3D Surface Imaging System Research Articles

Visual Coaching Based on 3D Surface Imaging for Improvement of the Reproducibility and Stability of Deep-inspiration Breath Hold for Radiation Therapy of Left-breast Cancer Patients

Visual Coaching Based on 3D Surface Imaging for Improvement of the Reproducibility and Stability of Deep-inspiration Breath Hold for Radiation Therapy of Left-breast Cancer Patients

SU‐GG‐J‐107: Improvement of the Stability and Reproducibility of Deep‐Inspiration Breath Hold for Left Breast Irradiation Using Video‐Based Visual Coaching and 3D Surface Imaging

Purpose: To assess and quantify the improvement in stability and reproducibility of Deep‐Inspiration Breath Hold (DIBH) for left breast irradiation when using video‐based visual coaching and 3D surface imaging. Method and Materials: Ten volunteers were asked to perform a series of four 20‐second DIBHs without coaching followed by a series of 4 DIBH with visual coaching. A 3D surface imaging system (Vision RT Ltd, London) was used to track the motion of the breast surface. Visual coaching was performed with the aid of video goggles which displayed the surface‐based respiratory signal tracked by the surface imaging system. During the non‐coached DIBHs a window level was identified for each volunteer at their DIBH level. When coached, the volunteers were asked to maintain their DIBH respiratory signal within the window level identified before. Reproducibility and stability of DIBH were measured for each volunteer. Reproducibility is defined as the standard deviation of the different DIBH levels. Stability is measured as the average standard deviation of the breathing signals within each individual DIBH. Results: With visual coaching all the volunteers improved reproducibility of the DIBH with respect to un‐coached DIBH, and 9 of the volunteers improved stability of the DIBH. The volunteer that did not improve stability had a very stable DIBH even without coaching. On average, reproducibility improved from ±1.6mm to ±0.3mm, while stability improved from ±1.3mm to ±0.6mm. Conclusion: This work indicates that gated radiotherapy of the left‐breast cancer will benefit from visual coaching of the patient. Visual coaching greatly improves reproducibility and stability of the DIBH, both properties that need to be guaranteed for an accurate and efficient treatment. A future study will be performed for left‐breast cancer patients. Conflict of Interests: Research sponsored by Vision RT Ltd.

Accuracy of a commercial optical 3D surface imaging system for realignment of patients for radiotherapy of the thorax

Accurate and reproducible patient setup is a prerequisite to fractionated radiotherapy. To evaluate the applicability and technical performance of a commercial 3D surface imaging system for repositioning of breast cancer patients, measurements were performed in a rigid anthropomorphic phantom as well as in healthy volunteers. The camera system records a respiration-gated surface model of the imaged object, which may be registered to a previously recorded reference model. A transformation is provided, which may be applied to the treatment couch to correct the setup of the patient. The system showed a high stability and detected pre-defined shifts of phantoms and healthy volunteers with an accuracy of 0.40 ± 0.26 mm and 1.02 ± 0.51 mm, respectively (spatial deviation between pre-defined shift and suggested correction). The accuracy of the suggested rotational correction around the vertical axis was always better than 0.3° in phantom measurements and 0.8° in volunteers, respectively. Comparison of the suggested setup correction with that detected by a second and independently operated marker-based optical system provided consistent results. The results demonstrate that the camera system provides highly accurate setup corrections in a phantom and healthy volunteers. The most efficient use of the system for improving the setup accuracy in breast cancer patients has to be investigated in routine patient treatments.

Anthropometric Precision and Accuracy of Digital Three-Dimensional Photogrammetry

