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目的在调强放疗期间,鼻咽癌患者存在不同程度的靶区及危及器官的解剖学及剂量学改变,通过评估这些解剖学及剂量学改变,研究自适应放疗的最佳干预时机。方法收集2012-08-2013-12广西壮族自治区人民医院入组19例鼻咽癌患者,在调强放疗过程中进行每周CT扫描,通过形变配准方法将计划CT与新CT进行融合,自动勾画靶区及危及器官,评估解剖学改变。将原始放疗计划通过剂量映射传递到新CT图像上,形成合成计划,分别与原始计划对比DVH。结果 GTVnx、GTVnd和腮腺的体积在放疗过程中逐渐缩小。与原始计划相比,各周合成计划中所有靶区的HI差异均无统计学意义。与原计划相比,PTVnx和PTV1的部分剂量学参数显著改善,特别是在第10次放疗后,这些参数包括PTVnx的Dmean、D95、V95和CI,以及PTV1的Dmean、D95和CI;PTVnd的剂量学参数只有D95和V95在某些时间点上有显著改善;对于PTV2,其D95和V95在某些时间点上显著变劣。部分器官如脑干、脊髓、腮腺、声门、右侧眼球和左侧晶体的剂量在某些时点上显著增加。结论鼻咽癌调强放疗过程中发生显著的靶区及危及器官的解剖学和剂量学改变。将PTV2的D95、V95及CI、脑干Dmax、脊髓Dmax、腮腺Dmean、声门喉Dmean、右侧眼球Dmax和左侧晶体Dmax作为预测自适应放疗时机的参数,经过分析建议在鼻咽癌调强放疗至第5次后和第15次后分别进行自适应计划优化。
Objective To investigate the anatomic and dosimetric changes of target organ and organ at risk in patients with nasopharyngeal carcinoma (NPC) during intensity modulated radiation therapy and to study the optimal timing of interventional radiotherapy by evaluating these anatomical and dosimetric changes. Methods We collected 19 patients with nasopharyngeal carcinoma from Guangxi Zhuang Autonomous Region People’s Hospital from August 2012 to December 2013 and performed weekly CT scans in the course of IMRT. The planned CT was fused with the new CT by means of deformation registration. Outline the target area and organs at risk and assess the anatomical changes. The original radiotherapy plan is delivered to the new CT image via dose mapping to form a composite plan that compares the DVH with the original plan, respectively. Results The volume of GTVnx, GTVnd and parotid glands diminished during radiotherapy. Compared with the original plan, there was no significant difference in HI among all the target areas in each week of synthetic programs. Part of the dosimetric parameters of PTVnx and PTV1 significantly improved compared with the original plan, especially after the 10th radiotherapy, including Dmean, D95, V95 and CI for PTVnx and Dmean, D95 and CI for PTV1; PTVnd Only the D95 and V95 dosimetric parameters were significantly improved at some time points; for PTV2, D95 and V95 were significantly worse at some time points. Doses of some organs such as the brain stem, spinal cord, parotid gland, glottis, right eyeball, and left lens significantly increased at some time points. Conclusion There are significant anatomical and dosimetric changes in target areas and organs at risk during intensity modulated radiotherapy of nasopharyngeal carcinoma. D95, V95 and CI in PTV2, Dmax in brain stem, Dmax in spinal cord, Dmean in parotid gland, Dmean in glomerular gland, Dmax in right eye and Dmax in left lens were used as parameters to predict the timing of adaptive radiotherapy. Strong radiotherapy until the 5th and 15th after the adaptive program optimization.