Emami Bahman, Sethi Anil, Petruzzelli Guy J
Department of Radiation Oncology, Loyola University Medical Center, Maywood, IL 60153, USA.
Int J Radiat Oncol Biol Phys. 2003 Oct 1;57(2):481-8. doi: 10.1016/s0360-3016(03)00570-4.
To compare CT and MRI target volumes for nasopharyngeal carcinoma (NPC) and evaluate the role of intensity-modulated radiotherapy (IMRT) in treating composite CT+MRI targets.
CT and T(1)/T(2)-weighted MRI scans were obtained for 8 consecutive 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 structures were outlined. For each patient, three treatment plans were developed: (1) a three-dimensional conformal RT (3D-CRT) plan using CT-based targets; (2) a 3D-CRT plan using composite CT+MRI targets; and (3) a IMRT plan using CT+MRI targets. The prescription dose was 57.6 Gy and 70.2 Gy to the initial and boost PTV, respectively. Treatment plans were compared using the PTV dose to 95% volume (D(95)), critical structure dose to 5% organ volume (D(5)), and mean dose.
Compared with CT, the MRI-based targets were 74% larger, more irregularly shaped, and did not always include the CT targets. For CT-based targets, 3D-CRT plans, in general, achieved adequate target coverage and sparing of critical structures. However, when these plans were evaluated using CT+MRI targets, the average PTV D(95) was approximately 60 Gy (14% underdosing), and critical structure doses were significantly worse. The use of IMRT for CT+MRI targets resulted in marked improvement in the PTV coverage and critical structure sparing: average PTV D(95) improved to 69.3 Gy, brainstem D(5) to <43 Gy (19% reduction), spinal cord D(5) to <37 Gy (19% reduction), and the mean dose to the parotids and cochlea reduced to below tolerance (23.7 Gy and 35.6 Gy, respectively).
CT/MRI fusion improved the determination of target volumes in NPC. In contrast to 3D-CRT, IMRT planning resulted in significantly improved coverage of composite CT+MRI targets and sparing of critical structures.
比较鼻咽癌（NPC）的CT和MRI靶区体积，并评估调强放疗（IMRT）在治疗复合CT+MRI靶区中的作用。
对8例连续的NPC患者进行CT和T（1）/T（2）加权MRI扫描。利用CT、MRI以及融合后的CT/MRI，勾勒出各种靶区体积（大体肿瘤体积、临床靶体积和计划靶体积[PTV]）及关键结构。对每位患者制定三个治疗计划：（1）基于CT靶区的三维适形放疗（3D-CRT）计划；（2）基于复合CT+MRI靶区的3D-CRT计划；（3）基于CT+MRI靶区的IMRT计划。初始PTV和推量PTV的处方剂量分别为57.6 Gy和70.2 Gy。使用PTV 95%体积的剂量（D（95））、关键结构5%器官体积的剂量（D（5））和平均剂量对治疗计划进行比较。
与CT相比，基于MRI的靶区大74%，形状更不规则，且并非总是包含CT靶区。对于基于CT的靶区，3D-CRT计划总体上实现了足够的靶区覆盖并保护了关键结构。然而，当使用CT+MRI靶区评估这些计划时，平均PTV D（95）约为60 Gy（剂量不足14%），关键结构剂量明显更差。使用IMRT治疗CT+MRI靶区使PTV覆盖和关键结构保护有显著改善：平均PTV D（95）提高到69.3 Gy，脑干D（5）降至<43 Gy（降低19%），脊髓D（5）降至<37 Gy（降低19%），腮腺和耳蜗的平均剂量降至耐受剂量以下（分别为23.7 Gy和35.6 Gy）。
CT/MRI融合改善了NPC靶区体积的确定。与3D-CRT相比，IMRT计划显著提高了复合CT+MRI靶区的覆盖并更好地保护了关键结构。
