Tinger A, Michalski J M, Cheng A, Low D A, Zhu R, Bosch W R, Purdy J A, Perez C A
Radiation Oncology Center, Barnes-Jewish Hospital, Washington University School of Medicine, St. Louis, MO 63110, USA.
Int J Radiat Oncol Biol Phys. 1998 Aug 1;42(1):213-21. doi: 10.1016/s0360-3016(98)00189-8.
To determine an adequate planning target volume (PTV) margin for three-dimensional conformal radiotherapy (3D CRT) of prostate cancer, the uncertainties in the internal positions of the prostate and seminal vesicles (SV) and in the treatment setups were measured.
Weekly computed tomography (CT) scans of the pelvis (n=51) and daily electronic portal images (n=1630) were reviewed for eight patients who received seven-field 3D CRT for prostate cancer. The CT scans were registered in three dimensions to the original planning CT scan using commercially available software to measure the center-of volume (COV) motion of the prostate and SV. The daily portal images were registered to the corresponding simulation films to measure the setup displacements. The standard deviation (SD) of the internal organ motions was added to the SD of the setups in quadrature to determine the total uncertainty. Positive directions were left, anterior, and superior. Rotations necessary to register the CT scans and portal images were minimal and not further analyzed.
The mean motion for the COV of the prostate+/-the SD was 0+/-0.9 mm in the left-right (LR), 0.5+/-2.6 mm in the anterior-posterior (AP), and 1.5+/-3.9 mm in the superior-inferior (SI) directions. The mean motion for the COV of the SV+/-the SD was 0.3+/-1.7 mm in the LR, 0.7+/-3.8 mm in the AP, and 0.9+/-3.5 mm in the SI directions. For all patients the mean isocenter displacement+/-the SD was 0+/-3.1 mm in the LR, 1.4+/-3.0 mm in the AP, and -0.4+/-2.1 mm in the SI directions. The total uncertainty for the prostate was 3.2 mm, 4.0 mm, and 4.4 mm in the LR, AP, and SI directions, respectively. For the SV, the total uncertainty was 3.5, 4.8, and 4.1 mm in the LR, AP, and SI directions, respectively.
PTV margins of 10 to 16 mm are required to encompass all (99%) possible positions of the prostate or SV during 3D CRT. PTV margins of 7 to 11 mm will encompass the measured uncertainties with a 95% probability. PTV margins of 5 mm may not adequately cover the intended volume.
为确定前列腺癌三维适形放疗（3D CRT）的合适计划靶区（PTV）边界，对前列腺和精囊（SV）内部位置及治疗摆位的不确定性进行了测量。
回顾了8例接受前列腺癌七野3D CRT治疗患者的骨盆每周计算机断层扫描（CT）图像（n = 51）和每日电子射野图像（n = 1630）。使用商用软件将CT扫描图像在三维空间中与原始计划CT扫描图像配准，以测量前列腺和SV的体积中心（COV）运动。将每日射野图像与相应的模拟片配准以测量摆位位移。将内部器官运动的标准差（SD）与摆位标准差进行正交相加，以确定总不确定性。正方向为左、前和上。配准CT扫描图像和射野图像所需的旋转极小，未作进一步分析。
前列腺COV的平均运动±SD在左右（LR）方向为0±0.9 mm，前后（AP）方向为0.5±2.6 mm，上下（SI）方向为1.5±3.9 mm。SV的COV平均运动±SD在LR方向为0.3±1.7 mm，AP方向为0.7±3.8 mm，SI方向为0.9±3.5 mm。所有患者等中心的平均位移±SD在LR方向为0±3.1 mm，AP方向为1.4±3.0 mm，SI方向为 -0.4±2.1 mm。前列腺在LR、AP和SI方向的总不确定性分别为3.2 mm、4.0 mm和4.4 mm。对于SV，在LR、AP和SI方向的总不确定性分别为3.5 mm、4.8 mm和4.1 mm。
在3D CRT期间，需要10至16 mm的PTV边界来涵盖前列腺或SV的所有（99%）可能位置。7至11 mm的PTV边界有95%的概率涵盖测量到的不确定性。5 mm的PTV边界可能无法充分覆盖目标体积。
