Brainlab ExacTrac Research Articles

PO-1836 Evaluation of the performance of Brainlab Exactrac Dynamic under different operation conditions

PO-1836 Evaluation of the performance of Brainlab Exactrac Dynamic under different operation conditions

A phantom-based study and clinical implementation of brainlab’s treatment planning system for radiosurgical treatments of arteriovenous malformations

Purpose. Development of a simple, phantom-based methodology allowing for pilot applications for the Elements TPS cranio-vascular module and clinical implementation prior to AVM treatments. Methods. A customized phantom was developed to be visible in MRI and CT images. High resolution digital subtraction angiograms (DSAs) and CT images of the phantom were acquired and imported into the Brainlab Elements treatment planning system. A clinical treatment plan with 5 arcs was generated in cranial vascular planning module and delivered to the phantom using a Varian TrueBeam STx Linac equipped with HD-MLCs and Brainlab ExacTrac imaging system for non-coplanar setup verification. The delivered dose was verified using a calibrated ionization chamber placed in the phantom. Upon verification of the TPS workflow, three patients with AVM who have been treated to date at our center using the Brainlab’s cranial vascular module for AVM are presented here for retrospective review. Results. The difference between the planed and measured dose by the ionization chamber was found to be less than 1%. Following a successful dose verification study, a clinical workflow was created. Currently, three AVM patients have been treated successfully. Clinical aspects of imaging and treatment planning consideration are presented in retrospective setting. Conclusions. Dose verification of the Brainlab Elements cranial vascular planning module for intracranial SRS treatments of AVM on Varian TrueBeam was successfully implemented using a custom-made phantom with <1% discrepancy. The Brainlab Elements’ cranial vascular module was successfully implemented in clinical workflow to treat patients with AVM. This manuscript provides a guideline for clinical implementation of frameless Linac-based AVM treatment using the Brainlab Elements TPS.

End to end comparison of surface-guided imaging versus stereoscopic X-rays for the SRS treatment of multiple metastases with a single isocenter using 3D anthropomorphic gel phantoms.

IntroductionTwo end‐to‐end tests evaluate the accuracy of a surface‐guided radiation therapy (SGRT) system (CRAD Catalyst HD) for position verification in comparison to a stereoscopic x‐ray imaging system (Brainlab Exactrac ) for single‐isocenter, multiple metastases stereotactic radiosurgery (SRS) using 3D polymer gel inserts.Materials and methodsA 3D‐printed phantom (Prime phantom, RTsafe PC, Athens, Greece) with two separate cylindrical polymer gel inserts were immobilized in open‐face masks and treated with a single isocentric, multitarget SRS plan. Planning was done in Brainlab (Elements) to treat five metastatic lesions in one fraction, and initial setup was done using cone beam computed tomography. Positional verification was done using orthogonal X‐ray imaging (Brainlab Exactrac) and/or a surface imaging system (CRAD Catalyst HD, Uppsala, Sweden), and shift discrepancies were recorded for each couch angle. Forty‐two hours after irradiation, the gel phantom was scanned in a 1.5 Tesla MRI, and images were fused with the patient computed tomography data/structure set for further analysis of spatial dose distribution.ResultsDiscrepancies between the CRAD Catalyst HD system and Brainlab Exactrac were <1 mm in the translational direction and <0.5° in the angular direction at noncoplanar couch angles. Dose parameters (D Mean% , D 95%) and 3D gamma index passing rates were evaluated for both setup modalities for each planned target volume (PTV) at a variety of thresholds: 3%/2 mm (Exactrac≥93.1% and CRAD ≥87.2%), 5%/2 mm (Exactrac≥95.6% and CRAD ≥94.6%), and 5%/1 mm (Exactrac≥81.8% and CRAD ≥83.7%).ConclusionDose metrics for a setup with surface imaging was found to be consistent with setup using x‐ray imaging, demonstrating high accuracy and reproducibility for treatment delivery. Results indicate the feasibility of using surface imaging for position verification at noncoplanar couch angles for single‐isocenter, multiple‐target SRS using end‐to‐end quality assurance (QA) testing with 3D polymer gel dosimetry.

