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Since the application of image-guided radiotherapy in clinical practice, cone-beam CT (CBCT) has become the most widely employed image-guided device. However, some problems remain to be cautioned in the application of CBCT, such as certain errors in the setup errors before and after the correction of CBCT, the failure of CBCT to correct dynamic changes, whether the influence of application frequency of CBCT on patients’ boundary of clinical target volume can be reduced, imaging conditions of CBCT lack of a certain degree of flexibility, and the effect of clinical value and application cost on the practicality of CBCT. Only by fully understanding the problems in CBCT application can CBCT be applied more reasonably and scientifically.
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Cone-beam computed tomography (CBCT) image based on a single layer of image and the choice of regions of interest (ROI) is affected by individual subjectivity, making it difficult to compare the image quality. In this article, a quantitative evaluation method of CBCT image quality based on three-dimensional parameters was proposed, which was extended from single layer to multi-layer and from pixel to voxel. The selection range of ROI was discussed to reduce the error of artificial selection and realize the quantitative evaluation of image quality by three-dimensional parameters.
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Cone-beam computed tomography (CBCT) image based on a single layer of image and the choice of regions of interest (ROI) is affected by individual subjectivity,making it difficult to compare the image quality.In this article,a quantitative evaluation method of CBCT image quality based on threedimensional parameters was proposed,which was extended from single layer to multi-layer and from pixel to voxel.The selection range of ROI was discussed to reduce the error of artificial selection and realize the quantitative evaluation of image quality by three-dimensional parameters.
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Radiotherapy is an indispensable treatment of lung cancer. However, movement of lung cancer brings challenges to precise radiotherapy. Four-dimensional cone-beam CT is a four-dimensional imaging technique, which can demonstrate the tumor trajectory to improve the accuracy of radiotherapy. In this article, the research status and development tendency of four-dimentional cone-beam CT in terms of measuring and correcting set-up errors, observing variability of tumor postion and movement, guiding delineation of target volumes as well as calculating radiation dose were retrospectively reviewed.
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Objective To investigate the precision and stability of optical surface imaging (OSI)system Catalyst in guiding radiotherapy positioning.Methods A total of 52 patients with five different tumor sites who underwent cone-beam computed tomography (CBCT)-guided radiotherapy were recruited in this investigation.For the first treatment fraction,the setup error was recorded as C after online CBCT correction,and the surface images of patients taken by Catalyst were set as the reference images Cref.For the following treatment fraction,patients were pre-corrected according to the Catalyst Cref image with the acceptable errors within 2 mm/ 2,and the pre-corrected errors were recorded as C1.Then,after online CBCT correction,the setup errors were recorded as C.The errors between post-corrected Catalyst surface image and Cref image were recorded as C2.For each treatment fraction,the difference between Catalyst correction errors C1 and CBCT corrected errors C was recorded as d1,and the difference between the post-corrected Catalyst errors C2 and Cref image was recorded as d2.d3=d1-d2.The values of d1 and d3 in the 6 dimensions were analyzed using single sample t-test.The correlation between C-C1 and d1-d2 was statistically analyzed by Pearson correlation analysis.Results The mean value of d1 and d3 for 52 patients were within 2 mm/2 °.CBCT-C1 and d1-d2 were both significantly correlated (R =3,7,P=0.00,0.01).Conclusions OSI system yield high accuracy and stability in radiotherapy positioning,which is of certain significance in radiotherapy positioning for cancer patients.
