Handrack Josefine, Tessonnier Thomas, Chen Wenjing, Liebl Jakob, Debus Jürgen, Bauer Julia, Parodi Katia
a Department of Radiation Oncology , Universitätsklinikum Heidelberg , Heidelberg , Germany.
b Department of Medical Physics , Ludwig-Maximilians-Universität München , Munich , Germany.
Acta Oncol. 2017 Nov;56(11):1451-1458. doi: 10.1080/0284186X.2017.1348628. Epub 2017 Sep 18.
Ion therapy, especially with modern scanning beam delivery, offers very sharp dose gradients for highly conformal cancer treatment. However, it is very sensitive to uncertainties of tissue stopping properties as well as to anatomical changes and setup errors, making range verification highly desirable. To this end, positron emission tomography (PET) can be used to measure decay products of β-emitters created in interactions inside the patient. This work investigates the sensitivity of post treatment PET/CT (computed tomography) to detect inter-fractional range variations.
Fourteen patients of different indication underwent PET/CT monitoring after selected treatment fractions with scanned proton or carbon ion beams. In addition to PET/CT measurements, PET and dose distributions were simulated on different co-registered CT data. Pairs of PET data were then analyzed in terms of longitudinal shifts along the beam path, as surrogate of inter-fractional range deviations. These findings were compared to changes of dose-volume-histogram indexes and corresponding dose as well as CT shifts to disentangle the origin of possible PET shifts.
Biological washout modeling (PET simulations) and low (<55 Bq/ml) activity concentrations (offline PET measurements, especially for C ions) were the main limitations for clinical treatment verification. For two selected cases, the benefit of improved washout modeling based on organ segmentation could be demonstrated. Overall, inter-fractional range shifts up to ±3 mm could be deduced from both PET measurements and simulations, and found well correlated (typically within 1.8 mm) to anatomical changes derived from CT scans, in agreement with dose data.
Despite known limitations of post treatment PET/CT imaging, this work indicates its potential for assessing inter-fractional changes and points to future developments for improved PET-based treatment verification.
离子治疗，尤其是采用现代扫描束流传输技术时，可为高度适形的癌症治疗提供非常陡峭的剂量梯度。然而，它对组织阻止特性的不确定性以及解剖结构变化和摆位误差非常敏感，因此亟需进行射程验证。为此，正电子发射断层扫描（PET）可用于测量患者体内相互作用产生的β发射体的衰变产物。本研究调查了治疗后PET/CT（计算机断层扫描）检测分次间射程变化的敏感性。
14例不同适应症的患者在接受选定的扫描质子或碳离子束治疗分次后，接受了PET/CT监测。除了PET/CT测量外，还在不同的配准CT数据上模拟了PET和剂量分布。然后根据沿束流路径的纵向位移分析PET数据对，作为分次间射程偏差的替代指标。将这些结果与剂量体积直方图指标、相应剂量的变化以及CT位移进行比较，以厘清可能的PET位移的来源。
生物洗脱模型（PET模拟）和低活性浓度（<55 Bq/ml）（离线PET测量，尤其是对于碳离子）是临床治疗验证的主要限制因素。对于两个选定的病例，可以证明基于器官分割改进洗脱模型的益处。总体而言，从PET测量和模拟中都可以推断出高达±3 mm的分次间射程位移，并且发现与CT扫描得出的解剖结构变化具有良好的相关性（通常在1.8 mm以内），与剂量数据一致。
尽管治疗后PET/CT成像存在已知的局限性，但本研究表明其在评估分次间变化方面的潜力，并指出了基于PET的治疗验证的未来发展方向。
