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Schematic of patient/couch coordinates system (X, Y, Z) where the lateral shifts are along x-axis, superior-inferior shifts are along the y-axis, and anterior-posterior shifts are along the z-axis. The pitch rotation is around x-axis, roll is around y-axis, and yaw is around z-axis.
Source publication
The purpose of this study is to evaluate patient setup accuracy and quantify indi-vidual and cumulative positioning uncertainties associated with different hardware and software components of the stereotactic radiotherapy (SRS/SRT) with the frameless 6D ExacTrac system. A statistical model is used to evaluate positioning uncertainties of the differ...
Contexts in source publication
Context 1
... correction, XC) are acquired and matched with reference DRRs from the simulation CT images that are generated using ExacTrac software. Matching of DRR and radiographic image is performed with rigid image fusion using bone-anatomy matching. This fusion generates translational and rotational 6D couch shifts used for patient setup, as shown in Fig. 2. If the shifts are below our institutional criteria, within 0.7 mm and 1°, then the treatment is initiated. Otherwise shifts are applied by moving a robotic couch that is capable of 6D translational and rotational shift correction. After application of the couch shifts, a second set of radiographic images (X-ray verification: XV) are ...
Context 2
... (σ) of transla- tional and rotational shifts are calculated for XC and XV for all fractions. If a patient has only one fraction, then this single data point is used as the mean and zero mm standard deviation. Histograms of the mean and σ are generated for XC and XV 6D-shifts (x (Lat), y (Long), z (Vert), ρ (Pitch), θ (Roll), φ (Yaw)), as shown in Fig. 2 ) for each fraction. Statistical significance of the means of the shifts in each direction is determined using the Student's t-test with values ≥ 0.05, indicating statistically insignificant differences in the 95% confidence ...
Similar publications
The aim of this study was to evaluate the impact of actual rotational setup errors on dose distributions in intracranial stereotactic radiotherapy (SRT) with different alternatives for treatment position selection. A total of 38 SRT fractions from 18 patients were retrospectively evaluated with rotational setup errors obtained from actual treatment...
Citations
... Several image guidance systems have been utilized in SRT. Examples include (1) onboard imaging, which allows KV and MV planar imaging, as well as conebeam CT (CBCT) imaging, (2) Optical Surface Monitoring System (OSMS, Varian Oncology, Palo Alto, CA, USA), a surface imaging system, and (3) ExacTrac system (BrainLAB A.G., Heimstetten, Germany), which integrates an infrared (IR)-based optical positioning system and a stereoscopic x-ray imaging system [5][6][7]. Among these systems, CBCT images are the 'gold-standard' images used for image guidance in modern LINAC systems. ...
Purpose: To evaluate the performance of an automated 2D-3D bone registration algorithm incorporating a grayscale compression method for quantifying patient position errors in non-coplanar radiotherapy.
Methods: An automated 2D-3D registration incorporating a grayscale compression method was proposed. Portal images containing only bone structures (Portal_bone) and digitally reconstructed radiographs containing only bone structures (DRR_bone) were used for registration. First, the portal image was filtered by a high-pass finite impulse response (FIR) filter. Then the grayscale range of the filtered portal image was compressed. Thresholds were determined based on the difference in gray values of bone structures in the filtered and compressed portal image to obtain Portal_bone. Another threshold was applied to generate DRR_bone when the CT image uses the ray-casting algorithm to generate DRR images. The compression performance was assessed by compressing the Portal_bone into various grayscale ranges. The proposed registration method was quantitatively and visually validated using (1) a CT image of an anthropomorphic head phantom and its portal images obtained in different poses and (2) CT images and pre-treatment portal images of 20 patients treated with non-coplanar radiotherapy.
Results: Mean absolute registration errors for the best compression grayscale range test were 0.642 mm, 0.574 mm, and 0.643 mm, with calculation times of 50.6 min, 42.2 min, and 49.6 min for grayscale ranges of 0-127, 0-63 and 0-31, respectively. For the accuracy validation (1), the mean absolute registration errors for four couch angles were 0.694 mm, 0.839 mm, 0.726 mm, 0.833 mm, and 0.873 mm, respectively. The translation error in the vertical direction contributed the most to the registration errors. Visual inspection of the patient registration results revealed success in every instance.
Conclusions: The implemented grayscale compression method successfully enhances and segments bone structures in portal images, allowing for accurate determination of patient setup errors in non-coplanar radiotherapy.
... Other studies have reported that intrafractional tumor changes during beam delivery are influenced by head immobilization. [21][22][23] However, the potential for interfractional tumor changes during the treatment period, such as tumor size, shape, and geometry, must be considered to improve the accuracy of dose delivery. Edema, changes in tumor volume, shifting of fluids and muscle mass, and postoperative changes have been reported by several authors. ...