Offline generator for digitally reconstructed radiographs of a commercial stereoscopic radiotherapy image-guidance system.

PurposeImage‐guided radiotherapy (IGRT) research sometimes involves simulated changes to patient positioning using retrospectively collected clinical data. For example, researchers may simulate patient misalignments to develop error detection algorithms or positioning optimization algorithms. The Brainlab ExacTrac system can be used to retrospectively “replay” simulated alignment scenarios but does not allow export of digitally reconstructed radiographs (DRRs) with simulated positioning variations for further analysis. Here we describe methods to overcome this limitation and replicate ExacTrac system DRRs by using projective geometry parameters contained in the ExacTrac configuration files saved for every imaged subject.MethodsTwo ExacTrac DRR generators were implemented, one with custom MATLAB software based on first principles, and the other using libraries from the Insight Segmentation and Registration Toolkit (ITK). A description of perspective projections for DRR rendering applications is included, with emphasis on linear operators in real projective space P3. We provide a general methodology for the extraction of relevant geometric values needed to replicate ExacTrac DRRs. Our generators were tested on phantom and patient images, both acquired in a known treatment position. We demonstrate the validity of our methods by comparing our generated DRRs to reference DRRs produced by the ExacTrac system during a treatment workflow using a manual landmark analysis as well as rigid registration with the elastix software package.ResultsManual landmarks selected between the corresponding DRR generators across patient and phantom images have an average displacement of 1.15 mm. For elastix image registrations, we found that absolute value vertical and horizontal translations were 0.18 and 0.35 mm on average, respectively. Rigid rotations were within 0.002 degrees.ConclusionCustom and ITK‐based algorithms successfully reproduce ExacTrac DRRs and have the distinctive advantage of incorporating any desired 6D couch position. An open‐source repository is provided separately for users to implement in IGRT patient positioning research.

Comparison of Setup Variations and Defining a CTV-PTV Margin in Fractionated Radiotherapy of Brain Tumor Using Novalis Tx Orthogonal OBI (kv) Versus Brain Lab ExacTrac (kv) Imaging Systems with Brain Lab Mask

The objective of this study is to evaluate the setup discrepancy between Brain Lab ExacTrac (kv) and Orthogonal Novalis Tx (kv) imaging systems and to obtain an optimal CTV-PTV margin. We recruited 35 consecutive brain tumor patients, immobilized with non-invasive thermoplastic BrainLab mask, between August 2016 and August 2017. The position verification done by ExacTrac, Infrared Positioning System was followed by a set of images by OBI at 0° and 90° position. The images were autofused and compared with DRR generated by TPS. The extent of translational and rotational shift was then applied and documented. The translational inter-fractional setup error (mean ± SD) in X-axis detected by OBI and ET was 0.002 ± 0.227 and −0.042 ± 0.084, respectively. In Y-axis, the error detected was −0.01 ± 0.176 and 0.075 ± 0.079, respectively, whereas in Z-axis the error with OBI and ET was 0.329 ± 0.521 and 0.051 ± 0.091, respectively. The P-value of inter-fractional errors in X, Y, and Z axes was 0.294, 0.013, and 0.004, which is statistically significant in Y- and Z-axes. Rotational inter-fractional setup errors (mean ± SD) for OBI and ET were −0.101 ± 0.257 and −0.076 ± 0.102, respectively. The rotational setup errors detected by ET in pitch and roll dimension are −0.003 ± 0.084 and −0.085 ± 0.073, respectively. The data obtained were put in Van Herk’s formula (PTV margin = 2.5 ∑ + 0.74 σ), and CTV-PTV margin was calculated. CTV-PTV margin for ET was 2.70, 2.72, and 2.94 mm and 3.38o, 2.84o, and 2.51o in lateral, longitudinal, vertical and pitch, roll, yaw dimension, respectively. The CTV-PTV margin for OBI was 7.40, 6.20, and 5.30 mm and 7.27o in lateral, longitudinal, vertical, and yaw dimension, respectively. Daily setup verifications that use the Brain LAB Exac Trac 6D image-guided system are very useful for brain tumor treatment; nevertheless, OBI kv imaging can be used for FRT of brain tumor with extended margin.

