Department of Radiation Oncology, University of Colorado Denver, Aurora, Colorado 80045, USA.
Med Phys. 2010 Feb;37(2):629-37. doi: 10.1118/1.3284249.
Anatomical deformations of prostate-bed, rectum, and bladder can compromise the targeting accuracy in post-prostatectomy cancer patients. In this work, the impact of anatomical interventions on the localization data from post-prostatectomy patients who received image-guided IMRT was analyzed.
Patients were localized daily with online kilovoltage cone-beam computed tomography (kV-CBCT). The target and the organs at risk (OARs) positional and volumetric changes were evaluated and couch shifts were applied. For patients with large target or OAR volumetric changes, quantified by either a rectal or bladder wall displacement of >5 mm on the CBCT sagittal images compared to the planning CT, repeated localization CBCT scans were performed following an interventional procedure. The procedure involves insertion of a catheter to deflate the rectum, evacuation of stools, and/or adjustment of bladder filling. The required shifts were then evaluated, and the IMRT treatment was subsequently delivered after proper patient positioning. The pre- and post-intervention shifts were compared in the lateral [left-right (LR)], longitudinal [superior-inferior (SI)], and vertical [anterior-posterior (AP)] directions. The percentage of shifts larger than 5 mm in all directions was also compared. Clinical target volume to planning target volume (CTV-to-PTV) expansion margins were estimated based on the pre- and post-intervention localization data.
Intervention was performed on all patients (n=17) treated between October 2008 and March 2009. The number of interventions ranged from 2 to 12 with a median number of 5, resulting in a total of 96 pairs of pre- and post-intervention shifts. The mean value (sigma) and standard deviation (sigma) of the shifts from pre- versus post-intervention data were LR, 0.0 +/- 3.0 mm vs. 0.5 +/- 2.8 mm; SI, 0.2 +/- 3.1 mm vs. -1.0 +/- 2.1 mm; and AP, -2.6 +/- 5.8 mm vs. 1.7 +/- 3.9 mm. The mean 3D shift distance was 7.0 +/- 3.1 mm vs. 5.0 +/- 2.6 mm. The percentage of pre-intervention shifts larger than 5 mm were 7%, 7%, and 45% in the LR, SI, and AP directions, respectively, compared to 8%, 4%, and 21% for post-intervention. Localization data from pre- and post-intervention procedures suggest that treatments that do not include intervention to correct for rectum/bladder anatomical variations require an additional 3.3 mm CTV-to-PTV margin.
Anatomical interventions reduced the localization errors arising from large volume and shape changes in the rectum and/or bladder compared to treatments without interventions.
前列腺床、直肠和膀胱的解剖变形会影响前列腺癌患者术后的靶区定位精度。本研究分析了接受图像引导调强适形放疗（IMRT）的前列腺癌术后患者，解剖干预对其定位数据的影响。
患者每天通过在线千伏锥形束 CT（kV-CBCT）进行定位。评估靶区和危及器官（OARs）的位置和体积变化，并进行床面移动。对于直肠或膀胱壁在 CBCT 矢状位图像上的位移大于 5mm（与计划 CT 相比），提示靶区或 OAR 体积发生较大变化的患者，在行干预性操作后，需重复进行定位 CBCT 扫描。该操作包括插入导管以排空直肠、排空粪便和/或调整膀胱充盈度。然后评估所需的移动量，并在适当的患者定位后进行 IMRT 治疗。比较干预前后的侧向（左右）[LR]、纵向（上下）[SI]和垂直（前后）[AP]方向的移动量。还比较了所有方向上大于 5mm 的移动量百分比。根据干预前后的定位数据，估计临床靶区体积到计划靶区体积（CTV-to-PTV）的扩展边界。
2008 年 10 月至 2009 年 3 月期间治疗的所有患者（n=17）均进行了干预。干预次数为 2-12 次，中位数为 5 次，共进行了 96 对干预前后的移动量比较。与干预前相比，干预后数据的移动量平均值（西格玛）和标准差（西格玛）为 LR，0.0±3.0mm 与 0.5±2.8mm；SI，0.2±3.1mm 与-1.0±2.1mm；AP，-2.6±5.8mm 与 1.7±3.9mm。3D 平均移动距离为 7.0±3.1mm 与 5.0±2.6mm。LR、SI 和 AP 方向的预干预移动量大于 5mm 的百分比分别为 7%、7%和 45%，而干预后的百分比分别为 8%、4%和 21%。干预前后的定位数据表明，对于不包括纠正直肠/膀胱解剖变化的治疗，需要额外的 3.3mm CTV-to-PTV 边界。
与未进行干预的治疗相比，解剖干预减少了直肠和/或膀胱的大体积和形状变化引起的定位误差。
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