湖北省7台加速器调强放疗靶体积和危及器官剂量及二维剂量分布验证方法研究

目的研究用热释光剂量计(TLD)和胶片(film)测量调强放疗(IMRT)靶体积(PTV)、危及器官(OAR)和二维剂量分布方法。方法选择湖北省7家三甲医院的7台不同型号医用直线加速器,国际原子能机构(IAEA)提供的聚苯乙烯专用模体,TLD和放射性免冲洗胶片(EPT3),经CT模拟定位机扫描模体,影像传输至治疗计划系统(TPS),分别勾画PTV、OAR处方剂量和相应的监督单位(MU),能量6 MV X射线束,对模体实施IMRT照射,照射后的TLD和胶片邮寄至中国疾病预防控制中心辐射防护与核安全医学所二级标准剂量学实验室测量和估算。结果按IAEA要求,OAR和PTV的TLD测量值与TPS计划处方剂量的相对偏差为±7.0%。7台加速器PTV的TLD测量值与TPS计划值相对偏差在-5.4%~6.5%范围内,均符合IAEA的要求;5台加速器的OAR的TLD测量值和TPS计划值相对偏差在-2.2%~6.7%范围内,2台加速器相对偏差为-8.6%和8.2%,超出IAEA的要求。按IAEA要求,二维剂量分布3 mm/3%通过率为90%。7台加速器的二维剂量分布通过率在90.3%~98.9%范围内,均符合IAEA要求。结论使用TLD和胶片做IMRT剂量验证,科学性强,操作简单,TLD和胶片便于邮件寄送,该方法可运用于今后对放疗机构调强放疗剂量大范围的质量核查。

Verification of doses to PTV and OAR and 2D dose distribution in IMRT for 7 accelerators in Hubei province

Objective To study a method to measure the doses to planned target volume (PTV) and organ at risk (OAR) and 2D dose distribution in IMRT by using TLD and radiochromic film for a verification purpose. Methods Totally 7 different types of medical linear accelerators were selected from seven hospitals in Hubei province. A polystyrene phantom provided by IAEA was CT scanned and then the scanned images were returned to the Treatment Planning System (TPS) for determining the prescribed doses to PTS and OAR and the corresponding MU. After the phantom was irradiated with 6 MV X-ray, the TLDs and films were transmitted to the secondary standard dosimetry laboratory of China CDC for measurement and estimation. Results The IAEA required the relative deviations between TLD-measured and TPS-planned doses to OAR and PTV be within±7.0%. For PTV, the measured-to-planned deviation values for 7 accelerator were within -5.4% to 6.5%, all consistent with the IAEA requirements. For OAR, the values for 5 accelerators were within -2.2% to 6.7%, not consistent the requirements, whereas the values for the other 2 were -8.6% and 8.2% respectively, beyond the required values. The IAEA required that the 2D dose distribution 3 mm/3% pass rate be higher than 90%. The measured values for 7 accelerators were in the range of 90.3%-98.9%, all consistent with the requirements. Conclusions It is feasible scientifically and easy to operate in practice for using TLD and film to carry out dose verification in IMRT. It would be advisable to apply this method to quality verification in IMRT in medical institutions to the extent possible.