Positioning accuracy of a single-isocenter multiple targets SRS treatment: A comparison between Varian TrueBeam CBCT and Brainlab ExacTrac.

This study compared the positioning accuracy between cone-beam CT (CBCT) and ExacTrac (ETX) for a single-isocenter multiple target stereotactic radiosurgery (SRS) on two TrueBeam STx systems. A single-isocenter treatment plan was simulated on an anthropomorphic head phantom with six spherical steel ball bearings (BBs). One of the BBs was chosen to be the isocenter. The five off-isocenter targets were located at various distances from the isocenter. MV portal images were generated to evaluate the deviations between the expected and the real center of the targets after CBCT and ETX positioning, respectively. The evaluation of the positioning accuracy for the isocenter target showed that CBCT and ETX positioning provided comparable, sub-millimetric results. Deviations in positioning accuracy were also calculated for all other targets, also showing comparable results for CBCT and ETX. Moreover, our study showed that the deviation between CBCT and ETX positioning were in better agreement for TBSTx1 and deviated slightly higher on TBSTx2 (maximum: 1.23mm at S/I direction), due to a less perfect alignment between the CBCT coordinate system and the ETX coordinate system on TBSTx2 compared to TBSTx1. This study also showed a correlation between the target positioning accuracy and the distance to the isocenter. The positioning accuracy of ETX and CBCT for targets located at isocenter and off-isocenter locations was compared on two treatment machines and found comparable. Our study highlights the importance of a proper calibration procedure, to ensure correct alignment between the CBCT, ETX and machine coordinate systems.

A phantom study to evaluate three different registration platform of 3D/3D, 2D/3D, and 3D surface match with 6D alignment for precise image-guided radiotherapy.

PurposeTo evaluate two three‐dimensional (3D)/3D registration platforms, one two‐dimensional (2D)/3D registration method, and one 3D surface registration method (3DS). These three technologies are available to perform six‐dimensional (6D) registrations for image‐guided radiotherapy treatment.MethodsFiducial markers were asymmetrically placed on the surfaces of an anthropomorphic head phantom (n = 13) and a body phantom (n = 8), respectively. The point match (PM) solution to the six‐dimensional (6D) transformation between the two image sets [planning computed tomography (CT) and cone beam CT (CBCT)] was determined through least‐square fitting of the fiducial positions using singular value decomposition (SVD). The transformation result from SVD was verified and was used as the gold standard to evaluate the 6D accuracy of 3D/3D registration in Varian’s platform (3D3DV), 3D/3D and 2D/3D registration in the BrainLab ExacTrac system (3D3DE and 2D3D), as well as 3DS in the AlignRT system. Image registration accuracy from each method was quantitatively evaluated by root mean square of target registration error (rmsTRE) on fiducial markers and by isocenter registration error (IRE). The Wilcoxon signed‐rank test was utilized to compare the difference of each registration method with PM. A P < 0.05 was considered significant.Results rmsTRE was in the range of 0.4 mm/0.7 mm (cranial/body), 0.5 mm/1 mm, 1.0 mm/1.5 mm, and 1.0 mm/1.2 mm for PM, 3D3D, 2D3D, and 3DS, respectively. Comparing to PM, the mean errors of IRE were 0.3 mm/1 mm for 3D3D, 0.5 mm/1.4 mm for 2D3D, and 1.6 mm/1.35 mm for 3DS for the cranial and body phantoms respectively. Both of 3D3D and 2D3D methods differed significantly in the roll direction as compared to the PM method for the cranial phantom. The 3DS method was significantly different from the PM method in all three translation dimensions for both the cranial (P = 0.003–P = 0.03) and body (P < 0.001–P = 0.008) phantoms.Conclusion3D3D using CBCT had the best image registration accuracy among all the tested methods. 2D3D method was slightly inferior to the 3D3D method but was still acceptable as a treatment position verification device. 3DS is comparable to 2D3D technique and could be a substitute for X‐ray or CBCT for pretreatment verification for treatment of anatomical sites that are rigid.

