Optical Surface Imaging System Research Articles

Clinical Implementation of Optical Surface Imaging Systems in Vulvar Cancer to Reduce Setup Error

Optical surface monitoring system (OSMS) could achieve continuous monitoring of patient position through a nonradiographic and noninvasive technology, which has been widely applied to many sites of radiation therapy including breast, intracranial, head and neck, abdomen, and the extremities. However, no study has investigated the application of OSMS in radiation therapy of vulvar cancer. In this study, we hypothesized using OSMS would reduce setup error in the vulvar cancer compared to standard laser-based setup (SLS). A single-center prospective trial included 10 patients with vulvar cancer treated with intensity modulated radiation therapy (IMRT) for a total of 250 fractions. Every patient was immobilized with Styrofoam in a frog-leg position and used marks on the patient's skin to align to the room lasers for pre-setup. The treatment couch values of lateral (Lat), longitudinal (Lng), vertical (Vrt) in three translation directions and Rtn (the rotation along the z axis), Pitch (the rotation along the x axis), Roll (the rotation along the y axis) in three rotations directions were recorded. Then completed the setup of patient with information from a surface imaging system and obtained deviation values. Setup is followed by pretreatment cone-beam computed tomography (CBCT) to further verify patient and target position by registering to the planning CT with respect to bony anatomy. With CBCT as a gold standard for patient setup, the absolute values of setup error and error distribution of SLS method and OSMS method from the same patient in above six directions were compared. The mean of absolute values of setup errors in the SLS method were significantly higher than those of OSMS method in Lat (0.34cm vs 0.20cm), Lng (0.42cm vs 0.29cm), Vrt (0.43cm vs 0.28cm) and Rtn (0.90° vs 0.67°) directions (P<0.05). The mean errors in SLS and OSMS methods in Pitch and Roll directions were 0.93° and 1.02° (P = 0.16), 0.42° and 0.45° (P = 0.48), respectively, with no significant difference. In the OSMS method, the distribution rates of the setup errors within 0.5cm in three translation directions and within 1.5° in three rotations directions were significantly higher in Lat (90.8% vs 80.4%), Lng (82.0% vs 68.8%), Vrt (83.2% vs 65.6%), and Rtn (91.2% vs 80.4%) directions than those of SLS method (P<0.05). In the Pitch (79.2% vs 80.4%) and Roll (97.2% vs 98.0%) directions, the distribution rates of the OSMS method were slightly lower than those of the SLS method, with no significant difference (P = 0.738 and P = 0.559). The implementation of OSMS in IMRT for vulvar cancer could reduce setup error and increase precision of setup, especially for the directions of Lat, Lng, Vrt and Rtn.

Can Optical Surface Imaging Replace Non-coplanar Cone-beam Computed Tomography for Non-coplanar Set-up Verification in Single-isocentre Non-coplanar Stereotactic Radiosurgery and Hypofractionated Stereotactic Radiotherapy for Single and Multiple Brain Metastases?

AimsTo conduct a direct comparison regarding the non-coplanar positioning accuracy between the optical surface imaging system Catalyst HDTM and non-coplanar cone-beam computed tomography (NC-CBCT) in intracranial single-isocentre non-coplanar stereotactic radiosurgery (SRS) and hypofractionated stereotactic radiotherapy (HSRT). Materials and methodsTwenty patients with between one and five brain metastases who underwent single-isocentre non-coplanar volumetric modulated arc therapy (NC-VMAT) SRS or HSRT were enrolled in this study. For each non-zero couch angle, both Catalyst HDTM and NC-CBCT were used for set-up verification prior to beam delivery. The set-up error reported by Catalyst HDTM was compared with the set-up error derived from NC-CBCT, which was defined as the gold standard. Additionally, the dose delivery accuracy of each non-coplanar field after using Catalyst HDTM and NC-CBCT for set-up correction was measured with SRS MapCHECKTM. ResultsThe median set-up error differences (absolute values) between the two positioning methods were 0.30 mm, 0.40 mm, 0.50 mm, 0.15°, 0.10° and 0.10° in the vertical, longitudinal, lateral, yaw, pitch and roll directions, respectively. The largest absolute set-up error differences regarding translation and rotation were 1.5 mm and 1.1°, which occurred in the longitudinal and yaw directions, respectively. Only 35.71% of the pairs of measurements were within the tolerance of 0.5 mm and 0.5° simultaneously. In addition, the non-coplanar field with NC-CBCT correction yielded a higher gamma passing rate than that with Catalyst HDTM correction (P < 0.05), especially for evaluation criteria of 1%/1 mm with a median increase of 12.8%. ConclusionsCatalyst HDTM may not replace NC-CBCT for non-coplanar set-up corrections in single-isocentre NC-VMAT SRS and HSRT for single and multiple brain metastases. The potential role of Catalyst HDTM in intracranial SRS/HSRT needs to be further studied in the future.

Reproducibility and stability of spirometer-guided deep inspiration breath-hold in left-breast treatments using an optical surface monitoring system.

