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Year : 2019  |  Volume : 15  |  Issue : 7  |  Page : 1430-1434

Expert consensus on computed tomography-assisted three-dimensional-printed coplanar template guidance for interstitial permanent radioactive 125I seed implantation therapy

1 Department of Radiation Oncology, Peking University 3rd Hospital, Beijing, China
2 Department of Thoracic Surgery, Tianjin Medical University 2nd Hospital; Department of Oncology, Tianjin Medical University 2nd Hospital, Tianjin, China
3 Department of Oncology, Daliang Zhong Shan University Hospital, Liaoning, China
4 Department of Oncology, Shandong Tengzhou Center Hospital, Shandong, China

Date of Submission20-Jun-2019
Date of Decision02-Sep-2019
Date of Acceptance26-Oct-2019
Date of Web Publication13-Jan-2020

Correspondence Address:
Prof. Junjie Wang
Peking University 3rd Hospital, Beijing
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jcrt.JCRT_434_19

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 > Abstract 

Interstitial permanent radioactive seed implantation delivers a high local dose to tumors and sharply drops off at surrounding normal tissues. Radioactive seeds implanted via ultrasound or computed tomography (CT) guidance are minimally invasive and facilitate quick recovery. Transrectal ultrasound-guided 125I seed implantation assisted by a transperineal plane template is standard for early-stage prostate carcinoma, with a highly consistent target volume dose distribution. The postplan dose evaluation is consistent with the preplan evaluation. Until now, there was no workflow for seed implantation elsewhere in the body, and it was difficult to effectively preplan for seed implantation because of patients' position changes, organ movement, and bone structure interference. Along with three-dimensional (3D) printing techniques and seed implantation planning systems for brachytherapy, coplanar and X Y axis coordinate templates were created, referred to as 3D-printed coplanar templates (3D-PCT). 125I seed implantation under CT guidance with 3D-PCT assistance has been very successful in some carcinomas. Preplanning was very consistent with postplanning of the gross tumor volume. All needles are kept parallel for 3D-PCT, with no coplanar needle rearrangement. No standard workflow for 3D-PCT-assisted seed implantation exists at present. The consensus topics for CT-assisted guidance compared to 3D-PCT-assisted guidance for seed implantation are as follows: Indications for seed implantation, preplanning, definition of radiation doses and dosimetry evaluation, 3D-PCT workflow, radiation protection, and quality of staff. Despite current data supporting 125I seed implantation for some solid carcinomas, there is a need for prospectively-randomized multicenter clinical trials to gather strong evidence for using 125I seed implantation in other solid carcinomas.

Keywords: 125I seed, brachytherapy, computed tomography guidance, interstitial permanent implantation, three-dimensional printing coplanar template

How to cite this article:
Wang J, Chai S, Wang R, Zheng G, Zhang K, Huo B, Huo X, Jiang Y, Ji Z, Jiang P, Peng R. Expert consensus on computed tomography-assisted three-dimensional-printed coplanar template guidance for interstitial permanent radioactive 125I seed implantation therapy. J Can Res Ther 2019;15:1430-4

How to cite this URL:
Wang J, Chai S, Wang R, Zheng G, Zhang K, Huo B, Huo X, Jiang Y, Ji Z, Jiang P, Peng R. Expert consensus on computed tomography-assisted three-dimensional-printed coplanar template guidance for interstitial permanent radioactive 125I seed implantation therapy. J Can Res Ther [serial online] 2019 [cited 2022 Jan 29];15:1430-4. Available from: https://www.cancerjournal.net/text.asp?2019/15/7/1430/275556

 > Introduction Top

Interstitial permanent radioactive 125 I seed implantation brachytherapy has become an important salvage treatment modality for all kinds of recurrent solid carcinomas.[1],[2],[3],[4],[5] The American Cancer Society, the Urology Society, the Clinical Oncology Society, the Radiation Oncology Society, the Brachytherapy Society, and the NCCN guidelines recommend seed implantation as the modality of choice for early-stage prostate carcinoma treatment.[6],[7],[8] Seed implantation techniques for prostate carcinomas are well-established and quality assurance is controlled by transperineal ultrasound-guidance combined with planar template assistance to achieve a precise three-dimensional (3D) distribution of seeds in the prostate and ensuring seed implantation treatment is strictly followed up as per preplanning.

