Prostate rotation detected from implanted markers can affect dose coverage and cannot be simply dismissed.
Prostate rotation detected from implanted markers can affect dose coverage and cannot be simply dismissed.
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DOI：
10.1120/jacmp.v14i3.4262
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发表时间：
2013-05-06
影响因子：
2.1
通讯作者：
Xia P
中科院分区：
文献类型：
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作者：
Shang Q;Sheplan Olsen LJ;Stephans K;Tendulkar R;Xia P
有了植入的标记物，每天的前列腺位移可以在六个自由度上自动检测到。然而，报道的旋转幅度通常大于六度治疗沙发的典型范围。本研究的目的是量化前列腺旋转未校正（ROT_NC）和可通过平移移位（ROT_C）补偿的几何和剂量效应。这项回顾性研究使用了来自5名患者的43千伏锥束ct （KV - CBCT）植入标记物。在每个KV - CBCT上，由医生手动勾画前列腺、膀胱和直肠的轮廓。手工对齐计划CT和CBCT的前列腺轮廓以达到最佳重叠。该轮廓配准作为基准方法，与两种标记点配准方法进行比较：(a)使用6个自由度，但不校正旋转（ROT_NC）；(b)使用三个自由度，同时将旋转补偿为平移位移（ROT_C）。用质心距离（CMD）和重叠指数（OI）对这两种方法进行评价。通过比较前列腺临床靶体积（CTV）的剂量覆盖与计划裕度的关系，还分析了剂量学效应。根据我们的分析，检测到的旋转以左右轴为主，系统分量为4.6°，随机分量为4.1°。当旋转角度大于10°时，85.7%的两种配准体的CMD差异大于5 mm；当旋转角度大于6°时，61.1%的组份CMD差异大于4 mm。当计划后缘为6mm / 4mm时，cbct中前列腺剂量至99% （D99）与前列腺计划D99之间的平均差异是ROT_NC注册和ROT_C注册。当计划切缘减小到后侧4 mm/2 mm时，ROT_NC和ROT_C方法的前列腺D99平均差值分别为和。综上所述，不能简单地忽略前列腺旋转，旋转误差的影响取决于植入标记物的等心与质心的距离以及旋转角度。PACS编号：87.55
With implanted markers, daily prostate displacements can be automatically detected with six degrees of freedom. The reported magnitudes of the rotations, however, are often greater than the typical range of a six‐degree treatment couch. The purpose of this study is to quantify geometric and dosimetric effects if the prostate rotations are not corrected (ROT_NC) and if they can be compensated with translational shifts (ROT_C). Forty‐three kilovoltage cone‐beam CTs (KV‐CBCT) with implanted markers from five patients were available for this retrospective study. On each KV‐CBCT, the prostate, bladder, and rectum were manually contoured by a physician. The prostate contours from the planning CT and CBCT were aligned manually to achieve the best overlaps. This contour registration served as the benchmark method for comparison with two marker registration methods: (a) using six degrees of freedom, but rotations were not corrected (ROT_NC); and (b) using three degrees of freedom while compensating rotations into the translational shifts (ROT_C). The center of mass distance (CMD) and overlap index (OI) were used to evaluate these two methods. The dosimetric effects were also analyzed by comparing the dose coverage of the prostate clinical target volume (CTV) in relation to the planning margins. According to our analysis, the detected rotations dominated in the left–right axis with systematic and random components of 4.6° and 4.1°, respectively. When the rotation angles were greater than 10°, the differences in CMD between the two registrations were greater than 5 mm in 85.7% of these fractions; when the rotation angles were greater than 6°, the differences of CMD were greater than 4 mm in 61.1% of these fractions. With 6 mm/4 mm posterior planning margins, the average difference between the dose to 99% (D99) of the prostate in CBCTs and the planning D99 of the prostate was for the ROT_NC registration, and for the ROT_C registration . When the planning margin decreased to 4 mm/2 mm posterior, the average difference in D99 of the prostate was and for the ROT_NC and ROT_C methods, respectively . In conclusion, prostate rotation cannot be simply dismissed, and the impact of the rotational errors depends on the distance between the isocenter and the centroid of implanted markers and the rotation angle. PACS number: 87.55