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Objective To evaluate the difference of set-up errors between thermoplastic mask and breast bracket in patients receiving intensity-modulated radiotherapy after breast conserving surgery,and the impact of clinical factors associated with set-up errors.Methods A total of 34 patients treated with intensity-modulated radiotherapy after breast conserving surgery from January 2016 to June 2018 were reviewed.Eighteen patients were fixed with thermoplastic mask,and sixteen were with breast bracket.Weekly CBCT scan records were used to analyze set-up errors,and group systematic and random errors were computed.The influence of clinical factors on set-up errors was also analyzed.Results The immobilization technique with thermoplastic mask showed great superior in comparison with breast bracket;however,only in the Ty(translation) and Ry(rotation),the differences had significance.Based on group systematic and random errors,PTV margins in Tx,Ty and Tzwere 2.65,4.36 and 2.87 mm in thermoplastic mask group,as well as 5.71,6.07 and 4.20 mm in breast bracket group,respectively.Multi-factor regression analysis showed that BMI was independent factors affecting set-up errors.Conclusions Compared with breast bracket,the immobilization technique with thermoplastic mask has the potential of reducing set-up errors and PTV margins in patients receiving intensity-modulated radiotherapy after breast conserving surgery,especially in patients with high BMI.
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Objective To investigate the effects of cleaning and disinfection of thermoplastic masks on the hospital infection in patients receiving precise radiotherapy for nasopharyngeal carcinoma ( NPC). Methods A prospective study was performed among 102 patients receiving precise radiotherapy for NPC from 2013 and 2016, consisting of 18 patients with early?stage ( I, Ⅱ) disease and 84 patients with advanced (Ⅲ, IV) disease. All patients were randomly divided into group A and group B using a random number table. For group A, the marker lines of thermoplastic masks were sandwiched by double plastic tapes;cleaning and disinfection plus ultraviolet ( UV ) disinfection were applied to the masks 1 h prior to radiotherapy and immediately after radiotherapy. For group B, only conventional UV disinfection was applied to the masks. The surface of the masks was examined and hospital infection during radiotherapy was evaluated. Results At the 18th radiotherapy, group A had a significantly lower mask surface colony count than group B (7.90±650 vs. 139.05±12929 CFU/cm2, P=0000). Group A also had a significantly lower incidence of hospital infection than group B (725% vs. 882%, P=0046). For the patients with early stage NPC, particularly, there was no significant difference in the incidence of infection between the two groups (556% vs. 667%, P=0629). For patients with advanced NPC, group A had a significantly lower incidence of infection than group B ( 762% vs. 929%, P=0035) . There were no significant differences in incidence rates of oral mucosal, skin, and respiratory system infections between the two groups ( 471% vs. 510%, P=0692;176% vs. 235%, P=0463;78% vs. 137%, P=0338) . In both groups A and B, the incidence of oral mucosal infection was significantly higher than the incidence rates of skin infection ( P=0001, 0000) and respiratory system infection ( P=0004, 0000) . Conclusions Thermoplastic mask is one of the risk factors for hospital infection in patients receiving precise radiotherapy for NPC. Timely cleaning and disinfection plus UV disinfection can significantly reduce the surface colony count and the incidence of hospital infection in patients with NPC, particularly in those with advanced NPC receiving precise radiotherapy. The incidence of hospital infection is the highest in the oral mucosa, followed by the skin and the respiratory system.
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Objective This study analyzes the effect of the shrinkage of thermoplastic mask on patient positioning. Methods Design of the two test. Test 1:thermoplastic film shrinkage test. Get some thermoplastic film by the size of 10 cm×5 cm, extrude it at a certain rate after heated. Measure the length of thermoplastic film on different time, and calculate the contraction. Test 2:phantom test. Take advantage of head and neck phantom, and simulate the procedure that from making mask for patients to radiation therapy. Measure the off set of isocenter which caused by the contraction of thermoplastic mask. Results The largest shrinkage of thermoplastic had happened in 20 minutes. Different tensile ratio had little effect on the shrinkage. The offset of isocenter which caused by the shrinkage of thermoplastic mask were:LR ( -0?? 1± 0?? 3) mm,SI (-0?? 2±0?? 2) mm, AP (0.6±0?? 4) mm,respectively. There was little change in the course of six weeks ( P= 0.185?0?? 961). Conclusions The cooling time should be more than 20 minutes, when making a mask for the patient. The setup errors which caused by the shrinkage of thermoplastic mask is at an acceptable level on this premise.
