van der Meer Marjolein C, Bosman Peter A N, Pieters Bradley R, Niatsetski Yury, van Wieringen Niek, Alderliesten Tanja, Bel Arjan
Department of Radiation Oncology, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands.
Life Sciences and Health Research Group, Centrum Wiskunde & Informatica, Amsterdam, the Netherlands.
J Appl Clin Med Phys. 2019 Apr;20(4):66-74. doi: 10.1002/acm2.12563. Epub 2019 Mar 18.
To investigate the variation in computed dose-volume (DV) indices for high-dose-rate (HDR) prostate brachytherapy that can result from typical differences in computation settings in treatment planning systems (TPSs).
Five factors were taken into account: number of dose-calculation points, radioactive source description, interpolation between delineated contours, intersections between delineated organ contours, and organ shape at the top and bottom contour using either full or partial slice thickness. Using in-house developed software, the DV indices of the treatment plans of 26 patients were calculated with different settings, and compared to a baseline setting that closely followed the default settings of the TPS used in our medical center. Studied organs were prostate and seminal vesicles, denoted as targets, and bladder, rectum, and urethra, denoted as organs at risk (OARs), which were delineated on MRI scans with a 3.3 mm slice thickness.
When sampling a fixed number of points in each organ, in order to achieve a width of the 95% confidence interval over all patients of the DV indices of 1% or less, only 32,000 points had to be sampled per target, but 256,000 points had to be sampled per OAR. For the remaining factors, DV indices changed up to 0.4% for rectum, 1.3% for urethra, and 2.6% for prostate. DV indices of the bladder changed especially if the high-dose-region was (partly) located at the most caudal contour, up to 8.5%, and DV indices of the vesicles changed especially if there were few delineated contours, up to 9.8%, both due to the use of full slice thickness for the top and bottom contour.
The values of DV indices used in prostate HDR brachytherapy treatment planning are influenced by the computation settings in a TPS, especially at the most caudal part of the bladder, as well as in the seminal vesicles.
研究高剂量率（HDR）前列腺近距离放射治疗中，因治疗计划系统（TPS）计算设置的典型差异而导致的计算剂量体积（DV）指数变化。
考虑五个因素：剂量计算点数量、放射源描述、勾画轮廓之间的插值、勾画的器官轮廓之间的交叉以及使用全层或部分层厚时顶部和底部轮廓处的器官形状。使用自行开发的软件，在不同设置下计算26例患者治疗计划的DV指数，并与紧密遵循我们医疗中心所使用TPS默认设置的基线设置进行比较。研究的器官包括前列腺和精囊，视为靶区，以及膀胱、直肠和尿道，视为危及器官（OAR），这些器官在层厚为3.3毫米的MRI扫描上进行勾画。
当在每个器官中采样固定数量的点时，为了使所有患者DV指数的95%置信区间宽度在1%或以下，每个靶区仅需采样32000个点，但每个OAR需采样256000个点。对于其余因素，直肠的DV指数变化高达0.4%，尿道为1.3%，前列腺为2.6%。膀胱的DV指数变化尤其明显，特别是当高剂量区域（部分）位于最尾端轮廓时，变化高达8.5%；精囊的DV指数变化尤其明显，特别是当勾画的轮廓较少时，变化高达9.8%，这两种情况均是由于顶部和底部轮廓使用了全层厚。
前列腺HDR近距离放射治疗计划中使用的DV指数值受TPS计算设置的影响，特别是在膀胱最尾端部分以及精囊中。