A retrospective analysis of setup and intrafraction positional variation in stereotactic radiotherapy treatments.

PurposeThe aim of this study was to provide a comprehensive assessment of patient intrafraction motion in linac‐based frameless stereotactic radiosurgery (SRS) and radiotherapy (SRT).MethodsA retrospective review was performed on 101 intracranial SRS/SRT patients immobilized with the Klarity stereotactic thermoplastic mask (compatible with the Brainlab frameless stereotactic system) and aligned on a 6 Degree of Freedom (DoF) couch with the Brainlab ExacTrac image guidance system. Both pretreatment and intrafraction correction data are provided as observed by the ExacTrac system. The effects of couch angle and treatment duration on positioning outcomes are also explored.ResultsInitial setup data for patients is shown to vary by up to ±4.18 mm, ±2.97°, but when corrected with a single x‐ray image set with ExacTrac, patient positions are corrected to within ±2.11 mm, ±2.27°. Intrafraction patient motion is shown to be uniformly random and independent of both time and couch angle. Patient motion was also limited to within approximately 3 mm, 3° by the thermoplastic mask.ConclusionsOur results indicate that since patient intrafraction motion is unrelated to couch rotation and treatment duration, intrafraction patient monitoring in 6 DoF is required to minimize intracranial SRS/SRT margins.

PD-0435: Brainlab ExacTrac Dynamic – First pre-clinical validation of surface- and X-Ray positioning accuracy

PD-0435: Brainlab ExacTrac Dynamic – First pre-clinical validation of surface- and X-Ray positioning accuracy

Initial Experience With Single-Isocenter Radiosurgery to Target Multiple Brain Metastases Using an Automated Treatment Planning Software: Clinical Outcomes and Optimal Target Volume Margins Strategy

PurposeOur purpose was to assess the clinical outcomes and target positioning accuracy of frameless linear accelerator single-isocenter multiple-target (SIMT) dynamic conformal arc (DCA) stereotactic radiosurgery (SRS) for multiple brain metastases (BM). Methods and MaterialsBetween October 2016 and September 2018, 31 consecutive patients ≥18 years old with 204 BM <3 cm in maximum size receiving SIMT DCA SRS were retrospectively evaluated. All plans were created using a dedicated automated treatment planning software (Brainlab, Munich, Germany), and treatments were performed with a Truebeam STx or a Novalis Tx (Brainlab and Varian Medical Systems, CA). The accuracy of setup and interfraction patient repositioning was assessed by Brainlab ExacTrac radiograph 6-dimensional image system and the risk of compromised target dose coverage evaluated. Brain control and overall survival were estimated by Kaplan-Meier method calculated from the time of SRS. ResultsFourteen patients were treated for 4 to 6 and 17 patients for 7 to 10 BM. The mean gross tumor volume (GTV) was 0.65 cm3 and the mean planning target volume (PTV) was 0.89 cm3. Mean V95 (the volume of the PTV covered by 95% of the prescription dose) and D95 (the prescription dose covering 95% of the PTV) were 99.5% and 21.1 Gy, respectively. With a median clinical follow-up of 11 months (range, 4-26 months), the 1-year survival was 68% and local control was 89%. As a consequence of plan isocenter residual errors, a loss of target coverage, defined as V95 < 95%, occurred in 28 PTVs (10 patients); using a 1 mm GTV-to-PTV margin, adequate dose coverage was maintained for all lesions. ConclusionsSIMT DCA SRS represents a fast and effective approach for patients with up to 10 BM. The dosimetric effects of residual set-up and intrafraction positioning errors are modest, although a GTV-to-PTV margin of 1 mm is recommended.