The aim of this study was to evaluate the reproducibility and stability of left breast positioning during spirometer-guided deep-inspiration breath-hold (DIBH) radiotherapy using an optical surface imaging system (AlignRT). The AlignRT optical tracking system was used to monitor five left-sided breast cancer patients treated using the Active Breathing Coordinator spirometer with DIBH technique. Treatment plans were created using an automated hybrid-VMAT technique on DIBH CTs. A prescribed dose of 60Gy to the tumor bed and 50Gy to the breast in 25 fractions was planned. During each treatment session, the antero-posterior (VRT), superior-inferior (LNG), and lateral (LAT) motion of patients was continuously recorded by AlignRT. The intra-breath-hold stability and the intra- and inter-fraction reproducibility were analyzed for all breath-holds and treatment fractions. The dosimetric impact of the residual motion during DIBH was evaluated from the isocenter shifts amplitudes obtained from the 50%, 90%, and 100% cumulative distribution functions of intra-fractional reproducibility. The positional variations of 590 breath-holds as measured by AlignRT were evaluated. The mean intra-breath-hold stability during DIBH was 1.0±0.4mm, 2.1±1.9mm, and 0.7±0.5mm in the VRT, LNG, and LAT directions, with a maximal value of 8.8mm in LNG direction. Similarly, the mean intra-breath-hold reproducibility was 1.4±0.8mm, 1.7±1.0mm, and 0.8±0.5mm in the VRT, LNG, and LAT directions, with a maximal value of 4.1mm in LNG direction. Inter-fractional reproducibility showed better reliability, with difference in breathing levels in all fractions of 0.3mm on average. Based on tolerance limits corresponding to the 90% cumulative distribution level, gating window widths of 1mm, 2mm, and 5mm in the LAT, VRT, and LNG directions were considered an appropriate choice. In conclusion, despite the use of a dedicated spirometer at constant tidal volume, a non-negligible variability of the breast surface position has been reported during breath-holds. The real-time monitoring of breast surface using surface-guided optical technology is strongly recommended.

Development and Longitudinal Analysis of Plan-Based Streamlined Quality Assurance on Multiple Positioning Guidance Systems With Single Phantom Setup.

PurposeThis study was to propose and validate an efficient and streamlined quality assurance (QA) method with a single phantom setup to check performances of patient positioning guidance systems including six-degree-of-freedom (6DoF) couch, X-ray modalities (kV–kV, MV–MV and CBCT), optical surface imaging system (AlignRT), lasers and optical distance indicator (ODI).Methods and MaterialsThe QA method was based on a pseudo-patient treatment plan using the AlignRT cube phantom. The cube was first randomly set up on the couch, and the initial position offsets were acquired by AlignRT and CBCT. The cube was restored to its reference position by 6DoF couch shift, during which the couch motion accuracy and tracking performances of AlignRT and CBCT were derived. After that, the residual offsets were acquired by kV–kV, MV–MV and AlignRT to derive the isocenter discrepancies. Finally, the laser alignment and ODI values were visually inspected. The QA procedure had been internally approved as a standard weekly QA test, and the results over 50 weeks were longitudinally analyzed for clinical validation.ResultsThe 6DoF couch motion errors as well as the tracking errors of AlignRT were sub-millimeter and sub-degree, and no deviation over 1 mm or 1 deg was identified. The ROI mode of isocenter (ISO) in AlignRT exhibited more consistent results than the centroid (CEN). While the isocenter discrepancy between CBCT and kV–kV was negligible, the maximal discrepancies between CBCT and MV–MV were 0.4 mm in LNG and 0.3 deg in PITCH. The isocenter discrepancies between CBCT and AlignRT were <0.5 mm in translation and <0.3 deg in rotation. For AlignRT, the isocenter discrepancies between the DICOM and SGRT references were about 0.6 mm in VRT, 0.5 mm in LNG and 0.2 deg in PITCH. As the therapists became familiar with the workflow, the average time to complete the whole procedure was around 23 min.ConclusionsThe streamlined QA exhibits desirable practicality as an efficient multipurpose performance check on positioning guidance systems. The stability, tracking performance and isocenter congruence of the positioning guidance systems have been fully validated for all clinical image guidance RT application, even SRS/SBRT, which requires the strictest tolerance.

Commissioning of optical surface imaging systems for cranial frameless stereotactic radiosurgery.

