Yamashita Hideomi, Takenaka Ryousuke, Sakumi Akira, Haga Akihiro, Otomo Kuni, Nakagawa Keiichi
Department of Radiology, University of Tokyo Hospital, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-8655, Japan.
Radiat Oncol. 2015 Jan 8;10:2. doi: 10.1186/s13014-014-0311-6.
The purpose of the present study was to quantify the inter-fractional motion of the rectum and the rectal and bladder volumes using CBCT scans taken during chemoradiation therapy (CRT) for rectal cancer. Also, assessment was made for a better margin for simultaneous integrated boost - intensity modulated radiation therapy (SIB-IMRT) for rectal cancer.
There were 32 patients in this study undergoing preoperative CRT for rectal cancer. Each rectum and bladder was contoured on all planning CTs and CBCTs (day 1, 7, 13, 19, 25). The target volume was configured by adding margins (0, 3, 5, 7, 10, and 15 mm) to the rectum on planning CT. The respective percentage of rectal volume that exceeds the target volume was calculated for each of these margins. The percentage of bladder volume that exceeds the bladder volume in the planning CT and motion of the center of gravity of rectum were also analyzed.
Planning CTs and series of each 5 CBCTs for 32 patients were analyzed in this study. The rectal volume tended to shrink week after week. The mean values (± SD) in the 32 series per patient of the percentage of rectum on the CBCTs exceeding target volume in which the margins of 0, 3, 5, 7, 10, and 15 mm were added to the rectum on planning CT were 20.7 ± 12.5%, 7.2 ± 8.3%, 3.9 ± 5.9%, 2.1 ± 3.9%, 0.7 ± 1.8%, and 0.1 ± 0.3%, respectively. No association was seen between the percentage of changes of bladder volume and motion of rectal centroid.
In this study, we estimated the motion of the rectum using planning CT and CBCT. Ten to fifteen mm is a sufficient margin for the rectum during SIB-IMRT for rectal cancer in the supine position.
本研究的目的是利用直肠癌放化疗（CRT）期间采集的CBCT扫描，对直肠的分次间运动以及直肠和膀胱体积进行量化。同时，对直肠癌同步整合加量调强放疗（SIB-IMRT）的更好边界进行评估。
本研究中有32例患者接受直肠癌术前CRT。在所有计划CT和CBCT（第1、7、13、19、25天）上对每个直肠和膀胱进行轮廓勾画。通过在计划CT上给直肠添加边界（0、3、5、7、10和15毫米）来配置靶体积。针对这些边界中的每一个，计算超过靶体积的直肠体积的相应百分比。还分析了计划CT中超过膀胱体积的膀胱体积百分比以及直肠重心的运动。
本研究分析了32例患者的计划CT和每组5次CBCT扫描序列。直肠体积呈逐周缩小趋势。在计划CT上给直肠添加0、3、5、7、10和15毫米边界的情况下，32例患者每组CBCT上超过靶体积的直肠百分比的平均值（±标准差）分别为20.7±12.5%、7.2±8.3%、3.9±5.9%、2.1±3.9%、0.7±1.8%和0.1±0.3%。未观察到膀胱体积变化百分比与直肠质心运动之间存在关联。
在本研究中，我们利用计划CT和CBCT评估了直肠的运动。对于仰卧位直肠癌SIB-IMRT，10至15毫米的边界对直肠来说是足够的。