Validation of histogram‐based virtual source models for different IGRT kV‐imaging systems

Image-guided radiotherapy (IGRT) improves tumor control but its intensive use may entrain late side effects caused by the additional imaging doses. There is a need to better quantify the additional imaging doses, so they can be integrated in the therapeutic workflow. Currently, no dedicated software enables to compute patient-specific imaging doses on a wide range of systems and protocols. As a first step toward this objective, we propose a common methodology to model four different kV-imaging systems used in radiotherapy (Varian's OBI, Elekta's XVI, Brainlab's ExacTrac, and Accuray's Cyberknife) using a new type of virtual source model based on Monte Carlo calculations. We first describe our method to build a simplified description of the photon output, or virtual source models (VSMs), of each imaging system. Instead of being constructed using measurement data, as it is most commonly the case, our VSM is used as the summary of the phase-space files (PSFs) resulting from a first Monte Carlo simulation of the considered x-ray tube. Second, the VSM is used as a photon generator for a second MC simulation in which we compute the dose. Then, the proposed VSM is thoroughly validated against standard MC simulation using PSFs on the XVI system. Last, each modeled system is compared to profiles and depth-dose-curve measurements performed in homogeneous phantom. Comparisons between PSF-based and VSM-based calculations highlight that VSMs could provide equivalent dose results (within 1% of difference) than PSFs inside the imaging field-of-view (FOV). In contrast, VSMs tend to underestimate (for up to 20%) calculated doses outside of the imaging FOV due to the assumptions underlying the VSM construction. In addition, we showed that the use of VSMs allows reducing calculation time by at least a factor of 2.8. Indeed, for identical simulation times, statistical uncertainties on dose distributions computed using VSMs were much lower than those obtained from PSF-based calculations. For each of the four imaging systems, VSMs were successfully validated against measurements in homogeneous phantoms, and are therefore ready to be used for future preclinical studies in heterogeneous or anthropomorphic phantoms. The cross system modeling methodology developed here should enable, later on, to estimate precisely and accurately patient-specific 3D dose maps delivered during a large range of kV-imaging procedures.

Evaluating the positional uncertainty of intrafraction, adjacent fields, and daily setup with the BrainLAB ExacTrac system in patients who are receiving craniospinal irradiation.

PurposeTo investigate the daily setup, interfraction motion, variability in the junction areas, and dosimetric effect in craniospinal irradiation (CSI) patients.MethodsFifteen CSI patients who had undergone split‐field IMRT were followed in the study. Previous, middle, and posttreatment, each target volume position was evaluated using the ExacTrac system. Interfraction and intrafraction motions, the margin of the junction in adjacent targets volumes, and the dosimetric effect of the longitudinal residual error were analyzed.ResultsThe lowest attainment rate within the tolerance of the initial setup error was 66.79% in six directions. The values of the initial error were within 15 mm (SD 4.5 mm) in the translation direction and 5° (SD 1.3°) in the rotation direction after the transposition of the treatment isocenter. With the guidance of the ExacTrac system, the interfraction and intrafraction residual errors were almost within the tolerance after correction, the margin of CTV‐to‐PCTV was in the range of target expansion criteria. The residual longitudinal errors resulted in only slight changes in the mean doses of PGTV and PCTV, while the maximum dose of the spinal cord increased by 16.1%. The patients did not exhibit any side‐effects by the overall treatment during the follow‐up period.ConclusionsPosition correction is necessary after setup and the transposition of the treatment isocenter. Intra‐fraction motion in the lateral direction should be monitored throughout treatment. The position errors in junction areas are almost within the tolerance after correction. The patients did not exhibit any side‐effects by the overall treatment.

IGRT stereotassica intracranica con Brainlab Exactrac e con sistema integrato OBI: feedback dell’equipe dell’U.O.C. Di Radioterapia del P.O. Perrino di Brindisi

The stereotactic intracranial Radiotherapy (SRS) Imaging-guided (IGRT) has increased its developments in few yearsbecause of the possibility to target lots of brain tumors also very small thanks to the new hardware tecnologies. SRSrepresents the main surgical alternative for patients with high risk complicances. This treatments requires a technology ensuring a great accuracy during X-ray exposure on the target as planned. In Perrino’s Radiotherapy there aretwo linacs with two different tecnologies ensuring the patient’s set-up accuracy (less than 1 mm). The first one is theOBI system mounted on Linac Trilogy, the second one Brainlab ExacTrac on Linac Unique. The aim of this comunication is to compare the two different system, to know which is the most appropriate ad finally to justify why a newtecnology such as Exactrac is installed on a less performing linac.

