摘要目的 研究用小探测器测量调强放射治疗多叶光栅(MLC)小野输出因子方法.方法 用MAX4000剂量仪,Unidos剂量仪分别接不同型号小电离室和二极管半导体探测器,瓦里安加速器,6MVX射线束,10 cm×10 cm(固定),变化二级准直器(多叶光栅片)形成照射野6 cm×6 cm,4 cm×4 cm,3 cm×3 cm,2 cm×2 cm,水下10 cm,照射:250 MU,3次读数取平均值.所有小野读数归一到10 cm×10 cm照射野,得到多叶光栅小野输出因子,用测量输出因子与出版输出因子进行比较.结果 Unidos剂量仪和0.015 cc电离室测量多叶光栅小野输出因子与出版输出因子相对偏差分别为1.0％、1.7％、1.5％和2.4％;Unidos剂量仪和0.007 cc电离室测量相对偏差分别为0.2％、0.8％、0.8％和1.4％;MAX4000剂量仪和0.007 cc电离室测量相对偏差分别为0.1％、0.5％、0.5％和0.9％;MAX4000剂量仪和二极管半导体探测器测量相对偏差分别为0.1％、1.5％、1.8％和2.4％(所有小野读数归一到10 cm×10 cm照射野读数),3 cm×3 cm,2 cm×2 cm归一到4 cm×4 cm照射野读数的相对偏差分别为0.1％和0.9％.结论 0.015 cc电离室测量多叶光栅野输出因子,3 cm×3 cm,2 cm×2 cm照射野的结果符合要求.按照国际原子能机构(IAEA)放射治疗剂量准确度要求,测量输出因子与出版输出因子的相对偏差应在±2％和±3％范围内.0.007 cc电离室测量结果好于0.015 cc电离室测量结果;二极管半导体探测器测量结果符合要求(归一到10 cm×10 cm照射野)和非常好(归一到4 cm×4 cm照射野).对多叶光栅片形成的小野,由于剂量学问题,小野输出因子必须用小电离室或二极管半导体探测器测量.该测量方法准确可靠,对所有小野测量结果应输入放射治疗计划系统作为制定临床放射治疗计划的依据.

abstractsObjective To develop the methods for using 0.015 cc pinpoint chambers, 0.007 cc miniature chambers and diode detector to measure Multi-leaf collimator (MLC) small field in IMRT.Methods MAX4000 and Unidos electrometers were connected with different types of small chambers and diode detectors.MLC shaped fields of10 cm×10 cm, 6 cm×6 cm, 4 cm×4 cm, 3 cm×3 cm, 2 cm× 2 cm were defined at 100 cm SSD.The field sizes for the Varian accelerator were defined by the tertiary MLC, while the secondary jaws were kept at 10 cm × 10 cm field, with the monitor units of 250 MU.Each field was measured three times to obtain the average value.The readings of all small fields were normalized to 10 cm × 10 cm field values for comparison of measured and published output factors.Results The relative deviations of the MLC small field output factors from the published outputs are 1.0％ , 1.7％ , 1.5％ and 2.4％, respectively, for Unidos electrometer connected with 0.015 cc pinpoint chamber;0.2％, 0.8％, 0.8％ and 1.4％, respectively, for Unidos electrometer connected with 0.007 cc miniature chamber;and 0.1％, 0.5％, 0.5％ and 0.9％, respectively, for MAX4000 electrometer connected with 0.007 cc miniature chamber.Conclusions The 0.015 cc chamber-measured MLC output factors for 3 cm × 3 cm and 2 cm × 2 cm fields are excellent.As required by IAEA, the relative deviations of the measured output factor from the published output factor are within ± 2％ for 2 cm × 2 cm fields and ± 3％ for larger fields.The results measured using 0.007 cc chamber are better than those measured using 0.015 cc chamber.The measured results using the diode detector, normalized to the 10 cm × 10 cm field, are consistent with the minimum requirements and excellent when being normalized to the 4 cm × 4 cm field.For dosimetric consideration, MLC small field output factor should be measured using small chamber and diode detector.The method is accurate and reliable, therefore, all measured output factors for MLC small fields should be input into radiation treatment plan system.