PurposeThis study aimed to evaluate and compare different system calibration methods from a large cohort of systems to establish a commissioning procedure for surface‐guided frameless cranial stereotactic radiosurgery (SRS) with intrafractional motion monitoring and gating. Using optical surface imaging (OSI) to guide non‐coplanar SRS treatments, the determination of OSI couch‐angle dependency, baseline drift, and gated‐delivered‐dose equivalency are essential.MethodsEleven trained physicists evaluated 17 OSI systems at nine clinical centers within our institution. Three calibration methods were examined, including 1‐level (2D), 2‐level plate (3D) calibration for both surface image reconstruction and isocenter determination, and cube phantom calibration to assess OSI‐megavoltage (MV) isocenter concordance. After each calibration, a couch‐angle dependency error was measured as the maximum registration error within the couch rotation range. A head phantom was immobilized on the treatment couch and the isocenter was set in the middle of the brain, marked with the room lasers. An on‐site reference image was acquired at couch zero, the facial region of interest (ROI) was defined, and static verification images were captured every 10° for 0°–90° and 360°–270°. The baseline drift was assessed with real‐time monitoring of the motionless phantom over 20 min. The gated‐delivered‐dose equivalency was assessed using the electron portal imaging device and gamma test (1%/1mm) in reference to non‐gated delivery.ResultsThe maximum couch‐angle dependency error occurs in longitudinal and lateral directions and is reduced significantly (P < 0.05) from 1‐level (1.3 ± 0.4 mm) to 2‐level (0.8 ± 0.3 mm) calibration. The MV cube calibration does not further reduce the couch‐angle dependency error (0.8 ± 0.2 mm) on average. The baseline drift error plateaus at 0.3 ± 0.1 mm after 10 min. The gated‐delivered‐dose equivalency has a >98% gamma‐test passing rate.ConclusionA commissioning method is recommended using the 3D plate calibration, which is verified by radiation isocenter and validated with couch‐angle dependency, baseline drift, and gated‐delivered‐dose equivalency tests. This method characterizes OSI uncertainties, ensuring motion‐monitoring accuracy for SRS treatments.

Evaluation of technical performance of optical surface imaging system using conventional and novel stereotactic radiosurgery algorithms.

The Catalyst HD (C‐RAD Positioning AB, Uppsala, Sweden) optical surface imaging (OSI) system is able to manage interfractional patient positioning, intrafractional motion monitoring, and non‐contact respiratory gating without x‐ray exposure for radiation therapy. In recent years, a novel high‐precision surface registration algorithm for stereotactic radiosurgery (SRS algorithm) has been released. This study aimed to evaluate the technical performance of the OSI system using rigid phantoms, by comparing the conventional and SRS algorithms. To determine the system’s technical performance, isocenter displacements were calculated by surface image registration via the OSI system using head, thorax, and pelvis rigid phantoms. The reproducibility of positioning was evaluated by the mean value calculated by repeating the registration 10 times, without moving each phantom. The accuracy of positioning was evaluated by the mean value of the residual error, where the 10 offset values given to each phantom were subtracted from the isocenter displacement values. The stability of motion monitoring was evaluated by measuring isocenter drift during 20 min and averaging it over 10 measurements. For the head phantom, all tests were compared with the mask types and algorithms. As a result, for all sites and both algorithms, the reproducibility, accuracy, and stability for translation and rotation were <0.1 mm and <0.1°, <1.0 mm and <1.0°, and <0.1 mm and <0.1°, respectively. In particular, the SRS algorithm had a small absolute error and standard deviation of calculated isocenter displacement, and a significantly higher reproducibility and accuracy than the conventional algorithm (P < 0.01). There was no difference in the stability between the algorithms (P = 0.0280). The SRS algorithm was found to be suitable for the treatment of rigid body sites with less deformation and small area, such as the head and face.

Characterisation of Time-of-Flight (ToF) imaging system for application in monitoring deep inspiration breath-hold radiotherapy (DIBH-RT)

The purpose of this study is to develop a method for characterisation of time-of-flight (ToF) imaging system for application in deep inspiration breath-hold radiotherapy (DIBH-RT). The performance of an Argos 3D P330 ToF camera (Bluetechnix, Austria) was studied for patient surface monitoring during DIBH-RT using a phantom to simulate the intra-patient and inter-patient stability of the camera. Patient setup error was also simulated by positioning the phantom at predefined shift positions (2, 5 and 10 mm) from the isocentre. The localisation accuracy of the phantom was measured using ToF imaging system and repeated using CBCT imaging alone (CBCT) and simultaneously using ToF imaging during CBCT imaging (ToF-CBCT). The mean and SD of the setup errors obtained from each of the imaging methods were calculated. Student t-test was used to compare the mean setup errors. Correlation and Bland-Altman analysis were also performed. The intra-and inter-patient stability of the camera were within 0.31 mm and 0.74 mm, respectively. The localisation accuracy in terms of the mean ±SD of the measured setup errors were 0.34 ± 0.98 mm, 0.12 ± 0.34 mm, and −0.24 ± 1.42 mm for ToF, CBCT and ToF-CBCT imaging, respectively. A strong correlation was seen between the phantom position and the measured position using ToF (r = 0.96), CBCT (r = 0.99) as well as ToF-CBCT (r = 0.92) imaging. The limits of agreement from Bland Altman analysis between the phantom position and ToF, CBCT and ToF-CBCT measured positions were −1.52, 2.31 mm, −0.55, 0.78 mm; and −3.03, 2.55 mm, respectively. The sensor shows good stability and high accuracy comparable to similar sensors in the market. The method developed is useful for characterisation of an optical surface imaging system for application in monitoring DIBH-RT.

