Liang Jian, Wu Qiuwen, Yan Di
Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48073, USA.
Int J Radiat Oncol Biol Phys. 2009 Mar 1;73(3):935-43. doi: 10.1016/j.ijrobp.2008.10.019. Epub 2008 Dec 26.
For patients with intermediate- and high-risk prostate cancer, the seminal vesicles (SVs) are included in the clinical target volume (CTV). The purposes of this study are to investigate interfraction motion characteristics of the SVs and determine proper margins for online computed tomography image guidance.
Twenty-four patients, each with 16 daily helical computed tomography scans, were included in this study. A binary image mask was used for image registration to determine daily organ motion. Two online image-guided radiotherapy strategies (prostate only and prostate + SVs) were simulated in a hypofractionated scheme. Three margin designs were studied for both three-dimensional conformal radiotherapy and intensity-modulated radiotherapy (IMRT). In prostate-only guidance, Margin A was uniformly applied to the whole CTV, and Margin B was applied to the SVs with a fixed 3-mm prostate margin. In prostate plus SV guidance, Margin C was uniformly applied to the CTV. The minimum margins were sought to satisfy the criterion that minimum cumulative CTV dose be more than those of the planning target volume in the plan for greater than 95% of patients.
The prostate and SVs move significantly more in the anterior-posterior and superior-inferior than right-left directions. The anterior-posterior motion of the prostate and SVs correlated (R(2) = 0.7). The SVs move significantly more than the prostate. The minimum margins found were 2.5 mm for three-dimensional conformal radiotherapy and 4.5, 4.5, and 3.0 mm for Margins A, B, and C for IMRT, respectively. Margins for IMRT were larger, but the irradiated volume and doses to critical structures were smaller. Minimum margins of 4.5 mm to the SVs and 3 mm to the prostate are recommended for IMRT with prostate-only guidance.
The SVs move independently from the prostate gland, and additional margins are necessary for image-guided radiotherapy.
对于中高危前列腺癌患者，精囊（SVs）包含在临床靶区（CTV）内。本研究的目的是调查精囊的分次间运动特征，并确定在线计算机断层扫描图像引导的合适边界。
本研究纳入了24例患者，每位患者进行16次每日螺旋计算机断层扫描。使用二进制图像掩码进行图像配准以确定每日器官运动。在大分割方案中模拟了两种在线图像引导放射治疗策略（仅前列腺和前列腺+精囊）。研究了三维适形放疗和调强放疗（IMRT）的三种边界设计。在仅前列腺引导中，边界A均匀应用于整个CTV，边界B应用于精囊，并带有固定的3 mm前列腺边界。在前列腺加精囊引导中，边界C均匀应用于CTV。寻求最小边界以满足在超过95%的患者计划中，最小累积CTV剂量大于计划靶区剂量的标准。
前列腺和精囊在前后方向和上下方向的移动明显多于左右方向。前列腺和精囊的前后运动具有相关性（R(2)=0.7）。精囊的移动明显多于前列腺。三维适形放疗发现的最小边界为2.5 mm，IMRT的边界A、B和C分别为4.5、4.5和3.0 mm。IMRT的边界更大，但对关键结构的照射体积和剂量更小。对于仅前列腺引导的IMRT，建议精囊的最小边界为4.5 mm，前列腺为3 mm。
精囊独立于前列腺移动，图像引导放射治疗需要额外的边界。
