Department of Heavy Ion Center of Wuwei Cancer Hospital, Gansu Wuwei Academy of Medical Sciences, Gansu Wuwei Tumor Hospital, Wuwei City, Gansu Province 733000, China.
Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou 730000, China.
Biomed Res Int. 2021 Oct 22;2021:8808537. doi: 10.1155/2021/8808537. eCollection 2021.
An experimental and mathematical study for determining the effective point of measurement ( ) for a Farmer-type cylindrical chamber in a carbon ion passive scatter beam is presented.
The ionization depth curves measured by the Bragg peak chamber were plotted according to the position of the inner surface of the entrance window, while the Farmer chamber was plotted at the tip of the cylindrical geometric center. The ionization depth curves measured by a cylindrical chamber in the 3D water phantom were then compared with a high-precision parallel-plate PTW Bragg peak chamber for inspecting the upstream shift correction of the cylindrical chamber in the carbon ion beam. A component of the vertical and horizontal integration method and the barrier model, cos = 1 - [2 /(1 + - )], for analyzing the shift of effective point of measurement in different carbon ion energies and various field sizes, were studied.
The shift between the maximum peak of the Bragg peak chamber and the Farmer chamber in a field size of 10 cm × 10 cm with an energy of 330 MeV/u of carbon ion is 2.3 mm. This upstream shift corresponds to (0.744 ± 0.07), where is the Farmer chamber inner radius of 3.05 mm. Carbon ion energy from 120 MeV/u to 400 MeV/u with different field sizes show different shifts of effective point of measurement in a range of (0.649 ± 0.02) to (0.843 ± 0.06) of 3 cm × 3 cm at an energy of 400 MeV/u and 10 cm × 10 cm at an energy of 120 MeV/u, respectively. The vertical and horizontal scatter analysis by the barrier model can precisely describe the shift of the effective point of measurement at different carbon ion energies with various field sizes.
We conclude that the Farmer chamber can be used for a patient-specific dose verification check in carbon ion beam treatment if is well calibrated.
提出了一种用于确定圆柱形碳离子被动散射射束中 Farmer 型圆柱形腔有效测量点（ ）的实验和数学研究。
根据入口窗内表面的位置绘制布拉格峰室测量的电离深度曲线，而 Farmer 室则绘制在圆柱几何中心的尖端。然后，将 3D 水模体中的圆柱形腔测量的电离深度曲线与高精度平行板 PTW Bragg 峰值室进行比较，以检查圆柱形腔在碳离子束中的上游平移校正。研究了垂直和水平积分法的一个分量和势垒模型， cos = 1 - [2 /(1 + - )]，用于分析不同碳离子能量和不同射野大小下有效测量点的位移。
在 330MeV/u 碳离子能量、射野大小为 10cm×10cm 的情况下，布拉格峰室的最大峰值与 Farmer 室之间的偏移量为 2.3mm。这种上游偏移量对应于（0.744±0.07），其中 是 3.05mm 的 Farmer 室内半径。从 120MeV/u 到 400MeV/u 的碳离子能量，在不同射野大小下，在 400MeV/u 能量的 3cm×3cm 和 120MeV/u 能量的 10cm×10cm 处，有效测量点的偏移量分别在（0.649±0.02）到（0.843±0.06）的范围内呈现出不同的变化。势垒模型的垂直和水平散射分析可以精确描述不同碳离子能量和不同射野大小下有效测量点的位移。
如果 得到很好的校准，我们得出结论，Farmer 室可用于碳离子束治疗中的患者特定剂量验证检查。
