Casares-Magaz Oscar, Moiseenko Vitali, Hopper Austin, Pettersson Niclas Johan, Thor Maria, Knopp Rick, Deasy Joseph O, Muren Ludvig Paul, Einck John
a Department of Medical Physics , Aarhus University Hospital , Aarhus , Denmark.
b Department of Radiation Medicine and Applied Sciences , University of California San Diego , La Jolla , CA , USA.
Acta Oncol. 2017 Jun;56(6):884-890. doi: 10.1080/0284186X.2017.1312014. Epub 2017 Apr 12.
Inter-fractional variation in urinary bladder volumes during the course of radiotherapy (RT) for prostate cancer causes deviations between planned and delivered doses. This study compared planned versus daily cone-beam CT (CBCT)-based spatial bladder dose distributions, for prostate cancer patients receiving local prostate treatment (local treatment) versus prostate including pelvic lymph node irradiation (pelvic treatment).
Twenty-seven patients (N = 15 local treatment; N = 12 pelvic treatment) were treated using daily image-guided RT (1.8 Gy@43-45 fx), adhering to a full bladder/empty rectum protocol. For each patient, 9-10 CBCTs were registered to the planning CT, using the clinically applied translations. The urinary bladder was manually segmented on each CBCT, 3 mm inner shells were generated, and semi and quadrant sectors were created using axial/coronal cuts. Planned and delivered DVH metrics were compared across patients and between the two groups of treatment (t-test, p < .05; Holm-Bonferroni correction). Associations between bladder volume variations and the dose-volume histograms (DVH) of the bladder and its sectors were evaluated (Spearman's rank correlation coefficient, r).
Bladder volumes varied considerably during RT (coefficient of variation: 16-58%). The population-averaged planned and delivered DVH metrics were not significantly different at any dose level. Larger treatment bladder volumes resulted in increased absolute volume of the posterior/inferior bladder sector receiving intermediate-high doses, in both groups. The superior bladder sector received less dose with larger bladder volumes for local treatments (r ± SD: -0.47 ± 0.32), but larger doses for pelvic treatments (r ± SD: 0.74 ± 0.24).
Substantial bladder volume changes during the treatment course occurred even though patients were treated under a full bladder/daily image-guided protocol. Larger bladder volumes resulted in less bladder wall spared at the posterior-inferior sector, regardless the treatment received. Contrary, larger bladder volumes meant larger delivered doses to the superior bladder sector for pelvic RT but smaller doses for local treatments.
前列腺癌放射治疗（RT）过程中膀胱体积的分次间变化会导致计划剂量与实际 delivered 剂量之间出现偏差。本研究比较了接受局部前列腺治疗（局部治疗）与包括盆腔淋巴结照射的前列腺治疗（盆腔治疗）的前列腺癌患者基于计划与每日锥形束CT（CBCT）的膀胱空间剂量分布。
27例患者（N = 15例局部治疗；N = 12例盆腔治疗）采用每日图像引导放疗（1.8 Gy@43 - 45次分割），遵循膀胱充盈/直肠排空方案。对于每位患者，使用临床应用的平移将9 - 10幅CBCT与计划CT进行配准。在每幅CBCT上手动分割膀胱，生成3mm的内壳，并使用轴向/冠状切面创建半区和象限区。比较患者之间以及两组治疗之间（t检验，p < 0.05；Holm - Bonferroni校正）计划和 delivered 的剂量体积直方图（DVH）指标。评估膀胱体积变化与膀胱及其各区的剂量体积直方图（DVH）之间的关联（Spearman等级相关系数，r）。
放疗期间膀胱体积变化很大（变异系数：16 - 58%）。在任何剂量水平下，总体平均计划和 delivered 的DVH指标均无显著差异。两组中，较大的治疗膀胱体积导致接受中高剂量的膀胱后/下区绝对体积增加。对于局部治疗，膀胱上区在膀胱体积较大时接受的剂量较少（r ± SD：-0.47 ± 0.32），但对于盆腔治疗，接受的剂量较大（r ± SD：0.74 ± 0.24）。
即使患者在膀胱充盈/每日图像引导方案下接受治疗，治疗过程中膀胱体积仍发生了显著变化。无论接受何种治疗，较大的膀胱体积导致膀胱后下区的膀胱壁受照较少。相反，较大的膀胱体积意味着盆腔放疗时膀胱上区接受的 delivered 剂量较大，而局部治疗时接受的剂量较小。