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Objective To compare the differences in setup error ( SE) assessment and correction between three-dimensional cone-beam computed tomography ( 3DCBCT ) and four-dimensional CBCT ( 4 DCBCT ) in breast irradiation patients during free breathing after breast-conserving surgery . Methods Twenty patients with breast cancer after breast-conserving surgery were recruited for external beam breast irradiation and 4DCBCT and 3DCBCT simulation. The target volumes were delineated. Volumetric modulated arc therapy plans were designed using the MONACO v510 treatment planning system. 3DCBCT and 4DCBCT images were collected alternately five times each before breast irradiation. The CT images were matched, and the interfraction SEs were acquired. After online setup correction, the residual errors were calculated, and the SEs, systematic errors, and random errors were compared. The paired t test was used for comparison between groups. Results The SEs acquired by 4DCBCT were significantly larger than those acquired by 3DCBCT in three directions ( P=0035, 0018, 0040 ) . After online setup correction, the random errors based on 3DCBCT were significantly smaller than those based on 4DCBCT in left-right and anterior-posterior ( AP ) directions ( 0.5± 039 mm vs. 0.7± 030 mm, P=0005;0.9± 109 mm vs. 1.2± 048 mm, P=0000) , and the residual errors based on 3DCBCT were also significantly smaller than those based on 4DCBCT in AP direction (0.2±033 mm vs. 0.6±063 mm, P=0000). The setup margins based on 4DCBCT was significantly larger than those based on 3DCBCT in AP direction both before and after online setup correction (P=0002). Conclusions Compared with 3DCBCT, 4DCBCT has more advantages in monitoring the SEs in three directions. Both 3DCBCT and 4DCBCT have similar efficacy in random error correction. The satisfying position repeatability and minimized target volume margins will be achieved by online setup correction.
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Objective To establish a quantitative evaluation of quality control image for the onboard imaging system of medical linear accelerator.Methods An MV planar image of electronic portal imaging device (EPID) is acquired by both Elekta iViewGT and Varian aS1000,and a kV planar image and cone-beam computed tomography (CBCT) images of CBCT are acquired by both Elekta X-ray volume imaging (XVI) and Varian On-board Imager (OBI).Phantoms used here included Las Vegas,TOR18FG,and Catphan504.A series of image quality indicators were evaluated by analyzing the images mentioned above using a quantitative method.Results A quantitative value was calculated to represent the contrast resolution of EPID.A modulation transfer function (MTF) to describe spatial resolution and a quantitative value representing contrast resolution were calculated for the kV planar image.As for the CBCT system,a series of quantitative results of noise,uniformity,CT value accuracy,and contrast resolution and a MTF were calculated to represent the performance of CBCT system.Conclusions Based on common phantoms,a complete set of quantitative methods to evaluate the image quality of EPID and CBCT has been developed,which could provide a very good reference for the establishment of quality control system for image-guided radiotherapy.
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Objective To develop a practical image acquisition strategy using intermittent breath?hold cone beam computed tomography (CBCT). Methods A breathing phantom was used to simulate the movement of tumor near the diaphragm during free breathing and breath hold and scanned by conventional breath?hold CBCT and type Ⅰ/Ⅱ intermittent breath?hold CBCT. In the conventional breath?hold CBCT, scan paused and free breathing occurred at the break of breath hold and free breathing was not included in the scan. In the intermittent breath?hold CBCT, one scan covered several breath holds separated by free breathing in a ratio of 3 vs1. Image quality and three?dimensional registration accuracy were quantitatively compared between conventional breath?hold CBCT and type Ⅰ/Ⅱ intermittent breath?hold CBCT. Comparison of image quality parameters between conventional breath?hold CBCT and intermittent breath?hold CBCT was made by paired t test. Results Motion artifacts arose in type I and Ⅱ intermittent breath?hold CBCT scans. There were no significant differences in the reconstructed pixel value or uniformity between intermittent breath?hold CBCT and conventional breath?hold CBCT ( P>0. 05, and P= 0. 02, 0. 53 ) . Compared with conventional breath?hold CBCT images, the signal?to?noise ratios of type I andⅡintermittent breath?hold CBCT images were reduced by 30% and 60%, respectively ( P<0. 05 ) . The registration error was up to 0 . 4 cm in the anterior?posterior direction and less than 0 . 1 cm in other directions . Conclusions The phantom study shows that intermittent breath?hold CBCT does not significantly reduce image quality or registration accuracy compared with conventional breath?hold CBCT. The feasibility of intermittent breath?hold CBCT in clinical application needs to be further validated among a large number of patients.