Accuracy of real-time respiratory motion tracking and time delay of gating radiotherapy based on optical surface imaging technique

BackgroundSurface-guided radiation therapy (SGRT) employs a non-invasive real-time optical surface imaging (OSI) technique for patient surface motion monitoring during radiotherapy. The main purpose of this study is to verify the real-time tracking accuracy of SGRT for respiratory motion and provide a fitting method to detect the time delay of gating.MethodsA respiratory motion phantom was utilized to simulate respiratory motion using 17 cosine breathing pattern curves with various periods and amplitudes. The motion tracking of the phantom was performed by the Catalyst™ system. The tracking accuracy of the system (with period and amplitude variations) was evaluated by analyzing the adjusted coefficient of determination (A_R2) and root mean square error (RMSE). Furthermore, 13 actual respiratory curves, which were categorized into regular and irregular patterns, were selected and then simulated by the phantom. The Fourier transform was applied to the respiratory curves, and tracking accuracy was compared through the quantitative analyses of curve similarity using the Pearson correlation coefficient (PCC). In addition, the time delay of amplitude-based respiratory-gating radiotherapy based on the OSI system with various beam hold times was tested using film dosimetry for the Elekta Versa-HD and Varian Edge linacs. A dose convolution-fitting method was provided to accurately measure the beam-on and beam-off time delays.ResultsA_R2 and RMSE for the cosine curves were 0.9990–0.9996 and 0.110–0.241 mm for periods ranging from 1 s to 10 s and 0.9990–0.9994 and 0.059–0.175 mm for amplitudes ranging from 3 mm to 15 mm. The PCC for the actual respiratory curves ranged from 0.9955 to 0.9994, which was not significantly affected by breathing patterns. For gating radiotherapy, the average beam-on and beam-off time delays were 1664 ± 72 and 25 ± 30 ms for Versa-HD and 303 ± 45 and 34 ± 25 ms for Edge, respectively. The time delay was relatively stable as the beam hold time increased.ConclusionsThe OSI technique provides high accuracy for respiratory motion tracking. The proposed dose convolution-fitting method can accurately measure the time delay of respiratory-gating radiotherapy. When the OSI technique is used for respiratory-gating radiotherapy, the time delay for the beam-on is considerably longer than the beam-off.

Application of Optical Laser 3D Surface imaging system (Sentinel) in breast cancer radiotherapy

It has been clearly confirmed that radiation therapy (RT) after breast conserving surgery (BCS) is an effective treatment modality comparable to mastectomy for early breast cancer. The purpose of this study was to further evaluate the accuracy of 3D surface imaging system (Sentinel) for breast cancer patients received BCS. The optical surface scans and CBCT scans were acquired before and immediately after couch movement correction. The deviation of the CBCT scans from the reference planning CT was considered an estimate for the residual errors for patient setup correction. The planning target volume (PTV) margins for treatment sessions was calculated according to the setup errors. We obtained a total of 245 sets of data collected from 49 breast cancer patients. Compared with Sentinel setup errors, the residual setup errors as determined by the CBCT scans after couch movement correction were reduced in the six directions. The PTV margins derived from the CBCT residual errors were all less than 5 mm in X, Y, and Z directions. Our results suggested that Optical surface imaging can be applied in positioning for breast cancer patient accurately without unnecessary imaging dose.

Characterizing a deformable registration algorithm for surface-guided breast radiotherapy.

Surface-guided radiation therapy (SGRT) is a nonionizing imaging approach for patient setup guidance, intra-fraction monitoring, and automated breath-hold gating of radiation treatments. SGRT employs the premise that the external patient surface correlates to the internal anatomy, to infer the treatment isocenter position at time of treatment delivery. Deformations and posture variations are known to impact the correlation between external and internal anatomy. However, the degree, magnitude, and algorithm dependence of this impact are not intuitive and currently no methods exist to assess this relationship. The primary aim of this work was to develop a framework to investigate and understand how a commercial optical surface imaging system (C-RAD, Uppsala, Sweden), which uses a nonrigid registration algorithm, handles rotations and surface deformations. A workflow consisting of a female torso phantom and software-introduced transformations to the corresponding digital reference surface was developed. To benchmark and validate the approach, known rigid translations and rotations were first applied. Relevant breast radiotherapy deformations related to breast size, hunching/arching back, distended/deflated abdomen, and an irregular surface to mimic a cover sheet over the lower part of the torso were investigated. The difference between rigid and deformed surfaces was evaluated as a function of isocenter location. For all introduced rigid body transformations, C-RAD computed isocenter shifts were determined within 1mm and 1˚. Additional translational shifts to correct for rotations as a function of isocenter location were determined with the same accuracy. For yaw setup errors, the difference in shift corrections between a plan with an isocenter placed in the center of the breast (BrstIso) and one located 12cm superiorly (SCFIso) was 2.3mm/1˚ in lateral direction. Pitch setup errors resulted in a difference of 2.1mm/1˚ in vertical direction. For some of the deformation scenarios, much larger differences up to 16mm and 7˚ in the calculated shifts between BrstIso and SCFIso were observed that could lead to large unintended gaps or overlap between adjacent matched fields if uncorrected. The methodology developed lends itself well for quality assurance (QA) of SGRT systems. The deformable C-RAD algorithm determined accurate shifts for rigid transformations, and this was independent of isocenter location. For surface deformations, the position of the isocenter had considerable impact on the registration result. It is recommended to avoid off-axis isocenters during treatment planning to optimally utilize the capabilities of the deformable image registration algorithm, especially when multiple isocenters are used with fields that share a field edge.

