Department of Radiation Oncology, Center for Advanced Radiotherapy Technologies, University of California, San Diego, La Jolla, CA, USA.
Int J Radiat Oncol Biol Phys. 2012 Aug 1;83(5):1500-5. doi: 10.1016/j.ijrobp.2011.10.027. Epub 2012 Jan 21.
To model interfraction clinical target volume (CTV) variation in patients with intact cervical cancer and design a planning target volume (PTV) that minimizes normal tissue dose while maximizing CTV coverage.
We analyzed 50 patients undergoing external-beam radiotherapy for intact cervical cancer using daily online cone-beam computed tomography (CBCT). The CBCTs (n = 972) for each patient were rigidly registered to the planning CT. The CTV was delineated on the planning CT (CTV(0)) and the set of CBCTs ({CTV(1)-CTV(25)}). Manual (n = 98) and automated (n = 668) landmarks were placed over the surface of CTV(0) with reference to defined anatomic structures. Normal vectors were extended from each landmark, and the minimum length required for a given probability of encompassing CTV(1)-CTV(25) was computed. The resulting expansions were used to generate an optimized PTV.
The mean (SD; range) normal vector length to ensure 95% coverage was 4.3 mm (2.7 mm; 1-16 mm). The uniform expansion required to ensure 95% probability of CTV coverage was 13 mm. An anisotropic margin of 20 mm anteriorly and posteriorly and 10 mm superiorly, inferiorly, and laterally also would have ensured a 95% probability of CTV coverage. The volume of the 95% optimized PTV (1470 cm(3)) was significantly lower than both the anisotropic PTV (2220 cm(3)) and the uniformly expanded PTV (2110 cm(3)) (p < 0.001). For a 95% probability of CTV coverage, normal lengths of 1-3 mm were found along the superior and lateral regions of CTV(0), 5-10 mm along the interfaces of CTV(0) with the bladder and rectum, and 10-14 mm along the anterior surface of CTV(0) at the level of the uterus.
Optimizing PTV definition according to surface landmarking resulted in a high probability of CTV coverage with reduced PTV volumes. Our results provide data justifying planning margins to use in practice and clinical trials.
对宫颈癌患者的分次间临床靶区（CTV）变化进行建模，并设计一个既能最大限度地覆盖 CTV，又能最小化正常组织剂量的计划靶区（PTV）。
我们分析了 50 例接受宫颈癌外照射放疗的患者，使用每日在线锥形束 CT（CBCT）。每位患者的 CBCT（n = 972）均与计划 CT 进行刚性配准。CTV 是在计划 CT（CTV(0)）和一系列 CBCT 上勾画的（CTV(1)-CTV(25)）。通过参考定义的解剖结构，手动（n = 98）和自动（n = 668）地标放置在 CTV(0)的表面上。从每个地标延伸出法向量，并计算出给定 CTV(1)-CTV(25)包络概率所需的最小长度。由此产生的扩展用于生成优化的 PTV。
确保 95%覆盖率所需的平均（标准差；范围）法向量长度为 4.3mm（2.7mm；1-16mm）。为确保 95%CTV 覆盖率概率所需的统一扩展为 13mm。在前部和后部各有 20mm、在上下部各有 10mm 的各向异性边界也将确保 95%CTV 覆盖率概率。95%优化 PTV（1470cm3）的体积明显低于各向异性 PTV（2220cm3）和均匀扩展 PTV（2110cm3）（p<0.001）。为了达到 95%CTV 覆盖率概率，在 CTV(0)的上侧和外侧区域发现法向量长度为 1-3mm，在 CTV(0)与膀胱和直肠的界面处发现 5-10mm，在前侧表面上发现 10-14mm CTV(0)的子宫水平。
根据表面标志定位优化 PTV 定义可使 CTV 覆盖率达到较高水平，同时减少 PTV 体积。我们的结果提供了数据，为实践和临床试验中使用的计划边缘提供了依据。
