Department of Radiation Oncology, Osaka University Graduate School of Medicine, Suita, Osaka, Japan; Department of Radiology, Osaka University Hospital, Suita, Osaka, Japan.
Int J Radiat Oncol Biol Phys. 2013 Nov 1;87(3):602-8. doi: 10.1016/j.ijrobp.2013.06.2054.
The actual dose delivered to critical organs will differ from the simulated dose because of interfractional organ motion and deformation. Here, we developed a method to estimate the rectal dose in prostate intensity modulated radiation therapy with consideration to interfractional organ motion using daily megavoltage cone-beam computed tomography (MVCBCT).
Under exemption status from our institutional review board, we retrospectively reviewed 231 series of MVCBCT of 8 patients with prostate cancer. On both planning CT (pCT) and MVCBCT images, the rectal contours were delineated and the CT value within the contours was replaced by the mean CT value within the pelvis, with the addition of 100 Hounsfield units. MVCBCT images were rigidly registered to pCT and then nonrigidly registered using B-Spline deformable image registration (DIR) with Velocity AI software. The concordance between the rectal contours on MVCBCT and pCT was evaluated using the Dice similarity coefficient (DSC). The dose distributions normalized for 1 fraction were also deformed and summed to estimate the actual total dose.
The DSC of all treatment fractions of 8 patients was improved from 0.75±0.04 (mean ±SD) to 0.90 ±0.02 by DIR. Six patients showed a decrease of the generalized equivalent uniform dose (gEUD) from total dose compared with treatment plans. Although the rectal volume of each treatment fraction did not show any correlation with the change in gEUD (R(2)=0.18±0.13), the displacement of the center of gravity of rectal contours in the anterior-posterior (AP) direction showed an intermediate relationship (R(2)=0.61±0.16).
We developed a method for evaluation of rectal dose using DIR and MVCBCT images and showed the necessity of DIR for the evaluation of total dose. Displacement of the rectum in the AP direction showed a greater effect on the change in rectal dose compared with the rectal volume.
由于分次间器官运动和变形，实际给予关键器官的剂量与模拟剂量会有所不同。在此，我们开发了一种在考虑分次间器官运动的情况下，使用每日兆伏锥形束 CT（MVCBCT）对前列腺调强放疗中的直肠剂量进行估计的方法。
根据我们机构审查委员会的豁免规定，我们回顾性地分析了 8 例前列腺癌患者的 231 组 MVCBCT 系列。在计划 CT（pCT）和 MVCBCT 图像上，勾勒直肠轮廓，并将轮廓内的 CT 值替换为骨盆内的平均 CT 值，外加 100 个亨氏单位。将 MVCBCT 图像刚性配准到 pCT 上，然后使用 Velocity AI 软件的 B 样条变形图像配准（DIR）进行非刚性配准。使用 Dice 相似系数（DSC）评估 MVCBCT 和 pCT 上直肠轮廓的一致性。归一化为 1 个分数的剂量分布也进行变形并求和，以估计实际总剂量。
8 例患者的所有治疗分数的 DSC 均由 0.75±0.04（平均值±标准差）提高至 0.90±0.02 通过 DIR。与治疗计划相比，6 例患者的总剂量的广义等效均匀剂量（gEUD）降低。尽管每个治疗分数的直肠体积与 gEUD 的变化均无相关性（R²=0.18±0.13），但直肠轮廓的重心在前后（AP）方向上的位移具有中等相关性（R²=0.61±0.16）。
我们开发了一种使用 DIR 和 MVCBCT 图像评估直肠剂量的方法，并表明 DIR 对于总剂量评估的必要性。与直肠体积相比，直肠在 AP 方向上的位移对直肠剂量变化的影响更大。