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Objective To compare the differences in setup error ( SE) assessment and correction between three-dimensional cone-beam computed tomography ( 3DCBCT ) and four-dimensional CBCT ( 4 DCBCT ) in breast irradiation patients during free breathing after breast-conserving surgery . Methods Twenty patients with breast cancer after breast-conserving surgery were recruited for external beam breast irradiation and 4DCBCT and 3DCBCT simulation. The target volumes were delineated. Volumetric modulated arc therapy plans were designed using the MONACO v510 treatment planning system. 3DCBCT and 4DCBCT images were collected alternately five times each before breast irradiation. The CT images were matched, and the interfraction SEs were acquired. After online setup correction, the residual errors were calculated, and the SEs, systematic errors, and random errors were compared. The paired t test was used for comparison between groups. Results The SEs acquired by 4DCBCT were significantly larger than those acquired by 3DCBCT in three directions ( P=0035, 0018, 0040 ) . After online setup correction, the random errors based on 3DCBCT were significantly smaller than those based on 4DCBCT in left-right and anterior-posterior ( AP ) directions ( 0.5± 039 mm vs. 0.7± 030 mm, P=0005;0.9± 109 mm vs. 1.2± 048 mm, P=0000) , and the residual errors based on 3DCBCT were also significantly smaller than those based on 4DCBCT in AP direction (0.2±033 mm vs. 0.6±063 mm, P=0000). The setup margins based on 4DCBCT was significantly larger than those based on 3DCBCT in AP direction both before and after online setup correction (P=0002). Conclusions Compared with 3DCBCT, 4DCBCT has more advantages in monitoring the SEs in three directions. Both 3DCBCT and 4DCBCT have similar efficacy in random error correction. The satisfying position repeatability and minimized target volume margins will be achieved by online setup correction.
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Objective To investigate the influence of fixation of both lower limbs with negative pressure vacuum cushion and fixation of both ankles with self-made foam mat on setup errors in radiotherapy for rectal cancer.Methods A total of 12 patients with rectal cancer were enrolled in 2014 and randomly divided into group A (using negative pressure vacuum cushion) and group B (using self-made foam mat).An offline registration analysis was performed for the images of 108 times (A,B group of 54 times) of kilovoltage cone-beam CT (CBCT) before and after treatment.Grey scale translation error registration was used,and the results of registration were analyzed.The setup errors in x-axis (left-right direction),y-axis (cranial-caudal direction),and z-axis (anterior-posterior direction) were compared between the two groups.Results There was no significant difference in the absolute setup error in the y-axis between the two groups (2.13±0.64 mm vs.2.61±1.17 mm,P=0.399),while group A showed significantly lower absolute setup errors in the x-axis and z-axis than group B (x-axis:1.51±0.28 mm vs.2.70±1.05 mm,P=0.039;with an error rate of 7.41％ vs.42.59％;z-axis:1.10±0.29 mm vs.2.37±0.71 mm,P=0.002;with an error rate of 1.85％ vs.35.19％).Conclusions In the radiotherapy positioning for rectal cancer,fixation of both lower limbs with negative pressure vacuum cushion effectively avoids the translation and rotation of both lower limbs,reduces absolute setup errors,and has higher accuracy than fixation of both ankles with self-made foam mat.
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Objective To compare the normal thickness of the esophageal wall measured by contrast?enhanced three?dimensional ( 3DCT ) , four?dimensional ( 4DCT ) , and cone beam computed tomography ( CBCT) ,and to provide a basis for target volume delineation in esophageal cancer. Methods From 2009 to 2016,thoracic contrast?enhanced 3DCT and 4DCT simulations were performed in 50 patients with lung cancer or metastatic lung cancer. Contrast?enhanced CBCT scans were acquired during the first three?dimensional conformal radiotherapy. The normal esophageal wall was contoured on 3DCT images, the end?exhalation phase of 4DCT images ( 4DCT50 ) , the maximum intensity projection of 4DCT images (4DCTMIP),and CBCT images. The wall thickness was measured on each segment and the average thickness of esophageal wall was obtained. Comparison of the thickness of a fixed segment of esophageal wall between different CT images was made by paired t test. Comparison of thickness on the same type of CT images between different segments of esophageal wall was made by one?way analysis of variance. Results For the thoracic and intra?abdominal segments,there was no significant difference in the thickness of esophageal wall between 3DCT and 4DCT50 images ( P= 0?056?0?550 );however, the thickness of esophageal wall was significantly smaller on 3DCT images than on 4DCTMIP or CBCT images (P=0?000?0?004).For the upper and middle thoracic segments,the thickness of esophageal wall was significantly larger on CBCT images than on 4DCTMIP images ( P= 0?008, P= 0?001 ) . On 3DCT, 4DCT50 , and 4DCTMIP images, the thickness of esophageal wall was significantly larger in the lower thoracic segment than in the upper or middle thoracic segments ( P=0.008~0?041);the intra?abdominal segment had a significantly larger thickness of esophageal wall than the thoracic segments ( all P=0?000 ) . There was no significant difference in wall thickness on CBCT images between three thoracic segments ( P=0.088~0?945) . Conclusions A uniform criterion can be adopted to judge the normal thickness of esophageal wall in gross tumor volume ( GTV ) delineation on 3DCT and 4DCT50 images for thoracic esophageal cancer. However,caution should be taken when 5 mm is used as a criterion for normal thickness of esophageal wall in GTV delineation on 4DCTMIP and CBCT images.
