Hansen David C, Seco Joao, Sørensen Thomas Sangild, Petersen Jørgen Breede Baltzer, Wildberger Joachim E, Verhaegen Frank, Landry Guillaume
a Department of Oncology , Aarhus University Hospital , Aarhus , Denmark.
b Massachussetts General Hospital and Harvard Medical School , Boston , USA.
Acta Oncol. 2015;54(9):1638-42. doi: 10.3109/0284186X.2015.1061212. Epub 2015 Jul 29.
Accurate stopping power estimation is crucial for treatment planning in proton therapy, and the uncertainties in stopping power are currently the largest contributor to the employed dose margins. Dual energy x-ray computed tomography (CT) (clinically available) and proton CT (in development) have both been proposed as methods for obtaining patient stopping power maps. The purpose of this work was to assess the accuracy of proton CT using dual energy CT scans of phantoms to establish reference accuracy levels.
A CT calibration phantom and an abdomen cross section phantom containing inserts were scanned with dual energy and single energy CT with a state-of-the-art dual energy CT scanner. Proton CT scans were simulated using Monte Carlo methods. The simulations followed the setup used in current prototype proton CT scanners and included realistic modeling of detectors and the corresponding noise characteristics. Stopping power maps were calculated for all three scans, and compared with the ground truth stopping power from the phantoms.
Proton CT gave slightly better stopping power estimates than the dual energy CT method, with root mean square errors of 0.2% and 0.5% (for each phantom) compared to 0.5% and 0.9%. Single energy CT root mean square errors were 2.7% and 1.6%. Maximal errors for proton, dual energy and single energy CT were 0.51%, 1.7% and 7.4%, respectively.
Better stopping power estimates could significantly reduce the range errors in proton therapy, but requires a large improvement in current methods which may be achievable with proton CT.
准确的阻止本领估计对于质子治疗中的治疗计划至关重要，并且阻止本领的不确定性目前是所采用的剂量裕度的最大贡献因素。双能X射线计算机断层扫描（CT）（临床可用）和质子CT（正在研发中）都已被提议作为获取患者阻止本领图的方法。这项工作的目的是使用体模的双能CT扫描来评估质子CT的准确性，以建立参考准确度水平。
使用一台先进的双能CT扫描仪对一个CT校准体模和一个包含插入物的腹部横截面体模进行双能和单能CT扫描。使用蒙特卡罗方法模拟质子CT扫描。模拟遵循当前原型质子CT扫描仪所使用的设置，包括对探测器及其相应噪声特性的真实建模。计算所有三次扫描的阻止本领图，并与体模的真实阻止本领进行比较。
质子CT给出的阻止本领估计略优于双能CT方法，均方根误差分别为0.2%和0.5%（针对每个体模），而双能CT为0.5%和0.9%。单能CT的均方根误差为2.7%和1.6%。质子CT、双能CT和单能CT的最大误差分别为0.51%、1.7%和7.4%。
更好的阻止本领估计可以显著减少质子治疗中的射程误差，但需要对当前方法有大幅改进，质子CT可能实现这一点。
