Bioengineering Unit, Clinical Department, National Center for Oncological Hadrontherapy (CNAO), Pavia, Italy.
Bioengineering Unit, Clinical Department, National Center for Oncological Hadrontherapy (CNAO), Pavia, Italy.
Phys Med. 2021 Oct;90:123-133. doi: 10.1016/j.ejmp.2021.09.012. Epub 2021 Oct 7.
Carbon ion radiotherapy (CIRT) is sensitive to anatomical density variations. We examined the dosimetric effect of variable intestinal filling condition during CIRT to ten sacral chordoma patients.
For each patient, eight virtual computed tomography scans (vCTs) were generated by varying the density distribution within the rectum and the sigmoid in the planning computed tomography (pCT) with a density override approach mimicking a heterogeneous combination of gas and feces. Totally full and empty intestinal preparations were modelled. In addition, five different intestinal filling conditions were modelled by a mixed density pattern derived from two combined and weighted Gaussian distributions simulating gas and feces respectively. Finally, a patient-specific mixing proportion was estimated by evaluating the daily amount of gas detected in the cone beam computed tomography (CBCT). Dose distribution was recalculated on each vCT and dose volume histograms (DVHs) were examined.
No target coverage degradation was observed at different vCTs. Rectum and sigma dose degradation ranged respectively between: [-6.7; 21.6]GyE and [-0.7; 15.4]GyE for D; [-377.4; 1197.9] and [-95.2; 1027.5] for AUC; [-1.2; 10.7]GyE and [-2.6; 21.5]GyE for D.
Variation of intestinal density can greatly influence the penetration depth of charged particle and might compromise dose distribution. In particular cases, with large clinical target volume in very close proximity to rectum and sigmoid colon, it is appropriate to evaluate the amount of gas present in the daily CBCT images even if it is totally included in the reference planning structures.
碳离子放疗（CIRT）对解剖密度变化敏感。我们检查了 10 例骶骨脊索瘤患者在 CIRT 过程中可变肠充盈状态的剂量学效应。
对于每个患者，通过在计划 CT（pCT）中用密度覆盖方法模拟气体和粪便的不均匀组合来改变直肠和乙状结肠内的密度分布，生成了 8 个虚拟 CT 扫描（vCT）。总共模拟了完全充盈和排空的肠道准备状态。此外，通过源自分别模拟气体和粪便的两个组合和加权高斯分布的混合密度模式模拟了 5 种不同的肠道填充条件。最后，通过评估锥形束 CT（CBCT）中每天检测到的气体量来估计患者特异性的混合比例。在每个 vCT 上重新计算剂量分布，并检查剂量体积直方图（DVH）。
在不同的 vCT 上没有观察到靶区覆盖的退化。直肠和乙状结肠剂量的退化范围分别为：D 值为[-6.7；21.6]GyE 和[-0.7；15.4]GyE；AUC 值为[-377.4；1197.9]和[-95.2；1027.5]；D 值为[-1.2；10.7]GyE 和[-2.6；21.5]GyE。
肠道密度的变化会极大地影响带电粒子的穿透深度，并可能影响剂量分布。在某些特殊情况下，对于非常接近直肠和乙状结肠的大临床靶区，即使它完全包含在参考计划结构中，也需要在每天的 CBCT 图像中评估气体的存在量。
