of the leaves that is provided to the controller, where motors to position the MLC midpoint aperture ends according to the position and target information. Each aperture end intersects a single point of a convolution of the target and the isocenter of the isocentric plane. Radiation source hold-conditions are provided according to predetermined undesirable operational and/or treatment states.

Method to track three-dimensional target motion with a dynamical multi-leaf collimator

http://lup.lub.lu.se/luur/download?func=downloadFile&recordOId=2157091&fileOId=2157748

Real-time dynamic MLC tracking for inversely optimized arc radiotherapy.

A method of determining a similarity with a portion of a physiological motion, includes obtaining a first image of an object, obtaining a second image of the object, determining a level of similarity between the first and second images, and correlating the determined level of similarity between the first and second images with a portion of the physiological motion. A computer product having a set of instructions, an execution of which causes a method of determining a similarity with a portion of a physiological motion to be performed, the method includes obtaining a first image of an object, obtaining a second image of the object, determining a level of similarity between the first and second images, and correlating the determined level of similarity between the first and second images with a portion of the physiological motion.

Video-Based Breathing Monitoring Without Fiducial Tracking

A marker system includes a marker, and a positioner coupled to the marker, the positioner configured to position the marker from a first predetermined position to a second predetermined position. A method of providing a marker system includes obtaining a first data representative of a first predetermined position, obtaining a second data representative of a second predetermined position, and moving a set of one or more markers from the first predetermined position to the second predetermined position, wherein the set of one or more markers is moved using a positioner. A method of using a marker system includes detecting a marker when the marker is located at a first position, moving the marker from the first position to a second position using a positioner, and detecting the marker when the marker is located at the second position.

Sergey Povzner

Papers

Management of three-dimensional intrafraction motion through real-time DMLC tracking

Method to track three-dimensional target motion with a dynamical multi-leaf collimator

Real-time dynamic MLC tracking for inversely optimized arc radiotherapy.

Video-Based Breathing Monitoring Without Fiducial Tracking

Marker system and method of using the same