Analysis of the setup deviations generated in the 6D ExacTrac X-ray system for patients in hypofractionated intracranial radiosurgery treatments

The purpose of this study was to evaluate the use of the pre-treatment daily imaging system with the Brainlab ExacTrac X-Ray 6D for patients in hypofractionated intracranial treatments and radiosurgery procedures in order to quantify setups errors and review margins used by the institution in the current planning protocol. The deviations generated in the translational and rotational coordinates were given in terms of the mean values and their respective standard deviations. The random and systematic errors were determined through the Stroom and Wang relation and 36 patients treated with intracranial hypofractionated radiosurgery from August 2015 to October 2016 were evaluated. The prescribed dose was 25-30 Gy in 5 fractions for 30 patients and 12-18 Gy in a single fraction for 6 patients. The calculated margin for the planning target volume (PTV) from the deviations analyzed was 1.3mm, consistent with that adopted by the institution. When the correlation between the volume of the PTV, vector and its respective loss of coverage is evaluated and a tendency can be observed for smaller volumes to suffer greater losses in coverage when the isocenters were displaced with the resulting margins. We can suggest that for volumes smaller than 2.6 cm3, margins greater than 1 mm are required in order to guarantee the expected coverage of the PTV.

Performance evaluation of the X-sight spine tracking system for abdominal tumors distal to spine: A 2D dosimetric analysis

The X-sight spine tracking system was integrated with Cyberknife unit to deliver radiosurgery treatments for spinal tumors without fiducial placement. However the tracking system can also be used for the treatment of abdominal tumors located in a certain distance from the spine. The aim of our study is to evaluate the tracking performance of the X-sight spine system for abdominal tumors distal to spine based on the 3 factors: tumor distance from the reference vertebra, the angle of tumor with the vertebra, and the amplitude of tumor motion due to respiration. An experimental setup was designed mainly with ovine lumbar vertebrae and the BrainLab ExacTrac gating phantom. Planning Target Volume (PTV) structures were delineated at different vertical distances from the reference vertebra. The dosimetric measurements were taken with GafChromic EBT3 film placed between slab phantoms so that they corresponded to centers of the target volumes. Dosimetric comparisons were performed based on dose-volume parameters and the gamma analysis. The measurements were then repeated for the same experimental conditions by using the Synchrony system to compare tracking performances. Using the X-sight system, percentage differences between the dose-volume parameters of the Treatment Planning System (TPS) calculations and the EBT3 film readings went up to 12% for the motion amplitude of 8 mm. The differences decreased with small motions while angles and vertical distances of the lesion locations did not induce major changes in dose discrepancies. Percentages of pixels passing gamma analysis were found to be below the acceptance threshold of 95%. Using the Synchrony system, the measured dose distributions had more similar patterns with those of the TPS system such that the percentage differences in the dose parameters were less than 4% and the gamma passing rates were found to be higher than 95%. Our results showed that the X-sight spine system should not be chosen for tracking abdominal tumors distal to the spine or osseous structures because of the effect of diaphragmatic motion on entire abdominal region. The fiducial-based Synchrony tracking system can be preferred for these tumors.

170. Implementing single-isocenter volumetric modulated arc therapy radiosurgery treatment for multiple intracranial metastases

