Cone-beam Computed Tomography Setup Research Articles

Interfractional variation in whole-breast VMAT irradiation: a dosimetric study with complementary SGRT and CBCT patient setup

BackgroundThe dosimetric effect of setup uncertainty and tissue deformations in left-sided whole-breast irradiation with complementary surface-guided radiotherapy (SGRT) and cone-beam computed tomography (CBCT) setup was evaluated.MethodTreatment courses of 40.05 Gy prescribed dose in 15 fractions were simulated for 29 patients by calculating the dose on deformed CT images, that were based on daily CBCT images, and deforming and accumulating the dose onto the planning CT image. Variability in clinical target volume (CTV) position and shape was assessed as the 95% Hausdorff distance (HD95) between the planning CTV and deformed CTV structures. DVH metrics were evaluated between the planned and simulated cumulative dose distributions using two treatment techniques: tangential volumetric modulated arc therapy (tVMAT) and conventional 3D-conformal radiotherapy (3D-CRT).ResultsBased on the HD95 values, the variations in CTV shape and position were enclosed by the 5 mm CTV-PTV margin in 85% of treatment fractions using complementary CBCT and SGRT setup. A residual error of 8.6 mm was observed between the initial SGRT setup and CBCT setup. The median CTV V95% coverage was 98.1% (range 93.1–99.8%) with tVMAT and 98.2% (range 84.5–99.7%) with 3D-CRT techniques with CBCT setup. With the initial SGRT-only setup, the corresponding coverages were 96.3% (range 92.6–99.4%) and 96.6% (range 84.2–99.4%), respectively. However, a considerable bias in vertical residual error between initial SGRT setup and CBCT setup was observed. Clinically relevant changes between the planned and cumulative doses to organs-at-risk (OARs) were not observed.ConclusionsThe CTV-to-PTV margin should not be reduced below 5 mm even with daily CBCT setup. Both tVMAT and 3D-CRT techniques were robust in terms of dose coverage to the target and OARs. Based on the shifts between setup methods, CBCT setup is recommended as a complementary method with SGRT.

A Pilot Study of Simulation-Free Hippocampal-Avoidance Whole Brain Radiotherapy Using Diagnostic MR-Based and Online Adaptive Planning

We aimed to demonstrate the clinical feasibility and safety of a simulation-free hippocampal avoidance whole brain radiotherapy (HA-WBRT) workflow in a Phase I clinical trial (NCT05096286). Feasibility was defined as successful completion of the simulation-free HA-WBRT workflow through treatment delivery in at last 70% of treated patients. Ten candidates for HA-WBRT were enrolled for treatment on a ring gantry CT-guided Linac with online adaptive capabilities. Structures were contoured on the diagnostic brain MRI, which was then registered to a separate head computed tomography (CT) of similar head shape, obtained from an atlas-based database. A HA-WBRT "pre-plan" was generated using the atlas-based CT (AB-CT) and the NRG-CC001 constraints. At first fraction, the AB-CT was used as the primary dataset and deformed to the patient's cone-beam CT (CBCT) for dose calculation. The brain, ventricles, and brainstem contours were matched through rigid translation and rotation to the corresponding anatomy on the CBCT to aid in alignment, given the differences in rotational head positioning from diagnostic MRI to CBCT setup. Lastly, the lens, optic nerves, and brain contours were manually edited based on CBCT visualization. Plans were then optimized, and the adaptive plan was chosen for treatment if the plan met all objectives. Workflow tasks were timed. In addition, conventional plans using patients' sim CTs were created for each patient for the purpose of prospective dosimetric comparison. The dosimetric parameters were compared for each patient between the delivered sim-free plan and the conventional sim CT plan using the sign test via statistical software, with p<.05 indicating significance. Median time from approved sim order to first fraction was 4 days (range: 2-7); median time in room (door-to-door) was 49 minutes (range: 35-70). All patients successfully completed all ten fractions and 90% of the simulation-free radiation plans met all NRG-CC001 constraints. For one patient, the sim-free plan at fraction one failed the planning target volume (PTV) coverage objective (coverage of 89%); this was deemed acceptable for delivery by the treating radiation oncologist. An offline replan was then performed to meet NRG-CC001 constraints and used for the subsequent nine fractions. There was no clinically meaningful difference in dosimetric constraints between the sim-free plan (calculated on AB-CT) and conventional CT sim plan. Statistically, the sim-free plans provided improved PTV coverage to higher doses compared to the conventional plans (Table). At a median follow-up of 43 days (range: 9 -280), the intracranial progression-free survival rate was 90%. Simulation-free HA-WBRT is feasible, results in plans that are dosimetrically comparable to conventional CT sim workflows and succeeds in decreasing time to initiation of HA-WBRT by at least 50%. Further studies with a larger cohort are warranted to optimize the workflow.

