Dosimetric comparison between 2-dimensional radiation therapy and intensity modulated radiation therapy in treatment of advanced T-STAGE nasopharyngeal carcinoma: To treat less or more in the planning organ-at-risk volume of the brainstem and spinal cord
Dosimetric comparison between 2-dimensional radiation therapy and intensity modulated radiation therapy in treatment of advanced T-STAGE nasopharyngeal carcinoma: To treat less or more in the planning organ-at-risk volume of the brainstem and spinal cord
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DOI：
10.1016/j.meddos.2007.02.006
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发表时间：
2007-12-01
影响因子：
1.2
通讯作者：
Chan, Anthony T. C.
中科院分区：
文献类型：
--
作者：
Chau, Ricky M. C.;Teo, Peter M. L.;Chan, Anthony T. C.
本研究旨在评估二维放射治疗（2DRT）在治疗晚期T3 - 4期鼻咽癌（NPC）时在靶区覆盖和器官保护方面的不足，并评估调强放射治疗（IMRT）所能达到的改善程度，尤其关注脑干和脊髓的计划危及器官体积（PRV）的剂量。对10例晚期T3 - 4期且N0 - 2期的鼻咽癌患者进行了剂量学研究。患者头部和颈部处于半伸展位固定，获取2.5毫米层厚的计算机断层扫描（CT）图像。为每位患者制定了基于何氏技术的二维计划以及基于7个共面射野排列的调强计划。二维放射治疗计划是依据模拟定位片上参照骨性标志绘制的射野边界和挡铅，经数字化后输入计划计算机以重建三维剂量分布。对二维放射治疗和调强放射治疗计划就靶区和危及器官（OARs）的剂量 - 体积直方图（DVHs）、肿瘤控制概率（TCP）以及正常组织并发症概率（NTCPs）进行评估和比较。采用调强放射治疗时，靶区的剂量覆盖优于二维放射治疗。大体肿瘤体积（GTV）和计划靶区体积（PTV）的平均最小剂量分别从二维放射治疗的33.7戈瑞提高到调强放射治疗的62.6戈瑞，以及从11.9戈瑞提高到47.8戈瑞。GTV和PTV的D - 95也分别从二维放射治疗的57.1戈瑞提高到调强放射治疗的67戈瑞，以及从45戈瑞提高到63.6戈瑞。调强放射治疗的肿瘤控制概率大幅提高到78.5%。调强放射治疗对关键正常器官也有更好的保护。脑干和脊髓所接受的平均最大剂量分别从二维放射治疗的61.8戈瑞显著降低到调强放射治疗的52.8戈瑞，以及从56戈瑞降低到43.6戈瑞，均在脑干54戈瑞和脊髓45戈瑞的常规剂量限值内。脑干和脊髓的计划危及器官体积上的平均最大沉积剂量分别为60.7戈瑞和51.6戈瑞，高于常规剂量限值。对于视交叉，平均最大剂量以及其体积的5%所接受的剂量分别从二维放射治疗的64.3戈瑞降低到调强放射治疗的53.7戈瑞，以及从62.8戈瑞降低到48.7戈瑞，相应的正常组织并发症概率从18.4%降低到2.1%。对于颞叶，其体积的10%（约4.6立方厘米）所接受的平均剂量从二维放射治疗的63.8戈瑞降低到调强放射治疗的55.4戈瑞，正常组织并发症概率从11.7%降低到3.4%。由于靶区覆盖和关键正常器官保护的改善，调强放射治疗技术可显著提高T3 - 4期鼻咽癌肿瘤的治疗比。尽管调强放射治疗中脑干和脊髓所接受的最大剂量可保持在或低于其常规剂量限值，但由于靶区和危及器官距离较近，计划危及器官体积上的最大沉积剂量往往超过这些限值。换句话说，对于T3 - 4期鼻咽癌肿瘤，调强放射治疗计划无法满足理想的剂量学考量。如果不想过度损害靶区剂量覆盖，就需要接受脑干和脊髓的计划危及器官体积的最大剂量限值的妥协。与二维放射治疗计划的剂量学比较表明，在局部晚期鼻咽癌的二维放射治疗计划中，这些计划危及器官体积的剂量限值也经常被超过。对大量接受二维放射治疗的T3 - 4期鼻咽癌患者的神经器官临床损伤发生率进行专门的回顾性研究，可能为探索在不损害正常器官功能的情况下最大程度提高靶区覆盖时计划危及器官体积剂量约束可放宽到何种程度提供有用的参考数据。（C）2007年美国医学剂量师协会
The aim of this study is to evaluate the deficiencies in target coverage and organ protection of 2-dimensional radiation therapy (2DRT) in the treatment of advanced T-stage T3-4) nasopharyngeal carcinoma (NPC), and assess the extent of improvement that could be achieved with intensity modulated radiation therapy IMRT), with special reference to of the dose to the planning organ-at-risk volume (PRV) of the brainstem and spinal cord. A dosimetric study was performed on 10 patients with advanced T-stage (T3-4 and N0-2) NPC. Computer tomography (CT) images of 2.5-mm slice thickness of the head and neck were acquired with the patient immobilized in semi-extended-head position. A 2D plan based on Ho's technique, and an IMRT plan based on a 7-coplanar portals arrangement, were established for each patient. 