A variety of commercially available three-dimensional (3D) surface imaging systems are currently in use by craniofacial specialists. Little is known, however, about how measurement data generated from alternative 3D systems compare, specifically in terms of accuracy and precision. The purpose of this study was to compare anthropometric measurements obtained by way of two different digital 3D photogrammetry systems (Genex and 3dMD) as well as direct anthropometry and to evaluate intraobserver precision across these three methods. On a sample of 18 mannequin heads, 12 linear distances were measured twice by each method. A two-factor repeated measures analysis of variance was used to test simultaneously for mean differences in precision across methods. Additional descriptive statistics (e.g., technical error of measurement [TEM]) were used to quantify measurement error magnitude. Statistically significant (P < 0.05) mean differences were observed across methods for nine anthropometric variables; however, the magnitude of these differences was consistently at the submillimeter level. No significant differences were noted for precision. Moreover, the magnitude of imprecision was determined to be very small, with TEM scores well under 1 mm, and intraclass correlation coefficients ranging from 0.98 to 1. Results indicate that overall mean differences across these three methods were small enough to be of little practical importance. In terms of intraobserver precision, all methods fared equally well. This study is the first attempt to simultaneously compare 3D surface imaging systems directly with one another and with traditional anthropometry. Results suggest that craniofacial surface data obtained by way of alternative 3D photogrammetric systems can be combined or compared statistically.

A phantom evaluation of a stereo‐vision surface imaging system for radiotherapy patient setup

External beam irradiation requires precise positioning of the target relative to the treatment planning coordinate system. A three-dimensional (3D) surface imaging system for patient positioning has recently been installed in one of our linear accelerator (linac) rooms. The device utilizes close-range photogrammetry to generate a 3D model of the patient's surface. This geometric model can be made to look like a digital camera image if wrapped with a gray-level image (texture mapping) that shows surface coloration. The system is calibrated to the linac coordinate system and has been designed as a patient setup device. To reproduce patient position in fractionated radiotherapy, the daily patient surface model is registered to a previously recorded reference surface. Using surface registration, the system calculates the rigid-body transformation that minimizes the distance between the treatment and the reference surface models in a region-of-interest (ROI). This transformation is expressed as a set of new couch coordinates at which the patient position best matches with the reference data. If respiratory motion is a concern, the surface can be obtained with a gated acquisition at a specified phase of the respiratory cycle. To analyze the accuracy of the system, we performed several experiments with phantoms to assess stability, alignment accuracy, precision of the gating function, and surface topology. The reproducibility of surface measurements was tested for periods up to 57 h. Each recorded frame was registered to the reference surface to calculate the required couch adjustment. The system stability over this time period was better than 0.5 mm. To measure the accuracy of the system to detect and quantify patient shift relative to a reference image, we compared the shift detected by the surface imaging system with known couch transitions in a phantom study. The maximum standard deviation was 0.75 mm for the three translational degrees of freedom, and less than 0.1 degrees for each rotation. Surface model precision was tested against computed tomography (CT)-derived surface topology. The root-mean-square rms of the distance between the surfaces was 0.65 mm, excluding regions where beam hardening caused artifacts in the CT data. Measurements were made to test the gated acquisition mode. The time-dependent amplitude was measured with the surface imaging system and an established respiratory gating system based on infrared (IR)-marker detection. The measured motion trajectories from both systems were compared to the known trajectory of the stage. The standard deviations of the amplitude differences to the motor trajectory were 0.04 and 0.15 mm for the IR-marker system and the 3D surface imaging system, respectively. A limitation of the surface-imaging device is the frame rate of 6.5 Hz, because rapid changes of the motion trajectory cannot be detected. In conclusion, the system is accurate and sufficiently stable to be used in the clinic. The errors computed when comparing the surface model with CT geometry were submillimeter, and deviations in the alignment and gating-signal tests were of the same magnitude.

Real time 3D surface imaging for the analysis of respiratory motion during radiotherapy

