湖北省调强放疗多叶光栅野光子线束吸收剂量和二维剂量分布验证研究

Verification of absorbed dose and single-field dosimetry of MLC-shaped IMRT photon beams in Hubei province

目的 用热释光剂量计（TLD）和放射性免冲洗胶片测量调强放疗（IMRT）多叶光栅（MLC）野光子线束吸收剂量并验证二维剂量分布。方法 选择湖北省7家三级甲等医院的7台不同型号医用直线加速器，使用国际原子能机构（IAEA）提供的15 cm×15 cm×15 cm聚苯乙烯专用模体，TLD和放射性免冲洗胶片，在源皮距90 cm，照射深度10 cm，照射野5 cm×5 cm，6 MV X射线，6 Gy吸收剂量照射条件下制定IMRT计划并实施照射，比较TLD和胶片吸收剂量测量值与放疗计划系统（TPS）预估剂量之间的偏差。同时，使用医院配备的30 cm×30 cm均质固体模体，在模体表面下5 cm处放置25 cm×25 cm放射性免冲洗胶片，并将IMRT计划中单个射野移植到模体中胶片层面上并实施照射，通过胶片剂量分析系统验证二维剂量分布。结果 所检医用直线加速器中，1号加速器TLD吸收剂量相对偏差和胶片吸收剂量相对偏差分别为-8.5%和-1.9%；7号加速器TLD吸收剂量相对偏差和胶片吸收剂量相对偏差分别为5.4%和0.5%；其余加速器TLD和胶片吸收剂量相对偏差均在±5%范围以内。所有加速器的二维剂量分布通过率均在90%以上。结论 TLD和胶片核查调强放疗剂量质量方法，操作简单，科学性强，TLD和胶片便于邮件方式寄送，该方法可运用于对放疗机构调强放疗剂量大范围的质量核查。

Objective To verify the absorbed dose and two-dimensional dosimetry delivered by MLC-shaped IMRT photon beams using thermoluminescent dosimeters （TLDs） and radiochromic films. Methods Different types of medical linear accelerators at 7 third-grade first-class hospitals in Hubei were selected for this audit study. Besides TLDs and films, a small polystyrene phantom measuring 15 cm×15 cm×15 cm, supplied by the International Atomic Energy Agency （IAEA）, was also used. The TPS dose calculation were performed with 6 MV X-ray beam and by delivering 6 Gy dose to the TLDs or films at 10 cm depth for 5 cm×5 cm field size at 90 cm SSD. After irradiation, comparations were conducted of dose derivations between TPS-calculated values and TLD-or film-measured values. The two-dimensional dosimetry audit was carried out by using 30 cm×30 cm homogeneous solid phantoms in which a 25 cm×25 cm film was located at 5 cm depth. A single-filed profile generated by TPS was delivered to the film, and the film was measured. And then, two-dimensional dose distribution was analyzed using the film analysis system. Results The results suggested that the relative deviations of TLD and film to TPS dose was -8.5% and -1.9% for accelerator 1, 5.4% and 0.5% for accelerator 7, respectively, whereas those for other accelerators were within ±5%. The passing rates for two-dimensional dose distribution at all accelerators were all higher than 90%. Conclusions TLD and film quality audit for IMRT can be applied for a wide range of application in view of its simplicity, reliability and postal convenience.