Virginia Commonwealth University, Richmond, VA 23298, United States.
Radiother Oncol. 2012 Nov;105(2):207-13. doi: 10.1016/j.radonc.2012.10.011. Epub 2012 Nov 29.
To investigate dose deformation-invariance in adaptive prostate radiation treatment.
A 19 patient prostate cancer-cohort with 8-13 CTs/patient is used. The 79.2 Gy plans are developed on the reference image using seven 6 and 18 MV intensity-modulated beams with identical RTOG 0126 objectives. Dose on the subsequent images is evaluated in two ways: (A1) Dose is recalculated on each image. (A2) The initially planned dose distribution is copied to each image. A2 assumes dose-invariance in the accelerator-coordinate-system. Effects of patient miss-alignment are simulated by 27 per-patient image shifts; 0 and ±10 mm in left-right, anterior-posterior and superior-inferior directions. The per-voxel dose differences for each patient image, total accumulated patient dose, and dose-volume metrics (CTV-D98 and -D90, bladder- and rectum-D50, -D35, -D25 and -D15) are used to compare A1 and A2.
The per-voxel mean percent difference in A1 and A2 dose over all patient images at 6 MV is (0.01±1.56)% and at 18 MV is (0.00±0.96)%. For 6 MV and 18 MV plans, the root-mean-square-percentage-error (RMSPE) in A2 over all patient image shifts are CTV-D98=0.94 and 0.55, CTV-D90=0.92 and 0.55, rectum-D50, -D35, -D25 and -D15=1.00, 0.96, 0.86, 0.80 and 0.84, 0.96, 0.92, 1.05; and bladder-D50, -D35, -D25, -D15=1.07, 0.88, 0.78, 0.72 and 1.61, 0.93, 0.67, 0.51. The dose differences are not correlated to the dice-similarity coefficients; with respective correlation-coefficients for CTV, rectum and bladder being -0.17, -0.17 and 0.081.
Assumption of shift- and deformation-invariant dose distributions on an average introduces <2% error in evaluated dose-volume metrics for 6 and 18 MV IMRT prostate plans. Use of invariant dose distributions has a potential to reduce online re-planning time and permit pre-planning based on tissue deformation models.
研究自适应前列腺放射治疗中的剂量变形不变性。
使用了一个有 19 名前列腺癌患者的队列，每个患者有 8-13 次 CT 扫描。在参考图像上使用 7 个 6 和 18 MV 强度调制束来开发 79.2 Gy 计划，这些束具有相同的 RTOG 0126 目标。随后在两种方式下评估图像上的剂量：（A1）重新计算每个图像上的剂量。（A2）将最初计划的剂量分布复制到每个图像上。A2 假设加速器坐标系中的剂量不变。通过每个患者 27 次图像移位模拟患者对位不良的影响；左右、前后和上下方向的 0 和±10 mm。对于每个患者图像，使用每个体素的剂量差异、总累积患者剂量以及剂量体积指标（CTV-D98 和-D90、膀胱和直肠-D50、-D35、-D25 和-D15）来比较 A1 和 A2。
在所有患者图像上，6 MV 时 A1 和 A2 剂量的体素平均百分比差异为（0.01±1.56）%，18 MV 时为（0.00±0.96）%。对于 6 MV 和 18 MV 计划，A2 在所有患者图像移位的均方根百分比误差（RMSPE）为 CTV-D98=0.94 和 0.55、CTV-D90=0.92 和 0.55、直肠-D50、-D35、-D25 和-D15=1.00、0.96、0.86、0.80 和 0.84、0.96、0.92、1.05；膀胱-D50、-D35、-D25、-D15=1.07、0.88、0.78、0.72 和 1.61、0.93、0.67、0.51。剂量差异与骰子相似性系数无关；CTV、直肠和膀胱的相应相关系数分别为-0.17、-0.17 和 0.081。
对于 6 和 18 MV IMRT 前列腺计划，假设剂量分布的移位和变形不变性平均会引入<2%的评估剂量体积指标误差。使用不变剂量分布有可能减少在线重新计划时间，并允许基于组织变形模型进行预计划。