In 2002, Chinese scholars introduced computed tomography (CT)-guided technology into the field of seed implantation for recurrent solid carcinomas in the head and neck, chest, abdomen, pelvis, and spinal cord, greatly improving the accuracy of seed implantation. The indications of seed implantation have been expanded and a series of clinical studies have been produced.[9],[10],[11],[12],[13],[14],[15],[16],[17],[18],[19] However, CT-guided puncturing for seed implantation is very complicated and time-consuming, and operators spend a very long time learning these skills. With patients' body movements and interference with organs at risk (OARs), it is difficult to completely follow the preplanning steps, and prescribed doses are not always appropriate in real-time operative conditions.[20] With the wide application of 3D-printing technology in medical science, a new digital guiding 3D-printing template for seed implantation has been developed and designed with digital information such as central X and Y axes and seed needles' path information with 5 mm between needle holes.[21] There are two kinds of digital templates according to their function: 3D-printing coplanar templates (3D-PCT) and 3D-printing noncoplanar templates (3D-PNCT). 3D-PCT is indicated when seed needles need to be kept in the same direction and parallel to each other. The optimal conformity of radiation doses of implanted seeds in most locations in the human body could be achieved by 3D-PCT guidance. A 3D-PNCT is used for noncoplanar needle distribution, where needles cannot be kept parallel, but with optimized conformity.[21] 3D-PCT is dependent on coordinated X and Y axes, with 0.5 mm of space between the needle holes, Arabic numbers on the X-axis, and English letters on the Y-axis. To visualize the X and Y axes on CT scans, X-ray markers were set to the end of the X and Y axes.[21],[22]

 > Basic Requirements of Computed Tomography-Assisted Three-Dimensional-Printed Coplanar Templates-Guided Radioactive Seed Implantation Top

Radioactive seed implantation brachytherapy is dependent on image guidance to precisely implant radioactive seeds into a tumor target according to preplanning. The distribution of the seeds in the target needs to be highly consistent with the preplan, and dose distribution conformity should meet requirements. Seed implantation is advantageous as it is minimally invasive, requires only one surgery, and each seed delivers a very small dose. At the same time, seed implantation brachytherapy is part of the field of external beam radiotherapy (EBRT). The basic principles of EBRT should apply to interstitial brachytherapy, including target determination, definitions of prescribed doses, and acceptable limits for OAR radiation doses, among others.[23],[24]

Definitions for target and OARs: According to Report 83 of the International Commission on Radiation Units and Measurement, the definitions for the tumor target and OARs are: (1) gross tumor volume (GTV): lesion area with a certain shape visible by various imaging and clinical examinations; (2) clinical target volume (CTV): including GTV and subclinical targets and which may be invaded by tumors; (3) planning target volume: including CTV, patient organ movement during irradiation, routine positioning movement, target displacement during treatment, and target volume changes, resulting in an appropriate expansion of irradiation volume. Internal target volume is a concept of EBRT, which is seldom considered in seed implantation; and (4) OAR refers to the area covered by the irradiated and adjacent normal tissues or organs.

Target prescription doses and dosimetric evaluation parameters: (1) Prescribed doses are defined according to evidence-based medicine or clinical experience. However, there are no prospective dose-escalation studies on prescribed doses for seed implantation therapy except in prostate cancer. The American Brachytherapy Society recommends prescribed doses of 140–160 Gy for 125 I seed implantation for prostate cancer (with at least 90% of prostate volume [D90] affected by the prescribed dose) and 115 Gy combined with EBRT.[7] The prescription doses for tumors in other organs have been based on those for prostate cancer, which have been published both in China and abroad. For recurrent solid tumors, 110–160 Gy with an activity of 0.3–0.7 mCi (11.1–25.9 Mbq) is recommended. (2) Dosimetric evaluation parameters including target and OAR: D90, D100, V100 (i.e., the percent of the prostate receiving 100% of the prescribed dose), V150, V200, and so on. In addition, the Conformal Index, Homogeneity Index, and External Target Volume Index were usually used to evaluate the quality of the treatment plan;

Limitation for OAR dose: For brachytherapy by 125 I seed implantation, the relationship between the doses to OARs and adverse effects are still unclear, and further randomized prospective clinical trials are needed. At present, low-dose seed implantation brachytherapy dose parameters for OARs are referred to as high-dose afterloading. Dose parameters for OARs in prostate cancer are as follows: Rectum: D2cc <100% prescription dose; D0.1cc <200 Gy. Urethra: D10 <150% prescription dose; D30 <130% prescription doses.[7]

125 I seed physical characteristics: Radioactive 125 I seeds are commonly used in the clinic, with a half-life of 60 days and delivering photon energy of 27 KeV. In recent years, loose seeds have been gradually replaced by stranded seeds because loose seeds tended to migrate in tissues.[24],[25]

 > Indications and Contraindications of Computed Tomography-Assisted Three-Dimensional-Printed Coplanar Templates-Guided Seed Implantation Top

Indications for radioactive 125 I seed implantation include: (1) any recurrent carcinoma after surgery or EBRT; or refusal of surgery or EBRT, when the diameter of the tumor is <7 cm; (2) pathological diagnosis; (3) satisfactory needle puncture path design in preplan; (4) no tendency of bleeding or hypercoagulability; (5) generally acceptable condition of the body with KPS >70; (6) able to tolerate radioactive seed implantation; and (7) estimated survival time of >3 months.

