Simon Antoine, Le Maitre Amandine, Nassef Mohamed, Rigaud Bastien, Castelli Joël, Acosta Oscar, Haigron Pascal, Lafond Caroline, de Crevoisier Renaud
INSERM, U1099, 35000 Rennes, France; Laboratoire Traitement du Signal et de l'Image, Université de Rennes 1, 35000 Rennes, France.
INSERM, U1099, 35000 Rennes, France; Laboratoire Traitement du Signal et de l'Image, Université de Rennes 1, 35000 Rennes, France.
Int J Radiat Oncol Biol Phys. 2017 Mar 15;97(4):830-838. doi: 10.1016/j.ijrobp.2016.12.011. Epub 2016 Dec 12.
To assess dose uncertainties resulting from the dose deformation-invariance hypothesis in prostate cone beam computed tomography (CT)-based image guided radiation therapy (IGRT), namely to evaluate whether rigidly propagated planned dose distribution enables good estimation of fraction dose distributions.
Twenty patients underwent a CT scan for planning intensity modulated radiation therapy-IGRT delivering 80 Gy to the prostate, followed by weekly CT scans. Two methods were used to obtain the dose distributions on the weekly CT scans: (1) recalculating the dose using the original treatment plan; and (2) rigidly propagating the planned dose distribution. The cumulative doses were then estimated in the organs at risk for each dose distribution by deformable image registration. The differences between recalculated and propagated doses were finally calculated for the fraction and the cumulative dose distributions, by use of per-voxel and dose-volume histogram (DVH) metrics.
For the fraction dose, the mean per-voxel absolute dose difference was <1 Gy for 98% and 95% of the fractions for the rectum and bladder, respectively. The maximum dose difference within 1 voxel reached, however, 7.4 Gy in the bladder and 8.0 Gy in the rectum. The mean dose differences were correlated with gas volume for the rectum and patient external contour variations for the bladder. The mean absolute differences for the considered volume receiving greater than or equal to dose x (V) of the DVH were between 0.37% and 0.70% for the rectum and between 0.53% and 1.22% for the bladder. For the cumulative dose, the mean differences in the DVH were between 0.23% and 1.11% for the rectum and between 0.55% and 1.66% for the bladder. The largest dose difference was 6.86%, for bladder V. The mean dose differences were <1.1 Gy for the rectum and <1 Gy for the bladder.
The deformation-invariance hypothesis was corroborated for the organs at risk in prostate IGRT except in cases of a large disappearance or appearance of rectal gas for the rectum and large external contour variations for the bladder.
评估在基于前列腺锥形束计算机断层扫描(CT)的图像引导放射治疗(IGRT)中,剂量变形不变性假设所导致的剂量不确定性,即评估刚性传播的计划剂量分布是否能够很好地估计分次剂量分布。
20例患者接受CT扫描以制定强度调制放射治疗 - IGRT计划,给予前列腺80 Gy剂量,随后每周进行CT扫描。采用两种方法在每周的CT扫描上获取剂量分布:(1)使用原始治疗计划重新计算剂量;(2)刚性传播计划剂量分布。然后通过可变形图像配准在每个剂量分布的危及器官中估计累积剂量。最后,通过体素和剂量体积直方图(DVH)指标计算重新计算剂量与传播剂量之间在分次剂量和累积剂量分布上的差异。
对于分次剂量,直肠和膀胱分别有98%和95%的分次体素平均绝对剂量差异<1 Gy。然而,在膀胱中1个体素内的最大剂量差异达到7.4 Gy,在直肠中为8.0 Gy。直肠的平均剂量差异与气体体积相关,膀胱的平均剂量差异与患者外部轮廓变化相关。对于DVH中接受大于或等于剂量x(V)的考虑体积,直肠的平均绝对差异在0.37%至0.70%之间,膀胱的平均绝对差异在0.53%至1.22%之间。对于累积剂量,直肠DVH中的平均差异在0.23%至1.11%之间,膀胱的平均差异在0.55%至1.66%之间。膀胱V的最大剂量差异为6.86%。直肠的平均剂量差异<1.1 Gy,膀胱的平均剂量差异<1 Gy。
除了直肠中出现大量直肠气体消失或出现以及膀胱外部轮廓有较大变化的情况外,前列腺IGRT中危及器官的变形不变性假设得到了证实。