A novel approach to Verify air gap and SSD for proton radiotherapy using surface imaging

PurposeTo develop a novel approach to accurately verify patient set up in proton radiotherapy, especially for the verification of the nozzle – body surface air gap and source-to-skin distance (SSD), the consistency and accuracy of which is extremely important in proton treatment.MethodsPatient body surfaces can be captured and monitored with the optical surface imaging system during radiation treatment for improved intrafraction accuracy. An in-house software package was developed to reconstruct the patient body surface in the treatment position from the optical surface imaging reference capture and to calculate the corresponding nozzle – body surface air gap and SSD. To validate this method, a mannequin was scanned on a CT simulator and proton plans were generated for a Mevion S250 Proton machine with 20 gantry/couch angle combinations, as well as two different snout sizes, in the Varian Eclipse Treatment Planning Systems (TPS). The surface generated in the TPS from the CT scan was imported into the optical imaging system as an RT Structure for the purpose of validating and establishing a benchmark for ground truth comparison. The optical imaging surface reference capture was acquired at the treatment setup position after orthogonal kV imaging to confirm the positioning. The air gaps and SSDs calculated with the developed method from the surface captured at the treatment setup position (VRT surface) and the CT based surface imported from the TPS were compared to those calculated in TPS. The same approach was also applied to 14 clinical treatment fields for 10 patients to further validate the methodology.ResultsThe air gaps and SSDs calculated from our program agreed well with the corresponding values derived from the TPS. For the phantom results, using the CT surface, the absolute differences in the air gap were 0.45 mm ± 0.33 mm for the small snout, and 0.51 mm ± 0.49 mm for the large snout, and the absolute differences in SSD were 0.68 mm ± 0.42 mm regardless of snout size. Using the VRT surface, the absolute differences in air gap were 1.17 mm ± 1.17 mm and 2.1 mm ± 3.09 mm for the small and large snouts, respectively, and the absolute differences in SSD were 0.81 mm ± 0.45 mm. Similarly, for patient data, using the CT surface, the absolute differences in air gap were 0.42 mm ± 0.49 mm, and the absolute differences in SSD were 1.92 mm ± 1.4 mm. Using the VRT surface, the absolute differences in the air gap were 2.35 mm ± 2.3 mm, and the absolute differences in SSD were 2.7 mm ± 2.17 mm.ConclusionThese results showed the feasibility and robustness of using an optical surface imaging approach to conveniently determine the air gap and SSD in proton treatment, providing an accurate and efficient way to confirm the target depth at treatment.

Clinical application of Catalyst system in cervical cancer radiotherapy

Objective To evaluate the clinical application of Catalyst system in positioning patients during cervical cancer radiotherapy, and to analyze its correlation with the bladder volume and body mass index (BMI) of patients. Methods A total of 33 patients diagnosed with cervical cancer from July to December 2017 in our hospital were included in the study. All patients were auxiliary positioned by an optical surface imaging system (C-Rad Catalyst) before each treatment. The CBCT imaging was executed twice a week. The setup errors from Catalyst and CBCT in the anterior-posterior (AP), superior-inferior (SI) and left-right (LR) directions were recorded. Each patient′s bladder volume and BMI were also recorded. Results The setup errors between Catalyst with masks and CBCT had the significant difference in SI (P 300 ml, the setup errors for Catalyst with masks had the significant association in AP (R=-0.493, P<0.05), and that without masks had the significant association in SI and LR (R=0.335, P<0.05, R=-0.348, P<0.05). For patients of<25 kg/m2, setup errors for Catalyst with masks had the significant association with the BMI in LR (R=0.197, P<0.05); for ≥25 kg/m2, that with masks had the significant association in AP and SI (R=0.818, P<0.05; R=-0.498, P<0.05), that without masks had the significant association in AP and LR (R=0.652, P<0.05; R=-0.558, P<0.05). Conclusion Unlike CBCT system, the patient positioning by Catalyst system was easily affected by the bladder volume and BMI of patients. Key words: Cervical neoplasms/radiotherapy; Cone beam-CT; C-Rad Catalyst; Setup error

A Practical Algorithm to Improve Tracking Accuracy of Symmetric Body Surface Using Optical Surface Imaging System