Contraindications of radioactive seed implantation include: (1) severe bleeding tendency, with platelets <50 × 1010/L and coagulation dysfunction (prothrombin time >18 s, prothrombin activity <40%; anticoagulant therapy and/or antiplatelet coagulants should be discontinued for at least 1 week before seed implantation); (2) burst tumor; (3) severe diabetes mellitus; (4) no suitable puncture paths according to preplan; and (5) the estimated target dose could not meet the designed prescribed dose requirements.

The relative contraindications of radioactive seed implantation are: (1) extensive metastasis with a predicted survival of <3 months; (2) severe complications, infectious period, low immune function, and renal insufficiency; and (3) allergy to iodine contrast agents.

Recommendation for CT-assisted 3D-PCT-guided seed implantation; CT-assisted 3D-PCT-guided radioactive seed implantation is a new minimally-invasive form of brachytherapy, which is suitable for salvage treatment of recurrent and metastatic solid tumors. Standardized workflows of CT-assisted 3D-PCT-guided seed implantation include patient position fixation, CT-simulated positioning, preplanning design, 3D-PCT image production, stabilization by 3D-PCT, needle puncture for seed implantation, implantation of 125 I seeds, and postplan evaluation [Table 1] and [Table 2]. The key to successful seed implantation is strict quality assurance in all steps.[26],[27]
Table 1: Detailed requirements and workflow

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Table 2: Characteristics of computed tomography-assisted three-dimensional-printed coplanar templates-guided seed implantation in different organs

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 > Workflow for Computed Tomography-Assisted Three-Dimensional-Printed Coplanar Templates-Guided Radioactive Seed Implantation Top

The flowchart was shown in [Figure 1].
Figure 1: The circuit diagram of computed tomography-assisted three-dimensional-printed coplanar templates guidance for seed implantation

Click here to view

 > Radiation Protection from 125 I Seed Implantation Top

The half-value layer of 125 I seeds is 0.025 mmPb, and its half-life is about 60 days. After 60 days, the energy of 125 I seeds decreases to half of its initial energy and 10% of its initial energy in 6 months, which is considered negligible after 1 year. Contact with children and pregnant women should be avoided within 2 months of seed implantation.[28],[29],[30] If long-term contact is required (more than a few hours), the patient should be kept at a distance of 1.5–2.0 cm or instructed to wear a lead neck, vest, and apron.

 > Management and Faculty Training of 125I Seed Implantation Therapy Top

At present, seed implantation brachytherapy in China is a restricted technology, which requires strict training to obtain a license. The relevant state administrative departments carry out supervision. In 2009, the Ministry of Health released the Technical Management Standards for Radioactive Seed Implantation Brachytherapy for the first time. In 2017, the National Health and Family Planning Commission released the Technical Management Standards for Radioactive Seed Implantation Brachytherapy (2017 edition), further amending and standardizing the institutional, personnel, and technical conditions and requirements for carrying out seed implantation. It was emphasized that physicians should receive systematic training for at least 3 months, participate in seed implantation therapy for at least 30 cases under the guidance of superior physicians, and participate in the entire management process of patients, including preoperative diagnosis, preoperative planning, implantation modality, postoperative dose verification, perioperative management, and follow-up. Only after passing the examination could they go on duty. Specific detailed requirements can be found on the official website of the National Health Commission.[30]

