The impact of daily setup variations on head-and-neck intensity-modulated radiation therapy
The impact of daily setup variations on head-and-neck intensity-modulated radiation therapy
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DOI：
10.1016/j.ijrobp.2004.07.696
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发表时间：
2005-03-01
影响因子：
7
通讯作者：
Harari, PM
中科院分区：
文献类型：
--
作者：
Hong, TS;Tomé, WA;Harari, PM
目的：强度调节放射治疗（IMRT）在头颈部（H&N）癌症的治疗中提供了减少正常组织毒性的机会，从而提高患者的生活质量。然而，高度适形的治疗技术通常在肿瘤和回避结构之间建立陡峭的剂量梯度。因此，日常设置的变化会显著影响理想的H&N IMRT输送的最终精度。本研究提供了关于每日设置变化对H&N IMRT整体完整性的潜在影响的详细分析。方法与材料：前瞻性纳入10例晚期H&N癌患者进行临床试验，以检查每日H&N放疗设置的准确性。这些患者采用三维治疗计划技术（非IMRT）进行常规收缩场设计治疗。使用现代H&N实践技术进行固定和对准，包括传统的热塑性遮盖，基底板固定到治疗床，三点激光对准和每周门静脉膜评估。在传统的激光对准之后，使用高精度光学引导的患者定位系统，每天通过测量与指定等心的3个笛卡尔和3个角偏差来评估每个患者的设置精度，该系统提供亚毫米级的设置精度。然后将这些位置误差应用于不同系列的10个H&N IMRT计划，详细分析在30天的治疗过程中，每日设置变化（无光学引导）对IMRT计划最终完整性的影响。对正常结构的剂量-体积直方图（DVH）、等效均匀剂量（EUD）、平均总剂量（mTd）和最大总剂量（mTd）进行了分析，分析了纳入和不纳入每日设置变化的IMRT计划。结果：采用常规的H&N掩蔽和激光对中进行日常定位，任意单一维度的平均设置误差平均为3.33 mm。然而，当考虑到所有六个自由度时，使用光学引导的患者定位系统，平均复合矢量偏移量为6.97 rum，标准差为3.63 mm。在理想的H&N IMRT治疗方案上叠加平均偏移向量，可以评估DVH、EUD、mTd和mTd计算结果的变化。当这些平均位置偏移合并时，部分地理肿瘤遗漏（GTV剂量不足）和正常组织过量是常见的。当应用最大偏移历史时，定义肿瘤体积的EUD下降幅度高达21%，当应用最小和中位偏移历史时，EUD下降幅度为3-14%。结论：成功实施H&N IMRT需要在6至7周的治疗过程中提供准确和可重复的治疗。传统的H&N掩蔽技术经常发生的每日设置变化的不利影响可能比认识到的要大得多。二维正交膜的等中心验证检查可能不足以提醒临床医生三维偏移矢量的大小及其对整体IMRT交付质量的影响。可能会发生未被识别的地理缺失和由此产生的靶剂量不足。同样，某些正常结构，如腮腺，可能接受比预期更高的剂量。这项研究的结果表明，比传统的遮盖和常规的患者设置跟踪方法更严格的固定技术对于精确监测和成功提供高质量的恶性肿瘤IMRT非常重要。(C) 2005爱思唯尔公司
Purpose: Intensity- modulated radiation therapy (IMRT) in the treatment of head-and-neck (H&N) cancer provides the opportunity to diminish normal tissue toxicity profiles and thereby enhance patient quality of life. However, highly conformal treatment techniques commonly establish steep dose gradients between tumor and avoidance structures. Daily setup variations can therefore significantly compromise the ultimate precision of idealized H&N IMRT delivery. This study provides a detailed analysis regarding the potential impact of daily setup variations on the overall integrity of H&N IMRT.Methods and Materials: A series of 10 patients with advanced H&N cancer were prospectively enrolled in a clinical trial to examine daily H&N radiation setup accuracy. These patients were treated with conventional shrinking field design using three-dimensional treatment planning techniques (not IMRT). Immobilization and alignment were performed using modern H&N practice techniques including conventional thermoplastic masking, baseplate fixation to the treatment couch, three-point laser alignment, and weekly portal film evaluation. After traditional laser alignment, setup accuracy was assessed daily for each patient by measuring 3 Cartesian and 3 angular deviations from the specified isocenter using a high-precision, optically guided patient localization system, which affords submillimeter setup accuracy. These positional errors were then applied to a distinct series of 10 H&N IMRT plans for detailed analysis regarding the impact of daily setup variation (without optical guidance) on the ultimate integrity of IMRT plans over a 30-day treatment course. Dose-volume histogram (DVH), equivalent uniform dose (EUD), mean total dose (mTd), and maximal total dose (MTD) for normal structures were analyzed for IMRT plans with and without incorporation of daily setup variation.Results: Using conventional H&N masking and laser alignment for daily positioning, the mean setup error in any single dimension averaged 3.33 mm. However, when all six degrees of freedom were accounted for, using the optically guided patient localization system, the mean composite vector offset was 6.97 rum with a standard deviation of 3.63 mm. Superimposition of mean offset vectors on idealized H&N IMRT treatment plans enabled evaluation of resultant shifts in DVH, EUD, mTd, and MTD calculations. Partial geographic tumor miss (GTV underdosing) and normal tissue overdosing was common when these mean positional offsets were incorporated. The decrease in EUD for defined tumor volumes ranged up to 21% when the largest offset histories were applied, and 3-14% for plans when the least and median offset histories were applied.Conclusion: The successful implementation of H&N IMRT requires accurate and reproducible treatment delivery over a 6- to 7-week treatment course. The adverse impact of daily setup variation, which occurs routinely with conventional H&N masking techniques, may be considerably greater than recognized. Isocenter verification checks on two-dimensional orthogonal films may not sufficiently alert the clinician to the magnitude of threedimensional offset vectors and the resultant impact on the quality of overall IMRT delivery. Unrecognized geographic miss and resultant target underdose may occur. Similarly, selected normal structures such as parotid glands may receive higher doses than intended. The results of this study suggest that more rigorous immobilization techniques than conventional masking and routine patient setup tracking methodologies are important for the accurate monitoring and successful delivery of high-quality IMRT for HN cancer. (C) 2005 Elsevier Inc.