The Comparation Of Calculating¹²⁵I Seeds Number With TPS And Empirical Formula

Objective: In1972，Whitomore firstly used Retropubic implantation ofiodine-125in the treatment of prostate cancer which became the base ofbrachytherapy today. At that time, Without the precise three-dimensionaltreatment planning system TPS and the technology of image management, theseeds were implanted by experiment which location can not be precisedesigned and delivered. the optimal dose and the number of¹²⁵I seed weredetermined by the doctor，s experience.The MPD can not be well calculated sothe complications occurred frequently. In the middle of the90era, thedeveloping of computer technology made the TPS become further perfect dayafter day which made the seeds implantation the standard therapy of the early-mid prostate cancer in America. Almost1000hospital in China use seedsimplantation to treat the people with cancer since1998, but90%of thehospitals lacke of TPS, doctors implanted the seeds with their experiment andthe¹²⁵I empirical formula to estimate the number of implanted particles whichmake the dose in the tumor volume unknown. Without TPS, how to accuratelycalculate the number of particles？Meningher H obtained Results fromcomputer simulations performed on different tumour shapes and volumes, thatshow a linear dependence between the total implanted activity and the tumourvolume. The total activity does not depend on the shape of the tumour. Thedependence between the number of particles and the tumour volume，surfacearea need to be studied.So the number of¹²⁵I seeds，used to be implanted toreach prescription dose for different sizes of tumors，simulated by using theTPS and¹²⁵I empirical formula，were compared with each other. At thesame time， This study explored the dependence between the number of¹²⁵Iseeds by using the TPS and the tumour volume，surface area respectively toprovide guidance for clinical seed implantation. Methods: This study was based on3simple assumptions. Frist, thetumour volume was approximated as a cube which length ranged from2cm to6.5cm （the interval was0.5cm）.Second, prescription dose （PD） was145Gy.Third, the activity was0.5mCi. There were two groups named groupA and group B in this study，the number of¹²⁵I seeds were computed by TPSin group A and empirical formula in group B.The empirical formula asfollow：the number of¹²⁵I seeds=（tumor length+width+thickness）/3×5÷the activity of each seed. Tumor volume and surface area for each case werecalculated. All the data were analysed by statistical software SPSS13.0.Results：With the increase of tumor volume and surface area, the morenumber of¹²⁵I seeds were needed，The number of¹²⁵I seeds in group B werestatistically significant different to A group（P <0.05）. A simple analyticalequation, y^∧=15.063＋1.059v－0.001v²（P <0.05）（defined as Formula1）,for the relationship between¹²⁵I seeds number（y） and the tumor volume （v）was derived. We also obtained a equation, y^∧=-0.545＋0.814s＋0.0004s²（P <0.05）（defined as Formula2）,for the¹²⁵I seeds number（y）-surfacearea（s） relationship.Conclusion：1. TPS has more beneficial clinical effects in calculating¹²⁵I seedsnumber than¹²⁵I empirical formula.2. In clinical，Results obtained from computer simulations show aquadratic dependence between¹²⁵I seeds number and tumour volume，surfacearea respectively.formula y^∧=15.063+1.059v-0.001v²、y^∧=-0.545+0.814s+0.0004s²can open a gap to calculate the number of¹²⁵I seeds.