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Objective:To evaluate the effect of rotational errors (antero-posterior) on dosimetric parameters of positive lymph nodes in the long target volumetric modulated arc therapy (VMAT) plan for advanced cervical cancer and investigate its coping strategies.Methods:Clinical data of patients with cervical cancer complicated with para-aortic or inguinal lymph node metastasis admitted to Affiliated Hospital of North Sichuan Medical College were randomly selected and retrospectively analyzed. The target areas of the lymph nodes at different distances from the center of the plan were outlined according to the requirements. After designing the VMAT plan on the CT images of each case, the rotational errors (antero-posterior) were introduced by changing the parameters of the treatment couch, and the dose distribution was reconstructed by dose calculation with other parameters unchanged. Then, the external boundary of the original lymph node target was added according to d=2πr(α/360) ( r is the distance from the center of the lymph node to the plan center), re-planned, and the changes of dosimetric parameters in the target area of the original lymph node were analyzed after the corresponding rotational errors were introduced. Results:When the distance between the lymph node target area and the plan center was 6 cm with an error of 3°, the distance was 9 cm and 12 cm with an error of 2.5°, the distance was 15 cm with an error of 2°, and the distance was 18 cm with an error of 1.5°, the mean change of D 95% was more than 5%. When the rotational errors were ≤1°, the mean change of D 95% in lymph node target area was less than 5%, and when the lymph node was 18 cm away from the treatment plan center, the mean change was more than 3%, reaching 3.75%. When the rotational errors were 0.5° and the distance from the plan center was 18 cm (0.5°, 18 cm), the dose change of lymph node target was more than 5%, reaching 5.58%. At (1°, 15 cm), the V 100% change reached 8.96%, and at (1°, 18 cm), the V 100% change was 14.5%. The D 95% and V 100% parameters of the original lymph node target were changed by less than 1% after adding the external boundary of the original lymph node target and introducing corresponding rotational errors. Conclusions:In the long target area radiotherapy of cervical cancer, the variation of dosimetric parameters of lymph node target was increased with the increase of rotational errors and with the increase of distance from the plan center. It is recommended to increase the efferent boundary of lymph nodes in different positions to avoid underdose by d=2πr(α/360).
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Objective To evaluate the value of two oral mucosal contouring methods for predicting acute radiation-induced oral mucositis (A-ROM) in nasopharyngeal carcinoma (NPC) patients.Methods A total of 150 AJCC 7th stage Ⅱ-ⅣB NPCs receiving radical tomotherapy (TOMO) in Zhejiang Cancer Hospital from 2017 to 2019 were included in this prospective observational study.Oral cavity contour (OCC) and mucosal surface contour (MSC) were applied to delineate the oral mucosal structure.A-ROM grade was prospectively assessed and recorded weekly according to RTOG scoring criteria.The prediction value of two methods for A-ROM was statistically compared.Results The incidence rate of ≥ 3 grade A-ROM was 33.3％.In univariate analysis,V5,V10,V15,V45,V50,V55,V60,V65 and V70 of OCC and V5,V10,V50,V55,V60,V65,V70 and Dmean of MSC were significantly correlated with the risk of ≥3 grade A-ROM (all P＜0.05).In binary logistic regression analysis,gender and smoking were significantly associated with the incidence of ≥3 grade A-ROM by using OCC (male vs.female:OR=0.141,95％CI=0.037-0.538,P=0.004;smoking vs.non-smoking:OR=5.109,95％CI=1.413-18.470,P=0.013).For MSC,gender,smoking,N stage and MSC-V55 were the independent predictors (male vs.female:OR=0.129,95％CI=0.032-0.519,P=0.004;smoking vs.non-smoking:OR=4.448,95％CI=1.224-16.164,P=0.023;N stage:OR=2.291,95％CI=1.268-4.137,P=0.006;MSC-V55:OR=1.432,95％CI=1.008-2.033,P=0.045).The cutoff value of MSC-V55 was 7.70％,the area under ROC curve was 0.754,the sensitivity and specificity were 0.680 and 0.740,retrospectively (all P＜0.001).Conclusions Compared with OCC,MSC yields a higher prediction accuracy for the severity of A-ROM in nasopharyngeal carcinoma patients receiving TOMO treatment.
