| Radiotherapy is one of the main methods for the treatment of nasopharyngeal carcinoma(NPC).Because of its complex target shape and close to many organs at risk(OARs),the requirement of dose conformability is high,so it is very suitable for helical tomotherapy(HT)to treat.Fixed jaw(FJ)mode irradiation will lead to a wider longitudinal penumbra of the target area,thus increasing the scattering dose of the surrounding OARs,but the dynamic jaw(DJ)can solve the above problem.The purpose of this study was to compare the plan quality of different jaw modes(FJ or DJ)and different field width(2.5cm or 5.0cm)combinations in HT for NPC treatment,so as to provide reference for clinical application.20 NPC patients underwent HT were selected and 4 groups of plans(2.5DJ,2.5FJ,5.0DJ and 5.0FJ)were designed with the same optimal conditions.The differences of dose parameters,beam on time(BOT)and Machine Unit(MU)in each group were compared and analyzed,and a comprehensive evaluation method was put forward to objectively evaluate the quality of the four groups of plans.The results showed that the PTVs' prescription dose coverage among the four plans could meet the clinical requirements,and the difference among these plans was less than 1%.Both the small field width group(2.5cm)and the dynamic jaw group could provide better protection for most of OARs,especially the normal tissues near to the longitudinal edge of the target area,including optic nervous,pituitary,temporal lobe and hippocampus(P<0.05).The OARs dose score in 2.5DJ group was the best,the 2.5FJ group and the 5.0DJ group were ranked second,and the 5.0FJ group was the worst.Compared with the 2.5cm group,the BOT and MU of the 5.0cm group were decreased by nearly 45%.Therefore,in the HT plan of nasopharyngeal carcinoma treatment,the selection of 5.0cm field width and DJ mode(5.0DJ)can achieve satisfactory dose distribution quality and greatly reduce the BOT and MU number.It is recommended as the best combination of field width and jaw mode for clinical HT of nasopharyngeal carcinoma.In the radiotherapy of esophageal cancer,in order to avoid pneumonia caused by large-scale low-dose radiation to both lungs,IMRT is often chosen instead of VMAT.However,the IMRT planning requires manual setting of the angle of the radiation beams,which depends on the experience of the planner,so angle optimization is very important for the IMRT planning of esophageal cancer.In this study,a method to optimize the IMRT planning angle of esophageal cancer based on VMAT plan was proposed(PlanA),and compared with commercial software beam angle optimization(PlanB),artificial field distribution planning(Planc)and uniform field distribution planning(PlanD),in order to provide reference for clinical application.10 patients with esophageal cancer who received radiotherapy were selected,and each patient designed the above four 5f-IMRT plans.The dosimetric differences among different groups of plans were compared,and plan quality among these plans were compared by comprehensive evaluation method.The results showed that the PTVs' prescription dose coverage among four groups of plans could meet the clinical requirements.For OARs,the protection of lung(V5,V10,V20,V30 and MLD)and heart(Dmean)in PlaneA group was better than that in PlanC group and PlanD group,and the difference was statistically significant(P<0.05).Among the four groups,the total(CSFPTV)of the comprehensive factor scores of the dosimetric parameters of the PTV,the total(CSFOARs)of the comprehensive factor scores of the dosimetric parameters of the OARs,and the total of the planned comprehensive factor scores(CSFTotai)of each group were all the best in the PlanA group and the PlanB group,and the corresponding CSF values of the two groups were 3,6 and 9.The CSFTotai of PlanC group was the worst,with a value of-10.Therefore,the method of optimizing the IMRT planning angle of esophageal cancer based on VMAT plan is feasible and effective,and it is suggested to be widely used in clinic. |
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