弧数目对鼻咽癌容积旋转调强放射治疗计划质量的影响及其可执行性分析OA

Objective:To study the impact of arc number on quality of volumetric modulated arc therapy(VMAT),and the feasibility of that for nasopharyngeal carcinoma.Methods:The images of computed tomography(CT),and target area of radiotherapy of 20 patients with nasopharyngeal carcinoma who admitted to Liuzhou Worker's Hospital from 2021 to 2023 were retrospectively selected.The RayStation plan system was adopted to design single-arc,double-arc,and triple-arc VMAT plan for each patient.The prescription doses of primary gross tumor volume(PGTVnx),plan target volume(PTV5 280)of prophylactic irradiation region and subclinical lesion region of nasopharyngeal carcinoma were respectively 6,996 cGy in 33 fractions,5,280 cGy in 33 fractions,and 6,600 cGy in 33 fractions.The tumor area of metastatic lymph node received different prescription doses according to high-risk level.The dose of target area,dose of organ-at-risk(OAR),and feasibility parameter of plan were statistically analyzed.One-way analysis of variance(ANOVA)for repeated measurement data,and Bonferroni correction method were adopted to analyze the differences of these indicators between dosimetric and feasibility parameters.Results:With increasing of arc number,the distribution of the dose of target volume was further optimized.The differences of indicators(D98%,Dmean,D2%,coverage rate of target area)of PGTVnx,and indicators(D98%,Dmean,coverage rate of target area)of PTV6 996,and indicators(D98%,Dmean,coverage rate of target area)of PTV6 600,and indicators(D98%,Dmean,coverage rate of target area)of PTV5 280,and conformity index(CI)of plan for nasopharyngeal carcinoma among single-arc,double-arc,and triple-arc VMAT plan were significant(F=36.578,29.527,130.748,28.542,19.278,21.787,15.819,24.683,16.026,16.973,86.285,100.416,88.660,21.714,P<0.05).With increasing of arc number,the exposure doses of some OAR decreased.The differences of brainstem D5%,left mandible D5%,right mandible D5%,right optic nerve D5%,oral cavity V50,left parotid V30,right parotid V30,spinal cord Dmax,left submandibular gland D50%,right submandibular gland D50%,thyroid D50%among single-arc,double-arc,and triple-arc VMAT plan were significant(F=22.567,5.074,8.296,6.184,7.524,7.366,9.646,16.636,25.482,21.408,54.000,P<0.05).The beam release time of the single-arc,double-arc and triple-arc plans were respectively(92.0±7.0)s,(153.1±2.3)s and(224.3±1.5)s.The monitor unit(MU)values of machine increased with the increasing of the number of arcs,and the MU values were respectively 769.1±121.1,817.4±98.9,and 933.7±101.4,and the differences of them among the single-arc,double-arc and triple-arc plans were significant(F=7 023.526,43.307,P<0.05).The beam release time of double-arc and triple-arc plans increased respectively 61.15 s and 132.35 s than that of single-arc plans.The MU values of double-arc and triple-arc plans were respectively 1.06 times and 1.21 times that of single-arc plan.Under 3%/3 mm conditions,the pass rate of verification of triple-arc plan was slightly lower than that of other two plans,and the difference was significant(F=4.925,P<0.05).Conclusion:With the increasing of arc number,the distribution of the dose of target area of nasopharyngeal carcinoma significantly enhances,and the exposure dose of the most of OAR is lower,but the duration of treatment is extended.The precision of feasibility of triple-arc plan decreases.It is suggested that the benefit and disadvantage should be weighed in designing plan,and the appropriate arc number should be selected based on the difficult level of plan.