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Objective To investigate the role of self-made auxiliary device in pelvic tumor radiotherapy with phantom immobilization using Varian cone-beam CT (CBCT).Methods A total of 50 patients with pelvic tumor were enrolled and randomly divided into study group and control group according to the order of enrollment.The patients in the study group were immobilized with thermoplastic phantom and self-made auxiliary device,and those in the control group were immobilized with thermoplastic phantom.CBCT scan and online matching were regularly performed before radiotherapy to obtain the setup errors of the left-right (x),cranial-caudal (y),and anterior-posterior (z) directions.The independent-samples t-test was used for comparison between groups.Results The set-up errors in the x-,y-,and z-directions in the study group were 1.56± 1.00 mm,1.60± 1.29 mm,and 1.36± 1.00 mm,respectively,and those in the control group were 1.76±1.33 mm,2.76±1.69 mm,and 1.92±0.91 mm,respectively (P=0.551,0.009,and 0.043).Conclusions Self-made auxiliary device helps to eliminate the errors in the cranial-caudal direction and solve the problem of involuntary activities of the lower limbs.
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Objective To analyze the data from intensity-modulated radiotherapy ( IMRT) for prostate cancer guided by kilovoltage cone-beam computed tomography (CBCT), and to provide a clinical basis for selecting the optimal image registration method and reasonable target volume margins.Methods A total of 16 patients with prostate cancer who received radical IMRT were enrolled, and CBCT for online position verification was performed 214 times.The images were obtained after conventional skin marking and laser alignment, and automatic registration, bone registration, soft tissue registration, and manual registration were performed for CBCT images and planned CT images.The differences between these four registration methods were evaluated, and the margins for extending clinical target volume into planning target volume (PTV) were calculated.Results The setup errors in left-right, anterior-posterior, and cranial-caudal directions for automatic registration, bone registration, soft tissue registration, and manual registration were-0.6±2.8 mm/-0.6±4.5 mm/-0.6±3.8 mm,-0.7±2.7 mm/-0.9±4.5 mm/-0.8±4.1 mm,-0.8± 2.6 mm/-0.3±4.4 mm/-1.1±4.0 mm, and-0.6±2.9 mm/-0.7±5.1 mm/-0.9±3.9 mm, respectively. There were no significant differences between the four registration methods.The margins for extension in the left-right, anterior-posterior, and cranial-caudal directions were calculated as 4.7 mm, 5.2 mm, and 6.5 mm, respectively.Conclusions With a comprehensive consideration of various factors, a default setting of automatic registration and manual fine adjustment is appropriate for CBCT-guided radiotherapy for prostate cancer.The margins for extension in the left-right, anterior-posterior, and cranial-caudal directions are 4.7 mm, 5.2 mm, and 6.5 mm, respectively.
