湖北省核查放射治疗非参考条件剂量学参数方法的验证

目的 研究用TLD核查医用电子加速器在非参考条件下，光子线束剂量随照射野、楔形板变化，电子线束剂量随照射野、源皮距变化的剂量学参数方法的可靠性。方法 在非参考条件下，用指形电离室测量光子线束水下10 cm处吸收剂量和电子线束最大剂量点处吸收剂量，并在同一位置放置TLD进行照射，将照射后的TLD邮寄到中国疾病预防控制中心辐射防护与核安全医学所进行测量并估算剂量。结果 光子线束剂量点共70个，其中58个点的TLD测量结果与指形电离室测量结果相对偏差在±7.0%以内（IAEA允许偏差±7.0%），合格率为82.8%。经过P_S值修正后，合格点数达到62个，合格率上升为88.6%；电子线束剂量点为24个，其TLD测量结果与指形电离室测量结果相对偏差均在±5.0%以内（IAEA允许偏差±5.0%），合格率为100%。结论 用TLD核查非参考条件电子线束剂量学参数方便，与指形电离室相互验证，可提高剂量测量的准确性。电子线束能量在5 MeV<E₀<10 MeV的范围内，用指形电离室测量吸收剂量参数，并用TLD验证，其结果精确可靠。

Verification of dosimetric methodology for auditing radiotherapy quality under non-reference condition in Hubei province

Objective To verify the reliability of TLD-based quality audit for radiotherapy dosimetry of medical electron accelerator in non-reference condition by monitoring the dose variations from electron beams with different field sizes and 45° wedge and the dose variations from photon beams with different field sizes and source-skin distance. Methods Both TLDs and finger ionization chambers were placed at a depth of 10 cm in water to measure the absorbed dose from photon beams, and also placed at the depth of maximum dose from electron beams under non-reference condition. TLDs were then mailed to National Institute for Radiological Protection, China CDC for further measurement. Results Among the 70 measuring points for photon beams, 58 points showed the results with a relative error less than ±7.0%(IAEA's acceptable deviation: ±7.0%)between TLDs and finger ionization chambers measurements, and the percentage of qualified point numbers was 82.8%. After corrected by P_s value, 62 points were qualified and the percentage was up to 88.6%. All of the measuring points for electron beams, with the total number of 24, presented a relative error within ±5.0% (IAEA's acceptable deviation: ±5.0%) between TLDs and finger ioization cylindrical chambers measurements. Conclusions TLD-based quality audit is convenient for determining radiotherapy dosimetric parameters of electron beams in non-reference condition and can improve the accuracy of the measuring parameters in connection with finger chambers. For electron beams of 5 MeV<E₀<10 MeV, the absorbed dose parameters measured by finger ionization chambers, combined with TLD audit, can help obtain the precise and reliable results.