Target Localization In Radiation Therapy Research Articles

Development of a Filtimator for Pediatric Image-Guided Radiation Therapy with Low Imaging Dose

We propose to use the filtimator (a filter and a collimator) for CBCT-based image-guided radiation therapy (IGRT) optimized for pediatric patients to minimize the imaging dose but not to sacrifice the imaging quality required for bony-based image fusion. The filtimator was made of Tin (0.6 - 1 mm) and Cu sheets (0.6 to 1.2mm) for filter and collimation with adjustable collimation with 4 to 6 cm fields at the isocenter. The thickness of the filter in the central and the peripheral regions were determined using vendor-provided image registration software and to ensure that the rigid image registration results from the CBCT were with and without the filtimator. The image quality of the filtered CBCT was compared with the regular CBCTs. Image registration accuracy was investigated by creating a < 2° shift in pitch, roll, and rotation and < 3 cm shifts in the lateral, vertical, and longitudinal directions, using commercial head and house-made phantoms. The imaging dose reduction factor of the filtimator was measured using a CT dose index phantom. The contrast-to-noise ratio substantially improved in the opening region of the filter, which provided better visualization of normal anatomy and target volumes. The slim filter reduced the imaging dose by > 98% in the filtered region, and the visualization of bony structures was well preserved, allowing for accurate rigid image registration with the filter. The imaging registration difference was < 0.2° shift in pitch, roll, and rotation and < 0.5 mm shift in the lateral, vertical, and longitudinal directions compared to the regular CBCT. The proposed dose reduction with the filtimator was demonstrated to be efficient and effective in considerably reducing the patient imaging dose while yielding accurate registration results. This novel technique can become a valuable tool for generating 3- and 4-dimensional images with a much-reduced dose to improve the precision of target localization in radiation therapy.

Low dose cone-beam computed tomography reconstruction via hybrid prior contour based total variation regularization (hybrid-PCTV).

Previously, we developed a prior contour based total variation (PCTV) method to use edge information derived from prior images for edge enhancement in low-dose cone-beam computed tomography (CBCT) reconstruction. However, the accuracy of edge enhancement in PCTV is affected by the deformable registration errors and anatomical changes from prior to on-board images. In this study, we develop a hybrid-PCTV method to address this limitation to enhance the robustness and accuracy of the PCTV method. Planning-CT is used as prior images and deformably registered with on-board CBCT reconstructed by the edge preserving TV (EPTV) method. Edges derived from planning CT are deformed based on the registered deformation vector fields to generate on-board edges for edge enhancement in PCTV reconstruction. Reference CBCT is reconstructed from the simulated projections of the deformed planning-CT. Image similarity map is then calculated between reference and on-board CBCT using structural similarity index (SSIM) method to estimate local registration accuracy. The hybrid-PCTV method enhances the edge information based on a weighted edge map that combines edges from both PCTV and EPTV methods. Higher weighting is given to PCTV edges at regions with high registration accuracy and to EPTV edges at regions with low registration accuracy. The hybrid-PCTV method was evaluated using both digital extended-cardiac-torso (XCAT) phantom and lung patient data. In XCAT study, breathing amplitude change, tumor shrinkage and new tumor were simulated from CT to CBCT. In the patient study, both simulated and real projections of lung patients were used for reconstruction. Results were compared with both EPTV and PCTV methods. EPTV led to blurring bony structures due to missing edge information, and PCTV led to blurring tumor edges due to inaccurate edge information caused by errors in the deformable registration. In contrast, hybrid-PCTV enhanced edges of both bone and tumor. In XCAT study using 30 half-fan CBCT projections, compared with ground truth, relative errors (REs) were 1.3%, 1.1% and 0.9% and edge cross-correlation were 0.66, 0.68 and 0.71 for EPTV, PCTV and hybrid-PCTV, respectively. Moreover, in the lung patient data, hybrid-PCTV avoided the wrong edge enhancement in the PCTV method while maintaining enhancements of the correct edges. Hybrid-PCTV further improved the robustness and accuracy of PCTV by accounting for uncertainties in deformable registration and anatomical changes between prior and onboard images. The accurate edge enhancement in hybrid-PCTV will be valuable for target localization in radiation therapy.

Assessing the feasibility of using deformable registration for onboard multimodality-based target localization in radiation therapy

Aim: This study aims to explore the feasibility of using prior images and deformable image registration to generate onboard multimodality images to improve the soft tissue contrast of cone beam computed tomography (CBCT), for target localization in radiation therapy. Methods: B-spline-based deformable registration is used to register magnetic resonance/computed tomography (MR/CT) images with CBCT images to generate synthetic onboard MR/CT images for onboard target localization. Liver, prostate, and breast patient data were used in the study to investigate the feasibility of the method. Results: Most of the tumor volume defined by the onboard synthetic images was covered by the planning target volume (PTV) based on the shifts applied in clinical practice. For 6 liver cases, 5 prostate cases, and all the breast cases, the synthetic images allowed the reduction of the PTV margin to 1.5–7 mm, 1–4 mm, and 1–1.5 mm, respectively. The dose to the normal tissue can be reduced based on the optimized margin. Conclusion: This study demonstrated the feasibility of using onboard synthetic multimodality imaging to improve the soft tissue contrast for target localization in low contrast regions. This new technique holds great promises to optimize the PTV margin and improve the treatment accuracy in radiation therapy.

