A Dosimetric Research On Radioactive ¹²⁵ I Seed Plane Implantation

Whitomore firstly used Retropubic implantation of iodine-125 in the treatment of prostatic cancer which became the base of brachytherapy today. Without the precise TPS and the technology of image management, the seeds were implanted by experiment which location can not be precise designed and delivered. The MPD can not be well calculated so the complications occurred frequently.In the middle of the 90 era, the developing of computer made the TPS become perfect day after day which made the seeds implantation the standard therapy of the prostate cancer in America. Due to the advantage of good therapeutic effect, less complication, micro-wound, seeds implantation used in other tumor soon abroad such as head and neck tumor, thoracic tumor, abdomen tumor and pelvic tumor. Almost 1000 hospital in China use seeds implantation to treat the people with cancer since 1998, but 90% doctor implanted the seeds with their experiment which make the dose in the tumor volume unknown. As a brachytherapy, just like the teletherapy, ¹²⁵I seeds implantation needs the preplan to make sure the dose in tumor volume reach the prescribe dose too. Plato C.Lee used the TPS to simulate the prostate seeds implantation and drew the conclusion of that the MaxV100/V (the rato of the maximum volume in the MPD and the target volume)of tight and the general arrangement of the seeds are 1.65 and o.99 respectively. This proved that the different arrangement have different dose effect strongly. The point of a successful brachytherapy is whether the dose in the target volume is accurate. The report number 24 of the ICRU pointed out that the accurate of tumor dose must better than±5% or the tumor would recurrence or complication occurred.So ¹²⁵I seeds in different distribution and activity were simulated by using the TPS. The area, radius and medical cost in the 80, 130, 145 and 200 Gy isodose curves were calculated by the professional image analysis software. Objective: To study the dosimetric effect and the medical cost of different ¹²⁵I seeds arrangements when implanted at the same number and activity in a plane.Methods: Two groups were established in this experiment. The activity in group A was 2.035×10⁷Bq(0.55mCi)and the activity in group B was 2.96×10⁷Bq(0.8mCi). The procedures were shown as follows, group A: Established 9 different arrangements of 2.035×10⁷Bq ¹²⁵I seed plane implantation using the three-dimensional treatment planning system (3D-TPS) and created the isodose curves of 80, 130, 145 and 200 Gy. The 9 arrangements were with different row(x) and line(y) intervals which named X0.5Y0.5, X0.5Y1, X0.5Y1.5, X1Y1, X1Y1.5, X1.5Y1.5, X0.5Y0.5(2)1(the intervals of line 1 and 3 were 0.5cm, interval line 2 was 1cm), X0.5Y1(2)0.5(the intervals of line 1 and 3 were 1cm, interval line 2 was 0.5cm), X1Y1,(2)0.5(the intervals of line 1 and 3 were 1cm, interval line 2 was 0.5cm). The area, radius and medical cost in the 80, 130, 145 and 200 Gy isodose curves were calculated by the professional image analysis software. Group B: Established 9 different arrangements of 2.96×10⁷ Bq ¹²⁵I seed plane implantation using the three-dimensional treatment planning system (3D-TPS) and created the isodose curves of 80, 130, 145 and 200 Gy. The 9 arrangements were with different row(x) and line(y) intervals which named X0.5Y0.5, X0.5Y0.5(2)1(the intervals of line 1 and 3 were 0.5cm, interval line 2 was 1cm), X0.5Y1, X0.5Y1.5, X1.5Y1.5, X1Y1, X1Y1(2)0.5(the intervals of line 1 and 3 were 1cm, interval line 2 was 0.5cm), X1Y1(2)1.5(the intervals of line 1 and 3 were 1cm, interval line 2 was 1.5cm), X1Y1.5. The area, radius and medical cost in the 80, 130, 145 and 200 Gy isodose curves were calculated by the professional image analysis software.Results: The area, radius and medical cost in the same isodose curves were dissimilar when the arrangement was different. In the group A the arrangements which had the maxima area in the 80, 130, 145 , 200 Gy isodose curves were x1y1, x1y1, x0.5y1, x0.5y1 and the areas were 849.08, 524.5, 481.20, 350.92 mm2 respectively. The arrangements which had the minimum medical cost in the 80 , 130 , 145 and 200 Gy isodose curves were X1Y1, X1Y1, X0.5Y1, X0.5Y1 which were 6.04, 9.78, 10.66, 14.62 yuan/mm2 . When the matched peripheral dose (MPD) were 130Gy, 145Gy and 200Gy, the arrangement of x0.5y1 might be better. When the MPD was 80 Gy, x1y1 might be better. In the group B the area, radius and medical cost in the same isodose curves were dissimilar when the arrangement was different. The arrangements which had the maxima area in the 80 , 130 , 145 and 200 Gy isodose curves were X1Y1.5, X1Y1(2)1.5, X1Y1, X1Y1(2)0.5 and the areas were 1166.42, 791.09, 718.27, 474.63 mm2 respectively. The arrangements which had the minimum medical cost in the 80 , 130 , 145 and 200 Gy isodose curves were X1Y1.5, X1Y1(2)1.5, X1Y1, X1Y1(2)0.5 which were 4.40, 6.48, 7.14, 11.55 yuan/mm2 . When the matched peripheral dose (MPD) was 200Gy, the arrangement of X1Y1(2)0.5 might be better. When the matched peripheral dose (MPD) was 145Gy, the arrangement of X1Y1 might be better. When the matched peripheral dose (MPD) was 130Gy, the arrangement of X1Y1(2)1.5 might be better. When the MPD was 80 Gy, X1Y1.5 might be better.Conclusions:1. The MPD and medical cost was influenced significantly by the arrangement of the seeds even the number and activity were equal.2. The MPD and medical cost was influenced significantly by the seeds activity even the number and arrangement were the same.3. The MPD could be calculated accurately using TPS which was unavoidable before the implantation.