Breast cancer is one of the most common malignant tumors in women [
With the development of new radiotherapy techniques such as intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and tomotherapy (TOMO), studies have focused on reducing positioning errors in order to improve dose accuracy [
Recently, optical surface imaging has been explored for verifying the patient’s pretreatment position and controlling for patient movement during the treatment, achieving agreement of about 1 mm [
Therefore, the aim of this study is to analyze 200 patient setups in 20 patients with breast cancer by analyzing the reliability and accuracy of OSMS compared with cone-beam CT (CBCT). In the present study, the Catalyst system was used for patient positioning. This system uses three high-power LEDs to project light with wavelengths of 405 (blue), 528 (green), and 624 nm (red) onto the object. The blue component is the measuring light for scanning the object and is detected by a monochrome CCD camera, with an acquisition speed of 202 frames per second. The green and red lights project surface mismatches (actual versus reference scan) onto the area where the mismatch is detected to aid patient positioning. Two custom settings embedded in the Catalyst software, namely, the gain and integration time (IT), can influence scan quality. The gain is the quantity of captured electrons required on a pixel of the CCD camera to convert light into electronic charge and hence a digital readout. IT defines the time of light absorption. The maximum scan volume is 80 cm width, 130 cm length, and 70 cm height. An individual region of interest related to the paradigm can also be defined.
This was a prospective study of 20 patients with breast cancer aged 36–57 years (median, 45 years), who were prescribed to receive radiotherapy at the Department of Radiation Oncology of the Yantai Yuhuangding Hospital between January 2015 and July 2016. The inclusion criteria were (1) breast cancer; (2) being prescribed adjuvant whole breast irradiation (WBI); and (3) receiving 4–8 cycles of chemotherapy before radiotherapy.
Fourteen patients received radiotherapy on the left side and six on the right side. Ten patients had received breast-conserving surgery (all had estrogen receptor-positive tumors and were pT1N0) and 10 had received radical surgery (all had T3-4N0-3 or TxN2-3 disease).
The study was approved by the ethics committee of the Yantai Yuhuangding Hospital. Written informed consent was obtained from each patient.
A Trilogy medical linear accelerator (Varian, Trilogy, CA, US) is used at our center. The Eclipse system (Varian, Palo Alto, CA, USA) was selected as the treatment planning system. Optical surface scanner with reprojection capabilities (C-RAD Catalyst, Uppsala, Sweden) was used in this study (Figure
The Catalyst Optical Surface Management System.
Patients were placed in an immobilization cradle (WingSTEP™, Elekta Ltd., UK) in the supine position and instructed to breathe normally. All patients received routine training before scanning, and calm breath was needed during the scanning. The patient was positioned with their two arms uplifted, elbows placed on the bracket, and the two hands holding rods. Body films were generally not used for immobilization. Three cross-shaped markers were placed on the body surface and they were positioned according to the surface markers.
An averaged CT (Discovery RT590, GE Healthcare, Waukesha, WI, USA) was performed (reconstructed slice thickness of 5 mm and pitch of 0.15) to account for breathing motions. CT images were obtained from the mandible to 5 cm below the diaphragm, covering the entire chest wall. The CT images were transmitted to the radiotherapy planning system (TPS). Based on the CT information, an automatically generated body outline (larger than −400 Hounsfield units, HU) was contoured in 3D with a point density of the triangulated mesh of about two vertices/cm2. This was then used as the CT reference image.
Treatment plans for all 20 patients were concluded with the use of the Eclipse 11.0 software (Varian, Palo Alto, CA, US). Planning target volumes (PTVs) were contoured by the treating physicians (volumes of 524–1425 cc, mean of 864 cc). The contours of the skin, lungs, and bones were sketched automatically by the system. Radiotherapy was performed with 6-MV X-ray using two tangent conformal fields (70–80% of total prescription) and two ARC fields (20–30% of total prescription). The two arcs were in an angle of
The patients were positioned according to the markings on the patients’ body surface and were further verified using a CBCT scan prior to the first treatment. Bony structures from the planning CT were used as a reference for the CBCT method. After matching the registration CT reference image (CTref), the displacement was acquired (Figure
The cone-beam computed tomography (CBCT) registration of the treatment areas. The table below the image shows the displacement after the CBCT registration.
Illustration of collecting the body surface information of the patients using the Optical Surface Management System.
The calculation of the setup errors by the OSMS registration.
Study flowchart.
Continuous data were presented as mean ± standard deviation and analyzed using the paired
For the 200 setups, the interfractional displacements on the LAT, LONG, and VERT directions for OSMS versus CBCT were
Interfractional displacements of the 200 setups in 20 patients with breast cancer.
