Cone Beam Computed Tomography Localization Research Articles

Frameless Stereotactic Radiosurgery on the Gamma Knife Icon: Early Experience From 100 Patients.

The Gamma Knife (GK) Icon (Elekta AB) uses a cone-beam computed tomography (CBCT) scanner and an infrared camera system to support the delivery of frameless stereotactic radiosurgery (SRS). There are limited data on patients treated with frameless GK radiosurgery (GKRS). To describe the early experience, process, technical details, and short-term outcomes with frameless GKRS at our institution. We reviewed our patient selection and described the workflow in detail, including image acquisition, treatment planning, mask-based immobilization, stereotactic CBCT localization, registration, treatment, and intrafraction monitoring. Because of the short interval of follow-up, we provide crude rates of local control. Data from 100 patients are reported. Median age is 67 yr old. 56 patients were treated definitively, 21 postoperatively, and 23 had salvage GKRS for recurrence after surgery. Forty-two patients had brain metastases, 26 meningiomas, 16 vestibular schwannomas, 9 high-grade gliomas, and 7 other histologies. Median doses to metastases were 20 Gy in 1 fraction (range: 14-21), 24 Gy in 3 fractions (range: 19.5-27), and 25 Gy in 5 fractions (range: 25-30 Gy). Thirteen patients underwent repeat SRS to the same area. Median treatment time was 17.7 min (range: 5.8-61.7). We found an improvement in our workflow and a greater number of patients eligible for GKRS because of the ability to fractionate treatments. We report a large cohort of consecutive patients treated with frameless GKRS. We look forward to studies with longer follow-up to provide valuable data on clinical outcomes and to further our understanding of the radiobiology of hypofractionation in the brain.

Gamma Knife® icon CBCT offers improved localization workflow for frame-based treatment.

ObjectThe purpose of this study was to compare two methods of stereotactic localization in Gamma Knife treatment planning: cone beam computed tomography (CBCT) or fiducial. While the fiducial method is the traditional method of localization, CBCT is now available for use with the Gamma Knife Icon. This study seeks to determine whether a difference exists between the two methods and then whether one is better than the other regarding accuracy and workflow optimization.MethodsCone beam computed tomography was used to define stereotactic space around the Elekta Film Pinprick phantom and then treated with film in place. The same phantom was offset known amounts from center and then imaged with CBCT and registered with the reference CBCT image to determine if measured offsets matched those known. Ten frameless and 10 frame‐based magnetic resonance imaging (MRI) to CBCT patient fusions were retrospectively evaluated using the TG‐132 TRE method. The stereotactic coordinates defined by CBCT and traditional fiducials were compared on the Elekta 8 cm Ball phantom, an anthropomorphic phantom, and actual patient data. Offsets were introduced to the anthropomorphic phantom in the stereotactic frame and CBCT's ability to detect those offsets was determined.ResultsCone beam computed tomography defines stereotactic space well within the established limits of the mechanical alignment system. The CBCT to CBCT registration can detect offsets accurately to within 0.1 mm and 0.5°. In all cases, some disagreement existed between fiducial localization and that of CBCT which in some cases was small, but also was as high as 0.43 mm in the phantom domain and as much as 1.54 mm in actual patients.ConclusionCone beam computed tomography demonstrates consistent accuracy in defining stereotactic space. Since both localization methods do not agree with each other consistently, the more reliable method must be identified. Cone beam computed tomography can accurately determine offsets occurring within stereotactic space that would be nondiscernible utilizing the fiducial method and seems to be more reliable. Using CBCT localization offers the opportunity to streamline workflow both from a patient and clinic perspective and also shows patient position immediately prior to treatment.

High-resolution Cone-beam Computed Tomography Localization of an Iatrogenic Vertebral Arteriovenous Fistula for Trans-arterial Target Embolization

High-resolution Cone-beam Computed Tomography Localization of an Iatrogenic Vertebral Arteriovenous Fistula for Trans-arterial Target Embolization

Phase 1 Trial of Everolimus and Radiation Therapy for Salvage Treatment of Biochemical Recurrence in Prostate Cancer Patients Following Prostatectomy

