调强放射治疗“end to end”质量控制核查中应用针尖电离室测量小野剂量的初步研究-《中国医学物理学杂志》

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Title:: Preliminary study on small-field dose measurement using pinpoint ionization chamber in dosimetric end to end audit of IMRT

文章编号:: 1005-202X（2021）12-1502-06

作者:: 薛娴1; 何志坚1; 袁继龙1; 王进2; 杨春勇2; 周文珊3; 胡传朋4; 曹兴江2; 孙刚涛3; 贾陈志4; 1.中国疾病预防控制中心辐射防护与核安全医学所，北京 100088； 2.江苏省疾病预防控制中心，江苏南京 210009； 3.湖北省疾病预防控制中心，湖北武汉 430079； 4.河南省职业病防治研究院，河南郑州 450052

Author(s):: XUE Xian1; HE Zhijian1; YUAN Jilong1; WANG Jin2; YANG Chunyong2; ZHOU Wenshan3; HU Chuanpeng4; CAO Xingjiang2; SUN Gangtao3; JIA Chenzhi4; 1. National Institute for Radiological Protection, China Centre for Disease Control and Prevention, Beijing 100088, China 2. Jiangsu Provincial Center for Disease Control and Prevention, Nanjing 210009, China 3. Hubei Provincial Center for Disease Control and Prevention, Wuhan 430079, China 4. Henan Institute for Occupational Health, Zhengzhou 450052, China

关键词:: 针尖电离室; 小野剂量; 调强放射治疗; 质量控制

Keywords:: Keywords: pinpoint ionization chamber small-field dose intensity-modulated radiotherapy quality control

分类号:: R318；R811.1

DOI:: DOI:10.3969/j.issn.1005-202X.2021.12.009

文献标志码:: A

摘要:: 目的：在调强放射治疗“end to end”质量核查中，探讨应用针尖电离室对调强放射治疗小野照射进行绝对剂量测量的研究。方法：选择3省20家医院，将放有热释光剂量计TLD（距模体表面距离约7.5 cm）和胶片的国际原子能机构（IAEA）模体进行CT扫描，图像导入放射治疗计划系统（TPS）中，设计治疗计划，进行7野等中心调强照射，MLC照射野大小>2 cm×2 cm且<4 cm×4 cm。同时针尖电离室（0.015 cc）放在固体水模体距模体表面7.5 cm下进行点剂量绝对剂量验证：（1）将治疗计划中射野角度归零平移到固体水模体中进行剂量验证；（2）治疗计划射野角度不归零时为实际治疗照射方向，平移到固体水模体中进行绝对剂量验证。结果：在调强放射治疗多叶光栅小野照射的固体水模体中，用针尖电离室测量的绝对剂量与TPS计算得到的绝对剂量比较，7野照射方向归为零度时，比较偏差<5%；实际照射方向时，比较偏差<5%。验证后的计划，在IAEA模体上进行实际7野调强治疗，模体中的高剂量靶区胶片（Gafchromic EBT3 film）绝对剂量通过率均≥90%（Gamma分析：3%, 3 mm），TLD偏差<7%。均符合IAEA提出的标准。结论：在调强放射治疗多叶光栅小野照射时，可以应用针尖电离室作为绝对剂量验证的一个方法。

Abstract:: Abstract: Objective To discuss the feasibility of using pinpoint ionization chamber for small-field absolute dose measurement in dosimetric end to end audit of IMRT. Methods The study involved 20 hospitals in 3 provinces. The CT scan of IAEA phantom placed with films and TLD which was 7.5 cm from the surface of phantom was transferred into treatment planning system for treatment planning. Seven-field isocenter IMRT in which the multileaf collimator (MLC) radiation field was larger than 2 cm×2 cm and smaller than 4 cm×4 cm was carried out. Meanwhile, pinpoint ionization chamber (0.015 cc) was placed in the solid water phantom where was 7.5 cm from the surface of the phantom for the absolute dose verification of point dose, including (1) dose verification when the treatment plan was translated to solid water phantom at field angles of 0° (2) absolute dose verification when the treatment plan was translated to solid water phantom at actual treatment angles. Results For solid water phantom receiving IMRT MLC small-field radiation, the comparison between absolute dose measured by pinpoint ionization chamber and that calculated by treatment planning system showed that the deviation was less than 5% when the 7-field radiation angles returned to 0°, and that it was also less than 5 % for actual treatment angles. After verification, the 7-field IMRT was performed on IAEA phantom, obtaining a TLD deviation less than 7% and ≥90% absolute dose passing rate (3%, 3 mm gamma criterion) for Gafchromic EBT3 film (high-dose planning target volume) in the phantom, which satisfied IAEA standard. Conclusion Pinpoint ionization chamber can be used for absolute dose verification for IMRT MLC small-field radiation.

《中国医学物理学杂志》[ISSN:1005-202X/CN:44-1351/R]

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