国产平板电离室剂量学参数测定与评价

Determination and Evaluation of Dosimetric Parameters of Domestic Parallel Plate Ionization Chamber

电离室作为一种高灵敏度的辐射探测器,在放疗剂量校准和辐射环境监测方面发挥重要作用。然而在放疗剂量测量领域高度依赖进口设备,国产探测器的剂量稳定性和可靠性尚无系统的实验数据支持。以国产QPPC40平板电离室为研究对象,通过定量测定其在医用加速器射线束的能量响应、离子复合、极化效应、重复性、漏电流和剂量线性等关键剂量学参数,以促进国产探测器剂量学性能的完善,并为临床应用提供实用性建议。测量结果表明:在6~25 MV光子束相对Co-60γ射线的能量响应修正因子kQ为0.991~0.961,重复性为0.02%,4~22 MeV电子束的kQ为0.953~0.887,工作电压为−400 V时,剂量率为0.04~5.13 Gy/min对应的离子复合修正值为1.002~1.008,极化修正因子为1.001,漏电流在±0.05%以内。所测试指标基本满足JJG912-2010治疗水平电离室检定规程技术要求,然而同一批次电离室校准系数和能响一致性略差,建议使用中进行期间核查并注意探测器水吸收剂量校准系数和能量响应的长期稳定性。

As a high-sensitivity radiation detector,ionization chambers play an important role in radiotherapy dose calibration and radiation environment monitoring.However,the field of radiotherapy dose measurement is highly dependent on imported equipment,and there is a lack of systematic experimental data supporting the dose stability and reliability of domestic detectors.This study focuses on the domestic QPPC40 parallel plate ionization chamber,quantitatively measuring its key dosimetric parameters in medical accelerator beams.These parameters include energy response,ion recombination,polarity effect,repeatability,leakage current,and dose linearity.The goal is to enhance the dosimetric performance of domestic detectors and provide practical recommendations for clinical applications.The measurement results indicate that the energy response correction factor kQ for 6~25 MV photon beam relative to Co-60γray ranges from 0.991 to 0.961,with a repeatability of 0.02%.For 4~22 MeV electron beams,the kQ factor ranges from 0.953 to 0.887.At an operating voltage of-400 V,the ion recombination correction values for dose rates of 0.04-5.13 Gy/min range from 1.002 to 1.008.The polarization correction factor is 1.001,and the leakage current is within±0.05%.The tested indicators generally meet the technical requirements of the JJG 912-2010 verification regulation for therapeutic level ionization chambers.However,the calibration coefficients and energy response consistency of ionization chambers from the same batch show some variability.It is recommended to conduct interim inspections during use and to monitor the long-term stability of the waterabsorbed dose calibration coefficient and energy response of the detector.