Treatment planning system simulation of central and peripheral dose distribution of 125I seeds：a comparison study / 介入放射学杂志

ABSTRACT

Objective To investigate the surrounding and central dosimetric distribution difference of the same activity, same number of 125I seeds. Methods 3D treatment planning system (3D-TPS) was used to separately sketch out 7 cubes with side length of 2 cm, 2.5 cm, 3 cm, 3.5 cm, 4 cm, 4.5 cm and 5 cm;simulations of different tumor sizes were established, into which 125I seeds with activity of 0.5 mCi were respectively loaded. All seeds were distributed at the periphery of the tumor (peripheral group) with the prescribed dose of 145 Gy. The dose volume histogram (DVH) was printed and the 90% of target volume absorbed dose (D90), 90% of prescription dose coverage target volume percentage (V90), the maximum dose and mean dose were determined. Then the seeds in every cube were distributed into the center (central group) and the above parameters were calculated by using the same method. Results The mean D90 of the peripheral and central group was (147.29 ±0.58) Gy and (106.08 ±9.40) Gy respectively, the difference between the two groups was statistically significant (t=-4.292, P=0.005). The mean V90 of the peripheral and central group was (95.46±0.44)% and (79.07±4.19)% respectively, the difference between the two groups was statistically significant (t=-3.831, P=0.009). The mean maximum dose of the peripheral and central group was (1 224.65 ±12.7) Gy and (1 532.48 ±48.54) Gy respectively, the difference between the two groups was statistically significant (t=6.823, P=0.000). The mean value of average dose of the peripheral and central group was (192.14 ±2.89) Gy and (179.81 ±5.40) Gy respectively, the difference between the two groups was statistically significant (t=-2.847, P=0.029). Conclusion The dose distribution is directly influenced by the distribution pattern of the 125I seeds. When the number and activity of the 125I seeds are the same, the peripheral seeds implantation has a better dose distribution.