CT/MRI影像融合对鼻咽癌肿瘤靶区及三维适形治疗影响

Influence of CT/MRI fusion image on target volume and 3-D conformal radiotherapy in nasopharyngeal carcinoma

背景与目的:精确地勾画鼻咽癌肿瘤靶区是制定最佳治疗计划、降低肿瘤的局部复发率和保护周围正常重要器官的首要条件。本研究的目的是比较CT和MR I来源的鼻咽癌肿瘤靶区,评价CT-MR I融合靶区容积应用于三维适形放射治疗时,对治疗剂量的影响。方法:收集8位患者的CT模拟定位和MR I扫描的图像,然后在CT、MR I和CT/MR I融合图像上分别勾画肿瘤靶区和周围重要的器官。每个病例都做2个治疗计划:①用CT图像上的靶区做1个三维适形放射治疗计划;②用CT/MR I融合图像上的靶区做1个三维适形放射治疗计划。肿瘤的处方剂量为70 Gy,然后,比较2个治疗计划中肿瘤靶区的95%容积(D95)受照平均剂量、周围正常组织的5%容积(D5)受照平均剂量。结果:MR I上的肿瘤靶区比CT上的肿瘤靶区大53.5%,但并不一定包括CT上的肿瘤靶区。用CT上勾画的靶区做三维适形放射治疗计划,剂量分布是满意的,但以上治疗计划应用于CT/MR I融合图像上的靶区,D95的剂量分布较低(59.78 Gy)。用CT/MR I融合图像上勾画的靶区做三维适形放射治疗计划,则D95剂量分布较好,但在有些治疗计划上周围重要器官的剂量分布较高。结论:CT/MR I融合图像有助于鼻咽癌靶区的确定,但也造成GTV扩大,在三维适形放射治疗计划上的肿瘤靶区剂量分布足够,但周围重要器官的受照剂量提高。鼻咽癌的治疗方案有待于进一步改进。

Background and purpose： Precising definition of the target volumes （ gross target volume GTV） is very important to develop optimal treatment plans that conform the prescribed dose to the target volume, improvement in tumor locoregional control and spare the uninvolved critical structures in nasopharyngeal carcinoma （NPC）. This paper tried to compare CT and MRI target volumes for NPC and evaluated the role of the three-dimensional conformal RT（3-DCRT） in treating composite CT/MRT targets. Methods： CT simulation and MRT scans were obtained for 8 NPC patients. Using CT, MRI, and fused CT/MRI, various target volumes（gross target volume, clinical target volume, and planning target volume [ PTV]） and critical organ at risk were outlined. For each patient, two sets of treatment plans were developed： ① contouring the treated area with CT image; ② contouring treated the area with the fusion of CT ＋ MRI image. The prescription dose was 70Gy. PTV dose to 95% volume （D95）, the dose to critical organ at risk volume （ D5）, and mean dose has been used to compare two sets of treatment plans. Results： Compared with CT, the MRI-based target volume was 53.5% larger, and did not always include the same volume as defined by CT. For CT-based targets, 3-DCRT plans achieved adequate target coverage with sparing of the critical organ at risk . When these plans were compared to the target defned by the fusion of CT ＋ MRI image, the average PTV D95 was lower （59.78Gy）. For CT/MRI fusion-based targets, 3-DCRT plans achieved adequate target coverage, but the dose to critical organ at risk was significantly worse in some case. Conclusions： CT/MRI fusion improved the contouring of target volumes in NPC, but GTV were also larger. And the dose to critical organs at risk could also be increased.