医疗卫生装备

目的:探讨剂量跌落环(dose fall-off ring,DFOR)联合虚拟限量环(virtual dose-limiting ring,VDLR)在优化鼻咽癌同步推量调强放疗(simultaneous integrated boost intensity-modulated radiotherapy,SIB-IMRT)计划剂量分布中的应用价值。方法:回顾性选取某院20例接受鼻咽癌SIB-IMRT的初治患者,基于Monaco计划系统对每位患者设计仅使用VDLR限制靶区外部剂量分布的SIB-IMRT₁计划和使用DFOR联合VDLR限制靶区外部剂量分布的SIBIMRT₂计划,评估2种SIB-IMRT计划计划靶区(planning target volume,PTV)、危及器官(organs at risk,OAR)的剂量学参数以及治疗参数(子野个数、机器跳数、出束时间)的差异。采用SPSS 26.0软件进行统计学分析。结果:2种SIB-IMRT计划剂量学参数均满足临床治疗要求。SIB-IMRT,计划的PTV_p、PTV_n和PTV₂的D_2%、D_mean和均匀性指数,PTV_p1的D_2%、D_mean和D_98%,PTV_n1的D_2%和均匀性指数,PTV_{6 006-6 996}的V_{6 006-6 996,6 600}及PTV_{2-6 006}的V_{2-6 006,6 006}劣于SIB-IMRT₂计划,差异有统计学意义(P<0.05);SIB-IMRT₁计划PTV_n1的D_98%和适形度指数优于SIB-IMRT₂计划,差异有统计学意义(P<0.05);SIB-IMRT₁计划腮腺、口腔和喉的D_mean以及body-PTV₂的V_{body-2,4 000}。劣于SIB-IMRT₂计划,差异有统计学意义(P<0.05)。SIB-IMRT₁计划的子野个数和机器跳数多于SIB-IMRT₂计划,差异有统计学意义(P<0.05);2种计划出束时间比较差异无统计学意义(P>0.05)。由剂量-体积直方图可知,与SIB-IMRT₁计划相比,SIB-IMRT₂计划部分靶区及OAR的剂量学参数和body-PTV₂的剂量学参数具有明显优势。结论:与单纯依赖VDLR的SIBIMRT₁计划相比,在出束时间未发生显著变化的前提下,联合使用DFOR与VDLR的SIB-IMRT₂计划不仅优化了部分靶区剂量学参数,同时在部分OAR和body-PTV₂的保护方面也展现出更优越的剂量学表现。

Objective To analyze the application value of combining a dose fall-off ring(DFOR) with a virtual doselimiting ring(VDLR) in optimizing the dose distribution of simultaneous integrated boost intensity-modulated radiotherapy(SIB-IMRT) plans for nasopharyngeal carcinoma(NPC). Methods Twenty newly diagnosed NPC patients treated at some hospital with SIB-IMRT were selected. For each patient, two SIB-IMRT plans were designed based on Monaco planning system: SIB-IMRT₁ which utilized VDLR alone to restrict dose distribution outside the target volumes and SIB-IMRT₂ which combined DFOR with VDLR to restrict dose distribution outside the target volumes. The two types of SIB-IMRT plans were compared in terms of dosimetric parameters for the planning target volume(PTV) and organs at risk(OAR), as well as treatment delivery parameters such as number of segments, monitor units(MU) and delivery time. Statistical analysis was carried out with SPSS 26.0 software. Results The dosimetric parameters of both the SIB-IMRT plans met the requirements for clinical treatment. The SIB-IMRT₁ plan had the D_2%, D_mean and homogeneity index(HI) of PTV_p, PTV_n and PTV₂, D_2%, D_mean and D_98% of PTV_p1, D_2% and HI of PTV_n1, V_{6 006-6 996, 6 600} of PTV_{6 006-6 996} and V_{2-6 006, 6 006} of PTV_{2-6 006} inferior to those of the SIB-IMRT₂ plan, with the differences being statistically significant(P < 0.05); the D_98% and conformity index(CI) of PTV_n1 in the SIB-IMRT₁ plan were slightly better than those in the SIB-IMRT₂ plan, with the differences being statistically significant(P < 0.05); the SIB-IMRT₁ plan had the D_mean of the parotid gland, oral cavity, and larynx and V_{body-2,4 000} of body-PTV₂ inferior to those of the SIB-IMRT₂ plan, with the differences being statistically significant(P < 0.05). The SIB-IMRT₁ plan had the numbers of segments and MU higher than those of the SIB-IMRT₂ plan, with the differences being statistically significant(P < 0.05); the two types of plans had no significant differences in the delivery time(P > 0.05). The dose-volume histogram showed that the SIB-IMRT₂ plan behaved better than the SIB-IMRT₁ plan in some dosimetric parameters of PTVs, OARs and body-PTV₂. Conclusion Compared to the SIB-IMRT₁ relying solely on VDLR, the SIB-IMRT₂ plan combining DFOR and VDLR without significantly altering the beam delivery time optimizes some PTV dosimetric parameters, and demonstrates superior dosimetric performance in sparing some OARs and bodyPTV₂.