Heidelberg Institute for Radiation Oncology (HIRO), National Center for Research in Radiation Oncology (NCRO), Heidelberg 69120, Germany.
Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Heidelberg 69120, Germany.
Phys Med Biol. 2024 Nov 6;69(22). doi: 10.1088/1361-6560/ad8870.
The highly conformal carbon-ion radiotherapy is associated with an increased sensitivity of the dose distributions to internal changes in the patient during the treatment course. Hence, monitoring methodologies capable of detecting such changes are of vital importance. We established experimental setup conditions to address the sensitivity of a monitoring approach based on secondary-fragment tracking for detecting clinically motivated air cavity dimensions in a homogeneous head-sized PMMA phantom in 40 mm depth.The air cavities were positioned within the entrance channel of a treatment field of 50 mm diameter at three lateral positions. The measured secondary-fragment emission profiles were compared to a reference measurement without cavities. The experiments were conducted at the Heidelberg Ion-Beam Therapy Center in Germany at typical doses and dose rates.Significances above a detectability threshold of 2for the larger cavities (20 mm diameter and 4 mm thickness, and 20 mm diameter and 2 mm thickness) across the entire treatment field. The smallest cavity of 10 mm diameter and 2 mm thickness, which is on the lower limit of clinical interest, could not be detected at any position. We also demonstrated that it is feasible to reconstruct the lateral position of the cavity on average within 2.8 mm, once the cavity is detected. This is sufficient for the clinicians to estimate medical effects of such a cavity and to decide about the need for a control imaging CT.This investigation defines well-controlled reference conditions for the evaluation of the performance of any kind of treatment monitoring method and its capability to detect internal changes within head-sized objects. Four air cavities with volumes between 0.31 cmand 1.26 cmwere narrowed down around the detectability threshold of this secondary-fragment-based monitoring method.
碳离子放射治疗具有高度适形性，因此在治疗过程中，剂量分布对患者内部变化的敏感性会增加。因此，能够检测到这些变化的监测方法至关重要。我们建立了实验设置条件，以解决基于次级碎片跟踪的监测方法的敏感性问题，该方法用于检测同质头部大小的 PMMA 体模中临床相关空气腔尺寸的变化，深度为 40mm。空气腔位于直径为 50mm 的治疗场的入口通道内，位于三个横向位置。测量的次级碎片发射轮廓与没有空腔的参考测量进行了比较。实验在德国海德堡离子束治疗中心进行，采用典型剂量和剂量率。在整个治疗场中，较大空腔（直径 20mm，厚度 4mm 和直径 20mm，厚度 2mm）的检测阈值超过 2 时具有显著性。最小的空腔直径为 10mm，厚度为 2mm，处于临床感兴趣的下限，在任何位置都无法检测到。我们还证明，一旦空腔被检测到，就可以平均在 2.8mm 内重建空腔的横向位置。这足以让临床医生估计这种空腔的医疗效果，并决定是否需要控制成像 CT。这项研究为评估任何类型的治疗监测方法的性能及其检测头大小物体内部变化的能力定义了良好控制的参考条件。4 个空腔体积在 0.31cm 和 1.26cm 之间，在基于次级碎片的监测方法的检测阈值附近缩小。
