Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY, USA.
Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, USA.
J Appl Clin Med Phys. 2019 Jul;20(7):121-127. doi: 10.1002/acm2.12665. Epub 2019 Jun 17.
To determine the impact of using fiducial match for daily image-guidance on pelvic lymph node (PLN) coverage for prostate cancer patients receiving stereotactic body radiation therapy (SBRT).
Thirty patients underwent SBRT treatment to the prostate and PLN from 2014 to 2016. Each patient received either 800cGy × 5 or 500cGy × 5 to the prostate and 500cGy × 5 to the PLN. A 5 mm clinical target volume (CTV)-to-planning target volume (PTV) margin around the PLN was used for planning. Two registrations with planning computed tomography (PCT) for each of the daily cone beam CTs (CBCTs) were performed: a rigid registration to fiducials and to the bony anatomy. The average translational difference between fiducial and bony match as well as percentage of fractions with differences > 5mm were calculated. Changes in bladder and rectal volume as well as center-of-mass (COM) position from simulation parameters, and their correlation with translational difference were also evaluated. The dosimetric impact of the translational differences was calculated by shifting the plan isocenter.
The average translational difference between fiducial and bony match was 0.06 ± 0.82, 2.1 ± 4.1, -2.8 ± 4.3, and 5.5 ± 4.2 mm for lateral, vertical, longitudinal, and vector directions. The average change in bladder and rectal volume from simulation was -67.2 ± 163.04 cc (-12 ± 52%) and -1.6 ± 18.75 (-2 ± 30%) cc. The average change in COM of bladder from the simulation position was 0.34 ± 2.49, 4.4 ± 8.1, and -3.9 ± 7.5 mm along the LR, AP, and SI directions. The corresponding COM change for the rectum was 0.17 ± 1.9, 1.34 ± 3.5, and -0.6 ± 5.2 mm.
The 5 mm margin covered ~75% of fractions receiving PLN irradiation with SBRT, daily CBCT and fiducial-guided setup. The dosimetric impact on PLN coverage was significant in 19% of fractions or 25% of patients. A larger translational shift was due to variation in rectal volume and changes in COM position of the bladder and rectum. A consistent bladder positioning and/or rectum filling compared with presimulation volume were essential for adequate coverage of PLN in a hypofractionated treatment regime.
确定在接受立体定向体放射治疗（SBRT）的前列腺癌患者中，使用基准点配准进行每日图像引导对骨盆淋巴结（PLN）覆盖的影响。
2014 年至 2016 年期间，30 名患者接受了前列腺和 PLN 的 SBRT 治疗。每位患者均接受前列腺 800cGy×5 或 500cGy×5，PLN 接受 500cGy×5。PLN 规划时使用 5mm 临床靶区（CTV）-计划靶区（PTV）边缘。每天的锥形束 CT（CBCT）进行了两次与计划 CT（PCT）的配准：一次是基于基准点的刚性配准，一次是基于骨性解剖结构的配准。计算了基准点和骨性配准之间的平均平移差异以及差异>5mm 的分数比例。还评估了膀胱和直肠体积以及中心质量（COM）位置从模拟参数的变化，以及它们与平移差异的相关性。通过移位计划等中心点来计算平移差异的剂量学影响。
基准点和骨性配准之间的平均平移差异分别为 0.06±0.82、2.1±4.1、-2.8±4.3 和 5.5±4.2mm，方向分别为横向、纵向、纵向和向量。从模拟中膀胱和直肠体积的平均变化为-67.2±163.04cc（-12±52%）和-1.6±18.75cc（-2±30%）。膀胱 COM 从模拟位置的平均变化分别为 0.34±2.49、4.4±8.1 和-3.9±7.5mm，沿 LR、AP 和 SI 方向。直肠对应的 COM 变化分别为 0.17±1.9、1.34±3.5 和-0.6±5.2mm。
在接受 SBRT、每日 CBCT 和基于基准点的设置的患者中，5mm 边缘覆盖了大约 75%的 PLN 照射分数。在 19%的分数或 25%的患者中，PLN 覆盖的剂量学影响显著。较大的平移偏移是由于直肠体积的变化以及膀胱和直肠 COM 位置的变化所致。在分次治疗方案中，为了充分覆盖 PLN，需要保持膀胱的一致定位和/或直肠的充盈，使其与预模拟体积相比。
