早期鼻咽癌15例自动IMRT计划与手动VMAT计划的剂量学比较

目的放射治疗已成为鼻咽癌最主要的治疗方法,选择何种放射治疗技术以及如何提高放射治疗计划的质量是现在研究的重点。本研究探讨早期鼻咽癌手动容积旋转调强放射治疗(manual volumetric modulated arc therapy,mVMAT)计划和自动调强放射治疗(automatic modulated radiation therapy,aIMRT)计划之间的剂量学差异,评估2种计划质量。方法选取2017-01-01-2018-12-31广州医科大学附属肿瘤医院收治的15例早期鼻咽癌患者。采用Pinnacle3计划系统对每位患者分别进行aIMRT计划和mVMAT计划的设计,统一给予计划肿瘤靶区(planning gross target volume,PGTV)处方剂量70Gy/32次,采用配对t检验和非参数秩和检验进行统计分析。分别对肿瘤靶区剂量分布、均匀性指数(homogeneity index,HI)、适形性指数(conformal index,CI)、危及器官的受照剂量、机器跳数和计划设计时间进行评估。结果 2种计划均能满足临床处方剂量要求。2种计划PGTV的HI(t=-0.86,P>0.05)和CI(t=0.71,P>0.05)差异无统计学意义,平均剂量(Dmean)差异有统计学意义,t=2.42,P=0.03;PTV2的HI(t=0.79,P>0.05)和CI(t=-0.56,P>0.05)差异无统计学意义。2种计划脊髓的受照剂量差异有统计学意义,t=7.22,P<0.01;aIMRT计划中脊髓平均剂量减少了约8.00%。同时aIMRT计划对降低脑干、视神经、视交叉等危及器官的受照剂量亦具有一定的优势。mVMAT计划中机器跳数少于aIMRT计划(t=-6.17,P<0.01),平均机器跳数减少了约15.18%;但是,mVMAT计划设计时间大于aIMRT计划(t=25.29,P<0.01),平均设计时间增加了约217.78%。结论相比手动VMAT计划,自动IMRT计划对早期鼻咽癌具有同等或相似的靶区适形度及剂量分布均匀性,降低危及器官的受照剂量,显著减少计划设计时间。自动IMRT计划具有临床可行性和有效性,可为早期鼻咽癌IMRT技术的选择提供数据参考与指导。

Dosimetric comparison of automatic IMRT plan and manual VMAT plan for 15 cases of early nasopharyngeal carcinoma

OBJECTIVE Radiotherapy has become the most important treatment for nasopharyngeal carcinoma.What kind of radiotherapy technology is selected and how to improve the quality of treatment plan for nasopharyngeal carcinoma have attracted the attention of many researchers.Therefore,the study aimed to investigate the dosimetric differences and estimate the quality of treatment plans between manual volumetric modulated arc therapy(VMAT)plan and automatic intensity modulated radiation therapy(IMRT)plan for early nasopharyngeal carcinoma.METHODS Fifteen patients with early nasopharyngeal carcinoma,admitted to Affiliated Cancer Hospital of Guangzhou Medical University from January 1,2017 to December 31,2018,were retrospectively investigated.Automatic IMRT plan(aIMRT)and manual VMAT plan(mVMAT)were generated by Pinnacle3 planning system for each patient.The prescribed dose was given70 Gy for planning gross target volume(PGTV)in 32 fractions.Statistical analysis was performed by using paired t test and nonparametric rank sum test.The dose distribution of target,homogeneity index(HI),conformal index(CI),and the irradiated doses of organs at risk were evaluated for each treatment scheme.Additionally,monitor unit and planning time were also compared and evaluated.RESULTS Both plans met the requirements of clinically prescribed doses.The HI and CI of two planned PGTV were not significantly different(t=-0.86,P>0.05;t=0.71,P>0.05,respectively),but the Dmean of two planned PGTV was significantly different(t=2.42,P=0.03).Whilst the HI and CI of two planned PTV2 were not significantly different(t=0.79,P>0.05;t=-0.56,P>0.05,respectively).There was a significant difference for irradiated dose of spinal cord between two plans(t=7.22,P<0.01).The average irradiated dose of spinal cord obtained from aIMRT plans was reduced by about 8.00%.Additionally,aIMRT plan also had certain advantages in reducing the irradiated doses of organs at risk,such as brain stem,optic nerve and optic chiasma.The monitor units of mVMAT plans were lower than those of aIMRT plans(t=-6.17,P<0.01),and average monitor unit of mVMAT plans was reduced by about 15.18%.However,the planning times of mVMAT plans were greater than those of aIMRT plans(t=25.29,P<0.01).The average planning time of mVMAT plans was increased by about 217.87%.CONCLUSION Compared with the manual VMAT plan,the automatic IMRT plan has the equivalent or similar target conformation and uniformity of dose distribution for early nasopharyngeal cancer,which can even reduce the irradiated doses to organs at risk and significantly decrease the planning time.