Levegrün Sabine, Pöttgen Christoph, Xydis Konstantinos, Guberina Maja, Abu Jawad Jehad, Stuschke Martin
Department of Radiotherapy, University Hospital Essen, Essen, Germany.
J Appl Clin Med Phys. 2021 Jan;22(1):226-241. doi: 10.1002/acm2.13138. Epub 2020 Dec 30.
To quantify daily residual deviations from the planned geometry after image-guided prostate radiotherapy with endorectal balloon and to evaluate their effect on the delivered dose distribution.
Daily kV-CBCT imaging was used for online setup-correction in six degrees of freedom (6-dof) for 24 patients receiving definitive (12 RT patients) or postoperative (12 RT patients) radiotherapy with endorectal balloon (overall 739 CBCTs). Residual deviations were evaluated using several spatial and dosimetric variables, including: (a) posterior Hausdorff distance HD (=maximum distance between planned and daily CTV contour), (b) point P with largest HD over all fractions, (c) equivalent uniform dose using a cell survival model (EUD ) and the generalized EUD concept (gEUD with parameter a = -7 and a = -20). EUD values were determined for planned ( ), daily ( ), and delivered dose distributions ( ) for plans with 6 mm (=clinical plans) and 2 mm CTV-to-PTV margin. Time series analyses of interfractional spatial and dosimetric deviations were conducted.
Large HD values ≥ 12.5 mm (≥15 mm) were observed in 20/739 (5/739) fractions distributed across 7 (3) patients. Points P were predominantly located at the posterior CTV boundary in the seminal vesicle region (16/24 patients, 6/7 patients with HD ≥ 12.5 mm). Time series analyses revealed a stationary white noise characteristic of HD and relative dose at P . The EUD difference between planned and accumulated dose distributions was < 5.4% for all 6-mm plans. Evaluating 2-mm plans, EUD deteriorated by < 10% (<5%) in 75% (58.5%) of the patients. was well described by the median value of the distribution. PTV margin calculation at P yielded 8.8 mm.
Accumulated dose distributions in prostate radiotherapy with endorectal balloon are forgiving of considerable residual distortions after 6-dof patient setup if they are observed in a minority of fractions and the median value of determined per fraction stays within 95% of prescribed dose. Common PTV margin calculations are overly conservative because after online correction of translational and rotational errors only residual deformations need to be included. These results provide guidelines regarding online navigation, margin optimization, and treatment adaptation strategies.
量化使用直肠内气囊进行图像引导前列腺放疗后与计划几何形状的每日残余偏差，并评估其对所交付剂量分布的影响。
对24例接受确定性（12例放疗患者）或术后（12例放疗患者）直肠内气囊放疗的患者（共739次CBCT扫描），每日使用千伏级锥形束CT成像进行六自由度（6-dof）在线摆位校正。使用几个空间和剂量学变量评估残余偏差，包括：（a）后向豪斯多夫距离HD（=计划CTV轮廓与每日CTV轮廓之间的最大距离），（b）所有分次中HD最大的点P，（c）使用细胞存活模型的等效均匀剂量（EUD）和广义EUD概念（参数a = -7和a = -20时的gEUD）。对于CTV到PTV边缘为6 mm（=临床计划）和2 mm的计划，确定计划（ ）、每日（ ）和所交付剂量分布（ ）的EUD值。对分次间的空间和剂量学偏差进行时间序列分析。
在739次分次中的20次（739次中的5次）观察到HD值≥12.5 mm（≥15 mm），分布在7例（3例）患者中。点P主要位于精囊区域的CTV后边界（24例患者中的16例，HD≥12.5 mm的7例患者中的6例）。时间序列分析显示HD和点P处相对剂量具有平稳白噪声特征。所有6 mm计划的计划剂量分布与累积剂量分布之间的EUD差异<5.4%。评估2 mm计划时，75%（58.5%）的患者EUD恶化<10%（<5%）。 可用 分布的中位数很好地描述。在点P处计算的PTV边缘为8.8 mm。
如果在少数分次中观察到使用直肠内气囊进行前列腺放疗时的累积剂量分布，并且每次分次确定的 的中位数保持在处方剂量的95%以内，则对6自由度患者摆位后的相当大的残余变形具有耐受性。常见的PTV边缘计算过于保守，因为在在线校正平移和旋转误差后，只需纳入残余变形。这些结果为在线导航、边缘优化和治疗适应策略提供了指导。