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Objective@#To evaluate the value of two oral mucosal contouring methods for predicting acute radiation-induced oral mucositis (A-ROM) in nasopharyngeal carcinoma (NPC) patients.@*Methods@#A total of 150 AJCC 7th stage Ⅱ-IVB NPCs receiving radical tomotherapy (TOMO) in Zhejiang Cancer Hospital from 2017 to 2019 were included in this prospective observational study. Oral cavity contour (OCC) and mucosal surface contour (MSC) were applied to delineate the oral mucosal structure. A-ROM grade was prospectively assessed and recorded weekly according to RTOG scoring criteria. The prediction value of two methods for A-ROM was statistically compared.@*Results@#The incidence rate of ≥3 grade A-ROM was 33.3%. In univariate analysis, V5, V10, V15, V45, V50, V55, V60, V65 and V70 of OCC and V5, V10, V50, V55, V60, V65, V70 and Dmean of MSC were significantly correlated with the risk of ≥3 grade A-ROM (all P<0.05). In binary logistic regression analysis, gender and smoking were significantly associated with the incidence of ≥3 grade A-ROM by using OCC (male vs. female: OR=0.141, 95%CI=0.037-0.538, P=0.004; smoking vs.non-smoking: OR=5.109, 95%CI=1.413-18.470, P=0.013). For MSC, gender, smoking, N stage and MSC- V55 were the independent predictors (male vs. female: OR=0.129, 95%CI=0.032-0.519, P=0.004; smoking vs.non-smoking: OR=4.448, 95%CI=1.224-16.164, P=0.023; N stage: OR=2.291, 95%CI=1.268-4.137, P=0.006; MSC-V55: OR=1.432, 95%CI=1.008-2.033, P=0.045). The cutoff value of MSC-V55 was 7.70%, the area under ROC curve was 0.754, the sensitivity and specificity were 0.680 and 0.740, retrospectively (all P<0.001).@*Conclusions@#Compared with OCC, MSC yields a higher prediction accuracy for the severity of A-ROM in nasopharyngeal carcinoma patients receiving TOMO treatment.
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Objective To evaluate the effect of stainless steel applicator on dose distribution in GZP 60 Co brachytherapy source and to obtain the dosimetric parameters of the 60 Co source with stainless steel applicator. Methods Geant4 was employed to obtain the mean adsorption dose of the 60 Co brachytherapy source in the range of 0-10 cm, and the dosimetric parameters were calculated according to the formula proposed by AAPM reports TG43 and TG43U1. The 60 Co source was located in the center of a sphere water phantom with a radius of 30 cm. Results For channel 1 and 2 of GZP 60 Co source, the results of Λ with stainless steel applicator were 1. 014 cGyh-1 U-1( with a difference of 0. 5％ compared with non-applicator) , the results of Λ with stainless steel applicator for channel 3 were 0. 998 cGyh-1 U-1 ( with a difference of 0. 1％ compared with non-applicator) . The radial dose function in the range of 0. 5-10. 0 cm in a longitudinal direction was calculated and the fitting formula for the function was obtained. The polynomial function for the radial dose function and the anisotropy function with a of 0°-175° and an r of 0. 5-10. 0 cm were obtained. Conclusion The dosimetric parameters of the 60 Co source with stainless steel applicator are obtained, which provide more accurate reference data for clinical application. In clinical practice, the effect of stainless steel applicator on dose distribution should be considered.
