Kooy Hanne M, Schaefer Matthew, Rosenthal Skip, Bortfeld Thomas
Northeast Proton Therapy Center, Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02461, USA.
Phys Med Biol. 2003 Sep 7;48(17):2797-808. doi: 10.1088/0031-9155/48/17/305.
We derive, from first principles, a model to predict the output factors for spread-out Bragg peak proton fields (SOBP). The model is based on the simple observation that the output factor is the ratio of SOBP plateau dose to the dose measured in the ionization reference chamber. The latter, in turn, equates to the entrance dose of the SOBP corrected for inverse square. We use a theoretical derivation of this ratio to establish the relationship between the output factor and the distal range and modulation width of the SOBP. In addition, the theoretical derivation reduces the dependence on the distal range and modulation width into a single factor r = (R - M)/M. We compare the theoretical derivation against measurements obtained at the Northeast Proton Therapy Facility for output factors for clinical fields. The agreement between measurements and prediction is 2.9%.
我们从基本原理出发，推导了一个用于预测扩展布拉格峰质子束流（SOBP）输出因子的模型。该模型基于一个简单的观察结果：输出因子是SOBP坪区剂量与在电离参考腔中测量的剂量之比。而后者又等同于经反平方修正后的SOBP入口剂量。我们利用这个比值的理论推导来建立输出因子与SOBP远端射程和调制宽度之间的关系。此外，理论推导将对远端射程和调制宽度的依赖性简化为一个单一因子r = (R - M)/M。我们将理论推导结果与在东北质子治疗设施获得的临床射野输出因子测量值进行了比较。测量值与预测值之间的一致性为2.9%。