Purpose:
We evaluated the dosimetric effect of tumor changes in patients with fractionated brain stereotactic radiation therapy (SRT) on the tumor and normal brain using repeat verification magnetic resonance imaging (MRI) in the middle of the treatment period.
Methods and materials:
Fifteen large intracranial metastatic lesions with fractionated SRT were scanned employing standardized planning MRI (MRI-1). Repeat verification MRI (MRI-2) were performed during the middle of the irradiation period. Gross tumor volume (GTV) was defined as the volume of the contrast-enhancing lesion on T1-weighted MRI with gadolinium contrast agent. The doses to the tumor and normal brain were evaluated on the MRI-1 scan. Beam configuration and intensity on the initial volumetric modulated arc therapy plan were used to evaluate the dose to the tumor and the normal brain on MRI-2. We evaluated the effect of D98% (percent dose irradiating 98% of the volume) on the GTV using the plans on the MRI-1 and MRI-2 scans. For the normal brain, the V90%, V80%, and V50% (volume of the normal brain receiving >90%, 80%, and 50% of the prescribed dose, respectively) were investigated.
Results:
Three (20% of the total) and 4 (26% of the total) tumors exhibited volume shrinkage or enlargement changes of >10%. Five (33% of the total) tumors exhibited volume shrinkage and enlargement changes of <10%. Three tumors (20% of the total) showed no volume changes. D98% of the GTV increased in patients with tumor shrinkage because of dose inhomogeneity and decreased in patients with tumor enlargement, with a coefficient of determination of 0.28. The V90%, V80%, and V50% increase with decreasing tumor volumes and were linearly related to the tumor volume difference with a coefficient of determination values of 0.97, 0.98, and 0.97, respectively.
Conclusions:
Repeat verification MRI for brain fractionated SRT during the treatment period should be considered to reduce the magnitude of target underdosing or normal brain overdosing.
... Based on this model, we selected ten patients with multiple brain metastasis targets treated with the single isocenter for multiple targets (SIMT) technique to test the impact of the isocenter selection method in clinical setting.The translation margin was set to 2 mm and rotational uncertainties were set to 1.0 • . [18][19][20][21] The number of brain metastases in each plan ranges from two to six. The separation distance ranges from 28.5 to 135.5 mm. ...
... For a modern IGRT program equipped with kV onboard imaging device and 6 • couch, the residual rotational uncertainty is generally about 0.5 • -1.0 • . [19][20][21][22] In this paper, the results of the optimal margin volume with σ D = 0.5 • and 1.0 • were calculated. As shown in Table 1, the rotational uncertainty (σ D ) has an important influence on the margin volume of optimal isocenter. ...
Purpose:
The single isocenter for multiple-target (SIMT) technique has become a popular treatment technique for multiple brain metastases. We have implemented a method to obtain a nonuniform margin for SIMT technique. In this study, we further propose a method to determine the isocenter position so that the total expanded margin volume is minimal.
Materials and method:
Based on a statistical model, the relationship between nonuniform margin and the distance d (from isocenter to target point), setup uncertainties, and significance level was established. Due to the existence of rotational error, there is a nonlinear relationship between the margin volume and the isocenter position. Using numerical simulation, we study the relationship between optimal isocenter position and translational error, rotational error, and target size. In order to find the optimal isocenter position quickly, adaptive simulated annealing (ASA) algorithm was used. This method was implemented in the Pinnacle3 treatment planning system and compared with isocenter at center-of-geometric (COG), center-of-volume (COV), and center-of-surface (COS). Ten patients with multiple brain metastasis targets treated with the SIMT technique was selected for evaluation.
Results:
When the size of tumors is equal, the optimal isocenter obtained by ASA and numerical simulation coincides with COG, COV, and COS. When the size of tumors is different, the optimal isocenter is close to the large tumor. The position of COS point is closer to the optimal point than the COV point for nearly all cases. Moreover, in some cases the COS point can be approximately selected as the optimal point. The ASA algorithm can reduce the calculating time from several hours to tens of seconds for three or more tumors. Using multiple brain metastases targets, a series of volume difference and calculating time were obtained for various tumor number, tumor size, and separation distances. Compared with the margin volume with isocenter at COG, the margin volume for optimal point can be reduced by up to 27.7%.
Conclusion:
Optimal treatment isocenter selection of multiple targets with large differences could reduce the total margin volume. ASA algorithm can significantly improve the speed of finding the optimal isocenter. This method can be used for clinical isocenter selection and is useful for the protection of normal tissue nearby.
