Graduate School of Medical Sciences, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Faculty of Medical Sciences, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Phys Med. 2018 Oct;54:66-76. doi: 10.1016/j.ejmp.2018.09.008. Epub 2018 Sep 29.
The aim of this study was to account for interfractional clinical target volume (CTV) shape variation and apply this to the planning target volume (PTV) margin for prostate cancer radiation treatment plans.
Interfractional CTV shape variations were estimated from weekly cone-beam computed tomography (CBCT) images using statistical point distribution models. The interfractional CTV shape variation was taken into account in the van Herk's margin formula. The PTV margins without and with the CTV shape variation, i.e., standard (PTV) and new (PTV) margins, were applied to 10 clinical cases that had weekly CBCT images acquired during their treatment sessions. Each patient was replanned for low-, intermediate-, and high-risk CTVs, using both margins. The dose indices (D98 and V70) of treatment plans with the two margins were compared on weekly pseudo-planning computed tomography (PCT) images, which were defined as PCT images registered using a deformable image registration technique with weekly CBCT images, including contours of the CTV, rectum, and bladder.
The percentage of treatment fractions of patients who received CTV D98 greater than 95% of a prescribed dose increased from 80.3 (PTV) to 81.8% (PTV) for low-risk CTVs, 78.8 (PTV) to 87.9% (PTV) for intermediate-risk CTVs, and 80.3 (PTV) to 87.9% (PTV) for high-risk CTVs. In most cases, the dose indices of the rectum and bladder were acceptable in clinical practice.
The results of this study suggest that interfractional CTV shape variations should be taken into account when determining PTV margins to increase CTV coverages.
本研究旨在解释分次临床靶区（CTV）形状变化，并将其应用于前列腺癌放射治疗计划的计划靶区（PTV）边界。
使用统计点分布模型从每周锥形束 CT（CBCT）图像估算分次 CTV 形状变化。将分次 CTV 形状变化纳入 van Herk 边界公式中。考虑到 CTV 形状变化的 PTV 边界（PTV）和新的（PTV）边界，应用于 10 例在治疗过程中每周获得 CBCT 图像的临床病例。对于低、中、高危 CTV，使用这两种边界对每个患者进行重新规划。使用这两种边界，在每周的假性计划 CT（PCT）图像上比较治疗计划的剂量指数（D98 和 V70），这些图像被定义为使用基于变形图像配准技术与每周 CBCT 图像进行配准的 PCT 图像，包括 CTV、直肠和膀胱的轮廓。
低危 CTV 患者接受 95%处方剂量以上 CTV D98 的治疗比例从 80.3%（PTV）增加到 81.8%（PTV），中危 CTV 患者从 78.8%（PTV）增加到 87.9%（PTV），高危 CTV 患者从 80.3%（PTV）增加到 87.9%（PTV）。在大多数情况下，直肠和膀胱的剂量指数在临床实践中是可以接受的。
本研究结果表明，在确定 PTV 边界以增加 CTV 覆盖率时，应考虑分次 CTV 形状变化。