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Objective To study the set-up errors by CBCT in IMRT with two different immobilization techniques for thoracic and abdominal tumors.Methods Sixty patients with thoracic and abdominal tumor were included in this study and separated into study group and the control group.The study group were immobilized with carbon fiber holder,vacuum bag and thermoplastic mask.The control group were immobilized with carbon fiber holder and thermoplastic mask.CBCT scan and auto-match online were regularly performed before the treatment.The setup of left-right(x),superior-inferior(y),anterior-posterior (z) were received.The value of the Mptv was calculated,meanwhile.The grouped t-test of was carried out between these two methods.Results The shift errors in x-,y-,z-dimension of the study group were (0.32 ± 2.58) mm,(-0.40 ± 3.89) mm,(-0.75 ± 2.43) mm.The Mrrv were 5.60 mm,6.08 mm,6.32 mm.The translation set-up errors in x-,y-,z-dimension of the control group were(0.62 ±3.60),(2.44 ± 4.93),(0.66 ±2.85) mm,respectively.The MPrv were 8.07,10.63,6.90 mm,respectively.The t-test value were t =-0.78,-5.11,-4.22,P =0.440,0.000,0.000,respectively.Conclusions The immobilization techniques with carbon fiber holder,vacuum bag and thermoplastic mask would be better than the techniques without the vacuum bag in reducing the setup errors.
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Objective To calculate the effects of thermoplastic mask on X-ray surface dose.Methods The BEAMnrc Monte Carlo Code system, designed especially for computer simulation of radioactive sources, was performed to evaluate the effects of thermoplastic mask on X-ray surface dose.Thermoplastic mask came from our center with a material density of 1.12 g/cm2. The masks without holes,with holes size of 0. 1 cm× 0. 1 cm, and with holes size of 0. 1 cm × 0. 2 cm, and masks with different depth (0.12 cm and 0.24 cm) were evaluated separately. For those with holes, the material width between adjacent holes was 0. 1 cm. Virtual masks with a material density of 1.38 g/cm3 without holes with two different depths were also evaluated. Results Thermoplastic mask affected X-rays surface dose. When using a thermoplastic mask with the depth of 0. 24 cm without holes, the surface dose was 74. 9% and 57.0% for those with the density of 1.38 g/cm3 and 1.12 g/cm3 respectively. When focusing on the masks with the density of 1.12 g/cm3, the surface dose was 41.2% for those with 0.12 cm depth without holes;57.0% for those with 0. 24 cm depth without holes;44. 5% for those with 0. 24 cm depth with holes size of 0.1 cm ×0.2 cm;and 54.1% for those with 0.24 cm depths with holes size of 0.1 cm ×0.1 cm.Conclusions Using thermoplastic mask during the radiation increases patient surface dose. The severity is relative to the hole size and the depth of thermoplastic mask. The surface dose change should be considered in radiation planning to avoid severe skin reaction.
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Objective To evaluate the systematic and random set-up errors in patients immobilized with thermoplastic device during radiotherapy, and to determine the proper margins extended from clinical target volume ( CTV ) or internal target volume ( ITV ) to planning target volume ( PTV ). Methods From March 2007 to September 2007,120 patients were included in this study, including 13 receiving head and neck irradiation, 67 thoracic irradiation and 40 abdominal irradiation. All patients were immobilized with thermoplastic device and received CT simulation and intensity modulated radiation therapy(IMRT). X-ray cone beam CT was regularly performed before treatment and the images were compared with the simulation CT images. The shift and rotation in right-left( R-L), superior-inferior(S-I) and anterior-posterior(A-P) directions were recorded and analyzed. The shift margin from CTV or ITV to PTV was calculated with the equation, margin = 2'mean + 0.7'standard deviation. Results In head and neck region, the shift errors in R-L,S-I and A-P directions were(0.13 ±0.15) cm, (0.13 ±0.17) cm and(0.11 ±0.14) cm,and the corresponding rotation errors were 1.05°± 0.77°,0.87°± 1.13° and 0.68°±0.89°. The margins from CTV to PTV were 0.37 cm,0.38 cm and 0.31 cm,respectively. In thoraci region,the shift errors in R-L,S-I and AP directions were(0.20 ±0.27) cm, (0.34 ±0.44) cm and(0.25±0.31 ) cm,and the corresponding rotation errors were 1.06°±1.45° ,0.85°±1.23° and 0.78°±1.08°. The shift margins from ITV to PTV were 0.59 cm, 1.00 cm and 0.72 cm. In abdominal region, the shift errors in R-L, S-I and A-P directions were (0.23 ± 0.30) cm, (0.37 ±0.45 ) cm and ( 0.27 ±0.34 ) cm, and the corresponding rotation errors were 1.22°±1.56°, 1.05°± 1.44°and 0.98°± 1.24°. The shift margins from CTV or ITV to PTV were 0.66 cm, 1.05 cm and 0.78 cm. Conclusions Cone beam CT can be used in the precise measure of set-up errors,which can provide institution-specific margins for PTV designing in patients immobilized with thermoplastic device.