Study On Shielding Protection Effect And Environmental Radiation After ¹²⁵I Seed Brachytherapy

ObjectivesThe difference of shielding protection effect of different lead equivalent shielding materials after radioactive ¹²⁵I seed implantation and its influence on ambient radiation were analyzed.Methods1.According to the CT scanning image immediately after radioactive ¹²⁵I seed implantation,the vertical distance from the seed implantation site to the patient’s body surface was measured and recorded;Within 24 hours after radioactive¹²⁵I seed implantation,when the shielding material was not covered,the dose rates at the vertical distance from the body surface marker point 30cm,40cm,50cm,60cm,70cm,80cm,90cm,100cm was measured by pocket radiometer,discussion on decay law of radioactive¹²⁵I seed.2.After the shielding materials of 0.25mmpb and 0.35mmpb were covered at the implanted site of seeds,the dose rates at 30cm,40cm,50cm,60cm,70cm,80cm,90cm,100cm was measured by pocket radiometer,and the dose rates of covering 0.25mmpb and0.35mmpb shielding materials at 30cm,50cm and 100cm were compared with when the shielding material is not covered.When covering and not covering the shielding material,whether there is a statistical difference in the dose rate between the two groups.Calculate and compare the dose rates measured at 30cm,50cm and 100cm after covering 0.25mmpb and 0.35mmpb shielding materials.At the same time,the shielding effect of 0.25mmpb and 0.35mmpb shielding materials to radiation is calculated and analyzed.3.Before the patients with radioactive ¹²⁵I seed implantation returned to the ward,the background dose rate in the ward was measured 5 times continuously,and the average value was taken as the natural background dose rate.Within 24 hours after radioactive¹²⁵I seed implantation,the dose rates at the vertical distance from the body surface marker point 100cm,200cm,300cm,400cm was measured by environmental monitor,compared with the natural background dose rate,calculated annual dose equivalent,the radiation pollution of radioactive ¹²⁵I seeds to the environment was studied.4.According to the formulas:D（n）=D（0）e^-λnλn and E（∞）=34.56TpD（0）Tr,the effective dose and precaution time were calculated,and the differences among the groups were compared.Results1.Within 24 hours after radioactive ¹²⁵I seed implantation,the dose rates at the vertical distance of 30cm,40cm,50cm,60cm,70cm,80cm,90cm,100cm from the body surface marker point were 11.307（5.210,17.020）uSv/h、7.326（2.795,11.613）uSv/h、5.775（1.990,8.850）uSv/h、4.217（1.355,6.150）uSv/h、3.362（1.110,5.043）uSv/h、2.650（0.865,4.240）uSv/h、2.065（0.783,3.100）uSv/h、1.551（0.590,2.415）uSv/h,respectively.And the relationship between dose rates and distance is y=22.975e^-0.027x.2.The dose rates measured after covering 0.25mmpb and 0.35mmpb shielding materials at the seed implantation site were compared with those measured when the shielding materials were not covered,the P value were 0.000,and the difference were statistically significant.The dose rates of shielding materials covered with 0.25mmpb and 0.35mmpb at 30cm were 0.288（0.143,0.390）uSv/h and 0.248（0.130,0.325）uSv/h,the difference was statistically significant（P=0.000）.The dose rates at 50cm were 0.242（0.130,0.308）uSv/h and 0.209（0.130,0.280）uSv/h,the difference was statistically significant（P=0.000）.The dose rates at 100cm were 0.177（0.130,0.210）uSv/h and 0.158（0.120,0.190）uSv/h,the difference was statistically significant（P=0.000）.The shielding materials of 0.25mmpb and 0.35mmpb can shield 88.59%⁹7.45%and 89.81%⁹7.81%of the rays,respectively.3.The natural background dose rate was 0.112±0.015uSv/h.The dose rates measured by environmental monitor at the vertical distance from the body surface marker point 100cm,200cm,300cm,400cm were 1.497±0.694uSv/h,0.187±0.043uSv/h,0.129±0.016uSv/h,0.114±0.016uSv/h.Compared with natural background dose rate,the P value at 100cm,200cm and 300cm was 0.000,the differences were statistically significant;and the P value at 400cm was 0.287,the difference was not statistically significant.The annual dose equivalents at the vertical distance from the body surface marker point 100cm,200cm,300cm and 400cm are 0.771mSv、0.096mSv、0.066mSv、0.059mSv,respectively.4.When the shielding material was not covered within 24 hours after operation,the precaution time of an adult family member that lives with but does not sleep with the patient,a pregnant family member and a child that lives with the patient,a co-worker that does not live with the patient and a nonpregnant adult family member that lives and sleeps with the patient were 1d,47d,75d and 113d,respectively.After covering the shielding materials of 0.25mmpb and 0.35mmpb,the precaution time of different populations were0d.Conclusions1.After operation,the shielding material covered with 0.25mmpb at 30cm can meet the radiation protective requirement.2.The environment away from the 100cm of the patient’s seed implantation site is safe and does not need to be shielded.With the prolongation of the distance,the radiation dose rate decreases gradually,the dose rate at400cm was close to the natural background dose rate,and there was no environmental radiation pollution.3.Individualized protective measures were formulated according to the specific population after operation.Figure1;Table7;Reference 53...