Analytical setup margin for spinal stereotactic body radiotherapy based on measured errors

BackgroundNo consensus currently exists about the correct margin size to use for spinal SBRT. Margins have been proposed to account for various errors individually, but not with all errors combined to result in a single margin value. The purpose of this work was to determine a setup margin for five-fraction spinal SBRT based on known errors during radiotherapy to achieve at least 90% coverage of the clinical target volume with the prescription dose for at least 90% of patients and not exceed a 30 Gy point dose or 23 Gy to 10% of the spinal cord subvolume.MethodsThe random and systematic error components of intrafraction motion, residual setup error, and end-to-end system accuracy were measured. The patient’s surface displacement was measured to quantify intrafraction motion, the residual setup error was quantified by re-registering accepted daily cone beam computed tomography setup images, and the displacement between measured and planned dose profiles in a phantom quantified the end-to-end system accuracy. These errors and parameters were used to identify the minimum acceptable margin size. The margin recommendation was validated by assessing dose delivery across 140 simulated patient plans suffering from various random shifts representative of the measured errors.ResultsThe errors were quantified in three dimensions and the analytical margin generated was 2.4 mm. With this margin applied in the superior/inferior direction only, at least 90% of the CTV was covered with the prescription dose for 96% of the 140 patients simulated with minimal negative effect on the spinal cord dose levels.ConclusionsThe findings of this work support that a 2.4 mm margin applied in the superior/inferior direction can achieve at least 90% coverage of the CTV for at least 90% of dual-arc volumetric modulated arc therapy spinal SBRT patients in the presence of errors when immobilized with vacuum bags.

End of treatment cone-beam computed tomography (CBCT) is predictive of radiation response and overall survival in oropharyngeal squamous cell carcinoma

BackgroundImage guidance in radiation oncology has resulted in significant improvements in the accuracy and precision of radiation therapy (RT). Recently, the resolution and quality of cone beam computed tomography (CBCT) for image guidance has increased so that tumor masses and lymph nodes are readily detectable and measurable. During treatment of head and neck squamous cell carcinoma (HNSCC), on-board CBCT setup imaging is routinely obtained; however, this CBCT imaging data is not utilized to predict patient outcomes. Here, we analyzed whether changes in CBCT measurements obtained during a course of radiation therapy correlate with responses on routine 3-month follow-up diagnostic imaging and overall survival (OS).Materials/methodsPatients with oropharyngeal primary tumors who received radiation therapy between 2015 and 2018 were included. Anatomical measurements were collected of largest nodal conglomerate (LNC) at CT simulation, end of radiation treatment (EOT CBCT), and routine 3-month post-RT imaging. At each timepoint anteroposterior (AP), mediolateral (ML) and craniocaudal (CC) measurements were obtained and used to create a 2-dimensional (2D) maximum.ResultsCBCT data from 64 node positive patients were analyzed. The largest nodal 2D maximum and CC measurements on EOT CBCT showed a statistically significant correlation with complete response on 3-month post-RT imaging (r = 0.313, p = 0.02 and r = 0.318, p = 0.02, respectively). Furthermore, patients who experienced a 30% or greater reduction in the CC dimension had improved OS (Binary Chi-Square HR 4.85, p = 0.028).ConclusionDecreased size of pathologic lymph nodes measured using CBCT setup imaging during a radiation course correlates with long term therapeutic response and overall survival of HNSCC patients. These results indicate that CBCT setup imaging may have utility as an early predictor of treatment response in oropharyngeal HNSCC.

Comparison of the dosimetric accuracy of proton breast treatment plans delivered with SGRT and CBCT setups.