... Increasing the PTV margin may reduce the failure rate but also increase toxicity [182,183]. IGRT is an effective way to reduce the PTV margin for reducing treatment toxicity while protecting the OARs with further escalation of the effective treatment dose and improving the OS [46,184,185]. ...
Image-guided radiotherapy (IGRT) is an advanced auxiliary radiotherapy technique. During cancer treatment, patients with oral cavity cancer (OCC) experience not only disease but also adverse effects due to RT. IGRT provides the relevant advantages of RT by precisely delivering tumoricidal doses via real-time knowledge of the target volume location and achieves maximal tumor control with minimal complications as recommended for cancer treatment. Additionally, studies have shown that IGRT can improve clinical outcomes in terms of not only treatment side effects but also survival benefits for cancer patients. IGRT can be performed alongside various imaging methods, including computed tomography and magnetic resonance imaging, and at different times during the radiotherapy regimen. This article reviews the literature to discuss the effects and importance of IGRT for patients with OCC, examines the rationale underlying the advantages of IGRT, discusses the limitations of IGRT with respect to different techniques, and summarizes the strategies and future prospects of IGRT in the treatment of OCC.
... Some of these efforts have been commercially available, [7,8] and the most applicable methods are skin fiducials with optical tracking system, laser-based surface body depiction and in-room X-ray imaging techniques. [43,44] Among mentioned techniques, optical tracking system in combination with external markers is a reliable method for patient re-positioning and verification of irradiation setup to quantify the amplitude of operator dependence target displacement. Then, the detected misalignment is automatically corrected by means of servo-controlled patient couch. ...
At image-guided radiotherapy, technique, different imaging, and monitoring systems are utilized for (i) organs border detection and tumor delineation during the treatment planning process and (ii) patient setup and tumor localization at pretreatment step and (iii) real-time tumor motion tracking for dynamic thorax tumors during the treatment. In this study, the effect of fuzzy logic is quantitatively investigated at different steps of image-guided radiotherapy. Fuzzy logic-based models and algorithms have been implemented at three steps, and the obtained results are compared with commonly available strategies. Required data are (i) real patients treated with Synchrony Cyberknife system at Georgetown University Hospital for real-time tumor motion prediction, (ii) computed tomography images taken from real patients for geometrical setup, and also (iii) tomography images of an anthropomorphic phantom for tumor delineation process. In real-time tumor tracking, the targeting error averages of the fuzzy correlation model in comparison with the Cyberknife modeler are 4.57 mm and 8.97 mm, respectively, for a given patient that shows remarkable error reduction. In the case of patient geometrical setup, the fuzzy logic-based algorithm has better influence in comparing with the artificial neural network, while the setup error averages is reduced from 1.47 to 0.4432 mm using the fuzzy logic-based method, for a given patient.Finally, the obtained results show that the fuzzy logic based image processing algorithm exhibits much better performance for edge detection compared to four conventional operators. This study is an effort to show that fuzzy logic based algorithms are also highly applicable at image-guided radiotherapy as one of the important treatment modalities for tumor delineation, patient setup error reduction, and intrafractional motion error compensation due to their inherent properties.
... Because of a limited view of projections, the ExacTrac cannot provide as much information as CBCT [9,10] . Yet, the ExacTrac could provide other clinical bene ts involving quicker patient position using the 6D robic couch, quicker image acquisition time, the ability to monitor patient motion during treatment, and a relatively low radiation dose to the patient [11][12][13] . Our recently study demonstrated that no statistically signi cant difference was shown in patient alignment between weekly 3D CBCT and 2D kV imaging [14] . ...
This study aimed to compare the different volume of interest (VOI) selection among the VOI of Head & Neck (HN), VOI of Head only (H), and VOI of Neck (N) only when used for cranial phantom with the imaging guidance system ExacTrac. Exactrac cranial anthropomorphic phantoms was positioned with known set-up deviations from the reference position in the linear accelerator. Verification accuracy was evaluated based on the residual root-mean-square (RMS) positioning error after image registration based on different volume of interest (VOI) selection. The RMS in the translational dimensions was < 0.6 mm for online matching and < 1.1 mm for VOI of Head & Neck (HN) and VOI of Head only (H) offline matching. For VOI of Neck only(N), the RMS in the translational dimensions with was < 0.8 mm. Furthermore, the RMS in the rotational dimensions was < 0.2° for VOI of Head & Neck (HN) and < 0.3° for VOI of Head only (H) offline matching. For VOI of Neck only (N), the RMS in the rotational dimensions was < 0.4°. The minimum setup errors were observed when VOI Head & Neck (HN) was selected. For 75 neck patients, the RMS were statistical significant (p < 0.05) in the longitudinal and vertical translational directions. For 75 head&neck cancer patients, the RMS of differences in vertical translational direction and pitch and yaw rotational directions with different selection of VOIs (PTV only and H&N) were statistical significant (p < 0.05). It was concluded that image registration method using larger VOI is helpful to improve the registration accuracy.
