基于形变配准的鼻咽癌调强放射治疗计划剂量学研究

目的 探讨形变配准技术在鼻咽癌患者治疗过程中靶区、正常组织的几何改变及相应的剂量学改变。方法 选取12例采用IMRT-SIB治疗的鼻咽癌患者,针对首次定位CT制定放疗计划为计划1(CT1), 治疗20~25次后,针对复位CT制定放疗计划为计划2(CT2)。将 CT1中的剂量分布形变配准至图像CT2上,为计划1(CT2);同时将患者CT1中25次治疗剂量和 CT2中的剩余5次治疗剂量进行剂量叠加,为计划1+2(CT2)。比较计划1(CT1)、计划1(CT2)和计划1+2(CT2)中的剂量分布。结果 图像CT2和CT1相比,右侧和左侧腮腺体积明显缩小(24.6±11.9)%、(35.1±20.1)%。与计划1 (CT1)相比,在计划1 (CT2)中靶区(D₉₅)和PGTV、PTV2(Dmean)明显降低,计划1+2 (CT2)中数据表明,如果25次后修改计划会提高靶区剂量。在12例患者中有5例患者如果不重新修改计划则脑干脊髓受量会超过剂量限制,如果修改计划则会降低。结论 鼻咽癌患者在治疗中靶区及腮腺体积有明显缩小,重新定位修改计划可确保靶区足够剂量,并且使危及器官受量控制在安全范围之内。

Dosimetric study of planning of intensity-modulated radiotherapy based on deformable registration for patients with nasopharyngeal carcinoma during the course

Objective To evaluate the anatomic changes and dosimetric variations of patients with nasopharyngeal carcinoma (NPC) during the course of simultaneous integrated boost intensity-modulated radiotherapy (SIB-IMRT) by comparison of the dosimetric differences with or without replanning. Methods Twelve cases with NPC treated with SIB-IMRT underwent repeated CT scans after 20-25 fractions of the initiation of therapy. The original treatment plan (Plan1) based on the first CT scan (CT1) and the second IMRT plan (Plan 2) based on the second CT scan (CT2) were calculated with an inverse planning system (Pinnacle³, Philips Medical System). In addition, the hybrid IMRT plan, Plan1 (CT2), was generated by deformable registration with MIMVISTA software, and the doses in Plan 1 (CT1) and Plan 2 (CT2) were accumulated based on CT2. The dosimetric differences were compared among the Plan 1 (CT1), Plan 1 (CT2) and Plan 1+2(CT2). Results Compared with CT1, the mean volumes of the right and left parotid glands in the CT2 were significantly smaller by (24.6±11.9)% and (35.1±20.1)%, respectively. Compared with Plan 1 (CT1), the dose received by 95% of the target ( D₉₅) to PGTV, PTV1 and PTV2, and mean dose (Dmean) to PGTV, and PTV2 were all significantly lower in the Plan 1 (CT2), indicating that the doses to targets decreased without replanning. With repeated CT and replanning after 25 fractions as shown in Plan 1+2(CT2), the doses to targets would be improved. The doses to normal tissue were increased without replanning, although no statistical significance was observed. In 5 of 12 cases, the doses to the spinal cord and brainstem exceeded the constraint without replanning, while the corresponding values decreased with replanning. Conclusions During the course of IMRT for cases with NPC, the volumes of the targets and parotid glands decrease significantly. Mid-treatment CT scanning and replanning should be recommended to ensure adequate doses to the targets and safe doses to the normal tissues.