《中国医学装备》杂志社

目的：研究弧数目对鼻咽癌容积旋转调强放射治疗(VMAT)计划质量及其可执行性的影响。方法：回顾性选取2021年至2023年柳州市工人医院收治的20例鼻咽癌患者的定位CT图像及放疗靶区，每例患者均采用RayStation计划系统设计单弧、双弧和三弧VMAT计划。鼻咽癌计划肿瘤体积(PGTVnx)处方剂量为6 996 cGy/33次，预防照射区域计划靶区(PTV_{5 280})处方剂量为5 280 cGy/33次，亚临床病灶区处方剂量为6 600 cGy/33次，转移淋巴结肿瘤区按高危程度给予不同的处方剂量，统计其靶区剂量、危及器官剂量、计划可执行性参数，采用单因素重复测量方差分析，Bonferroni校正法，分析其剂量学和可执行性参数之间的差异。结果：随着弧数目的增加，靶区剂量分布进一步优化，单弧、双弧、三弧计划之间比较，鼻咽癌PGTVnx的D_98%、D_mean、D_2%及靶区覆盖率，PTV_{6 996}的D_98%、D_mean、靶区覆盖率，PTV_{6 600}的D_98%、D_mean、靶区覆盖率，PTV_{5 280}的D_98%、D_mean、靶区覆盖率、适形指数(CI)的差异均有统计学意义(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)；随着弧数目的增加，部分危及器官的受照剂量降低，单弧、双弧、三弧计划的脑干D_5%、左下颌骨D_5%、右下颌骨D_5%、右视神经D_5%、口腔V₅₀、左腮腺V₃₀、右腮腺V₃₀、脊髓D_max、左颌下腺D_50%、右颌下腺D_50%、甲状腺D_50%比较差异均有统计学意义(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)；单弧、双弧、三弧计划的出束时间分别为(92.0±7.0)s、(153.1±2.3)s和(224.3±1.5)s，机器跳数(MU)随弧数目之间的增加而增加，MU值分别为769.1±121.1、817.4±98.9和933.7±101.4，差异均有统计学意义(F=7023.526、43.307,P<0.05)。双弧和三弧计划的出束时间分别比单弧计划增加了61.15和132.35 s，双弧和三弧计划的机器跳数分别为单弧计划的1.06倍和1.21倍，三弧计划3%/3 mm条件下的验证通过率略低于其他两种计划，差异有统计学意义(F=4.925,P<0.05)。结论：随着弧数目的增加，鼻咽癌靶区剂量分布显著提升，大部分危及器官的受照剂量更低，但治疗时间增加，三弧计划的执行精度下降。建议在计划设计时权衡利弊，根据计划的难易程度选择合适的弧数目。

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(PTV_{5 280}) 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 highrisk level. The dose of target area, dose of organ-at-risk(OAR), and feasibility parameter of plan were statistically analyzed. Oneway 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(D_98%, D_mean, D_2%, coverage rate of target area) of PGTVnx, and indicators(D_98%, D_mean, coverage rate of target area) of PTV_{6 996}, and indicators(D_98%, D_mean, coverage rate of target area)of PTV_{6 600}, and indicators(D_98%, D_mean, coverage rate of target area) of PTV_{5 280}, 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 D_5%, left mandible D_5%, right mandible D_5%, right optic nerve D_5%, oral cavity V₅₀, left parotid V₃₀, right parotid V₃₀, spinal cord D_max, left submandibular gland D_50%, right submandibular gland D_50%, thyroid D_50% 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.