... The studied misalignments in 6 DoF, reported by ET XV for 38 single-isocenter non-coplanar SRS patients with multiple brain metastases, revealed an accurate and precise ET-based setup in all DoF. The results from pre-positioning were compared to reported data from the literature and turned out to be similar [19,21,35,36]. The overall misalignment values after manual positioning were of relatively high magnitude. ...
Frameless single-isocenter non-coplanar stereotactic radiosurgery (SRS) for patients with multiple brain metastases is a treatment at high geometrical complexity. The goal of this study is to analyze the dosimetric impact of non-coplanar image guidance with stereoscopic X-ray imaging. Such an analysis is meant to provide insights on the adequacy of safety margins, and to evaluate the benefit of imaging at non-coplanar configurations.
The ExacTrac® (ET) system (Brainlab AG, Munich, Germany) was used for stereoscopic X-ray imaging in frameless single-isocenter non-coplanar SRS for multiple brain metastases. Sub-millimeter precision was found for the ET-based pre-treatment setup, whereas a degradation was noted for non-coplanar treatment angles. Misalignments without intra-fractional positioning corrections were reconstructed in 6 degrees of freedom (DoF) to resemble the situation without non-coplanar image guidance.
Dose recalculation in 20 SRS patients with applied positioning corrections did not reveal any significant differences in D98% for 75 planning target volumes (PTVs) and gross tumor volumes (GTVs). For recalculation without applied positioning corrections, significant differences (p < 0.05) were reported in D98% for both PTVs and GTVs, with stronger effects for small PTV volumes. A worst-case analysis at increasing translational and rotational misalignment revealed that dosimetric changes are a complex function of the combination thereof.
This study highlighted the important role of positioning correction with ET at non-coplanar configurations in frameless single-isocenter non-coplanar SRS for patients with multiple brain metastases. Uncorrected patient misalignments at non-coplanar couch angles were linked to a significant loss of PTV coverage, with effects varying according to the combination of single DoF and PTV geometrical properties.
... [13] There are several published quantitative analyses of patient setup uncertainty using the ExacTrac stereoscopic X-ray system. [14][15][16][17] The tests and tolerances in this report are intended to be a suggestion for departments commissioning ExacTrac ® Dynamic for clinical use. conclusIon This paper summarizes recommended testing for commissioning of the ExacTrac ® Dynamic system. ...
This paper aims to provide guidance and a framework for commissioning tests and tolerances for the ExacTrac Dynamic image-guided and surface-guided radiotherapy (SGRT) system. ExacTrac Dynamic includes a stereoscopic X-ray system, a structured light projector, stereoscopic cameras, thermal camera for SGRT, and has the capability to track breath holds and internal markers. The system provides fast and accurate image guidance and intrafraction guidance for stereotactic radiosurgery and stereotactic ablative radiotherapy. ExacTrac Dynamic was commissioned on a recently installed Elekta Versa HD. Commissioning tests are described including safety, isocenter calibration, dosimetry, image quality, data transfer, SGRT stability, SGRT localization, gating, fusion, implanted markers, breath hold, and end-to-end testing. Custom phantom designs have been implemented for assessment of the deep inspiration breath-hold workflow, the implanted markers workflow, and for gating tests where remote-controlled movement of a phantom is required. Commissioning tests were all found to be in tolerance, with maximum translational and rotational deviations in SGRT of 0.3 mm and 0.4°, respectively, and X-ray image fusion reproducibility standard deviation of 0.08 mm. Tolerances were based on published documents and upon the performance characteristics of the system as specified by the vendor. The unique configuration of ExacTrac Dynamic requires the end user to design commissioning tests that validate the system for use in the clinical implementation adopted in the department. As there are multiple customizable workflows available, tests should be designed around these workflows, and can be ongoing as workflows are progressively introduced into departmental procedures.
... For linac-based non-coplanar SRS treatment, a couch should be rotated by considering the clearance between the patient and the treatment machine. Keeling et al. [25] reported that patient setup errors occurred when a couch was rotated using non-coplanar beams due to couch sagging shifts for various couch angles and patient weights. Furthermore, several studies have conducted comprehensive evaluation of the patient positioning uncertainty with immobilization systems in the case of a rotating couch by considering the couch sagging shifts [25][26][27]. ...