PurposeTo compare the dosimetric accuracy of surface‐guided radiation therapy (SGRT) and cone‐beam computed tomography (CBCT) setups in proton breast treatment plans.MethodsData from 30 patients were retrospectively analyzed in this IRB‐approved study. Patients were prescribed 4256–5040 cGy in 16–28 fractions. CBCT and AlignRT (SGRT; Vision RT Ltd.) were used for treatment setup during the first three fractions, then daily AlignRT and weekly CBCT thereafter. Each patient underwent a quality assurance CT (QA‐CT) scan midway through the treatment course to assess anatomical and dosimetric changes. To emulate the SGRT and CBCT setups during treatment, the planning CT and QA‐CT images were registered in two ways: (1) by registering the volume within the CTs covered by the CBCT field of view; and (2) by contouring and registering the surface surveyed by the AlignRT system. The original plan was copied onto these two datasets and the dose was recalculated. The clinical treatment volume (CTV): V95%; heart: V25Gy, V15Gy, and mean dose; and ipsilateral lung: V20Gy, V10Gy, and V5Gy, were recorded. Multi and univariate analyses of variance were performed to assess the differences in dose metric values between the planning CT and the SGRT and CBCT setups.ResultsThe CTV V95% and lung V20Gy, V10Gy, and V5Gy dose metrics were all significantly (p < 0.01) lower on the QA‐CT in both the CBCT and SGRT setup. The differences were not clinically significant and were, on average, 1.4–1.6% lower for CTV V95% and 1.8%–6.0% lower for the lung dose metrics. When comparing the lung and CTV V95% dose metrics between the CBCT and SGRT setups, no significant difference was observed. This indicates that the SGRT setup provides similar dosimetric accuracy as CBCT.ConclusionThis study supports the daily use of SGRT systems for the accurate dose delivery of proton breast treatment plans.

Accuracy of surface-guided patient setup for conventional radiotherapy of brain and nasopharynx cancer.

PurposeTo evaluate the accuracy of surface‐guided radiotherapy (SGRT) in cranial patient setup by direct comparison between optical surface imaging (OSI) and cone‐beam computed tomography (CBCT), before applying SGRT‐only setup for conventional radiotherapy of brain and nasopharynx cancer.Methods and MaterialsUsing CBCT as reference, SGRT setup accuracy was examined based on 269 patients (415 treatments) treated with frameless cranial stereotactic radiosurgery (SRS) during 2018‐2019. Patients were immobilized in customized head molds and open‐face masks and monitored using OSI during treatment. The facial skin area in planning CT was used as OSI region of interest (ROI) for automatic surface alignment and the skull was used as the landmark for automatic CBCT/CT registration. A 6 degrees of freedom (6DOF) couch was used. Immediately after CBCT setup, an OSI verification image was captured, recording the SGRT setup differences. These differences were analyzed in 6DOFs and as a function of isocenter positions away from the anterior surface to assess OSI‐ROI bias. The SGRT in‐room setup time was estimated and compared with CBCT and orthogonal 2D kilovoltage (2DkV) setups.ResultsThe SGRT setup difference (magnitude) is found to be 1.0 ± 2.5 mm and 0.1˚±1.4˚ on average among 415 treatments and within 5 mm/3˚ with greater than 95% confidence level (P < 0.001). Outliers were observed for very‐posterior isocenters: 15 differences (3.6%) are >5.0mm and 9 (2.2%) are >3.0˚. The setup differences show minor correlations (|r| < 0.45) between translational and rotational DOFs and a minor increasing trend (<1.0 mm) in the anterior‐to‐posterior direction. The SGRT setup time is 0.8 ± 0.3 min, much shorter than CBCT (5 ± 2 min) and 2DkV (2 ± 1 min) setups.ConclusionThis study demonstrates that SGRT has sufficient accuracy for fast in‐room patient setup and allows real‐time motion monitoring for beam holding during treatment, potentially useful to guide radiotherapy of brain and nasopharynx cancer with standard fractionation.

Auto-calibration by locally consistent contours for dental CBCT

The image quality of dental cone-beam computed tomography (CBCT) is limited by the accuracy of device calibration. Inaccurate calibration introduces errors in the reconstruction process, which may lead to severe artifacts in the reconstructed volume. Patient motion during scan acquisition induces similar effects. This paper introduces a novel auto-calibration approach calculating geometrical projection parameters from unknown patient geometry. We formulate consistency conditions linking the information of consecutive projection images and a regularization technique to prevent overall distortions. Implemented as a global optimization problem we present an efficient greedy optimizer as well. Our strategy turns out to be robust towards inaccurate initialization. As our method does not rely on consistency between projection data and tomography reconstruction it is robust towards reconstruction artifacts such as e.g. truncation. Applying our approach for auto-calibration shows a relative improvement of sharpness up to of in a standard dental CBCT setup. Evaluation is performed on digital reconstructed radiographs (DRRs) of a CT head-scan. In particular different motion types are considered and the number of anatomical structures used for calibration is varied to achieve an understanding of the behavior of the approach.