In up to half of patients treated with salvage radiation therapy (SRT) for rising prostate-specific antigen levels, a second biochemical recurrence ultimately develops.Phosphatase and tensin homolog inactivation is implicated in prostate cancer progression, and upregulation of the mammalian target of rapamycin pathway can lead to tumor hypoxia and radioresistance. Everolimus is a mammalian target of rapamycin inhibitor with both antitumor and radiosensitizing effects. We performed a phase 1 study using a modified 3+3 dose-escalation design to evaluate the safety and tolerability of everolimus in combination with standard SRT for the treatment of biochemical recurrence following prostatectomy.After a 2-week run-in period of everolimus daily therapy, patients received prostate bed irradiation with daily cone beam computed tomography localization in 37 fractions of 1.8Gy each (total dose, 66.6Gy). Patients were monitored for both acute (≤90days) and chronic (>90days) treatment-related toxicities. Eighteen patients received everolimus at dose levels of 5mg (n=6), 7.5mg (n=6), or 10mg (n=6) daily in conjunction with SRT. No dose-limiting toxicities were observed. Common acute treatment-related toxicities included grade 1 or 2 mucositis (55.6%), grade 1 or 2 fatigue (38.9%), grade 1 or 2 rash (61.1%), and grade 1 urinary symptoms (61.1%). A grade 3 acute toxicity occurred in 4 patients (22.2%) (n=1 for rash, anemia, lymphopenia, and neutropenia), and no patients had a chronic toxicity of grade 3 or greater. After a median follow-up time of 17.8months (range, 1.2-46.0months), an undetectable prostate-specific antigen nadir was achieved in 9 patients (56.3%) and a second biochemical recurrence developed in 5 patients (31.3%). Everolimus at a dose of ≤10mg daily appears to be safe and tolerable in combination with fractionated post-prostatectomy radiation therapy.

SU‐G‐JeP1‐01: A Combination of Real Time Electromagnetic Localization and Tracking with Cone Beam Computed Tomography in Stereotactic Radiosurgery for Brain Tumors

Purpose:1. online verification of patient position during treatment using calypso electromagnetic localization and tracking system. 2. Verification and comparison of positional accuracy between cone beam computed tomography and calypso system. 3. Presenting the advantage of continuation localization in Stereotactic radiosurgery treatments.Methods:Ten brain tumor cases were taken for this study. Patients with head mask were under gone Computed Tomography (CT). Before scanning, mask was cut on the fore head area to keep surface beacons on the skin. Slice thickness of 0.65 mm were taken for this study. x, y, z coordinates of these beacons in TPS were entered into tracking station. Varian True Beam accelerator, equipped with On Board Imager was used to take Cone beam Computed Tomography (CBCT) to localize the patient. Simultaneously Surface beacons were used to localize and track the patient throughout the treatment. The localization values were compared in both systems. For localization CBCT considered as reference. Tracking was done throughout the treatment using Calypso tracking system using electromagnetic array. This array was in tracking position during imaging and treatment. Flattening Filter free beams of 6MV photons along with Volumetric Modulated Arc Therapy was used for the treatment. The patient movement was observed throughout the treatment ranging from 2 min to 4 min.Results:The average variation observed between calypso system and CBCT localization was less than 0.5 mm. These variations were due to manual errors while keeping beacon on the patient. Less than 0.05 cm intra‐fraction motion was observed throughout the treatment with the help of continuous tracking.Conclusion:Calypso target localization system is one of the finest tools to perform radiosurgery in combination with CBCT. This non radiographic method of tracking is a real beneficial method to treat patients confidently while observing real‐time motion information of the patient.

Bioluminescence Tomography–Guided Radiation Therapy for Preclinical Research

In preclinical radiation research, it is challenging to localize soft tissue targets based on cone beam computed tomography (CBCT) guidance. As a more effective method to localize soft tissue targets, we developed an online bioluminescence tomography (BLT) system for small-animal radiation research platform (SARRP). We demonstrated BLT-guided radiation therapy and validated targeting accuracy based on a newly developed reconstruction algorithm. The BLT system was designed to dock with the SARRP for image acquisition and to be detached before radiation delivery. A 3-mirror system was devised to reflect the bioluminescence emitted from the subject to a stationary charge-coupled device (CCD) camera. Multispectral BLT and the incomplete variables truncated conjugate gradient method with a permissible region shrinking strategy were used as the optimization scheme to reconstruct bioluminescent source distributions. To validate BLT targeting accuracy, a small cylindrical light source with high CBCT contrast was placed in a phantom and also in the abdomen of a mouse carcass. The center of mass (CoM) of the source was recovered from BLT and used to guide radiation delivery. The accuracy of the BLT-guided targeting was validated with films and compared with the CBCT-guided delivery. In vivo experiments were conducted to demonstrate BLT localization capability for various source geometries. Online BLT was able to recover the CoM of the embedded light source with an average accuracy of 1 mm compared to that with CBCT localization. Differences between BLT- and CBCT-guided irradiation shown on the films were consistent with the source localization revealed in the BLT and CBCT images. In vivo results demonstrated that our BLT system could potentially be applied for multiple targets and tumors. The online BLT/CBCT/SARRP system provides an effective solution for soft tissue targeting, particularly for small, nonpalpable, or orthotopic tumor models.