... Keeling et al. [25] reported that patient setup errors occurred when a couch was rotated using non-coplanar beams due to couch sagging shifts for various couch angles and patient weights. Furthermore, several studies have conducted comprehensive evaluation of the patient positioning uncertainty with immobilization systems in the case of a rotating couch by considering the couch sagging shifts [25][26][27]. They revealed that patient positioning errors were detected after couch rotation, and the planning target volume (PTV) margin should be enlarged by 1.0-2.0 ...
The objectives of this study were to develop a frameless immobilization system that allows roll rotation corrections and to investigate the performance of this system for stereotactic radiosurgery (SRS) treatment. We designed the support frame of a frameless immobilization system based on the commercial Brainlab immobilization system. The support frame consisted of a fixed component and a rotating component. With rack and pinion gears and guide holes installed in the system, the rotating component was configured to be rotated along the longitudinal axis of the patient with respect to the fixed component. To evaluate the performance of the system, the six degree-of-freedom (6D) positioning corrections (translational and rotational corrections) were assessed by image verification between planning computed tomography (CT) and cone-beam computed tomography (CBCT) images. The commercial immobilization system was evaluated in the same manner for comparison. The mean translational shifts for the commercial system were 0.68 ± 0.19 mm, 0.73 ± 0.24 mm and 0.78 ± 0.19 mm, while those for the developed system were 0.44 ± 0.31 mm, 0.43 ± 0.25 mm and 0.60 ± 0.14 mm in the lateral, longitudinal and vertical directions, respectively. The mean rotational shifts for the commercial system were 0.37° ± 0.12°, 0.32° ± 0.16° and 0.38° ± 0.14°, while those for the developed system were 0.04° ± 0.04°, 0.11° ± 0.06° and 0.15° ± 0.12° along the lateral, vertical and longitudinal axes of the patient, respectively. For institutions that do not have 6D robotic couches installed, the use of the developed immobilization system can provide 6D corrections, resulting in shorter treatment times and higher patient positioning accuracy.
... These systems include corrections in 6 dimensions with translations in 3 dimensions (3D) and isocentric rotations in 3 dimensions (roll, pitch and yaw) by means of robotic table [20]. However, the dosimetric impact of setup errors due to 3D rotations has been analyzed in few studies [15][16][17][18][19][20][21][22][23][24][25][26][27]. ...
... These uncertainties depend on factors such as the volume, shape and relative position of the lesion with respect to the isocenter [16,17]. Defining sufficient margins to ensure coverage of the planning target volumes (PTV) is a solution, but it can entail an overdose impact in organs at risk (OAR) and healthy brain [18][19][20]. A 1 mm margin to the PTV has been proposed to ensure enough coverage for the distribution of setup errors and improve local recurrence for targets up to 8 cm from the isocenter [14,23,24]. ...
... Dosimetric variations have been related as a function of the effective target displacement [25][26][27][28][29]. For example, one method recalculates dose from the displaced anatomy and the plan with the original parameters [19]. Another approach is to shift the original plan dose distribution matrix relative to the fixed anatomy [9,30]. ...
Purpose
To optimize PTV margins for single isocenter multiple metastases stereotactic radiosurgery through a genetic algorithm (GA) that determines the maximum effective displacement of each target (GTV) due to rotations.
Method
10 plans were optimized. The plans were created with Elements Multiple Mets™ (Brainlab AG, Munchen, Germany) from a predefined template. The mean number of metastases per plan was 5 ± 2 [3,9] and the mean volume of GTV was 1.1 ± 1.3 cc [0.02, 5.1]. PTV margin criterion was based on GTV-isocenter distance and target dimensions. The effective displacement to perform specific rotational combination (roll, pitch, yaw) was optimized by GA. The original plans were re-calculated using the PTV optimized margin and new dosimetric variations were obtained. The Dmean, D99, Paddick conformity index (PCI), gradient index (GI) and dose variations in healthy brain were studied.
Results
Regarding targets located shorter than 50 mm from the isocenter, the maximum calculated displacement was 2.5 mm. The differences between both PTV margin criteria were statistically significant for Dmean (p = 0.0163), D99 (p = 0.0439), PCI (p = 0.0242), GI (p = 0.0160) and for healthy brain V12 (p = 0.0218) and V10 (p = 0.0264).
Conclusion
The GA allows to determine an optimized PTV margin based on the maximum displacement. Optimized PTV margins reduce the detriment of dosimetric parameters. Greater PTV margins are associated with an increase in healthy brain volume.