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Objective To compare the dosimetric parameters of volumetric modulated arc therapy(VMAT),fixed field intensity modulated radiation therapy(IMRT)and three-dimensional conformal radiotherapy(3D-CRT)in the radiotherapy for the patients with locally recurrent nasopharyngeal carcinoma, and to analyze their characteristics. Methods Twelve patients with locally recurrent nasopharyngeal carcinoma were treated with VMAT, IMRT and 3D-CRT plan designed by Pinnacle 9.2 and Preciseplan 2.03 treatment planning system.The dosimetric parameters of targeted volumes and organs at risk were compared between three groups. Results The conformation indexes (CI)of VMAT and IMRT plans were similar,and they were both better than 3D-CRT plan,the difference was significant(P0.05).The monitor units(MU)and beam time in 3D-CRT group were better than those in other two groups,and VMRT group was better than IMRT group,the statistical differences were observed between three groups (P0.05).The doses of the spinal cord,optic nerve,optic chiasm and temporal lobe of brain in VMAT and IMRT groups were better than those in 3D-CRT group,there were statistical differences between them(P0.05).Conclusion There are differences of the targeted dose distribution between the three kinds of radiation technology, while VMAT and IMRT plans can cover the targeted areas and reduce the received doses of organs at risk.The CI,MU and beam time of VMAT plan are better than those of IMRT plan. 3D-CRT plan only has advantage in the MU and beam time.
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Objective To compare the dosimetric characteristics of intensity-modulated arc therapy( IMAT ),fixed-gantry intensity-modulated radiotherapy ( IMRT ) and 3-dimensional conformal radiotherapy (3D-CRT) for the thoracic esophageal cancer.Methods A total of 15 patients with thoracic esophageal cancer were enrolled.3D-CRT,5-field IMRT( IMRT5 ),7-field IMRT( IMRT7 ),9-field IMRT ( IMRT9 ),single arc ( Arc1 ) and double arc ( Arc2 ) RapidArc plans were generated for each patient.All plans were prescribed 40 Gy in 20 fractions and 19.6 Gy in 14 fractions to PTV at 95％ isodose line.Results RapidArc and all IMRT treatment plans in dosimetric parameters of target volumes were obviously better compared to 3-dimentional conformal treatments( t =5.77,3.52,P ＜ 0.05 ).The result of V95 of PTV for 3D-CRT,IMRT5,IMRT7,IMRT9,Arc1 and Arc2 plans was 91.55 ±2.90,96.66 ±1.05,96.87 ± 1.23,96.81 ± 1.16,94.98 ± 1.41 and 95.93 ± 1.32,respectively.The best conformation index in PTV was observed in the RapidArc plans ( t =3.76,10.01,P ＜ 0.05 ),and the best homogeneity index in PTV was observed in the IMRT plans( t =3.93,3.37,P ＜ 0.05 ).In terms of organ sparing,no statistical difference was observed between IMRT and RapidArc plans( P ＞ 0.05 ),while 3D-CRT provided the lowest number of V1 cGy and V5 cGy for total lung.Compared with the IMRT treatment plans,the number of monitor units was lower in all 3D-CRT and RapidArc cases with differences of 75％.Conclusions All the IMRT and RapidArc plans could offer high quality treatment for patients.3D-CRT might show advantage in low-dose region to organs at risk.Compared with IMRT,no obvious advantage in PTV dosimetric parameters could be observed in RapidArc plans.
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The ?-radioactive seed brachytherapy source has been widely employed in the implantation therapy for the prostatic carcinoma and the ophthalmic lesions.In this study the dosimetric parameters for characterization of a low-energy interstitial brachytherapy source 125I were calculated according to dose calculation formalism recommended by AAPM TG-43U1.For data processing,a 0.28 cm active length was used for the geometry function.The dosimetry parameter air-Kerma strength,dose rate constant,radial dose function and anisotropy function were estimated by means of the EGS5 Monte Carlo code.The results obtained from this study are in good agreement with the corresponding values recommended by TG-43U1 and with the data reported by Dolan,et al.