Chuang Cynthia F, Verhey Lynn J, Xia Ping
Department of Radiation Oncology, University of California at San Francisco, Comprehensive Cancer Center, 94143, USA.
Med Phys. 2002 Jun;29(6):1109-15. doi: 10.1118/1.1481520.
(Received 22 October 2001; accepted for publication 26 March 2002; published 22 May 2002) With advanced conformal radiotherapy using intensity modulated beams, it is important to have radiation dose verification measurements prior to treatment. Metal oxide semiconductor field effect transistors (MOSFET) have the advantage of a faster and simpler reading procedure compared to thermoluminescent dosimeters (TLD), and with the commercial MOSFET system, multiple detectors can be used simultaneously. In addition, the small size of the detector could be advantageous, especially for point dose measurements in small homogeneous dose regions. To evaluate the feasibility of MOSFET for routine IMRT dosimetry, a comprehensive set of experiments has been conducted, to investigate the stability, linearity, energy, and angular dependence. For a period of two weeks, under a standard measurement setup, the measured dose standard deviation using the MOSFETs was +/- 0.015 Gy with the mean dose being 1.00 Gy. For a measured dose range of 0.3 Gy to 4.2 Gy, the MOSFETs present a linear response, with a linearity coefficient of 0.998. Under a 10 x 10 cm2 square field, the dose variations measured by the MOSFETs for every 10 degrees from 0 to 180 degrees is +/- 2.5%. The percent depth dose (PDD) measurements were used to verify the energy dependence. The measured PDD using the MOSFETs from 0.5 cm to 34 cm depth agreed to within +/- 3% when compared to that of the ionization chamber. For IMRT dose verification, two special phantoms were designed. One is a solid water slab with 81 possible MOSFET placement holes, and another is a cylindrical phantom with 48 placement holes. For each IMRT phantom verification, an ionization chamber and 3 to 5 MOSFETs were used to measure multiple point doses at different locations. Preliminary results show that the agreement between dose measured by MOSFET and that calculated by Corvus is within 5% error, while the agreement between ionization chamber measurement and the calculation is within 3% error. In conclusion, MOSFET detectors are suitable for routine IMRT dose verification.
（2001年10月22日收到；2002年3月26日接受发表；2002年5月22日发表） 在使用调强射束的先进适形放射治疗中，在治疗前进行放射剂量验证测量很重要。与热释光剂量计（TLD）相比，金属氧化物半导体场效应晶体管（MOSFET）具有读取过程更快、更简单的优点，并且使用商业MOSFET系统时，可以同时使用多个探测器。此外，探测器尺寸小可能具有优势，特别是对于小的均匀剂量区域中的点剂量测量。为了评估MOSFET用于常规调强放疗剂量测定的可行性，已进行了一系列全面的实验，以研究其稳定性、线性、能量和角度依赖性。在标准测量设置下，持续两周时间，使用MOSFET测量的剂量标准偏差为±0.015 Gy，平均剂量为1.00 Gy。对于0.3 Gy至4.2 Gy的测量剂量范围，MOSFET呈现线性响应，线性系数为0.998。在10×10 cm²的方形射野下，MOSFET在0至180度每隔10度测量的剂量变化为±2.5%。百分深度剂量（PDD）测量用于验证能量依赖性。与电离室测量结果相比，使用MOSFET在0.5 cm至34 cm深度测量的PDD在±3%范围内一致。对于调强放疗剂量验证，设计了两个特殊模体。一个是具有81个可能的MOSFET放置孔的固体水板，另一个是具有48个放置孔的圆柱形模体。对于每个调强放疗模体验证，使用一个电离室和3至5个MOSFET在不同位置测量多个点剂量。初步结果表明，MOSFET测量的剂量与Corvus计算的剂量之间的误差在5%以内，而电离室测量与计算之间的误差在3%以内。总之，MOSFET探测器适用于常规调强放疗剂量验证。
