Schaffner B, Pedroni E
Division of Radiation Medicine, Paul Scherrer Institute, Villigen-PSI, Switzerland.
Phys Med Biol. 1998 Jun;43(6):1579-92. doi: 10.1088/0031-9155/43/6/016.
The precision in proton radiotherapy treatment planning depends on the accuracy of the information used to calculate the stopping power properties of the tissues in the patient's body. This information is obtained from computed tomography (CT) images using a calibration curve to convert CT Hounsfield units into relative proton stopping power values. The validity of a stoichiometric method to create the calibration curve has been verified by measuring pairs of Hounsfield units and stopping power values for animal tissue samples. It was found that the agreement between measurement and calibration curve is better than 1% if beam hardening effects in the acquisition of the CT images can be neglected. The influence of beam hardening effects on the quantitative reading of the CT measurements is discussed and an estimation for the overall range precision of proton beams is given. It is expected that the range of protons in the human body can be controlled to better than +/-1.1% of the water equivalent range in soft tissue and +/-1.8% in bone, which translates into a range precision of about 1-3 mm in typical treatment situations.
质子放射治疗计划的精度取决于用于计算患者体内组织阻止本领特性的信息的准确性。该信息通过计算机断层扫描（CT）图像获得，使用校准曲线将CT亨氏单位转换为相对质子阻止本领值。通过测量动物组织样本的亨氏单位和阻止本领值对，验证了一种化学计量学方法创建校准曲线的有效性。结果发现，如果在CT图像采集过程中的束硬化效应可以忽略不计，测量值与校准曲线之间的一致性优于1%。讨论了束硬化效应对CT测量定量读数的影响，并给出了质子束总体射程精度的估计。预计人体中质子的射程在软组织中可控制在水等效射程的±1.1%以内，在骨骼中可控制在±1.8%以内，这在典型治疗情况下转化为约1-3毫米的射程精度。
