Proton dose distribution measurements using a MOSFET detector with a simple dose-weighted correction method for LET effects
Proton dose distribution measurements using a MOSFET detector with a simple dose-weighted correction method for LET effects
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DOI：
10.1120/jacmp.v12i2.3431
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发表时间：
2011-01-01
影响因子：
2.1
通讯作者：
Ogino, Takashi
中科院分区：
文献类型：
--
作者：
Kohno, Ryosuke;Hotta, Kenji;Ogino, Takashi
我们通过实验评估了新型金属氧化物半导体场效应晶体管 (MOSFET) 探测器的质子束剂量再现性、灵敏度、角度依赖性和深度-剂量关系。该探测器采用更薄的氧化层制成，并在高偏置电压下运行。为了准确测量剂量分布，我们开发了一种实用方法来校正 MOSFET 对质子束的响应。通过检查质子穿过 L 形团块形成的横向剂量分布来测试探测器。使用 190 MeV 质子束评估剂量再现性、角度依赖性和深度剂量响应。将使用 MOSFET 探测器产生的深度输出曲线与使用电离室 (IC) 获得的结果进行比较。由于质子剂量分布的精确测量需要对 LET 效应进行校正，因此我们开发了一种简单的剂量加权校正方法。校正因子被确定为质子穿透深度或剩余范围的函数。使用笔形束算法计算每个测量点的残余质子范围。获得了原始光束和 SOBP 光束的体模横向测量结果。 MOSFET探测器的再现性在2%以内，角度依赖性小于9%。该探测器在布拉格峰处表现出良好的响应（相对于 IC 探测器为 0.74）。对于质子通过 L 形团所产生的剂量分布，校正后的 MOSFET 剂量与 IC 结果非常吻合。使用 MOSFET 探测器可以进行绝对质子剂量测定，精度约为 3% (1 sigma)。较薄的氧化层厚度改善了质子剂量测定中的 LET。通过采用 LET 依赖性的校正方法，可以使用 MOSFET 探测器测量绝对质子剂量。
We experimentally evaluated the proton beam dose reproducibility, sensitivity, angular dependence and depth-dose relationships for a new Metal Oxide Semiconductor Field Effect Transistor (MOSFET) detector. The detector was fabricated with a thinner oxide layer and was operated at high-bias voltages. In order to accurately measure dose distributions, we developed a practical method for correcting the MOSFET response to proton beams. The detector was tested by examining lateral dose profiles formed by protons passing through an L-shaped bolus. The dose reproducibility, angular dependence and depth-dose response were evaluated using a 190 MeV proton beam. Depth-output curves produced using the MOSFET detectors were compared with results obtained using an ionization chamber (IC). Since accurate measurements of proton dose distribution require correction for LET effects, we developed a simple dose-weighted correction method. The correction factors were determined as a function of proton penetration depth, or residual range. The residual proton range at each measurement point was calculated using the pencil beam algorithm. Lateral measurements in a phantom were obtained for pristine and SOBP beams. The reproducibility of the MOSFET detector was within 2%, and the angular dependence was less than 9%. The detector exhibited a good response at the Bragg peak (0.74 relative to the IC detector). For dose distributions resulting from protons passing through an L-shaped bolus, the corrected MOSFET dose agreed well with the IC results. Absolute proton dosimetry can be performed using MOSFET detectors to a precision of about 3% (1 sigma). A thinner oxide layer thickness improved the LET in proton dosimetry. By employing correction methods for LET dependence, it is possible to measure absolute proton dose using MOSFET detectors.