Pearson David, Gill Sukhdeep K, Campbell Nina, Reddy Krishna
University of Toledo.
J Appl Clin Med Phys. 2016 Nov 8;17(6):107-117. doi: 10.1120/jacmp.v17i6.6207.
Delivered dose can be calculated by transferring the planned treatment beams onto the daily CBCT. Bladder and rectum volumetric doses were calculated and cor-related to the daily bladder and rectum fullness. Patients for this study underwent hypofractionated prostate IMRT to 70 Gy in 28 fractions. Daily CBCT was utilized for image guidance. A clinically acceptable plan was created using a CTV-to-PTV uniform margin of 5 mm. Image fusion was performed to transfer the bladder and rectum contours onto each CBCT. Contours were then edited to match the anatomy of each CBCT. Using the daily treatment isocenter, the planned beams were transferred onto the CBCT and daily and cumulative DVHs calculated. For the results a total of 168 daily CBCTs were evaluated. The bladder was found to be smaller for 74.7% of the 168 daily CBCTs accessed in this study. This reduction in volume correlated to an increase in the cumulative bladder V70 Gy from 9.47% on the planning CT to 10.99% during treatment. V70Gy for the rectum was 7.27% on the planning CT, when all six patients were averaged, and increased to 11.56% on the average of all daily treatment CBCTs. Increases in volumetric rectum dose correlated with increases in rectal volume. For one patient, the rectum and blad-der absolute V70 Gy, averaged over the course of treatment, increased by 295% and 61%, respectively. Larger variations in the daily bladder and rectal volume were observed and these correlated to large deviations from the volumetric dose received by these structures. In summary, bladder and rectum volume changes during treatment have an effect on the cumulative dose received by these organs. It was observed that the volumetric dose received by the bladder decreases as the volume of the bladder increases. The inverse was true for the rectum.
通过将计划的治疗射束转移到每日的锥形束CT（CBCT）上，可以计算出实际给予的剂量。计算膀胱和直肠的体积剂量，并将其与每日膀胱和直肠的充盈情况相关联。本研究中的患者接受了大分割前列腺调强放疗（IMRT），28次分割，总剂量70 Gy。每日使用CBCT进行图像引导。使用临床靶区（CTV）到计划靶区（PTV）5 mm的均匀边界创建临床可接受的计划。进行图像融合以将膀胱和直肠轮廓转移到每个CBCT上。然后编辑轮廓以匹配每个CBCT的解剖结构。使用每日治疗等中心，将计划射束转移到CBCT上，并计算每日和累积剂量体积直方图（DVH）。结果共评估了168次每日CBCT。在本研究中获取的168次每日CBCT中，74.7%的膀胱体积较小。这种体积减小与膀胱累积V70 Gy从计划CT上的9.47%增加到治疗期间的10.99%相关。当对所有6名患者进行平均时，直肠的V70Gy在计划CT上为7.27%，在所有每日治疗CBCT的平均值上增加到11.56%。直肠体积剂量的增加与直肠体积的增加相关。对于一名患者，在整个治疗过程中，直肠和膀胱的绝对V70 Gy分别平均增加了295%和61%。观察到每日膀胱和直肠体积的较大变化，这些变化与这些结构接受的体积剂量的较大偏差相关。总之，治疗期间膀胱和直肠体积的变化对这些器官接受的累积剂量有影响。观察到膀胱接受的体积剂量随着膀胱体积的增加而降低。直肠则相反。
