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The hardware and software faults in the image guidance system may cause ring-shaped artifacts,which is more commonly induced by the aging of the hardware.During troubleshooting,the first step should be checking whether there are obvious faults in the basic hardware.Subsequently,OBI background image is collected to confirm the bad point status.If the bad point is not shielded,it can be compensated by updating the image processing bad point.The invoked Pixel Correction Maps are adopted compensate for the bad point and calibrate the image.If it is still unable to repair,replacing the detection board can be considered.Cone-beam CT (CBCT) image guidance system is an important approach to verify the position orientation and positioning accuracy in modem radiotherapy,which effectively guarantees for the safety and accuracy of radiotherapy.We should fully understand its law of aging,maintain the equipment on a regular basis and verify the image quality to ensure the normal operation of the equipment.
ABSTRACT
Hepatocellular carcinoma is a common malignant tumor, which has a poor prognosis and a high mortality rate. Under the influence of respiratory motion, the position error of liver cancer is relatively high. The image-guided radiotherapy is a combination of radiotherapy and imaging device, which can detect and correct the error caused by the movement of the organs and the position of the pendulum to improve the accuracy of radiotherapy.
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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 the set-up accuracy in radiotherapy of thoracic neoplasms by improving the body immobilization method.Methods Fifty patients with thoracic neoplasms were randomly divided into conventional group (without electrode paste) and improved group (with electrode paste).Using simulator for position calibration and center field digital image reconstruction from treatment planning system.Then compare the set-up accuracy of two groups with different body methods by grouped t-test.Results Set-up error in the left-right,superior-inferior,anterior-posterior direction were 2.5 ± 1.5 and 2.4 ± 1.4(P =0.010),4.4 ± 2.0 and 2.2 ± 1.2 (P =0.000),2.2 ± 1.3 and 2.1 ± 1.0 (P =0.100) in conventional group and improved group,respectively.Conclusions The improved body immobilization method improves setup accuracy in radiotherapy for thoracic neoplasms which also will be effective for clinical treatment.
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Objective To investigate the setup errors of super chest segment of esophageal cancer patients before radiotherapy delivery by KV cone beam CT,and evaluate the margin from CTV to PTV.Methods From 2010 to 2012,13 patients with super chest segment of esophageal cancer whose IMRT planning CT images were included in this study.Delineate target on the CT images of treatment planning and enlarge the margin of CTV to form ITV,then enlarge the margin of ITV gradually 10 times by 1 mm each time to form varied PTV,and create the plan according to the size of the PTV,simulate setup errors in the new plan to obtain the simulation of the actual exposure curve and find a suitable PTV to assure 95％ ITV volume as ever to approach the prescription dose,obtained the outside enlarge distance of CTV → PTV.Results The maximum setup errors in the direction of the anterior and posterior positioning was (3.42 ±2.19) mm.The margin of ITV→PTV is 5 mm which was figured out by PTN enlarging method.Compared to the original plan that under the condition of draw up the radiotherapy plan that based on the method of PTV enlarging obtained the CTV→PTV and simulate the actual dose distribution according to the setup errors:total lung V5,spinal cord D1cm3,increased by about 0.87％,4.95 Gy,heart V40,PTV D95,PTV V100,ITV D95,ITV V100 were reduced about 0.62％,4.95 Gy,8.38％,1.84 Gy,1.87％,all of them have statistically difference.Conclusions Range of external expansion of the left to right,superior to inferior and anterior to posterior is 7 mm,8 mm and 7 mm respectively,according to the method of PTV enlarging obtained the margin of CTV→PTV of super chest segment of esophageal cancer patients.
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Objective To investigate the impact of metal plate on radiation dose distribution in surrounding tissues in cadaver specimens.Methods Stainless steel plate, titanium plate, and muscle strip were implanted into the left thigh of a corpse, respectively.All the specimens were irradiated with 6 MV X-ray , SSD = 100 cm.The absorbed dose of surface was measured by thermoluminiscent elements.Results Surface dose distributions differed significantly among the three different materials (F = 57.35, P < 0.01),with the amounts of 1.18 Gy ± 0.04 Gy (stainless steel plate), 1.12 Gy ± 0.04 Gy (titanium plate) and 0.97 Gy ±0.03 Gy (muscle strip), respectively.The surface absorbed doses on incident plane of stainless steel plate and titanium plate were significantly increased by 21.65% and 15.46% respectively as compared with that of muscle strip.The absorbed doses on the exit surface of stainless steel plate, titanium plate and muscle strip were 0.87 Gy ± 0.03 Gy, 0.90 Gy ± 0.02 Gy and 0.95 Gy ± 0.04 Gy, respectively (F =13.37, P <0.01).The doses on the exit surface of stainless steel plate and titanium plate were significantly lowered by 8.42% and 5.26% when compared with that of muscle strip.Using treatment planning system,the differences between dose distribution with and without metal plate were compared.Within 1 cm away from the incident plate, there was an obvious increase in the absorbed dose, while the influence was less than 5% 1cm outside the surface.The effect of dose distribution on exit surface was less than 2%.Conclusions The influence of metal plate on the radiotherapy dose distribution is significant.The deviations ranges from 5% to 29%.Under the same condition, the impact of stainless steel plate is much more than that of titanium alloy plate.
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Accurate simulation is the key of improve local control rates for radiotherapy esophageal carcinoma. CT simulation is an excellent tool that advances our capabilities of 3-D conformal radiation therapy so that higher radiation dose can be delivered to the target with a corresponding expectation of increased tumor control, possibly combined with a decrease in morbidity for radiotherapy esophageal carcinoma. PET/CT has an advantage in delineation of lateral extension of esophageal tumor, has more values for simulation in radiotherapy esophageal.
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Objective To study the dose distribution of intra-cavitary NiTi metal-stent for correction in radiotherapy of esophageal carcinoma.Methods Thermoluminescence Dosimeter(TLD) with LiF dose units was used to simulate the dose variation in wax phantom with or without Chinese and Japanese metal stents in esophageal lumen on 60Co, 4 MV X-ray and 6 MV X-ray machines. The dose distribution on the stent fringe (i.e.,on the esophageal mucosa) was compared with that at the center of esophagus without metal stent.Results When a single anterior field was used to irradiate the esophageal carcinoma, the dose enhancement on the anterior and posterior point of the Chinese metal stent was 16.2% and 7.8% by 60Co,15.4% and 6.8% by 4 MV X-ray and 12.8% and 5.8% by 6 MV X-ray. With the same set-up, the dose enhancement of Japanese stent was 13.0% by 6 MV X-ray. When anterioposterior and posterioanterior (AP/PA) opposing fields were used ,the dose enhancement ratio was 11.7%～24.0%. When three fields from three different directions were used ,the dose were increased by 3.2～16.2%.Conclusions When irradiating esophageal carcinoma with intra-cavitary metal stent,we suggest the fraction dose be below 1.7 Gy when one field is used and not exceed 1.5 Gy when AP/PA fields are used. It is advisable to use the three field technique with the diameter of the stent limited to 1.5 cm.