PurposeRecently an increase in radiosurgery treatments for multiple metastases has been observed. Traditionally these lesions were treated using one isocenter for each target and the patient had to be shifted during a single session for repositioning.The implementation of single-isocenter volumetric modulated arc therapy (VMAT) radiosurgery technique for multiple intracranial lesions allows a significant reduction of treatment times, as well as enhancing accuracy by reducing the potential intrafraction motion [1]. MethodsFor 20 patients treated with VMAT for multiple brain metastases we have analyzed the treatment process. Each case had different number and distribution of metastases. We performed a CT simulation scan with 1.25 mm thickness slice for all patients. The simulation images were registered with a MR in order to define the targets. For each case we compared the VMAT single-isocenter technique plan with the sums of the plans of every single lesion. Plans were evaluated using Dose Volume Histograms, Conformity and Uniformity Indexes. All the plans were optimized with 6 MV flattened filter free arcs. Set up checks were performed using both BrainLAB ExacTrac and Varian Cone Beam CT (CBCT). For 10 patients we also evaluated the intrafraction motion. ResultsNo significant difference was detected between the two techniques. The single-isocenter technique comes out better for the dose distributions especially for low doses. We discovered a good agreement between ExacTrac and CBCT and a minimum intrafraction movement (<1 mm) which was dosimetrically insignificant also for peripheral lesions. We underline a very significant reduction of treatment times. ConclusionsBoth methods achieve good dosimetric results. Single-isocenter VMAT radiosurgery treatment for multiple metastases is a faster technique and could be performed safely using image guided radiotherapy treatment thus relieving patient discomfort.

Fractionated stereotactic radiation therapy for adrenal metastases: contributing to local tumor control with low toxicity.

To report on the Erlangen (UK-Er) experience with linear accelerator stereotactic body radiation therapy (LINAC SBRT) for adrenal metastasis from various primary tumors. 33patients were treated. Primary sites included lung (n = 19), melanoma (n = 8), colorectal (n = 2), hepatocellular (n = 1), esophageal (n = 2), and breast cancer (n = 1). 14patients were treated palliatively, 19patients were treated with local curative intent. Treatment planning was done based on an exhale, mid-ventilation, and inspiration CT series. Further planning CTs were done to check for the correctness of the breathing pattern. Irradiation was performed using aNOVALIS (Varian, Palo Alto, CA, USA; Brainlab AG, München, Germany) linear accelerator. The isocenter was verified before each treatment session using the BrainLab ExacTrac® (BrainlabAG, München, Germany) system to minimize setup errors. Dose was prescribed to the planning target volume (PTV) surrounding 90% isodose. Depending on their overall performance status and prognosis, patients received clinical check-ups and radiological imaging. Median follow-up was 11months. IBM SPSS v.24 was used for univariate analysis using Kaplan-Meier curves, nonparametric Kruskal-Wallis test, and the chi-square test for frequency distributions. Toxicity was graded according to NCI CTCAE v4.0. Depending on radiologic imaging, patients were classified as stable, regression, and progression. Median survival was 11months, median PFS was 5months. Median local failure-free survival was 21months. Patients who were treated with curative intent showed abetter survival curve (p < 0.0001) and PFS (p = 0.004). BED ranged from 42 to 108.8 Gy, median BED was 67.2 Gy. Three BED groups were formed. Overall survival curves differed significantly (p = 0.046), favoring the high-dose group. 21patients were free from any adverse events or discomfort. In 7cases, agradeI toxicity was noted.

Intrafraction Verification Using ExacTrac 6D Imaging for Frameless Cranial Radiosurgery