Digital tomosynthesis (DTS) for verification of target position in early stage lung cancer patients

The ability to verify intrafraction tumor position is clinically useful for hypofractionated treatments. Short arc kV digital tomosynthesis (DTS) could facilitate more frequent target verification. The authors used DTS combined with triangulation to determine the mean temporal position of small-volume lung tumor targets treated with stereotactic radiotherapy. DTS registration results were benchmarked against online clinical localization using registration between free-breathing cone-beam computed tomography (CBCT) and the average intensity projection (AvIP) of the planning 4DCT. In this retrospective study, 76 sets of kV-projection images from online CBCT scans of 13 patients were used to generate DTS image slices (CB-DTS) with nonclinical research software (DTS Toolkit, Varian Medical Systems). Three-dimensional tumor motion was 1.3-4 mm in six patients and 6.1-25.4 mm in seven patients on 4DCT (significant difference in the mean of the groups, P < 0.01). The 4DCT AvIP was used to digitally reconstruct the Reference-DTS. DTS registration and DTS registration combined with triangulation were investigated. Progressive shortening of total DTS arc lengths from 95° to 35° around 0° gantry position was evaluated for different scenarios: DTS registration using the entire arc; DTS registration plus triangulation using two nonoverlapping arcs; and for 55° and 45° total gantry rotation, DTS registration plus triangulation using two overlapping arcs. Finally, DTS registration plus triangulation performed at eight gantry angles, each separated by 45° was evaluated using full fan kV projection data for one patient with an immobile tumor and five patients with mobile tumors. For DTS registration alone, shortening arc length did not influence accuracy in X- and Y-directions, but in Z-direction, mean deviations from online CBCT localization systematically increased for shorter arc length (P < 0.05). For example, using a 95° arc mean DTS-CBCT difference was 0.8 mm (1 SD = 0.6 mm) and for a 35° arc the mean was 2.4 mm (1 SD = 1.7 mm). DTS plus triangulation using nonoverlapping-arcs increased accuracy in Z-direction for tested arc lengths ≤55° (P < 0.01). Overlapping arcs increased accuracy in Y-direction for tumors with motion >4 mm (P < 0.02) but increased Z-direction accuracy was only observed with 55° total gantry rotation. The 95th percentile deviations with this overlapping technique in X-, Y-, and Z-directions were 1.3, 2.0, and 2.5 mm, respectively. For the five patients with mobile tumors where DTS + triangulation was performed with 45° intervals, the pooled deviation from online CBCT correction showed, for X-, Y-, and Z-directions, mean of 1.1 mm, standard deviations (SD) of 0.9, 1.0, and 0.9 mm, respectively. The mean + 2 SD was <3 mm for each direction. Short-arc DTS verification of time averaged lung tumor position is feasible using free-breathing kV projection data and the AvIP of the 4DCT as a reference. Observed differences between DTS and online CBCT registration with AvIP were ≤3 mm (mean + 2 SD), however, the increased temporal resolution of DTS + triangulation also identified short period deviations from the average target position on the CBCT. Short-arc DTS appears promising for intrafraction tumor position monitoring during stereotactic lung radiotherapy delivered with a rotational technique.

