Department of Medical Physics, Ludwig-Maximilians-Universität München, Garching b. München, Germany. The author to whom correspondence may be addressed.
Phys Med Biol. 2019 Jun 12;64(12):125008. doi: 10.1088/1361-6560/ab0fdf.
Ion computed tomography (iCT) represents a potential replacement for x-ray CT (xCT) in ion therapy treatment planning to reduce range uncertainties, inherent in the semi-empirical conversion of xCT information into relative stopping power (RSP). In this work, we aim to quantify the increase in dosimetric accuracy associated with using proton-, helium- and carbon-CT compared to conventional xCT for clinical scenarios in proton therapy. Three cases imaged with active beam-delivery using an ideal single-particle-tracking detector were investigated using FLUKA Monte-Carlo (MC) simulations. The RSP accuracy of the iCTs was evaluated against the ground truth at similar physical dose. Next, the resulting dosimetric accuracy was investigated by using the RSP images as a patient model in proton therapy treatment planning, in comparison to common uncertainties associated with xCT. Finally, changes in relative biological effectiveness (RBE) with iCT particle type/spectrum were investigated by incorporating the repair-misrepair-fixation (RMF) model into FLUKA, to enable first insights on the associated biological imaging dose. Helium-CT provided the lowest overall RSP error, whereas carbon-CT offered the highest accuracy for bone and proton-CT for soft tissue. For a single field, the average relative proton beam-range variation was -1.00%, +0.09%, -0.08% and -0.35% for xCT, proton-, helium- and carbon-CT, respectively. Using a 0.5%/0.5mm gamma-evaluation, all iCTs offered comparable accuracy with a better than 99% passing rate, compared to 83% for xCT. The RMF model predictions for RBE for cell death relative to a diagnostic xCT spectrum were 0.82-0.85, 0.85-0.89 and 0.97-1.03 for proton-, helium-, and carbon-CT, respectively. The corresponding RBE for DNA double-strand break induction was generally below one. iCT offers great clinical potential for proton therapy treatment planning by providing superior dose calculation accuracy as well as lower physical and potentially biological dose exposure compared to xCT. For the investigated dose level and ideal detector, proton-CT and helium-CT yielded the best performance.
离子计算机断层扫描（iCT）代表了一种替代 X 射线计算机断层扫描（xCT）的可能性，用于离子治疗计划，以降低固有于 X 射线 CT 信息到相对阻止本领（RSP）的半经验转换中的范围不确定性。在这项工作中，我们旨在量化与使用质子、氦和碳 CT 相比，与传统 X 射线 CT 相比，在质子治疗的临床情况下与剂量学准确性相关的增加。使用理想的单粒子跟踪探测器，使用主动束传输对三个病例进行了成像，并使用 FLUKA 蒙特卡罗（MC）模拟进行了研究。在类似的物理剂量下，评估了 iCT 的 RSP 精度与真实值的比较。接下来，通过将 RSP 图像用作质子治疗计划中的患者模型，并与 X 射线 CT 相关的常见不确定性进行比较，研究了由此产生的剂量学准确性。最后，通过将修复-错误修复-固定（RMF）模型纳入到 FLUKA 中，研究了与 iCT 粒子类型/光谱相关的相对生物有效性（RBE）的变化，以实现对相关生物成像剂量的初步了解。氦 CT 提供了最低的整体 RSP 误差，而碳 CT 则提供了骨骼的最高精度，质子 CT 则提供了软组织的最高精度。对于单个射野，xCT、质子 CT、氦 CT 和碳 CT 的平均相对质子束射程变化分别为-1.00%、+0.09%、-0.08%和-0.35%。使用 0.5%/0.5mm 的伽马评估，与 X 射线 CT 相比，所有 iCT 均提供了相当的准确性，通过率超过 99%，而 X 射线 CT 的通过率为 83%。细胞死亡相对于诊断 X 射线 CT 光谱的 RBE 的 RMF 模型预测值分别为质子 CT、氦 CT 和碳 CT 的 0.82-0.85、0.85-0.89 和 0.97-1.03。DNA 双链断裂诱导的相应 RBE 通常低于 1。与 X 射线 CT 相比，iCT 通过提供更高的剂量计算准确性以及更低的物理和潜在的生物剂量暴露，为质子治疗计划提供了巨大的临床潜力。在研究的剂量水平和理想的探测器中，质子 CT 和氦 CT 表现最佳。