With the introduction of advanced treatments such as CRT and IMRT, the effects of respiratory motion are now becoming increasingly significant during both the planning and delivery of radiotherapy. The purpose of this study is to record movements resulting from respiration using real-time 3D surface imaging to determine metrics with which the motion can be quantified, and to thus measure the extent to which breathing varies both according to anatomical site and from patient to patient. AlignRT, a video based real-time 3D surface imaging system, was used to record 3D sequences of surface data of the torso region over 8–15 second periods at 3 frames/second. 3D surface data was acquired from 14 patients in the intended treatment position during CT simulation. In order to analyse the data, software tools were developed to extract transverse contours through the thorax, abdomen and pelvis, for all recorded frames for each patient. For each contour, 3 points were monitored (mid-line and 6–7.5cm LtsRt of mid-line). The Y coordinates (AP) of these points were measured. These values were plotted against time along both transverse and sagittal contours. Amplitudes, periods and phase shifts were compared across the contours and from patient to patient. Table 1(table 1) shows the results from the various patients imaged. Thoracic and abdominal contours were visible on seven patients, abdominal and pelvic contours were visible on five patients and all three contours were visible on two patients. On every patient the plots clearly showed respiratory motion. There was no measurable phase shift between the various contours monitored and the period of respiratory cycle for all patients ranged from 3s to 7s (mean 4.2s, SD 1.2s). With some of the pelvic contours, AlignRT was able to detect sub-millimetre movements of equivalent period and phase as significantly larger movements measured along abdominal and thoracic contours. With the exception of one instance where the thoracic contour moved more than the abdominal, the measured abdominal movements were larger than their thoracic counterparts. As expected, the amplitudes of the pelvic movements were consistently smaller than those across the other contours. The above results demonstrate that respiratory motion can be effectively monitored using real time 3D surface imaging and that there is significant variation in the extent of motion both according to anatomical location and from patient to patient.

Application of 3d digital surface imaging for patient positioning

Purpose/Objective: Accurate patient positioning is an important aspect of treatment especially for conformal treatments such as IMRT, which has high gradients and smaller margins. Studies have identified target positional errors of up to 5mm for even well immobilized patients using standard techniques. These errors may reduce the dose delivered to the target volume in the range of 7 to 15%, which can significantly reduce the probability of tumour control. The purpose of the study is to prove that improved accuracy and efficiency in patient positioning can be achieved by monitoring the external 3D patient surface and correcting the patient set-up using the 3D surface displacement information. This will provide improvements over iterative conventional set-up methodologies. The superior resolution of the system should enable more accurate set-up than the existing techniques. Materials/Methods: This technique uses a photogrammetry based 3D Digital Surface Imaging system to improve accuracy and efficiency in patient set-up. The Digital Surface Imaging system consists of two stereoscopic video cameras, a LCD projector, and image acquisition and registration software. The cameras and the projector are mounted on a stand, which allows rotation and translation with 5 degrees of freedom. Well-defined dot patterns are projected onto a surface and the cameras simultaneously acquire sequences of 2D digital images. Using triangulation between the 2 stereoscopic images and the projected dots a 3D digital surface image is constructed. An initial reference 3D surface-image or a CT surface-image is fused with subsequent surface images and the displacement between the two image sets is measured in terms of translation and rotation. The displacement information can be used to re-position a patient in the planned reference position. In the Phantom study the phantom is deliberately translated and rotated to a known position and the Digital Surface Imaging system is used to predict the translated and rotated positions. The results are compared to evaluate the system accuracy. Similar measurements were performed on volunteers. The system was characterized in terms of its resolution, effect of ambient light and the distance of the object from the camera. Results: In the 3D Digital Surface Imaging system the resolution is characterized by using a step-wedge with steps of 2mm height. The height of the steps is reproduced to within 0.3mm for a camera-to-object distance of 1m. To test the system’s registration accuracy known translations and rotations of a phantom head are compared to the displacements measured by the system. The deviation from the known x- and z-translations is 0.2mm at 3σ in the interval -3.5 to 3.5cm, and for all rotational directions a 0.2° deviation at 3σ is observed for a known rotation in the interval -5 to 5°. The clinical use of the system is currently tested on volunteers wearing a non-invasive head frame and positioned on a GE CT-sim couch. A set of markers on the face of the volunteer is used to measure the repositioning accuracy by reading the laser co-ordinates at the laser-marker intersection. The resulting displacement due to repositioning as well as deliberate displacement is compared to the registered displacement from the 3D Digital Surface Imaging system. Preliminary results agree well within 1mm. Conclusions: We have demonstrated that a 3D Digital Surface Imaging system can accurately calculate the rotation and translation to within 1mm and 1° accuracy. The data obtained with volunteers indicate that this system is capable of reproducing the patient set-up to within 1mm.