Parameter | LAT (cm) | LONG (cm) | VERT (cm) | Time (s) | ||||
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OSMS | CBCT | OSMS | CBCT | OSMS | CBCT | OSMS | CBCT | |
Mean | 0.049 | 0.041 | 0.018 | 0.040 | 0.062 | 0.065 | 66.810 | 308.040 |
Standard deviation | 0.254 | 0.244 | 0.261 | 0.242 | 0.254 | 0.240 | 17.732 | 10.283 |
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0.330 | −1.029 | −0.126 | −215.262 | ||||
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0.742 | 0.305 | 0.900 | 0.000 |
(a) Interfractional displacement (cm) of 200 setups in 20 breast cancer patients in the LAT direction using the OSMS and CBCT scan. The horizontal axis represents the 200 sets of data from the 20 breast cancer patients on the LAT direction, and the vertical axis represents the interfractional displacement between the OSMS and CBCT scan. The blue line shows the displacement of the OSMS scan; the red line indicates the displacement of the CBCT scan. (b) Interfractional displacement (cm) of 200 setups in 20 breast cancer patients in the LONG direction using OSMS and CBCT scan. The horizontal axis represents the 200 sets of data from the 20 breast cancer patients on the LONG direction, and the vertical axis represents the interfractional displacement between the OSMS and CBCT scan. The blue line shows the displacement of the OSMS scan; the red line indicates the displacement of the CBCT scan. (c) Interfractional displacement (cm) of 200 setups in 20 breast cancer patients in the VERT direction using OSMS and CBCT scan. The horizontal axis represents the 200 sets of data from the 20 breast cancer patients on the VERT direction, and the vertical axis represents the interfractional displacement between the OSMS and CBCT scan. The blue line indicates the displacement of the OSMS scan; the red line shows the displacement of the CBCT scan.
Analysis of Bland-Altman consistency in the three axes. The graphs show the mean value of 10 setups for each of the 20 patients; that is, a total of 200 setups are considered.
Table
Comparison of overall positioning errors in 20 breast cancer patients using OSMS and CBCT scan.
Patient number | (1) | (2) | (3) | (4) | (5) | (6) | (7) | (8) | (9) | (10) |
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OSMS (cm) |
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CBCT (cm) |
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0.65 | 0.13 | 0.15 | 0.17 | 0.18 | 0.18 | 0.94 | 0.15 | 0.58 | 0.67 |
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Patient number | (11) | (12) | (13) | (14) | (15) | (16) | (17) | (18) | (19) | (20) |
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OSMS (cm) |
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CBCT (cm) |
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1.00 | 0.38 | 0.50 | 0.83 | 0.65 | 0.09 | 0.88 | 0.11 | 0.61 | 0.55 |
OSMS: Optical Surface Management System; CBCT: cone-beam computed tomography. The
External beam radiotherapy requires reproducible and precise patient positioning and continuous monitoring. The OSMS shows promising accuracy, but studies in actual breast cancer patients are rare. Therefore, this study aimed to analyze 200 patient setups in 20 patients with breast cancer by comparing OSMS with CBCT. The results showed that OSMS is an efficient tool to improve the accuracy and increase the speed for verifying and complementing patient positioning in radiotherapy for breast cancer.
Systems for target delineation and patient positioning can be divided into radiographic imaging (such as X-ray imaging) and nonradioactive systems. Imaging and positioning systems (e.g., nonradioactive optical scanning systems) can be used to obtain accurate 3D information of patients, based on 2D data input. CBCT is a standard method for verifying the position. With excellent 3D imaging capabilities and high kV-level resolution, this method has become an important means of position verification prior to radiotherapy [
Furthermore, note that CBCT requires the use of X-ray, and thus the patients receive additional radiation doses during the treatment. Zhang and Gao [
CBCT scanning needs a CBCT gantry rotating to obtain and reconstruct a CT image within volume [
There are some limitations of OSMS, such as greater errors in imaging for relatively deeper target areas, insensitivity to fluctuations of smooth surface (e.g., the patient with fixed body film on surface), and blind angle at the neck. Stieler et al. [
An advantage of OSMS is the real-time monitoring in the entire treatment process. When the patient’s breathing rate exceeds a certain threshold (e.g., longer than 1 cm), the radiation beam is shut down to prevent toxicity. In addition to Catalyst, the OSMS also has a Real-time Position Management (RPM) system. The RPM system (Varian Medical System Company, Palo Alto, CA, USA) is aligned to the patient by an infrared source and camera. This device is installed at the foot end of the couch. It is installed on a plastic box with a reflective marker on the breast of a cancer patient to track his/her breathing movement.
Bekke et al. [
The present study still has some limitations. The sample size was small and all patients were from the same hospital and thus possibly introducing some bias.
In conclusion, the OSMS is an efficient tool to improve the accuracy and speed for verifying and complementing patient positioning in radiotherapy for breast cancer. OSMS could be used in future potential applications in gating, adaptive therapy, and 3D or 4D image fusion between most imaging modalities and image processing [
All authors declare that they have no conflicts of interest.
Zhao Ma and Wei Zhang contributed equally to this work.
The authors acknowledge Zhao Ma, Yi Su, and Yi Peng Song, for their guidance and help.