Deep-Inspiration Breath-Hold Intensity Modulated Radiation Therapy to the Mediastinum for Lymphoma Patients: Setup Uncertainties and Margins

Patient setup for treating large target volumes can be challenging. In the present study, we measured the local uncertainties in the treatment of mediastinal lymphoma and investigated the need for region-specific planning target volume (PTV) margins. The data from 30 patients who had undergone radiation therapy for mediastinal lymphoma were retrospectively analyzed. A computed tomography (CT)-on-rails (CTOR) system in the treatment room was used for daily image guidance. The total PTV was split into 6 regions: neck, supraclavicular fossa, axilla, mediastinum, upper heart, and lower heart. The total PTV and the 6 local regions were separately aligned to the planning CT scan using automatic rigid registration. The residual local errors using 3 setup strategies were investigated: no image guidance, CTOR setup to total PTV, and simulated cone beam CT setup to the mediastinum. Errors were recorded in the anteroposterior, superoinferior, and right-left directions separately. Using the residual error calculations, the margins required to cover 95% of the clinical target volume for 90% of the patients was estimated. For each patient, 12 to 21 days of daily CTOR data were available for analysis. The residual errors for the total PTV and mediastinum setups were both smaller than those with no image guidance. The lower heart region had more uncertainty with all 3 setup strategies. Margin analysis revealed that the magnitude of the margin is dependent on the imaging strategy, direction, and local region inside the PTV. Margins >7 mm are necessary to account for uncertainty in the neck, lower heart, and axilla regions even under daily CT guidance. Setup uncertainties in the mediastinum are not uniform and are dependent on target location and imaging strategy. However, with the appropriate margin, we can target regions that might not be visualized with the available on-board imager system.

X-ray microtomographic confirmation of the reliability of CBCT in identifying the scalar location of cochlear implant electrode after round window insertion

Cone-beam computed tomography (CBCT) plays a key role in cochlear implantation in both planning implantation before surgery and quality control during surgery due to the high spatial resolution and convenience of application in the operation theater. We recently designed a novel, highresolution cone-beam acquisition system that has been tested in temporal bones with cochlear implantation to identify the scalar localization of the electrode arrays. The current study aimed to verify the reliability of the experimental CBCT set-up using high-resolution in vitro X-ray microtomography (μCT) imaging as a reference. Nine human temporal bones were studied by inserting a straight electrode of a cochlear implant using the round window approach followed by sequential imaging using experimental CBCT and μCT with and without 1% iodine as the contrast agent. In the CBCT images, the electrodes were located in the scala tympani and near the lateral wall in all temporal bones. In the μCT images, the cochlear fine structures, including Reissner's membrane, stria vascularis, spiral ligament, basilar membrane, spiral limbus, osseous spiral lamina, and Rosenthal's canal that hosts the spiral ganglion cells, were clearly delineated; the electrode array avoided the lateral wall of the scala tympani in the hook region and then ran along the lateral wall of the scala tympani without any exception, a feature that was also detected in a temporal bone with ruptures in the basilar and Reissner's membranes. In conclusion, the current in vitro μCT imaging system produced high-quality images that could demonstrate the fine cochlear structures faithfully and verify the reliability of a novel experimental CBCT set-up aimed for clinical application in identifying the scalar localization of the electrode array. The straight electrode is safe for cochlear structures with low risk of translocation and is suitable for atraumatic implantation, although a large gap between the contacts and the modiolus exists.

Digital reconstruction of high-quality daily 4D cone-beam CT images using prior knowledge of anatomy and respiratory motion

Conventional in-room cone-beam computed tomography (CBCT) lacks explicit representation of patient respiratory motion and usually has poor image quality and inaccurate CT numbers for target delineation and/or adaptive treatment planning. In-room four-dimensional (4D) CBCT image acquisition is still time consuming and suffers the same issue of poor image quality. To overcome this limitation, we developed a computational framework to digitally synthesize high-quality daily 4D CBCT images using the prior knowledge of motion and appearance learned from the planning 4D CT dataset. A patient-specific respiratory motion model was first constructed from the planning 4D CT images using principal component analysis of displacement vector fields across different respiratory phases. Subsequently, the respiratory motion model as well as the image content of the planning CT was spatially mapped onto the daily CBCT using deformable image registration. The synthesized 4D images possess explicit patient motion while maintaining the geometric accuracy of patient's anatomy at the time of treatment. We validated our model by quantitatively comparing the synthesized 4D CBCT against the 4D CT dataset acquired in the same day from protocol patients undergoing daily in-room CBCT setup and weekly 4D CT for treatment evaluation. Our preliminary results have demonstrated good agreement of contours in different motion phases between the synthesized and acquired scans. Various imaging artifacts were also suppressed and soft-tissue visibility was enhanced.