Background: Radiosurgery has been an integral component in the management of intracranial tumors. It involves the administration of a high dose to the tumor. An essential aspect of this kind of treatment delivery is accurate localization of the tumor target that is precisely reproducible during treatment. To achieve this, the methods of positioning and immobilization of the patient play a critical role. Conventionally, the patient has been immobilized with invasive head frame and the location of internal anatomy deduced by external coordinates. This method has some drawbacks. - It works on the assumption that the external coordinates represent the isocentre location correctly. - It depends on the spatial relationships between the frame and the skull. Slippage and deformity of the frame, although rare, can cause an error in positioning. - From the patient's perspective, the placement of the frame is a source of discomfort. It also puts them at risk for bleeding and infection. Frameless SRS has come into use in recent times. This is a noninvasive method. However, giving up the use of an invasive head frame leads to increased intrafraction motion. To overcome this, we require constant verification of the patient's positioning at every step of the treatment. Aim: The objective of this study is to compare the precision and accuracy between Brainlab ExacTrac imaging and CBCT and evaluate the intrafraction motion of patient undergoing intracranial SRT. Methods: For this study we included 10 patients with intracranial tumors who are eligible to undergo SRS. A frameless stereotactic head frame mask was prepared to immobilize the head during SRS. During treatment the patients were immobilized with the same frame and the 6D positional accuracy was checked for every single field before the treatment execution by taking verification image using 6D ExacTrac and Onboard Imagers. The 6D ExacTrac tolerance were set to rotation &lt; 1.00 and translational shift &lt; 0.7 mm. We make sure of intrafarction movement by taking frequent ExacTrac images during the treatment of every 30 s. After the treatment the registration between the planning CT image and CBCT image taken before treatment were cross verified 6 dimensionally using offline review. The difference in shift between ExacTrac and CBCT are evaluated by means of RMS. Results: The RMS of the difference in the translational dimensions between the ExacTrac System and CBCT was &lt; 1.0 for online matching and &lt; 1.10 for offline matching. Furthermore, the RMS of the difference in the rotational dimensions between the ExacTrac System and CBCT were &lt; 0.81 for online matching and &lt; 0.96 for offline matching. Conclusion: It is concluded that the discrepancies in residual set-up error between the ExacTrac 6D x-ray and the CBCT were minor. ExacTrac 6D imaging provides additional advantage of patient intrafraction movement control by means of imaging during treatment.

IGRT stereotassica intracranica con Brainlab Exactrac e con sistema integrato OBI: feedback dell’equipe dell’U.O.C. Di Radioterapia del P.O. Perrino di Brindisi

The stereotactic intracranial Radiotherapy (SRS) Imaging-guided (IGRT) has increased its developments in few years because of the possibility to target lots of brain tumors also very small thanks to the new hardware tecnologies. SRS represents the main surgical alternative for patients with high risk complicances. This treatments requires a technology ensuring a great accuracy during X-ray exposure on the target as planned. In Perrino's Radiotherapy there are two linacs with two different tecnologies ensuring the patient's set-up accuracy (less than 1 mm). The first one is the OBI system mounted on Linac Trilogy, the second one Brainlab ExacTrac on Linac Unique. The aim of this comunication is to compare the two different system, to know which is the most appropriate ad finally to justify why a new tecnology such as Exactrac is installed on a less performing linac.

Monitoring frequency of intra-fraction patient motion using the ExacTrac system for LINAC-based SRS treatments.

PurposeThe aim of this study was to investigate the intra‐fractional patient motion using the ExacTrac system in LINAC‐based stereotactic radiosurgery (SRS).MethodA retrospective analysis of 104 SRS patients with kilovoltage image‐guided setup (Brainlab ExacTrac) data was performed. Each patient was imaged pre‐treatment, and at two time points during treatment (1st and 2nd mid‐treatment), and bony anatomy of the skull was used to establish setup error at each time point. The datasets included the translational and rotational setup error, as well as the time period between image acquisitions. After each image acquisition, the patient was repositioned using the calculated shift to correct the setup error. Only translational errors were corrected due to the absence of a 6D treatment table. Setup time and directional shift values were analyzed to determine correlation between shift magnitudes as well as time between acquisitions.ResultsThe average magnitude translation was 0.64 ± 0.59 mm, 0.79 ± 0.45 mm, and 0.65 ± 0.35 mm for the pre‐treatment, 1st mid‐treatment, and 2nd mid‐treatment imaging time points. The average time from pre‐treatment image acquisition to 1st mid‐treatment image acquisition was 7.98 ± 0.45 min, from 1st to 2nd mid‐treatment image was 4.87 ± 1.96 min. The greatest translation was 3.64 mm, occurring in the pre‐treatment image. No patient had a 1st or 2nd mid‐treatment image with greater than 2 mm magnitude shifts.ConclusionThere was no correlation between patient motion over time, in direction or magnitude, and duration of treatment. The imaging frequency could be reduced to decrease imaging dose and treatment time without significant changes in patient position.