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Objective To investigate the dose distribution and radiation risk of Varian thoracic cone beam computed tomography (CBCT) with default parameters with reference to Monte Carlo simulation and International Commission on Radiological Protection (ICRP) report 110.Methods EGSnrc/BEAMnrc code was used to simulate the material, thickness, and geometry of the kV CBCT source (kVS) to establish the kVS model.A benchmarked MCSIM code was applied to calculate the dose distribution in the ICRP phantom after the scan with the standard thoracic parameters (110 kV, 20 mA, and 262 mAs), and the conversion coefficient of absolute dose was obtained in a spherical phantom following the TG-61 protocol.The results of Monte Carlo simulation were validated by PDD and Profile in a water phantom and the measurement of the absolute dose in the computed tomography dose index (CTDI) phantom and Alderson phantom.The models including BEIR VⅡ were used to evaluate the radiation risks.Results With reference to the criterion of 3%/1 mm, the uncertainties of PDD and Profile were less than 2%.The difference between the measured and calculated values was<2.9% in the CTDI phantom and ≤0.05 cGy in the Alderson phantom.In the ICRP110 phantom, the doses to the left lung, right lung, left breast, right breast, heart, thyroid, trachea, cancellous bone, and cortical bone were 1.28, 1.39, 1.74, 1.80, 1.46, 0.48, 0.88, 0.85, and 1.84 cGy, respectively.The relative risks of ischemic heart disease, breast cancer, lung cancer, thyroid cancer, and tracheal cancer in a standard scan were1.001 , 1.009, 1.019, 1.000, and 1.008, respectively. Conclusions The accumulated dose and long-term risks of CBCT during image-guided thoracic radiotherapy cannot be neglected and should be effectively controlled.
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Objective To evaluate the image quality and registration accuracy of a three?dimensional ( 3D ) dynamic phantom in four?dimensional computed tomography ( 4DCT ) and four?dimensional cone?beam computed tomography ( 4DCBCT) . Methods The Computerized Imaging Reference Systems Dynamic Thorax Phantom Model 008A was scanned to get 4DCT and 4DCBCT images. Two balls with different diameters ( ?= 1 cm and ?= 2 cm) were used to simulate tumors with different sizes. The motion mode of the balls was 3D sinusoidal motion at 0?25 Hz ( the amplitudes along the x, y, and z axes were ±1?0 cm, ±0?4 cm, and ±0?2 cm, respectively). Gross target volumes (GTVs) from 10?phase bins, internal gross target volumes (IGTV), and target volumes on maximum intensity projection (MIP) and mean intensity projection (MeanIP) images were contoured and calculated. Target volumes on 4DCT or 4DCBCT images were compared with the static and dynamic volumes of the balls ( VS and VD ) . The matching index ( MI) of target volumes between the 4DCT and 4DCBCT images was analyzed after rigid image registration. Results The GTV in each phase of the image was larger than VS . The difference between the average GTV derived from 10 phases of 4DCT or 4DCBCT images and Vs of the small ball was larger than that of the large ball ( 35?03% vs. 22?66%;32?62% vs. 17?00%) . All the IGTVs and target volumes on MIP images were slightly larger than VD , but target volumes on MeanIP images were smaller than VD . The average MI of 10?phase bins of the small ball was smaller than that of the large ball ( 66?76% vs. 82?21%) . Moreover, MIs of IGTV,MIP, and MeanIP of the small ball were also smaller than those of the large ball ( 77?39% vs. 90?29%;75?90% vs. 89?28%;74?47% vs. 82?74%) . Conclusions In the case of a relatively small tumor volume and a relatively large motion amplitude, 4DCT and 4DCBCT should be used with caution for comparison of image registration.
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Objective To study the methods of matching kilovolt CBCT image with planning CT scan. Methods A total of 121 CBCT scans were matched with planning CT scan using a manual and four automatic match methods by four observers in the offline. In the manual match, the live contour was used as a surrogate for image registration. Four automatic match methods, including routine soft?tissue match, routine bone match, automatic liver match and vertebral body match, were performed using image registration sofeware. First, the stability of the sofeware was tested. Then, the reproducibility of the same automatic match method was evaluated by comparing different observers’ match results. After the manual match by four observers, the mean of the match results was used as a standard to compare with others. The differerces was test by McNemar method. Results In the uniform match factors, automatic match result would not change. The reproducibility of routine soft?tissue and bone match are best, automatic vertebral body match is better than automatic liver match. Howerver, the automatic liver match result is the most similar to manual match, the percentages of match result have an absolute error no more than 3 mm in left?right, superior?inferior and anterior?posterior directions are 84?? 3%, 77?? 7% and 92?? 6%. Conclusions Automatic liver match can be used in image?guided radiotherapy for liver cancer, however, it should be performed by experienced oncologist and technologist together in each fraction, after that, the matching result should be adjusted carefully according to live contour.