The human body surface has a property of right-left symmetry. Some anatomical sites, such as breasts, legs, and arms, also possess rotational symmetry. This geometric symmetry constitutes a difficult technical barrier for 3D scanner-based optical surface imaging systems. Such systems only measure the distance between the interrogation light source and points of interest on the body surface. Because of this, these systems are unable to differentiate those points on the body surface that move along the symmetry direction or rotate about the symmetry axis simultaneously. This technical limitation hinders their applications on symmetric body surfaces. To overcome this technical barrier, we have developed an algorithm which can calculate a surface-specific region of interest (ROI) for accurate surface tracking. Our algorithm consists of 6 steps: 1) remove background noise; 2) create a seed ROI; 3) add a maximal margin to the seed ROI; 4) rectify ROI overexpansion; 5) eliminate flat topography; and 6) maximize asymmetry and height differences of ROI. Briefly, the algorithm starts by cutting off irrelevant surfaces, including floor, couch, head, lower body, and immobilization devices. A square seed ROI is computed and centered on isocenter, assigned an initial size of 80x80 mm in x and y-axis. The algorithm searches for the maximal and minimal height (z-axis) within it. Thereafter, a 200 mm growth margin is added to the seed ROI. The algorithm compares z-values of two neighboring points in the new ROI. If they are significantly different, then there is a change in topographic feature. ROI grows and repeats the same operation along this direction. The algorithm stops if z-values are too close. The algorithm may expand into body lateral side. To avoid it, a z-value thresholding technique is used so that points with a height lower than the set threshold are eliminated. Two additional thresholding techniques are employed to eliminate a surface with very flat topography. Finally, a symmetry break-up loop is used to maximize the asymmetry and height standard deviation of the ROI. To speed up algorithm performance and circumvent unexpected noise features (such as mask and sheet), the idea of contour line is used in the algorithm. With the ROIs generated by our algorithm, it was found that our optimized asymmetric ROIs were more effective and accurate in detecting shifts by symmetric body surfaces than using symmetric ROIs. It is particularly effective and sensitive in detecting rotational shifts by body surfaces with a rotational symmetry. For optical surface imaging systems, poorly defined large ROIs may produce stable, but often wrong tracking results. This problem is particularly pronounced for symmetric surfaces, such as the breast surface. Our novel concept of optimized asymmetric ROI with a limited size is extremely valuable for real-time patient local tracking applications.

Real-time intra-fraction motion management in breast cancer radiotherapy: analysis of 2028 treatment sessions

BackgroundIntra-fraction motion represents a crucial issue in the era of precise radiotherapy in several settings, including breast irradiation. To date, only few data exist on real-time measured intra-fraction motion in breast cancer patients. Continuous surface imaging using visible light offers the capability to monitor patient movements in three-dimensional space without any additional radiation exposure. The aim of the present study was to quantify the uncertainties of possible intra-fractional motion during breast radiotherapy.Material and methodsOne hundred and four consecutive patients that underwent postoperative radiotherapy following breast conserving surgery or mastectomy were prospectively evaluated during 2028 treatment sessions. During each treatment session the patients’ motion was continuously measured using the Catalyst™ optical surface scanner (C-RAD AB, Sweden) and compared to a reference scan acquired at the beginning of each session. The Catalyst system works through an optical surface imaging with light emitting diode (LED) light and reprojection captured by a charge coupled device (CCD) camera, which provide target position control during treatment delivery with a motion detection accuracy of 0.5 mm. For 3D surface reconstruction, the system uses a non-rigid body algorithm to calculate the distance between the surface and the isocentre and using the principle of optical triangulation. Three-dimensional deviations and relative position differences during the whole treatment fraction were calculated by the system and analyzed statistically.ResultsOverall, the maximum magnitude of the deviation vector showed a mean change of 1.93 mm ± 1.14 mm (standard deviation [SD]) (95%-confidence interval: [0.48–4.65] mm) and a median change of 1.63 mm during dose application (beam-on time only). Along the lateral and longitudinal axis changes were quite similar (0.18 mm ± 1.06 mm vs. 0.17 mm ± 1.32 mm), on the vertical axis the mean change was 0.68 mm ± 1.53 mm. The mean treatment session time was 154 ± 53 (SD) seconds and the mean beam-on time only was 55 ± 16 s. According to Friedman’s test differences in the distributions of the three possible directions (lateral, longitudinal and vertical) were significant (p < 0.01), in post-hoc analysis there were no similarities between any two of the three directions.ConclusionThe optical surface imaging system is an accurate and easy tool for real-time motion management in breast cancer radiotherapy. Intra-fraction motion was reported within five millimeters in all directions. Thus, intra-fraction motion in our series of 2028 treatment sessions seems to be of minor clinical relevance in postoperative radiotherapy of breast cancer.

