术中放疗加速器中子剂量当量率的测量研究

Measurement of the neutron dose equivalent rate from a dedicated intraoperative radiation therapy accelerator

目的 测量并分析术中放疗加速器9和12 MeV电子线在手术室内引起的中子剂量当量率，与西门子Primus加速器相同电子线能量档产生的中子污染进行比较，为放射治疗引起的二次致癌风险提供数据参考。方法 利用中子探测仪测量术中放疗加速器在9和12 MeV电子线于机头两端、限光筒底端、患者治疗平面，以及其他关键位置产生的中子剂量当量率。取相似的位置在西门子Primus加速器上进行相同方法的测量。分析测量结果，并将两种加速器产生的中子进行比较。结果 手术过程中使用9和12 MeV的电子线治疗时会产生中子，对患者以及工作人员产生潜在的健康隐患。9 MeV时，术中放疗加速器机头两端以及限光筒底端两侧的中子剂量当量率分别为（51.8±3.1）、（45.2±1.5）、（70.5±4.9）和（68.2±3.3）μSv/h，比12 MeV产生的中子分别低5.9%、5.4%、17.8%和21.5%。手术室门内侧在9和12 MeV时产生的中子剂量当量率极低，可以忽略。西门子加速器出束9 MeV时，在相似测量点处产生的中子剂量当量率为（277.3±1.2）、（285.1±1.6）、（185.1±1.8）、（182.8±2.4）μSv/h，比12 MeV的分别低48.8%、47.6%、48.7%、和52.2%。能量达到12 MeV时，西门子Primus加速器产生的中子剂量当量率是术中加速器的10倍以上。结论 两种医用加速器12 MeV电子线产生的中子剂量当量率远高于9 MeV产生的中子，增加了患者第二原发癌的风险；传统医用加速器在相同能量档产生的中子剂量当量率远高于术中电子加速器，应采取适当的屏蔽防护。

Objective To measure and analyze the neutron dose equivalent rate produced by an IORT accelerator with 9 and 12 MeV electron energyies, and compare them with those from a Siemens Primus linear accelerator with the same electron energy, in order to provide data reference for the risk of secondary cancer induced by radiotherapy. Methods Using the neutron detector LB6411, the neutron dose equivalent rates produced by the IORT accelerator of 9 and 12 MeV were measured on some key locations, such as the head of the accelerator, cylinder bottom, patient plane with electron energies 9 and 12 MeV. The similar measurements were also performed on the same locations on a Siemens conventional accelerator. The data were collected and analyzed and the result wer compared between the two accelerators. Results Neutron dose equivalent rates from the IORT accelerator with 9 MeV energy were （51.8±3.1）, （45.5±1.5）, （70.5±4.9） and （68.2±3.3） μSv/h near the head of the accelerator,cylinder bottom, patient plane, with 5.9%, 5.4%, 17.8% and 21.5% lower than at 12 MeV, respectively. The dose equivalent rates at the similar locations from the Siemens Primus accelerator were （277.3±1.2）, （285.1±1.6）, （185.1±1.8） and （182.8±2.4） μSv/h at 9 MeV, with 48.8%, 47.6%, 48.7%, 52.2% lower than those at 12 MeV, respectively. At the energy of 12MeV, the neutron equivalent dose rate from the IORT was lower by a factor of about 10 than for Siemens Primus accelerator. Conclusions The neutron dose equivalent rates generaged by both the IORT and the Siemens Primus are higher at 12 MeV than at 9 MeV, which would lead to an increased risk of secondary cancer to patients. The traditional medical accelerator produces much higher neutron dose equivalent rates than the intraoperative electron accelerator, for which the appropriate shielding should be takn.