Basic Study About Possibility Of Radiation Myelopathy Reduced By ¹²⁵Ⅰ Interstitial Brachytherapy Combinding With Percutaneous Vertebroplasty In Vitro

To establish the model of thoracic vertebrae 9(T₉)being implanted with ¹²⁵I seeds combinding with percutaneous vertebroplasty(PVP),whose prescription dose being designed by treatment planning system(TPS).To detect radiation apparent activity of T₉ and calculate the total cumulated dose of spinal cord surface.Then to study the possibility of radiation myelopathy reduced by ¹²⁵I interstitial brachytherapy combinding with PVP.Methods 1)T₉(n=15)were taken from adult cadaver,age from 25 to 40 years and being saved in formalin for 2-7 months.All vertebras were detected with bone mineral density (BMD)and were fit to bone mineral content(BMC)lossen standard.Taking the presume tumor in vertebrea as target,3-D treatment plan were designed,so the position and prescription dose of ¹²⁵I seeds was determined.16 ¹²⁵I seeds(total irradiation activity≈8.0 mCi)were implanted into each T₉ vertebraes as below:All seeds were in center of tumor in Particle group(Group A,n=5),All seeds were implanted as treatment plan in TPS group (Group B,n=5);All seeds were implanted around tumor randomly as clinical in Clinical group(Group C,n=5).Radiation apparent activity,geometry deta of T₉ were detected and the total cumulated dose of spinal cord surface in 6 half life periods(D_6T1/2)was calculated by equation.2)Polymethlmethacrylate cylinder(Cylinder PMMA,n=5)and Cancellous Bone cylinder(Cylinder CB,n=5)were made(diameter=1.2cm),in which 2 seeds(total irradiation activity≈1.0 mCi)being implanted in center.The radiation apparent activity and dose rate on cylinder surface was detected or caculated.All deta different between each groups were analyzed with SPSS 11.5,different between all groups by one-way analysis of variance and different between two groups by least significant difference.According to the analysis,to evaluate the possibility of radiation myelopathy reduced by ¹²⁵I interstitial brachytherapy combinding with PVP.Results 1)D_6T1/2in Group A,B,and C are 707.75±200.53cGy/year,979.70±46.01 cGy/year,1296.10±356.78 cGy/year with statistic meaning(P＜0.05),lower than tolerance dose of spinal cord(4000 cGy/4-5months).Compared with Group B,D_6T1/2in Group A is lower by 27.8%with statistic meaning(P＜0.05);D_6T1/2in Group C is higher by 32.3% with statistic meaning(P＜0.05).Compared between Group A and Group C,D_6T1/2in the former is lower than in the latter by 83.1%with significant meaning(P＜0.01).2)The radiation dose rate on Cylinder PMMA is 0.142±0.002cGy/hour and 0.165±0.003 cGy/hour on Cylinder CB.The former is lower than the latter by 69.1%with significant meaning(P＜0.01).Conclusions 1)Taken the dose designed by TPS as premise,¹²⁵I interstitial brachytherapy combinding with PVP will not lead to radiation myelopathy;2)Vertebrae taken from adult cadaver,age from 25 to 40 years and being saved in formalin for 2-7 months, is suit for BMC lossen model of tumor bone;3)TPS design of ¹²⁵I interstitial brachytherapy combinding with PVP is different to that in the other organs;4)PMMA can decrease the irradiation dose rate of BT-125-1 model ¹²⁵I seed more greatly than cancellous bone.