Systematic measurements of whole‐body imaging dose distributions in image‐guided radiation therapy

The full benefit of the increased precision of contemporary treatment techniques can only be exploited if the accuracy of the patient positioning is guaranteed. Therefore, more and more imaging modalities are used in the process of the patient setup in clinical routine of radiation therapy. The improved accuracy in patient positioning, however, results in additional dose contributions to the integral patient dose. To quantify this, absorbed dose measurements from typical imaging procedures involved in an image-guided radiation therapy treatment were measured in an anthropomorphic phantom for a complete course of treatment. The experimental setup, including the measurement positions in the phantom, was exactly the same as in a preceding study of radiotherapy stray dose measurements. This allows a direct combination of imaging dose distributions with the therapy dose distribution. Individually calibrated thermoluminescent dosimeters were used to measure absorbed dose in an anthropomorphic phantom at 184 locations. The dose distributions from imaging devices used with treatment machines from the manufacturers Accuray, Elekta, Siemens, and Varian and from computed tomography scanners from GE Healthcare were determined and the resulting effective dose was calculated. The list of investigated imaging techniques consisted of cone beam computed tomography (kilo- and megavoltage), megavoltage fan beam computed tomography, kilo- and megavoltage planar imaging, planning computed tomography with and without gating methods and planar scout views. A conventional 3D planning CT resulted in an effective dose additional to the treatment stray dose of less than 1 mSv outside of the treated volume, whereas a 4D planning CT resulted in a 10 times larger dose. For a daily setup of the patient with two planar kilovoltage images or with a fan beam CT at the TomoTherapy unit, an additional effective dose outside of the treated volume of less than 0.4 mSv and 1.4 mSv was measured, respectively. Using kilovoltage or megavoltage radiation to obtain cone beam computed tomography scans led to an additional dose of 8-46 mSv. For treatment verification images performed once per week using double exposure technique, an additional effective dose of up to 18 mSv was measured. Daily setup imaging using kilovoltage planar images or TomoTherapy megavoltage fan beam CT imaging can be used as a standard procedure in clinical routine. Daily kilovoltage and megavoltage cone beam computed tomography setup imaging should be applied on an individual or indication based protocol. Depending on the imaging scheme applied, image-guided radiation therapy can be administered without increasing the dose outside of the treated volume compared to therapies without image guidance.

Motion monitoring for cranial frameless stereotactic radiosurgery using video‐based three‐dimensional optical surface imaging

To establish a new clinical procedure in frameless stereotactic radiosurgery (SRS) for patient setup verification at treatment couch angles as well as for head-motion monitoring during treatment using video-based optical surface imaging (OSI). A video-based three-dimensional (3D) OSI system with three ceiling-mounted camera pods was employed to verify setup at treatment couch angles as well as to monitor head motion during treatment. A noninvasive head immobilization device was utilized, which includes an alpha head mold and a dental mouthpiece with vacuum suction; both were locked to the treatment couch. Cone beam computed tomography (CBCT) was used as the standard for image-guided setup. Orthogonal 2D-kV imaging was applied for setup verification before treatment, between couch rotations, and after treatment at zero couch angle. At various treatment couch angles, OSI setup verification was performed, relative to initial OSI setup verification at zero couch angle after CBCT setup through a coordinate transformation. For motion monitoring, the setup uncertainty was decoupled by taking an on-site surface image as new reference to detect motion-induced misalignment in near real-time (1-2 frames per second). Initial thermal instability baseline of the real-time monitoring was corrected. An anthropomorphous head phantom and a 1D positioning platform were used to assess the OSI accuracy in motion detection in longitudinal and lateral directions. Two hypofractionated (9 Gy x 3 and 6 Gy x 5) frameless stereotactic radiotherapy (SRT) patients as well as two single-fraction (21 and 18 Gy) frameless SRS patients were treated using this frameless procedure. For comparison, 11 conventional frame-based SRS patients were monitored using the OSI to serve as clinical standards. Multiple noncoplanar conformal beams were used for planning both frameless and frame-based SRS with a micromultileaf collimator. The accuracy of the OSI in 1D motion detection was found to be 0.1 mm with uncertainty of +/- 0.1 mm using the head phantom. The OSI registration against simulation computed tomography (CT) external contour was found to be dependent on the CT skin definition with -0.4 mm variation. For frame-based SRS patients, head-motion magnitude was detected to be <1.0 mm (0.3 +/- 0.2 mm) and <1.0 degree (0.2 degrees +/- 0.2 degrees) for 98% of treatment time, with exception of one patient with head rotation <1.5 degrees for 98% of the time. For frameless SRT/SRS patients, similar motion magnitudes were observed with an average of 0.3 +/- 0.2 mm and 0.2 degrees +/- 0.1 degree in ten treatments. For 98% of the time, the motion magnitude was <1.1 mm and 1.0 degree. Complex head-motion patterns within 1.0 mm were observed for frameless SRT/SRS patients. The OSI setup verification at treatment couch angles was found to be within 1.0 mm. The OSI system is capable of detecting 0.1 +/- 0.1 mm 1D spatial displacement of a phantom in near real time and useful in head-motion monitoring. This new frameless SRS procedure using the mask-less head-fixation system provides immobilization similar to that of conventional frame-based SRS. Head-motion monitoring using near-real-time surface imaging provides adequate accuracy and is necessary for frameless SRS in case of unexpected head motion that exceeds a set tolerance.