Setup errors and effectiveness of Optical Laser 3D Surface imaging system (Sentinel) in postoperative radiotherapy of breast cancer

Breast-conserving surgery (BCS) plus postoperative radiotherapy has become the standard treatment for early-stage breast cancer. The aim of this study was to compare the setup accuracy of optical surface imaging by the Sentinel system with cone-beam computerized tomography (CBCT) imaging currently used in our clinic for patients received BCS. Two optical surface scans were acquired before and immediately after couch movement correction. The correlation between the setup errors as determined by the initial optical surface scan and CBCT was analyzed. The deviation of the second optical surface scan from the reference planning CT was considered an estimate for the residual errors for the new method for patient setup correction. The consequences in terms for necessary planning target volume (PTV) margins for treatment sessions without setup correction applied. We analyzed 145 scans in 27 patients treated for early stage breast cancer. The setup errors of skin marker based patient alignment by optical surface scan and CBCT were correlated, and the residual setup errors as determined by the optical surface scan after couch movement correction were reduced. Optical surface imaging provides a convenient method for improving the setup accuracy for breast cancer patient without unnecessary imaging dose.

Catalyst system in patient positioning during breast cancer radiotherapy: clinical application and influencing factors

Objective To evaluate the clinical application of Catalyst system in patient positioning during breast cancer radiotherapy, and to analyze its correlation with age and body mass index (BMI). Methods Twenty-four patients with breast cancer who were admitted to our hospital from May to August, 2016 were enrolled as subjects. For all patients, auxiliary positioning was made by the optical surface imaging system (C-Rad Catalyst) before each treatment. The kV-kV imaging was executed weekly to verify positioning. Age, BMI, and setup errors of the two systems in the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) directions were recorded and analyzed by independent samples t-test and Pearson correlation analysis. Results The C-Rad Catalyst system had a significantly larger setup error in the AP direction than the kV-kV imaging (0.22±0.17 vs. 0.18±0.13 cm, P 0.05; 0.28±0.28 vs. 0.20±0.15 cm, P>0.05). Age and BMI of patients had significant impacts on the C-Rad Catalyst system but the kV-kV imaging (P>0.05): there were significant differences in setup errors in the AP and SI directions between patients ≤44 years of age and those 45-59 years of age (all P<0.05); there were significant differences in setup errors in the AP and LR directions between patients ≤44 years of age and those ≥60 years of age (all P<0.05); there was a significant difference in setup error in the LR direction between patients 45-59 years of age and those ≥60 years of age (P<0.05); there was a significant difference in setup error in the SI direction between patients with BMIs of<25 and ≥25 kg/m2(P<0.05). For patients ≥60 years of age, setup error of the C-Rad Catalyst system in the SI direction was correlated with age (r=-0.496, P<0.05). For patients with BMI of<25 kg/m2, setup error of the C-Rad Catalyst system in the AP direction was correlated with BMI (r=-0.445, P<0.05). For patients with a BMI of ≥25 kg/m2, setup error of the C-Rad Catalyst system in the SI direction was correlated with BMI (r=-0.252, P<0.05). Conclusions There is significant difference in setup error in the AP direction between the C-Rad Catalyst system and the kV-kV imaging. Age and BMI have impacts on patient positioning by the C-Rad Catalyst system. Key words: Breast neoplasms/radiotherapy; Radiotherapy planning, computer-assisted; C-Rad Catalyst; Setup error

Analysis of utility of optical surface imaging system for patients who received radiotherapy with active breath control

Objective To analyze the precision and stability of optical surface imaging system for patients who received radiotherapy with active breath control. Methods Eighteen radiotherapy patients with lung metastasis were managed by active breath control (ABC). The difference error detected by optical surface imaging system and CBCT were defined as the precision of optical surface imaging system. The variation among the error of optical surface imaging positioning the value of correction of treatment position and the error detected by optical surface imaging again were defined as the stability of optical surface imaging system. Intrafractional errors were analyzed by optical surface imaging system through whole treatment process (including breath hold and free breath). Results The optical surface imaging system had precision (systematic (Σ) and random errors (σ)) of 1.78/3.42 mm 2.54/6.57 mm and 2.79/3.22 mm respectively and stability of2.12/2.54 mm 3.09/4.02 mm and 1.37/3.55 mm respectively in lateral-medial superior-inferior and anterior-posterior directions. The intrafractional errors (Σ and σ) were 0.42/0.85 mm 0.41/1.47 mm and 0.41/1.47 mm respectively for breath hold duration and 4.76/4.16 mm 6.54/7.78 mm and 3.13/5.92 mm for free breath duration in lateral-medial superior-inferior and anterior-posterior directions. Conclusions As an effective method for validate breath hold; Optical surface imaging system can improve the precision and safety of active breath control. However, the factors that affect the accuracy and stability of the optical surface imaging system in patients undergoing radiotherapy with ABC are not clear; it cannot replace the CBCT for positioning verification. Key words: Tomography, X-ray computed, three-dimensional; Active breath control; Systematic error; Setting error

SU‐F‐J‐21: Clinical Evaluation of Surface Scanning Systems in Different Treatment Locations