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

 > References Top

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Lin L, Wang J, Jiang Y, Meng N, Tian S, Yang R, et al. Interstitial 125I seed implantation for cervical lymph node recurrence after multimodal treatment of thoracic esophageal squamous cell carcinoma. Technol Cancer Res Treat 2015;14:201-7.  Back to cited text no. 2
Jiang YL, Meng N, Wang JJ, Ran WQ, Yuan HS, Qu A, et al. Percutaneous computed tomography/ultrasonography-guided permanent iodine-125 implantation as salvage therapy for recurrent squamous cell cancers of head and neck. Cancer Biol Ther 2010;9:959-66.  Back to cited text no. 3
Jiang P, Liu C, Wang J, Yang R, Jiang Y, Tian S, et al. Computed tomography (CT)-guided interstitial permanent implantation of 125 I seeds for refractory chest wall metastasis or recurrence. Technol Cancer Res Treat 2015;14:11-8.  Back to cited text no. 4
Wang JJ, Yuan HS, Li JN, Jiang WJ, Jiang YL, Tian SQ, et al. Interstitial permanent implantation of 125I seeds as salvage therapy for re-recurrent rectal carcinoma. Int J Colorectal Dis 2009;24:391-9.  Back to cited text no. 5
Mohler J, Bahnson RR, Boston B, Busby JE, D'Amico A, Eastham JA, et al. NCCN clinical practice guidelines in oncology: Prostate cancer. J Natl Compr Canc Netw 2010;8:162-200.  Back to cited text no. 6
Nag S, Beyer D, Friedland J, Grimm P, Nath R. American brachytherapy society (ABS) recommendations for transperineal permanent brachytherapy of prostate cancer. Int J Radiat Oncol Biol Phys 1999;44:789-99.  Back to cited text no. 7
Davis BJ, Horwitz EM, Lee WR, Crook JM, Stock RG, Merrick GS, et al. American brachytherapy society consensus guidelines for transrectal ultrasound-guided permanent prostate brachytherapy. Brachytherapy 2012;11:6-19.  Back to cited text no. 8
Jiang YL, Meng N, Wang JJ, Jiang P, Yuan HSh, Liu C, et al. CT-guided iodine-125 seed permanent implantation for recurrent head and neck cancers. Radiat Oncol 2010;5:68.  Back to cited text no. 9
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Cao Q, Wang H, Meng N, Jiang Y, Jiang P, Gao Y, et al. CT-guidance interstitial 125 Iodine seed brachytherapy as a salvage therapy for recurrent spinal primary tumors. Radiat Oncol 2014;9:301.  Back to cited text no. 11
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Yao L, Cao Q, Wang J, Yang J, Meng N, Guo F, et al. CT-guided 125 I seed interstitial brachytherapy as a salvage treatment for recurrent spinal metastases after external beam radiotherapy. Biomed Res Int 2016:Articles ID 8265907:10.  Back to cited text no. 13
Li J, Wang J, Meng N, Qu A, Yuan H, Liu C, et al. Image-guided percutaneous 125 I seed implantation as a salvage treatment for recurrent soft tissue sarcomas after surgery and radiotherapy. Cancer Biother Radiopharm 2011;26:113-20.  Back to cited text no. 14
Liu B, Zhou T, Geng J, Zhang F, Wang J, Li Y. Percutaneous computed tomography-guided iodine-125 seeds implantation for unresectable pancreatic cancer. Indian J Cancer 2015;52 Suppl 2:e69-74.  Back to cited text no. 15
Lin ZY, Yang JY, Chen J, Chen J. Evaluating the effectiveness of computed tomography-guided 125 I seed interstitial implantation in patients with secondary adrenal carcinoma. J Cancer Res Ther 2019;15:813-7.  Back to cited text no. 16
Li Z, Wang X, Fang K, Shi J, Qi X, Sun R. Concurrent computed tomography-guided radioactive iodine-125 seeds percutaneous interstitial implantation and chemotherapy for treatment of cervical lymph node metastases. J Cancer Res Ther 2018;14:S1163-9.  Back to cited text no. 17
Wang W, Liu Z, Zhu J, Wu C, Liu M, Wang Y, et al. Brachytherapy with iodine 125 seeds for bone metastases. J Cancer Res Ther 2017;13:742-7.  Back to cited text no. 18
He C, Liu Y, Li Y, Yang L, Li YT, Li SL, et al. Efficacy and safety of computed tomography-guided 125I brachytherapy for lymph node metastatic from hepatocellular carcinoma. J Cancer Res Ther 2018;14:754-9.  Back to cited text no. 19
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Ran P, Yuliang J, Zhe J, Fuxin G, Haitao S, Junjie W, et al. Comparison of dosimetric evaluation data of pre-and post-operative plans of 3D-printing coordinative coplanar template and CT guided radioactive seeds implanting surgery. Brachytherapy 2017,16:S105.  Back to cited text no. 21
Ji Z, Jiang Y, Guo F, Sun H, Fan J, Zhang L, et al. Dosimetry verification of radioactive seed implantation for malignant tumors assisted by 3D printing individual templates and CT guidance. Appl Radiat Isot 2017;124:68-74.  Back to cited text no. 22
Devlin, PM, Cormack RA, Holloway CL, Stewart AJ. Brachytherapy Applicantions and Techniques. 2nd ed. New York: Demos Medical Publishing; 2015.  Back to cited text no. 23
Lee WR, deGuzman AF, Tomlinson SK, McCullough DL. Radioactive sources embedded in suture are associated with improved postimplant dosimetry in men treated with prostate brachytherapy. Radiother Oncol 2002;65:123-7.  Back to cited text no. 24
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