MO-D-BRB-10: Optical Surface Imaging for Online Rotation Correction and Real-Time Motion Monitoring with Threshold Gating for Frameless Cranial Stereotactic Radiosurgery

Purpose: To develop an image‐guided procedure for online head‐rotation correction and real‐time motion monitoring with threshold gating for clinical frameless stereotactic radiosurgery(SRS) using video‐based optical 3D surfaceimaging (AlignRT) to ensure accurate tumor localization and clinically‐acceptable head motion at all treatment couch angles during treatment. Methods: Eight patients, immobilized with a deep‐head mold and a mouth‐piece fixed to the couch, were treated with single‐fraction frameless SRS. The planning target volume was defined by a 3.0mm‐margin around the gross tumor volume for these patients with brainmetastasis. A ceiling‐mounted AlignRT system with three camera pods was used to correct residual head rotation before cone‐beam computed tomography(CBCT) setup, verify setup at all treatment couch angles, and monitor the head motion with 1.0mm gating threshold for beam hold. The external contour of the planing CT and on‐site surface reference images were used for setup verification and motion monitoring, respectively, using the maximum visible skin surface within the entire mid‐to‐upper face as the region of interest. An anthropomorphous head phantom and an adjustable platform (accuracy of 0.1 mm) were used to determine the geometric accuracy of frameless setup procedure and AlignRT motion detection. Results: The phantom experiment shows that the motion detection accuracy was less than 0.1 mm. For these patients, <1 degree head rotation was achieved at the setup by using surface‐image‐guided head repositioning. The patient head motion was found to be <1.0mm for 98% of the time after CBCT setup, while the beam‐hold gating was used for <1% of beam‐on time. The required workload and machine time of this procedure are similar to those of conventional frame‐based SRS. Conclusions: This non‐invasive frameless SRS procedure provides accurate and reliable means to perform clinical SRS. The image‐guided setup and motion control provides adequate accuracy, yet more convenient to the patients, comparing with frame‐based SRS. This research is in part supported by VisionRT through a clinical research agreement.

Application of IMRT Combined with Cone-beam Computed Tomography in Treatment of Intracranial Tumor

Objective To evaluate the interfractional three-dimensional(3D) setup error and propose optimum margin of planning target volume(PTV) in radiotherapy for intracranial tumor at risk of using intensity modulated radiotherapy(IMRT) guided with cone-beam computed tomography(CBCT).MethodsThirty-six patients received radiotherapy of IMRT imaging-guided with megavolt MVision CBCT scans equipped in ONCOR Linear Accelerator.The initial five fractional CBCT volume-imaging and data obtained by CBCT scans after initial setup and after re-positioning were dimensionally matched with planned CT images.Results The interfractional setup errors on X,Y and Z axes were(2.22±1.37) mm,(2.62±1.50) mm and(2.77±1.34) mm,respectively,for 36 intracranial tumors.Comparing with the pre-correction position,the post-correction setup errors decreased significantly on all three axes(P0.05),whereas there were no statistically significant difference in five fractional setup errors(P0.05).While without correction of CBCT setup errors,PTV margin in three dimension were Lat(cm)-X:2.94 mm,Long(cm)-Y:3.31mm,Vert(cm)-Z:3.52 mm.While with correction of CBCT setup errors,PTV margin in three dimension were,Lat(cm)-X: 1.00 mm,Long(cm)-Y: 1.19 mm,Vert(cm)-Z: 1.68 mm.Conclusion The set-up margins were 4 mm in all directions.Measurement and correction of interfractional setup errors and PTV margins before fractional radiotherapy using megavolt MVision CBCT could help to improve the precision of IMRT radiotherapy for intracranial tumors.