Purpose:To reduce imaging dose in fractionated IGRT, the ability of optical surface imaging systems (OSIS) to detect setup errors was tested. Therefore, clinical studies to evaluate for different treatment locations setup corrections derived by OSIS in comparison with x‐ray image guidance in fractionated radiation therapy was performed.Methods:The setup correction accuracy of an OSIS system (AlignRT, VisionRT, London, UK) will be analysed for the 4 tumour locations Pelvis, Upper Abdomen, Thorax and Breast, 20 patients for each location in comparison to a different system (Sentinel, C‐RAD, SE). For each patient, the setup corrections of the cone‐beam computed tomography (CBCT) of an Elekta Versa HD linear accelerator (Elekta, Crawley, UK) is considered as gold‐standard and then compared with those of the OSIS for the first ten fractions retrospectively. There were no clinical decisions made based on the surrogate system. For the OSIS, the reference surface is highly important as it represents the actual ground truth. It can be obtained either with the system itself or the surface structure delineated in the planning CT can be imported via DICOM interface. In this paper, the first results for the treatment region thorax are presented. The reference image modalities were compared.Results:Table 1 displays the difference between the setup corrections obtained with OSIS and CBCT in lateral (LAT), longitudinal (LNG) and vertical (VRT) direction for the DICOM reference image. While the median deviations are within a few millimeters, some outliers showed large deviations. Generally, the mean deviation as well as the spread was smallest in lateral and largest in vertical direction.Conclusion:Although the system allows fast, simple and non‐invasive determination of setup corrections, it should be evaluated treatment region dependant. Therefore, the study is ongoing. The application of OSIS may help to reduce the imaging dose for the patient.We gratefully acknowledge the support by our colleagues from the Radiological University Clinic Heidelberg, where the study was performed. This work was funded by the Federal Ministry of Education and Research (BMBF) Germany, grant number 01IB13001B.

Characteristics of gated treatment using an optical surface imaging and gating system on an Elekta linac.

BackgroundKnowing the technical characteristics of gated radiotherapy equipment is crucial for ensuring precise and accurate treatment when using techniques such as Deep-Inspiration Breath-Hold and gating under free breathing. With one of the first installations of the novel surface imaging system Catalyst™ (C-RAD AB, Sweden) in connection with an Elekta Synergy linear accelerator (Elekta AB, Sweden) via the Elekta Response Interface, characteristics like dose delivery accuracy and time delay were investigated prior to clinical implementation of gated treatments in our institution.MethodsIn this study a moving phantom was used to simulate respiratory motion which was registered by the Catalyst™ system. The gating level was set manually. Within this gating window a trigger signal is automatically sent to the linac initiating treatment delivery. Dose measurements of gated linac treatment beams with different gating levels were recorded with a static 2D-Diode Array (MapCheck2, Sun Nuclear Co., USA) and compared to ungated reference measurements for different field sizes. In addition, the time delay of gated treatment beams was measured using radiographic film.ResultsThe difference in dose delivery between gated and ungated treatment decreases with the size of the chosen gating level. For clinically relevant gating levels of about 30%, the differences in dose delivery accuracy remain below 1%. In comparison with other system configurations in literature, the beam-on time delay shows a large deviation of 851 ms ± 100 ms.ConclusionsWhen performing gated treatment, especially for free-breathing gating, factors as time delay and dose delivery have to be evaluated regularly in terms of a quality assurance process. Once these parameters are known they can be accounted and compensated for, e.g. by adjusting the pre-selected gating level or the internal target volume margins and by using prediction algorithms for breathing curves. The usage of prediction algorithms becomes inevitable with the high beam-on time delay which is reported here.

Reliability and reproducibility of landmarks on three-dimensional soft-tissue cephalometrics using different placement methods.

Affixing markers on the face in vivo with an optical surface imaging system and placing landmarks on a computed tomographic reconstructive facial model represent two helpful approaches prevailing in three-dimensional cephalometric analysis of facial aesthetics. In this study, the authors determine the suitability of these methods for soft-tissue evaluation along with the reproducibility and reliability of landmark placement. Thirty-seven soft-tissue landmarks were investigated in 35 normal healthy volunteers who underwent cephalometric analysis by direct and indirect placement methods. Two operators performed the analysis twice for each method at a 1-week interval. Landmark positions were measured on the three-dimensional coordinates, and data were standardized and converted into landmark placement errors for the estimation, by two-way random intraclass correlation coefficients. Using the direct method, 86.5 percent of the landmarks had a higher intraclass correlation coefficient than 0.75, and 67.6 percent were higher than 0.90. The authors found that 75.7 percent were higher than 0.75 and 43.2 percent were higher than 0.90 with the indirect method. Both methods showed good reliability in identifying midline-related structures, although the correlations of markers surrounding eyelashes and lips were better using the direct method. The direct method had a significantly smaller landmark placement error and better reproducibility than that identified indirectly (p<0.05). When evaluating well-defined contours and the natural texture of the face, the direct placement method shows better accuracy than the indirect method. The three-dimensional evaluation emphasizes the eye, lip, and some structures more laterally, therefore providing comprehensive analysis for clinical diagnosis. Diagnostic, II.