A Feasibility Study of Tumor Motion Estimate With Regional Deformable Registration Method for 4-Dimensional Radiation Therapy of Lung Cancer.

This study aims to employ 4-dimensional computed tomography to quantify intrafractional tumor motion for patients with lung cancer to improve target localization in radiation therapy. A multistage regional deformable registration was implemented to calculate the excursion of gross tumor volume (GTV) during a breathing cycle. GTV was initially delineated on 0% phase of 4-dimensional computed tomography manually, and a subregion with 20 mm margin supplemented to GTV was generated with Eclipse treatment planning system (Varian Medical Systems, Palo Alto, California). The structures, together with the 4-dimensional computed tomography set, were exported into an in-house software, with which a 3-stage B-spline deformable registration was carried out to map the subregion and warp GTV contour to other breathing phases. The center of mass of the GTV was computed using the contours, and the tumor motion was appraised as the excursion of the center of mass between 0% phase and other phases. Application of the algorithm to the 10 patients showed that clinically satisfactory outcomes were achievable with a spatial accuracy around 2 mm for GTV contour propagation between adjacent phases and 3 mm between opposite phases. The tumor excursion was determined in the vast range of 1 mm through 1.6 cm, depending on the tumor location and tumor size. Compared to the traditional whole image-based registration, the regional method was found computationally a factor of 5 more efficient. The proposed technique has demonstrated its capability in extracting thoracic tumor motion and should find its application in 4-dimensional radiation therapy in the future to maximally utilize the available spatial-temporal information.

TU-A-201-00: Image Guidance Technologies and Management Strategies

Recent years have seen a widespread proliferation of available in-room image guidance systems for radiation therapy target localization with many centers having multiple in-room options. In this session, available imaging systems for in-room IGRT will be reviewed highlighting the main differences in workflow efficiency, targeting accuracy and image quality as it relates to target visualization. Decision-making strategies for integrating these tools into clinical image guidance protocols that are tailored to specific disease sites like H&N, lung, pelvis, and spine SBRT will be discussed. Learning Objectives: 1.  Major system characteristics of a wide range of available in-room imaging systems for IGRT. 2.  Advantages / disadvantages of different systems for site-specific IGRT considerations. 3.  Concepts of targeting accuracy and time efficiency in designing clinical imaging protocols.

TU-A-201-02: Treatment Site-Specific Considerations for Clinical IGRT

Recent years have seen a widespread proliferation of available in-room image guidance systems for radiation therapy target localization with many centers having multiple in-room options. In this session, available imaging systems for in-room IGRT will be reviewed highlighting the main differences in workflow efficiency, targeting accuracy and image quality as it relates to target visualization. Decision-making strategies for integrating these tools into clinical image guidance protocols that are tailored to specific disease sites like H&N, lung, pelvis, and spine SBRT will be discussed. Learning Objectives: 1.Major system characteristics of a wide range of available in-room imaging systems for IGRT. 2.Advantages / disadvantages of different systems for site-specific IGRT considerations. 3.Concepts of targeting accuracy and time efficiency in designing clinical imaging protocols.

TU-A-201-01: Introduction to In-Room Imaging System Characteristics

Recent years have seen a widespread proliferation of available in-room image guidance systems for radiation therapy target localization with many centers having multiple in-room options. In this session, available imaging systems for in-room IGRT will be reviewed highlighting the main differences in workflow efficiency, targeting accuracy and image quality as it relates to target visualization. Decision-making strategies for integrating these tools into clinical image guidance protocols that are tailored to specific disease sites like H&N, lung, pelvis, and spine SBRT will be discussed. Learning Objectives: 1.  Major system characteristics of a wide range of available in-room imaging systems for IGRT. 2.  Advantages / disadvantages of different systems for site-specific IGRT considerations. 3.  Concepts of targeting accuracy and time efficiency in designing clinical imaging protocols.

Target Positioning Accuracy of a Novel Technology for Target Localization in Radiation Therapy

Target Positioning Accuracy of a Novel Technology for Target Localization in Radiation Therapy

Online Digital Tomosynthesis (DTS): A Novel Technique for Improving Target Localization in Radiation Therapy

Online Digital Tomosynthesis (DTS): A Novel Technique for Improving Target Localization in Radiation Therapy

Principles of ac magnetic fields for objective and continuous target localization in radiation therapy

A new system capable of performing continuous, objective, real-time tracking of the treatment target during radiation has been developed. It is based on AC magnetic fields utilizing permanently implantable wireless transponders without the need of additional ionizing radiation.

Principles of ac magnetic fields for objective and continuous target localization in radiation therapy

A new system capable of performing continuous, objective, real-time tracking of the treatment target during radiation has been developed. It is based on AC magnetic fields utilizing permanently implantable wireless transponders without the need of additional ionizing radiation.