Study of Cone Beam Computed Tomography Setup Accuracy in Stereotactic Body Radiation Therapy for Lung Cancer Treatment-free Breathing vs. Controlled Breathing

Study of Cone Beam Computed Tomography Setup Accuracy in Stereotactic Body Radiation Therapy for Lung Cancer Treatment-free Breathing vs. Controlled Breathing

SU-DD-A4-01: Phantom Study of Cone Beam Computed Tomography Setup Accuracy in Stereotactic Body Radiation Therapy for Lung Cancer Treatment

Purpose: To evaluate the accuracy of cone beam computed tomography(CBCT) guided positioning in the case of motion patterns associated with regular and irregular breathing for lungcancer stereotactic body radiation therapy(SBRT).Methods and Materials: Five irregular motion patterns have been used in phantom‐simulated cases using a solid ball to create four‐dimensional (4D) CT datasets. Images are transferred to the Pinnacle Planning System 8.0m (Phillips) where a planning treatment volume (PTV) is constructed for planning. Subsequently the same phantom simulated cases are imaged with a CBCT (Elekta XVI) in volumetric reconstruction mode. Images defining the PTV using CBCT are compared with PTV determined from 4DCT images. Breathing motion patterns used in these phantom studies were from actual patients' data taken at random. For comparisons regular breathing motion data have been also used for reference in PTV matching derived from 4DCT and CBCT. The actual time dependant target position was known in each phantom‐simulated case from the driver files associated with the motion generator. Results For regular motion, CBCT exhibited up to 2mm shift between 4DCT derived PTV and CBCT defined PTV. For irregular motion, the CBCT derived PTV exhibited up to3.7mm shift relative to 4DCT derived PTV. However, we found that neither the 4DCT nor the CBCT accurately reflect of the actual PTV motion and geometry (up to 4.9mm) derived from known target dimensions and knowledge of motion data. Dosimetric impact of this error will be reported. Conclusions The setup of target for SBRTtreatment of lungtumor based on CBCT derived PTV is consistent with treatment plan based on 4DCT. This clinically positive result is not based, however, on accurate representation of clinically used PTV with true geometrical representation of PTV target derived from known target dimensions and known pattern of target motion in the phantom.

Application of a Newly Developed High-Accuracy Image Guided Radiation Therapy System to Stereotactic Radiosurgery

Our newly developed Image-Guided Radiation Therapy (IGRT) system has a high degree of isocenter accuracy compared to conventional linac systems. This accuracy is obtained because beam directions are actively controlled by gimbals mechanism. The system also has a kilovoltage (kV) X-ray imaging subsystem and an on-line image registration tool to provide easy and accurate image-guided setup. The aim of this study was to examine the operational performance when the IGRT system is applied to stereotactic radiosurgery for intracranial lesion. In the IGRT system, a megavoltage (MV) X-ray head and an imaging subsystem are installed on a rigid round gantry called O-ring. The O-ring gantry rotates around a vertical axis instead of couch rotation, so that a patient geometry does not change throughout a treatment after setup completion even if non-coplanar beams are applied. The gimbals mechanism supports the X-ray head with a multileaf collimator and controls beam directions to focus onto the isocenter in any gantry position with an accuracy of 0.1 mm. Semi-automatic isocenter accuracy testing is routinely carried out every morning which takes less than 5 minutes. The imaging subsystem consists of two sets of a kV X-ray tube combined with a flat panel detector. It provides two orthogonal X-ray images simultaneously, and also provides cone beam computed tomography (CBCT) images. The images are compared with reference images in an on-line fashion, and the difference can be measured manually on a display or automatically using an image registration software. In this study, a treatment simulation using a head phantom was performed according to a virtual stereotactic radiosurgery plan for an intracranial round tumor which was preparatively made with a radiation treatment planning system. The procedure consisted of the phantom setup, kV X-ray images acquisition, CBCT reconstruction, image registration, and treatment beam delivery. Before the simulation, beam arrangements were confirmed to be deliverable without any collision of the gantry with the couch. Operation time excluding the time for human interaction was measured for every process as well as the total process for the purpose of assessing the system operational performance. Orthogonal X-ray imaging setup including image registration took 1 minute 15 seconds in the first operation and 40 seconds from the 2nd. The time for CBCT setup including image registration was 2 minutes 40 seconds when the images were reconstructed with 1 mm thickness and 1 mm pitch. Beam-on time and total delivery time was 7.5 and 11 minutes, respectively, to deliver 25 Gy (3700 MU) to the isocenter with 4 conformal arcs that had 480 degrees of gantry rotation in total. The total treatment time was estimated from 22 minutes to 25 which process included patient entrance, patient immobilization, orthogonal X-ray imaging setup, CBCT setup, setup verification by an operator, beam delivery, and release of the patient. The operation was performed smoothly without entering of the operator to the treatment room after patient setup. The IGRT system showed to have suitable operational performance maintaining high geometrical accuracy in the application to stereotactic radiosurgery for intracranial lesion.

