Abstract: Objective To explore the radiation levels of the main environmental concerns around the head Gamma Knife device and evaluate the personal doses of medical personnel working in this environment. Methods The ionization chamber dosimeter was used to detect focal dose rate of gamma knife from November 2011 to April 2021. At the same time,the SW88 X-γ radiation dosimeter was used to monitor the radiation levels of different environmental focus points inside and outside the OUR-XGD head gamma knife treatment room. Based on dose equivalent rate of the standing position where the medical staff stood close to the treatment bed for assisted treatment and a certain number of patients,personal dose of the staff member can be obtained by approximate calculation. Results Focal dose rate of gamma knife decayed exponentially.The radiation level monitoring of the surrounding environment concerns of the gamma knife showed that during the staff-assisted positioning treatment the average dose equivalent rate in the standing position decreased from 5.10 μSv/h to 1.145 μSv/h. Furthermore,the dose equivalent rate at the edge of the Gamma Knife machine room had been reduced to near background radiation levels. Based on the average annual treatment of 200 people and mean retention time of 10 minutes for each patient,total personal dose was approximately calculated with the value of 0.094 mSv,which met the standards for ionizing radiation protection and radiation source safety. Conclusion Under normal treatment conditions,the personal dose level of operating staff from OUR-XGD gamma knife during the process of assisting patient positioning meets the safety requirements of national standards. Moreover,it has no obvious effect on the radiation level of indoor and outdoor environment under the condition of good shielding.

Key words: Gamma knife, Radioactive source, Personal dose, Focal dose rate, Dose equivalent rate