河南省8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)和免冲洗胶片(film)测量调强放疗(IMRT)计划靶区(PTV)、危及器官(OAR)处方剂量和二维剂量分布验证方法。方法选择河南省的8台不同型号医用直线加速器,国际原子能机构(IAEA)提供聚苯乙烯专用模体,经CT模拟定位机扫描,影像传输至治疗计划系统(TPS),分别勾画PTV和OAR的处方剂量,能量6 MV X射线。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,对PTV和OAR处方剂量,TLD测量剂量与TPS计划处方剂量的相对偏差为±7.0%。对PTV的剂量验证结果表明,8台加速器的相对偏差在-0.3%~6.9%范围内,符合要求。对OAR剂量验证结果表明,6台加速器的相对偏差在-7.0%~0.3%范围内,符合要求,2台加速器的相对偏差在-10.8%^-8.4%范围内,不符合要求。按IAEA要求,二维剂量分布3 mm/3%通过率≥90%。7台加速器通过率在90.2%~99.9%范围内,符合要求,1台加速器通过率为70.0%,不符合要求。结论免冲洗胶片和热释光剂量计验证调强放疗靶体积和危及器官处方剂量及二维剂量分布,方法简单可靠,是开展调强放射治疗质量控制的重要步骤,可为医疗机构或第三方服务机构核查临床处方剂量提供有力支撑。

Verification of doses to PTV and OAR and 2D dose distribution in IMRT for 8 accelerators in Henan province

Objective To use TLDs and radiochromic films to verify the prescribed doses to both planned target volume(PTV)and organ at risk(OAR)and the 2D dose distribution in IMRT.Methods Eight accelerators of different models were selected in Henan province.The polystyrene phantom provided by IAEA was scanned using CT scanners and then the scanned images were transmitted to treatment planning system(TPS)for prescribing respectively the doses to PTV and OAR.IMRT was performed with phantom exposed to a 6 MV X-rays.The irradiated TLDs and films were delivered for measurement and estimation at Secondary Standard Dosimetry Laboratory at National Institute for Radiological Protection,Chinese Center for Disease Control and Prevention.Results According to IAEA requirements,the relative deviations of the TLD-measured and TPS-planned values were within±7.0%for the prescribed doses to PTV and OAR.The measured results for PTV have shown that the relative deviation of TLD-measured and TPS-planned values were within-0.3%to 6.9%for 8 accelerators,all consistent with the IAEA requirements.For OAR,the relative deviations of TLD-measured and TPS-planned were within-7.0%to 0.3%for 6 accelerators,consistent with the requirements,whereas those for other 2 accelerators were within-10.8%to-8.4%,not up to the requirements.IAEA required that,for 2D dose distribution,the pass rate of 3 mm/3%be≥90%.The measured values for 7 accelerators were from 90.2%to 99.9%,consistent with the requirements,whereas that for another one was 70.0%,not meeting the requirement.Conclusions The method to verify,using radiochromic film and TLD,the prescribed doses to PTV and OAR and the pass rate of 2D dose distribution is simple and reliable.It is an important step to implement quality control for IMRT and can provide effective support for medical or third-party service institution to verify clinically prescribed dose.