Dosimetry Verification of 125I Seeds Implantation With Three-Dimensional Printing Noncoplanar Templates and CT Guidance for Paravertebral/Retroperitoneal Malignant Tumors

Objective: To compare dose distributions of postoperative plans with preoperative plans for radioactive seed implantation of paravertebral/retroperitoneal tumors assisted by 3-dimensional printing noncoplanar templates and computed tomography. Methods: Sixteen patients with paravertebral/retroperitoneal tumors (21 lesions) underwent radioactive seed implantation with 3-dimensional printing noncoplanar templates. Prescribed dose was 110 to 160 Gy. We compared the dose distribution of the postoperative plan with the preoperative plan. Dose parameters were D90, minimum peripheral dose, V100, V150, conformal index and external index of the target volume, and the dose received by 2 cm(3) of normal tissue of organs at risk (spinal cord, aorta, and kidney). Results: Sixteen 3-dimensional printing noncoplanar templates were produced for 21 treatment areas. Mean gross tumor volume (preoperative) of patients was 61.1 cm(3), mean needle number was 17, mean number of implanted I-125 seeds was 65, and mean D90 of postoperative target area (gross tumor volume) was 131.1 Gy. Actual number of seeds postbrachytherapy increased by 1 to 12 in 8 cases. For postoperative plans, the mean D90, minimum peripheral dose, V100, V150 was 131.1 Gy, 67.1 Gy, 90.2%, and 64.1%, respectively, and 135.0 Gy, 64.7 Gy, 90.9%, and 64.1%, respectively, in preoperative plans. Comparing with the preplanned cases, the dose of the target volume was slightly lower and the high-dose area of the target volume was larger in postoperative cases, but the difference was not statistically significant (P > .05). Actual dose conformity of the target volume was lower than preplanned, and the difference was statistically significant (P = .005). Conclusion: Three-dimensional printing noncoplanar templates can provide good accuracy for positioning and direction in radioactive seed implantation.