Analysis of automatic match results for cone-beam computed tomography localization of conventionally fractionated lung tumors

To evaluate the dependence of an automatic match process on the size of the user-defined region of interest (ROI), the structure volume of interest (VOI), and changes in tumor volume when using cone-beam computed tomography (CBCT) for tumor localization and to compare these results with a gold standard defined by a physician's manual match. Daily CBCT images for 11 patients with lung cancer treated with conventionally fractionated radiation therapy were retrospectively matched to a reference CT image using the Varian On Board Imager software (Varian, Palo Alto, CA) and a 3-step automatic matching protocol. Matches were performed with 3 ROI sizes (small, medium, large), with and without a structure VOI (internal target volume [ITV] or planning target volume [PTV]) used in the last step. Additionally, matches were performed using an intensity range that isolated the bony anatomy of the spinal column. All automatic matches were compared with a manual match made by a physician. The CBCT images from 109 fractions were analyzed. Automatic match results depend on ROI size and the structure VOI. Compared with the physician's manual match, automatic matches using the PTV as the structure VOI and a small ROI resulted in differences ≥ 5 mm in 1.8% of comparisons. Automatic matches using no VOI and a large ROI differed by ≥ 5 mm in 30.3% of comparisons. Differences between manual and automatic matches using the ITV as the structure VOI increased as tumor size decreased during the treatment course. Users of automatic matching techniques should carefully consider how user-defined parameters affect tumor localization. Automatic matches using the PTV as the structure VOI and a small ROI were most consistent with a physician's manual match, and were independent of volumetric tumor changes.

Assessment of Using Endorectal Balloon in Prostate Radiation Therapy on Daily Kilovoltage Cone Beam Computed Tomography Localization

To assess the effect of using endorectal balloon (ERB) in prostate radiation therapy on daily kilovoltage (kV) cone beam computed tomography (CBCT) shifts. Thirty consecutive patients treated for prostate cancer with VMAT or IMRT techniques were localized using daily kV CBCT. Half of the patients were simulated and treated using ERB with air volume of 80 to 90 cc. Selection of patients receiving ERB was at the discretion of the physician. With the exception of the ERB, all patients were simulated using the same conditions: supine, with full bladder and empty rectum, and immobilized from the knees down using a Vac-Lok cushion. All patients had three to four fiducials implanted for image guidance and localization using CBCT. Treatment isocenter was marked on the skin during simulation and the marks were used for initial setup at treatment. Daily CBCT shift records of the superior-inferior (SI), left-right (LR), anterior-posterior (AP), and overall 3-dimensional (3D) displacements were collected and analyzed for a total of 1251 treatment sessions. The statistical significance in the absolute value of the shift data of the two groups was investigated using two-tailed unequal-variance t-test. Random (σ) errors, defined as the standard deviation (SD) of the distribution of shifts of all patients within a group, and systematic errors (∑), defined as the SD of the distribution of the means of patients' shifts in a group, and PTV margins, defined as 2.5∑+0.7σ, were derived for both patient groups. The statistical results of the daily CBCT shifts are tabulated below. The mean of the 3D shifts for the patient group treated with ERB was 1.4 mm lower than that for the group treated without ERB. The t-test analysis of the data yielded statistically significant difference in shift data between the two groups in the SI (p<0.0001), AP (p = 0.02), and 3D displacement (p<0.0001). No significant difference was observed in the LR direction. Random and systematic errors and derived margins were consistently lower for patients treated with ERB than for those treated without ERB.Poster Viewing Abstract 3327; TableParameter/DirectionCBCT absolute shift (mm) with ERBCBCT absolute shift (mm) without ERBSILRAP3DSILRAP3DMinimum00000000Maximum1013121412112020Mean3.12.43.55.94.52.43.97.3Random error (σ)2.22.02.62.82.92.13.33.4Systematic error (∑)1.40.81.11.41.90.92.32.2Derived PTV margins (2.5∑+0.7σ)53557488 Open table in a new tab Using ERB in prostate radiation therapy yields a statistically significant reduction in the 3D displacement of the CBCT setup shift. The demonstrated reduction in the systematic and random errors in the patient group treated with ERB can potentially translate in a reduction of PTV margins for this group using published formulation.

SU-E-J-59: Dual Imaging Guided Localization System for Spine Radiosurgery.

