Department of Radiation and Cellular Oncology, The University of Chicago Medical Center, IL, USA.
Radiother Oncol. 2012 May;103(2):270-4. doi: 10.1016/j.radonc.2011.07.024. Epub 2011 Sep 2.
To determine the total setup error and the required planning target volume (PTV) margin for prostate bed without image guided radiotherapy (IGRT), and to demonstrate the feasibility and dosimetric benefit of IGRT post prostatectomy using surgical clips.
Seventeen patients were treated with intensity modulated radiotherapy (IMRT) to the prostate bed with a 1cm PTV margin. Three-dimensional shifts of the surgical clips inside the prostate bed were measured with respect to the isocenter from 364 orthogonal kV image pairs, and the total setup error was calculated to determine the required PTV margin. Alternative IMRT plans using 5mm or 1cm PTV expansion were generated and compared for rectal and bladder sparing.
Surgical clips were reproducibly and reliably identified. The mean (standard deviation) shifts in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP), axes were: -0.1 mm (1.7 mm), 0.6 mm (2.4 mm), and -2.1 mm (2.6 mm), respectively. The required PTV margins were calculated to be 6, 8, and 9 mm in the LR, AP, and SI axis, respectively. A PTV expansion of 5mm, compared to 1cm, significantly reduced V65 Gy to the rectum by 10%.
In the absence of IGRT, a non-uniform PTV margin of 6mm LR, 8mm AP, and 9 mm SI should be considered. Use of clips as fiducial markers can decrease the total setup error, enable a smaller PTV margin, and improve rectal sparing.
确定无影像引导放疗（IGRT）时前列腺床的总摆位误差和所需计划靶区（PTV）边界，并展示前列腺切除术后使用手术夹进行 IGRT 的可行性和剂量学优势。
17 例患者接受了前列腺床强度调制放疗（IMRT），PTV 边界为 1cm。通过 364 对正交千伏图像对，测量了前列腺内手术夹相对于等中心的三维移位，并计算总摆位误差，以确定所需的 PTV 边界。生成了使用 5mm 或 1cm PTV 扩展的替代 IMRT 计划，并对直肠和膀胱保护进行了比较。
手术夹可重复且可靠地识别。左右（LR）、上下（SI）和前后（AP）轴的平均（标准差）移位分别为：-0.1mm（1.7mm）、0.6mm（2.4mm）和-2.1mm（2.6mm）。LR、AP 和 SI 轴的 PTV 边界分别计算为 6、8 和 9mm。与 1cm 相比，PTV 扩展 5mm 可使直肠的 V65Gy 显著减少 10%。
在没有 IGRT 的情况下，LR 应为 6mm、AP 应为 8mm、SI 应为 9mm 的非均匀 PTV 边界应被考虑。使用夹作为基准标记可以减少总摆位误差，使 PTV 边界更小，并改善直肠保护。