Accuracy and feasibility of cone‐beam computed tomography for stereotactic radiosurgery setup

Image fusion, target localization, and setup accuracy of cone-beam computed tomography (CBCT) for stereotactic radiosurgery (SRS) were investigated in this study. A Rando head phantom rigidly attached to a stereotactic Brown-Roberts-Wells (BRW) frame was utilized to study the geometric accuracy of CBCT. Measurements of distances and angular separations between selected pairs of multiple radio-opaque targets embedded in the head phantom from a conventional simulation CT provided comparative data for geometric accuracy analysis. Localization accuracy of the CBCT scan was investigated from an analysis of BRW localization of four cylindrical objects (9 mm in diameter and 25 mm in length) independently computed from CBCT and conventional CT scans. Image fusion accuracy was quantitatively evaluated from BRW localization of multiple simulated targets from the CBCT and conventional CT scan. Finally, a CBCT setup procedure for stereotactic radiosurgery treatments was proposed and its accuracy was assessed using orthogonal target verification imaging. Our study showed that CBCT did not present any significant geometric distortions. Stereotactic coordinates of the four cylindrical objects as determined from the CBCT differed from those determined from the conventional CT on average by 0.30 mm with a standard deviation (SD) of 0.09 mm. The mean image registration accuracy of CBCT with conventional CT was 0.28 mm (SD = 0.10 mm). Setup uncertainty of our proposed CBCT setup procedure was on the same order as the conventional framed-based stereotactic systems reported in the literature (mean = 1.34 mm, SD = 0.33 mm). In conclusion, CBCT can be used to guide SRS treatment setup with accuracy comparable to the currently used frame-based stereotactic radiosurgery systems provided that intra-treatment patient motion is prevented.

Kilo-Voltage Cone-Beam Computed Tomography Setup Measurements for Lung Cancer Patients; First Clinical Results and Comparison With Electronic Portal-Imaging Device

Kilovoltage cone-beam computed tomography (CBCT) has been developed to provide accurate soft-tissue and bony setup information. We evaluated clinical CBCT setup data and compared CBCT measurements with electronic portal imaging device (EPID) images for lung cancer patients. The setup error for CBCT scans at the treatment unit relative to the planning CT was measured for 62 patients (524 scans). For 19 of these patients (172 scans) portal images were also made. The mean, systematic setup error (Sigma), and random setup error (sigma) were calculated for the CBCT and the EPID. The differences between CBCT and EPID and the rotational setup error derived from the CBCT were also evaluated. An offline shrinking action level correction protocol, based on the CBCT measurements, was used to reduce systematic setup errors and the impact of this protocol was evaluated. The CBCT setup errors were significantly larger than the EPID setup errors for the cranial-caudal and anterior-posterior directions (p < 0.05). The mean overall setup errors after correction measured with the CBCT were 0.2 mm (Sigma = 1.6 mm, sigma = 2.9 mm) in the left-right, -0.8 mm (Sigma = 1.7 mm, sigma = 4.0 mm) in cranial-caudal and 0.0 mm (Sigma = 1.5 mm, sigma = 2.0 mm) in the anterior-posterior direction. Using our correction protocol only 2 patients had mean setup errors larger than 5 mm, without this correction protocol 51% of the patients would have had a setup error larger than 5 mm. Use of CBCT scans provided more accurate information concerning the setup of lung cancer patients than did portal imaging.

Cone-beam CT in an offline image guidance strategy: Margin and efficiency gains

Cone-beam CT in an offline image guidance strategy: Margin and efficiency gains