局部晚期鼻咽癌调强放疗中解剖结构改变及剂量分布变化研究

Anatomical changes and dose distribution deviations of locally advanced nasopharyngeal carcinoma patients during IMRT

目的 探讨局部晚期鼻咽癌患者在调强放疗（IMRT）期间的解剖结构体积改变及剂量分布变化。方法 选取18例局部晚期鼻咽癌患者，利用每周锥形束CT （CBCT）分析患者的解剖结构体积变化，并在放疗20次后再次进行IMRT计划设计，探讨二程IMRT计划的剂量学。结果 GTVnx每周平均缩小3.15%，共缩小22.03%；GTVnd每周平均缩小5.67%，共缩小39.68%；左右腮腺每周分别缩小4.93%和5.26%，总共缩小29.60%和31.56%。GTVnd和腮腺在放疗前4周有较大退缩，放疗4周后体积改变趋于平缓。与初始Plan 1相比，Plan 2中PGTVnd的D95下降2.20%（t=2.382，P〈0.05），而PGTVnx、PTV1和PTV2的D95没有显著变化；左腮腺Dmean、D50和V30分别增加7.34%、12.68%和10.90%，与放疗前比较差异均有统计学意义（t=-3.376、-3.738、-3.679，P〈0.05）；右腮腺Dmean、D50和V30分别增加6.13%、11.17%和9.72%，与放疗前比较差异均有统计学意义（t=-2.550、-2.446、-2.673，P〈0.05）；喉的Dmean平均增加8.69%，与放疗前比较差异均有统计学意义（t=-3.099，P〈0.05）。相比较于Plan 2，综合计划Plan （1＋2）中PGTVnd的D95增加1.37%，差异有统计学意义（t=-3.555，P〈0.05），左腮腺Dmean、D50和V30分别平均降低了2.90%、2.73%和4.62%，差异有统计学意义（t=3.089、2.718、2.705，P〈0.05）；右腮腺Dmean、D50和V30分别降低3.49%、3.44%和3.80%，与放疗前比较，差异均有统计学意义（t=2.781、2.958、4.275，P〈0.05）；喉的Dmean平均降低3.29%（t=2.747，P〈0.05）。结论 局部晚期鼻咽癌患者在IMRT期间靶区和腮腺体积均会显著缩小；放疗中期有必要设计二程放疗计划，以此来提高靶区剂量并一定程度上降低靶区周围危及器官的剂量。Replanning is necessary during the middle of IMRT to improve the target coverage and to spare the organ at risks （OARs）.

Objective To investigate the anatomical changes and dose distribution deviations of locally advanced nasopharyngeal carcinoma （NPC） patients during intensity-modulated radiation therapy （IMRT）. Methods Weekly cone beam CT （CBCT） was applied to investigate the anatomical changes of enrolled 18 patients with locally advanced NPC. Dosimetric deviations were investigated with new IMRT plans after 20 fractions. Results The volumes of gross tumor volume （GTVnx） and GTVnd were decreased by 3.15% and 5.67% weekly, and decreased by a total of 22.03% and 39.68%,respectiely. The volumes of left and right parotids were decreased by 4.93% and 5.26% weekly, and decreased by a total of 29.60% and 31.56%, respectively. The volumes of GTVnd and parotids showed significant retraction in the first four weeks of radiation, then the retraction slowed down. The D95 of PGTVnd in Plan 2 decreased by 2.20% （t=2.382, P〈0.05） compared that in the initial Plan 1, while there was no significant difference on the D95 of PGTVnx, PTV1 and PTV2.The Dmean, D50 and V30 of the left and right parotids in Plan 2 increased by 7.34%, 12.68%, 10.90% （t=-3.376, -3.738, -3.679,P〈0.05）, and 6.13%, 11.17%, 9.72% （t=-2.550, -2.446, -2.673, P〈0.05）, respectively, compared with Plan 1. The Dmean of larynx increased by 8.69% in Plan 2 compared with Plan 1 （t=-3.099, P〈0.05）. The D95 of PGTVnd in Plan（1＋2） increased by 1.37% （t=-3.555, P〈0.05） compared with Plan 2.The Dmean, D50 and V30 of the left and right parotids in Plan（1＋2） were decreased by 2.90%, 2.73%, 4.62% （t=3.089, 2.718,2.705, P〈0.05）, and decreased by 3.49%, 3.44%, 3.80% （t=2.781, 2.958,4.275, P〈0.05）, respectively, compared with Plan 1. The Dmean of larynx decreased by 3.29% （t=2.747, P〈0.05） in Plan（1＋2） compared with Plan 1. Conclusions The volumes of GTV and parotids of locally advanced NPC patients showed significant shrinks during IMRT.