Richter Daniel, Graeff Christian, Jäkel Oliver, Combs Stephanie E, Durante Marco, Bert Christoph
GSI Helmholtzzentrum für Schwerionenforschung, Dept. of Biophysics, Darmstadt, Germany; TU Darmstadt, Germany; University of Erlangen, Dept. of Radiation Oncology, Germany.
GSI Helmholtzzentrum für Schwerionenforschung, Dept. of Biophysics, Darmstadt, Germany.
Radiother Oncol. 2014 Nov;113(2):290-5. doi: 10.1016/j.radonc.2014.11.020. Epub 2014 Nov 25.
Interplay effects may limit the applicability of scanned ion beam therapy for moving tumors even if the motion amplitude is reduced by techniques such as gating or abdominal compression (AC). We investigate the potential of enhanced pencil beam overlap to mitigate residual motion interplay effects in scanned ion beam therapy.
Eight patients with hepato cellular carcinoma were selected who were either treated under AC (5 clinical target volumes (CTVs)) or with gating (6 CTVs). We performed 4D dose calculations for treatment plans with variable beam parameters (lateral raster spacing, beam full-width-at-half-maximum (FWHM), iso-energy slice spacing, gating window (GW)) and assessed under- and overdose (V95 and V107), dose homogeneity (HI=D5-D95), and dose volume histograms. The influence of the beam parameters on HI was studied by multivariate regression models.
Motion amplitude and FWHM had the largest impact on dose homogeneity, while decreased iso-energy slice spacing and lateral raster spacing had a much smaller or no significant effect, respectively. The multivariate regression models including FWHM, motion amplitude, and IES-spacing explained 86%, 42%, and 71% of the observed variance for AC, 30% and 50% GW, respectively.
Residual motion in scanned carbon ion therapy of liver tumors can lead to considerable dose heterogeneities. Using an increased beam spot size dose degradation can be significantly mitigated. Especially for large tumors, increasing the beam spot size is an efficient motion mitigation option readily available at most scanning facilities.
相互作用效应可能会限制扫描离子束疗法对移动肿瘤的适用性，即便通过门控或腹部压迫（AC）等技术可减小运动幅度。我们研究增强笔形束重叠在扫描离子束疗法中减轻残余运动相互作用效应的潜力。
选取8例肝细胞癌患者，其中5例临床靶区（CTV）接受AC治疗，6例接受门控治疗。我们针对具有可变束参数（横向光栅间距、束半高宽（FWHM）、等能量切片间距、门控窗（GW））的治疗计划进行4D剂量计算，并评估低剂量和高剂量（V95和V107）、剂量均匀性（HI = D5 - D95）以及剂量体积直方图。通过多元回归模型研究束参数对HI的影响。
运动幅度和FWHM对剂量均匀性影响最大，而等能量切片间距减小和横向光栅间距减小分别产生小得多的影响或无显著影响。包含FWHM、运动幅度和等能量切片间距的多元回归模型分别解释了AC情况下86%、42%和71%的观测方差，以及GW情况下30%和50%的观测方差。
肝脏肿瘤扫描碳离子治疗中的残余运动可导致相当大的剂量不均匀性。增大束斑尺寸可显著减轻剂量退化。特别是对于大肿瘤，增大束斑尺寸是大多数扫描设备都 readily available 的一种有效的运动减轻方案。 （注：“readily available”直译为“随时可用”，结合语境这里可能是指“容易实现”之类的意思，但按要求保留原文未翻译完整）