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Objective To study CT numbers correction of kilo?voltage cone?beam CT (KV?CBCT) images for dose calculation. Method Aligning the CBCT images with plan CT images, then obtain the background scatter by subtracting CT images from CBCT images. The background scatter is then processed by low?pass filter. The final CBCT images are acquired by subtracting the background scatter from the raw CBCT. KV?CBCT images of Catphan600 phantom and four patients with pelvic tumors were obtained with the linac?integrated CBCT system. The CBCT images were modified to correct the CT numbers. Finally, compare HU numbers between corrected CBCT and planning CT by paired T test. Evaluate the image quality and accuracy of dose calculation of the modified CBCT images. Results The proposed method reduces the artifacts of CBCT images significantly. The differences of CT numbers were 232 HU, 89 HU, 29 HU and 66 HU for air, fat, muscle and femoral head between CT and CBCT respectively (P= 0?? 39,0?? 66,0?? 59,1).The differences of CT numbers between CT and CBCT was reduced to within 5 HU. And the error of dose calculation with corrected CBCT images was within 2%. Conclusions The CT numbers of corrected CBCT are similar with plan CT images and dose calculations based on the modified CBCT show good agreement with plan CT.
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Objective To investigate the accuracy and reliability of the image automatic matching using X-ray volumetric image (ⅩⅥ) system with the accelerator Elekta Synergy and to compare the matches with different methods and area.Methods A simulation plan using the head and neck phantom was designed and sent to ⅩⅥ system for CBCT scanning.During the scanning,the couch for certain distance was moved and the data of ⅩⅥ image automatic Matching in different matching methods and area was collected.Results The result of ⅩⅥ image automatic matching is consistent and correct to direction and distance which the couch had been moved (x:(0.11 ± 0.41) mm,y:(-0.04± 2.6) mm,z:(0.28 ± 0.74 mm)).There are not significant differences between the results that matching in different matching methods and different matching area.Conclusions The automatic image Matching of ⅩⅥ is accuracy and high reliability in recognition of offset error.But there are some significant differences on the automatic image Matching in different matching methods and different matching area.
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Objective To study the image quality control system to ensure that equipment meet clinical needs.Methods It was scanning the Catphan504 phantom with models of high quality head,standard dose head and pelvis,we could get the results of CT numbers linearity,uniformity,spatial resolution,contrast resolution.Using T test to compare different scanning technique results.Results The standard dose head scanning technique was better than the pelvis scanning technique in CT numbers linearity test,and gets the best result in uniformity test.The result of CT numbers uniformity was higher in the standard dose head scanning than the high quality head and the pelvis scanning (9.7 ±3.9 vs.17.9 ±5.3,P =0.00 and 9.5 ± 4.0 vs.31.1 ± 5.7,P =0.00).The result of contrast resolution was higher in the pelvis scanning than the high quality head and the pelvis scanning (5.6 ± 0.1 vs.1.3 ± 0.5,P =0.00 and 6.0 ± 1.0 vs.1.3 ± 0.5,P =0.00).The result of spatial linear distance was very accurate,the range was 4.98 -5.06 cm.Conclusions The results of spatial linearity test are stable and accuracy,but CT numbers linearity and uniformity test are affected by the scanning technique significantly for device.To spatial resolution test and contrast resolution test,we need to set the standard and tolerance according to each linear accelerator specialty.
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Objective To study the CBCT image registration of PTV enlarging distance and IMRT planning(CT-1) for patients with lung cancer,and evaluate their characters.Methods Ten patients with lung cancer were included in the study.Two sets image,before and after radiotherapy,were acquired every week.Then delineated the targeted volume and made the planning (CT-2) according the enlarging distance data.To comparize the parameters of DVH for lung and spinal cord,volumes and dose of PTV and NTCP with CT-1 and CT-2.The difference of two plan was analyzed by covariance analysis or Wilcoxson's z-test.Results The max,min and mean dose of PTV,the lung V5,V10,V20,V30,V50 were similar in both plans (P =0.242-0.663).There was superiority in CT-2 of PTV and lung's mean dose(P =0.049,0,035).The NTCP had the decent tendency followed by the increasing of lung Vs,V10,V20(P =0.146,0.053,0.000).Conclusions CBCT based image registration can reduce PTV,the mean dose of lung,NTCP,and increase PTV dose.This provides a tool for exploring acurate radiotherapy strategies.