Brachytherapy, with its unique physical advantages of precisely confining high-dose radiation to the tumor target area and rapidly tapering off to protect surrounding normal tissues, has become an indispensable pillar of modern radiation oncology. As the ultimate device that delivers radioactive sources to the target site, the performance of brachytherapy needles directly determines whether this advantage can be fully realized. From the prostate to the cervix, from the breast to the skin, from intracavitary to interstitial applications, therapeutic needles are widely used in curative or palliative treatment of various cancers, acting as the "brush" for precise dose sculpting.

I. Prostate Cancer: The "Gold Standard" Tool for Dose Escalation

Prostate cancer is one of the most mature and widely applied areas for brachytherapy, mainly including low-dose-rate brachytherapy (LDR-BT) with permanent seed implantation and high-dose-rate brachytherapy (HDR-BT) with temporary interstitial implantation.

Permanent Seed Implantation (e.g., Iodine-125, Palladium-103): Under real-time ultrasound guidance, dozens of fine needles (typically 17G–18G) loaded with radioactive seeds are precisely implanted into the prostate via a transperineal template. The therapeutic needle serves as both a seed carrier and a spatial locator. The puncture accuracy (parallelism, depth) of the needle directly determines the consistency between the spatial distribution of seeds and the preoperative plan, thereby affecting the conformality of dose distribution. The double-bevel tip, with its straight puncture trajectory, is the first choice for parallel needle placement under template guidance, ensuring geometric accuracy. After the procedure, the needle is removed, and the seeds remain permanently in the body to continuously emit low-dose radiation.

High-Dose-Rate Temporary Interstitial Implantation (HDR-BT): Similar transperineal puncture is performed to implant hollow applicator needles. Subsequently, an afterloading treatment machine, under computer control, delivers a high-activity Iridium-192 source to irradiate at different dwell positions in each needle. The therapeutic needle acts as a temporary channel for the radioactive source. It requires extremely high lumen smoothness and diameter consistency to ensure unobstructed movement and precise positioning of the source. After treatment, all needles are removed. HDR-BT is often used as a boost therapy after external beam radiation or combined therapy for intermediate-to-high risk prostate cancer.

Clinical Value: Brachytherapy delivers a highly localized dose to prostate cancer. Due to rapid dose fall-off, it better protects the rectum, bladder, and urethral sphincter compared to external beam radiation alone, significantly reducing the risk of long-term urinary incontinence and rectal bleeding.

II. Cervical Cancer: A Mainstay of Curative Treatment

Intracavitary combined with interstitial brachytherapy is a standard component of curative radiation therapy (combined with external beam radiation) for locally advanced cervical cancer.

Intracavitary Therapy: A uterine tandem and vaginal applicator (e.g., ovoids) are used to irradiate the cervix and proximal parametrial regions. Although "needles" are not directly used, applicators themselves are an important branch of brachytherapy devices.

Interstitial Implantation: For large tumors or irregular shapes involving the parametrium, multiple interstitial needles are punctured transvaginally or transperineally into the parametrial, cervical, or even lymph node regions invaded by the tumor under imaging guidance (e.g., CT, MRI). These needles are usually longer and thinner (e.g., 17G, length up to 20 cm or more), requiring excellent rigidity to traverse the vaginal fornix and parametrial tissue, while tip penetration (often using Mitsubishi or double-bevel tips) is critical. MRI guidance clearly delineates soft-tissue targets, enabling more precise implantation.

Clinical Value: By directly delivering high-dose radiation to the tumor, it effectively compensates for the insufficient dose of external beam radiation, which is key to improving local control rates and reducing central recurrence risk.

III. Breast Cancer: Precise Boost After Breast-Conserving Surgery

For early breast cancer patients undergoing breast-conserving surgery, intraoperative or postoperative interstitial brachytherapy can serve as a tumor bed boost after whole-breast radiation or a single modality for accelerated partial breast irradiation (APBI).

Intraoperative Radiation Therapy (IORT): Immediately after tumor resection, applicator tubes or needle sleeves are placed in the surgical cavity for a single high-dose irradiation.

Postoperative Implantation: Under imaging guidance, multiple flexible applicator tubes or hollow needles are percutaneously punctured to form a three-dimensional array around the surgical cavity. Therapeutic needles need to adapt to the soft nature of breast tissue while providing sufficient puncture force to penetrate potential fibrous tissue. Mitsubishi tips offer distinct advantages in dense breasts. Treatment is usually administered in multiple fractions (HDR).

Clinical Value: High-dose radiation is precisely concentrated on the tumor bed, the area most prone to recurrence. While ensuring efficacy, it significantly shortens treatment time (APBI can be completed within 1 week) and reduces scattered doses to the heart, lungs, and contralateral breast from whole-breast radiation.

IV. Other Clinical Applications

Skin Cancer: Surface applicators or interstitial needles are used for irradiation of basal cell carcinoma and squamous cell carcinoma, especially for surgically challenging sites such as the nose and eyelid.

Head and Neck Cancer: Interstitial implantation for tumors of the floor of the mouth, tongue, buccal mucosa, etc., as an adjunct to surgery or external beam radiation, effectively protecting vital organs such as the mandible and salivary glands.

Soft Tissue Sarcoma: Adjuvant therapy after surgery, with implantation in the tumor bed to reduce local recurrence rates.

Hepatobiliary and Pancreatic Cancer: Percutaneous or intraoperative implantation for palliative pain relief or local control.

Prevention of Vascular Restenosis: Intravascular brachytherapy (using catheters rather than needles, but with similar principles) prevents restenosis after coronary or peripheral angioplasty.

V. Future Trends and Challenges

Ultimate Imaging Guidance: Real-time MRI-guided brachytherapy is becoming a research hotspot and advanced clinical practice in prostate, cervical, and other cancers. This requires therapeutic needles to be fully MRI-compatible (non-magnetic, minimal artifacts), driving wider application of titanium alloy materials. Integration of novel imaging technologies such as ultrasound elastography and CT perfusion with brachytherapy planning will enable more precise target delineation and needle position verification.

Automation and Intelligence in Dose Calculation and Delivery: Artificial intelligence (AI) is used to automatically optimize needle positions and dose distributions; robot-assisted puncture systems improve puncture accuracy and reproducibility, reducing reliance on surgeon experience.

Functional Integration of Therapeutic Needles: Future therapeutic needles may integrate micro-sensors to monitor tip temperature, tissue impedance, or pressure in real time, providing feedback on puncture resistance and tissue type; they may even integrate micro-ultrasound probes to enable real-time imaging at the needle tip, ensuring precise positioning.

Combined Therapy Platforms: Integrating brachytherapy with hyperthermia, local immunotherapy injection, photodynamic therapy (PDT), etc. Therapeutic needles can serve as multi-functional channels for synergistic treatment of other modalities while placing radioactive sources.

Continuous Innovation in Materials and Processes: Advanced biocompatible coatings to reduce infection and adhesion; biodegradable temporary applicators to eliminate secondary removal surgery; 3D-printed customized applicators to perfectly fit individual patient anatomy.

VI. Conclusion

The brachytherapy needle, a seemingly simple metal tube, is in fact a critical bridge connecting physical dose plans and biological tumor targets. It has proven irreplaceable value in multi-cancer treatments, from precise array placement in the prostate, curative implantation in the cervix, to breast-conserving boosts in breast cancer. With the rapid development of imaging, robotics, and materials science, therapeutic needles are evolving from passive delivery tools to active, intelligent treatment platforms. In the future, they will continue to play an increasingly precise and core role in precision oncology treatment, bringing hope for cure and higher quality of life to more patients.