Brachytherapy with Radioactive Seed Implantation

In recent years, advancements in cancer treatment have introduced brachytherapy with radioactive seed implantation as an innovative approach for treating solid tumors. This minimally invasive technique offers a promising alternative to surgery, achieving comparable local control and cure rates for certain early-stage malignant tumors, with less damage than surgical procedures. For advanced-stage cancers, it significantly extends survival time and enhances the quality of life.

What Is Brachytherapy with Radioactive Seed Implantation?

Brachytherapy involves implanting miniature radioactive sources (seeds) directly into the tumor or tissues infiltrated by the tumor. Among these, iodine-125 (¹²⁵I) seeds are widely used. The seeds emit low-energy gamma rays that maximize radiation damage to tumor tissues while sparing surrounding healthy tissues, thereby achieving effective treatment with minimal side effects.

Commonly used permanent implant seeds include gold, iodine, and palladium, with ¹²⁵I being the most prevalent. This therapy is extensively applied for various malignancies, including prostate cancer, brain tumors, lung cancer, head and neck cancers, pancreatic cancer, liver cancer, kidney and adrenal tumors, orbital tumors, and soft tissue sarcomas. Notably, for early-stage prostate cancer, seed implantation has become a standard treatment, demonstrating equivalent outcomes to surgery but with fewer complications and side effects, ensuring better post-treatment quality of life.

Advantages of Seed Implantation Therapy

Precision Targeting
The radioactive seeds can be accurately placed to conform to the tumor's shape, delivering targeted radiation to the tumor while protecting surrounding healthy tissues.

High Localized Dose with Minimal Side Effects
With a tissue half-value layer of only 1.7 cm, the seeds provide a high dose to the tumor without excessive exposure to nearby organs.

Long-Lasting Effect
¹²⁵I seeds have a half-life of about 60 days, offering continuous low-dose radiation for 4-6 months (2-3 half-lives), effectively eliminating tumor cells.

Minimally Invasive and Low Pain
The procedure is a minimally invasive surgery performed under local anesthesia. Guided by imaging, the seeds are implanted into the tumor via fine needles, causing minimal pain.

Low Radiation Exposure
The seeds emit low-energy radiation, posing minimal risk to others. Maintaining a distance of 1 meter from pregnant women and children is sufficient for safety.

Indications for Seed Implantation Therapy

Locally advanced tumors not eligible for surgery (excluding prostate cancer).
Tumor diameter ≤7 cm.
Recurrent or metastatic tumors post-surgery or radiotherapy with ≤5 metastatic lesions, each ≤5 cm in diameter.
Patients with a Karnofsky Performance Status (KPS) score ≥70.
Accessible percutaneous puncture path.
Malignant obstruction of hollow organs (esophagus, bile duct, portal vein, etc.).
Absence of severe contraindications to puncture.
Life expectancy ≥3 months.
Patients who refuse other treatments.

Patients must meet at least two criteria from items 1-3 and three or more from items 4-9 to be considered eligible. This therapy is particularly suited for recurrent tumors post-surgery or radiotherapy, or for patients unable to undergo surgery or tolerate conventional treatments.

Prescription Dose

The treatment plan is finalized through consultation among senior oncologists. The treating physician delineates the target area and determines the prescribed dose.

Studies have shown that iodine-125 seed implantation can effectively treat locally recurrent refractory thyroid cancer with doses ranging from 100 to 140 Gy, a median of 120 Gy. Patients experienced no local recurrence or severe adverse events.

For thyroid cancer:

Tumor diameter ≤3 cm: curative doses of 120-140 Gy.
Tumor diameter >3 cm:
- Initial implantation: 100-120 Gy.
- Recurrent tumors post-external radiotherapy: 80-100 Gy.
Seed implantation is recommended 2-3 months post-external radiotherapy, with attention to tolerance levels for surrounding structures like skin, esophagus, trachea, blood vessels, and nerves.

Procedure for Radioactive Iodine-125 Seed Implantation

1. Preoperative Localization

A physicist fixes the patient’s position using a vacuum cushion one week before surgery. For patients undergoing 3D-printed template guidance, CT scans are performed with markers on the skin for reference lines. For freehand CT-guided implantation, only a standard contrast-enhanced CT scan is required. The vacuum cushion is reserved for intraoperative use.

2. Positioning

Ensure consistency between preoperative CT and intraoperative positioning, including headrest height and head angle. Positioning must meet puncture pathway requirements while maximizing patient comfort.

3. Treatment Planning

CT images are uploaded to the treatment planning system (TPS) to outline the gross tumor volume (GTV) and clinical target volume (CTV, GTV + 0.5 cm margin). Dose parameters such as D90 (dose covering 90% of the target), V100 (>95%), and V150 (<100%) must meet minimum requirements.

For 3D-printed templates, individualized designs include needle paths and seed positions. The physicist maps pathways to avoid critical structures and loads the seeds into applicators.

4. Seed Inspection

Radioactive activity is measured per IAEA standards. A 10% sample of seeds is tested to ensure accuracy within 5% error.

5. Seed Implantation

Positioning: Patients are positioned using vacuum cushions and aligned with preoperative markers.
Sterilization and Anesthesia: The operative site is sterilized, draped, and locally anesthetized with lidocaine (1%-2%).
Implantation:
- For 3D-printed templates, guide needles are placed, verified via CT, and adjusted as needed. Seeds are implanted according to the plan, with real-time CT scans verifying placement.
- For freehand implantation, the surgeon adjusts needle direction and depth under CT guidance, ensuring precise placement based on intraoperative TPS adjustments.

6. Intraoperative Planning

Physicists verify the dose distribution and adjust placement to eliminate “cold” or “hot” spots. TPS guidance minimizes risks to critical structures like the esophagus and skin.

Postoperative Care

Monitor puncture sites for bleeding, discharge, or color changes. Report abnormalities immediately.
Manage puncture site pain with prescribed analgesics as needed.
Apply pressure to puncture sites for at least 5 minutes to reduce bleeding risk.
Monitor for fever and administer antibiotics if infection is suspected.
Address gastrointestinal symptoms such as nausea and vomiting with dietary adjustments (fluid diet for 2-3 hours, soft foods after 8 hours).
Promote a balanced diet with high-calorie, high-protein, and vitamin-rich foods for recovery.
Maintain a positive mindset, as emotional well-being aids in postoperative recovery.

This state-of-the-art treatment approach combines precision, minimal invasiveness, and effectiveness, making it a promising option for various solid tumors.