2DRT was planned with the field borders and shielding drawn on the simulator radiograph with reference to bony landmarks, digitized, and entered into a planning computer for reconstruction of the 3D dose distribution. The 2DRT and IMRT treatment plans were evaluated and compared with respect to the dose-volume histograms (DVHs) of the targets and the organs-at-risk (OARs), tumor control probability (TCP), and normal tissue complication probabilities (NTCPs). With IMRT, the dose coverage of the target was superior to that of 2DRT. The mean minimum dose of the GTV and PTV were increased from 33.7 Gy (2DRT) to 62.6 Gy (IMRT), and 11.9 Gy (2DRT) to 47.8 Gy (IMRT), respectively. The D-95 of the GTV and PTV were also increased from 57.1 Gy (2DRT) to 67 Gy (IMRT), and 45 Gy (2DRT) to 63.6 Gy (IMRT), respectively. The TCP was substantially increased to 78.5% in IMRT. Better protection of the critical normal organs was also achieved with IMRT. The mean maximum dose delivered to the brainstem and spinal cord were reduced significantly from 61.8 Gy (2DRT) to 52.8 Gy IMRT) and 56 Gy (2DRT) to 43.6 Gy IMRT), respectively, which were within the conventional dose limits of 54 Gy for brainstem and of 45 Gy for spinal cord. The mean maximum doses deposited on the PRV of the brainstem and spinal cord were 60.7 Gy and 51.6 Gy respectively, which were above the conventional dose limits. For the chiasm, the mean dose maximum and the dose to 5% of its volume were reduced from 64.3 Gy (2DRT) to 53.7 Gy (IMRT) and from 62.8 Gy (2DRT) to 48.7 Gy IMRT), respectively, and the corresponding NTCP was reduced from 18.4% to 2.1%. For the temporal lobes, the mean dose to 10 % of its volume (about 4.6 cc) was reduced from 63.8 Gy (2DRT) to 55.4 Gy (IMRT) and the NTCP was decreased from 11.7% to 3.4%. The therapeutic ratio for T3-4 NPC tumors can be significantly improved with IMRT treatment technique due to improvement both in target coverage and the sparing of the critical normal organ. Although the maximum doses delivered to the brainstem, and spinal cord in IMRT can be kept at or below their conventional dose limits, the maximum doses deposited on the PRV often exceed these limits due to the close proximity between the target and OARs. In other words, ideal dosimetric considerations cannot be fulfilled in IMRT planning for T34 NPC tumors. A compromise of the maximal dose limit to the PRV of the brainstem and spinal cord would need be accepted if dose coverage to the targets is not to be unacceptably compromised. Dosimetric comparison with 2DRT plans show that these dose limits to PRV were also frequently exceeded in 2DRT plans for locally advanced NPC.A dedicated retrospective study on the incidence of clinical injury to neurological organs in a large seriesof patients with T3-4 NPC treated by 2DRT may provide useful reference data in exploring how far the PRV dose constraints may be relaxed, to maximize the target coverage without compromising the normal organ function. (C) 2007 American Association of Medical Dosimetrists.