To compare localization accuracies between an ExacTrac and cone beam computed tomography (CBCT) systems for single fraction spine adiosurgery. The work also aimed to evaluate the inherent systematic deviation of both ExacTrac and CBCT systems to achieve highly accurate localization in the spine radiosurgery. ExacTrac and CBCT imaging systems were evaluated using the linac isocenter as the mutual reference point. First, a BB was placed in an anthropomorphic pelvic phantom. The phantom was localized with both imaging systems and the procedure was repeated 12 times. These results were used to devise a localization protocol using both imaging systems in spine radiosurgery, and employed for 51 patients (81 isocenters) prescribed for single fraction treatment. The displacement discrepancy between the isocenter and two systems were quantified in four dimensions (three translations, one rotation). A Student's two-tailed t-test was used to test for significant differences between the two imaging systems. The phantom study showed 1.4±0.5, 0.6±0.5, and 0.1±0.5 mm differences between the two imaging systems in the anterior/posterior (A/P), superior/inferior (S/I) and left/right (L/R) directions, respectively. The angular difference was minimal along all three axes. The patient study revealed similar isocenter discrepancies between ExacTrac and CBCT of 1.1 ± 0.7 mm, 1.0±0.9 mm, and 0.2±0.9 mm in the A/P, S/I, and L/R directions, respectively, with the A/P and S/I directions showing statistical significance ((t(80) = 13.5 and 7.6 respectively, p = 0.000). The couch yaw discrepancy was 0 ± 0.3°. Overall, 1 mm systematic differences were observed in the A/P and S/I directions between ExacTrac and CBCT localization systems, both in phantom and patient. A procedure was developed to mitigate this systematic discrepancy. These findings have justified our patient localization tolerance levels of 2 mm translation and 1 degree rotation for spine SRS treatment.

Comparing Digital Tomosynthesis to Cone-Beam CT for Position Verification in Patients Undergoing Partial Breast Irradiation

To evaluate digital tomosynthesis (DTS) technology for daily positioning of patients receiving accelerated partial breast irradiation (APBI) and to compare the positioning accuracy of DTS to three-dimensional cone-beam computed tomography (CBCT). Ten patients who underwent APBI were scanned daily with on-board CBCT. A subset of the CBCT projections was used to reconstruct a stack of DTS image slices. To optimize soft-tissue visibility, the DTS images were reconstructed in oblique directions so that the tumor bed, breast tissue, ribs, and lungs were well separated. Coronal and sagittal DTS images were also reconstructed. Translational shifts of DTS images were obtained on different days from the same patients and were compared with the translational shifts of corresponding CBCT images. Seventy-seven CBCT scans and 291 DTS scans were obtained from nine evaluable patients. Tumor beds were best visible in the oblique DTS scans. One-dimensional positioning differences between DTS and CBCT images were 0.8-1.7 mm for the six patients with clips present and 1.2-2.0 mm for the three patients without clips. Because of the limited DTS scan angle, the DTS registration accuracy along the off-plane direction is lower than the accuracy along the in-plane directions. For patients receiving APBI, DTS localization offers comparable accuracy to CBCT localization for daily patient positioning while reducing mechanical constraints and imaging dose.

SU-FF-J-49: Reducting of Motion Artifacts in Cone Beam CT Using a Patient Specific Respiratory Motion Model

Purpose: Respiratory motion degrades the quality of cone beam computed tomography (CBCT) images in the thorax and abdomen and limits its localization accuracy. We describe a method of reducing motion-induced artifacts in CBCT images in the thorax using a patient-specific model to estimate 3-dimensional respiration-induced motion. Method and Materials: The patient-specific model is derived from, and applied to, the same CBCT data, thus avoiding inconsistencies caused by changes in patient's breathing pattern when using different image sets. The CBCT scan uses a 1-minute gantry rotation while recording patient respiration with an external monitor. The projection images are sorted into 4 to 6 phase bins according to the respiratory signal. Each phase bin is reconstructed to produce a series of 3D images. Nonrigid image registration calculates a series of deformation fields that maps each 3D image to a reference image at end expiration. A principle component analysis (PCA) reduces noise and redundancy in the deformation fields. The resultant deformation fields correct each 3D image by morphing it to the reference motion state. The corrected 3D images are combined to obtain a high-resolution CBCT image. We evaluate the model by comparing CBCT images before and after motion correction, in patients receiving radiation treatment for lung cancer. Results: Motion-corrected CBCT images show less respiration-induced blurring and streaking artifacts compared to standard CBCT. Fine-detailed features in lung tumor and airways become visible, and the liver boundary is more discernable. Conclusion: Preliminary results indicate that the proposed method is a potentially useful tool for improving CBCT image quality and localization accuracy in the thorax. Repeating the process at other phase bins can yield a high quality respiration-correlated (4D) CBCT image set for evaluating respiration-induced motion.