How can the close-range treatment needles be designed at the millimeter level to adapt to various clinical scenarios? In the precise system of close-range radiotherapy, the treatment planning system (TPS) delineates the "dose map" that destroys the tumor, while the treatment needle is the "construction conduit" that turns this map into reality. Its physical specifications - length and diameter (Gauge) - are not standardized products but personalized engineering solutions that have been rigorously calculated and clinically verified. These minute differences measured in millimeters directly determine whether the needle can reach the deep target area, how to minimize the puncture trauma, and whether it can accommodate the specific radiation source. Leading manufacturers provide a systematic specification matrix to transform the complex tumor anatomy and radiation physics requirements into clear and executable tool selection guidelines, thereby finding the best balance between treatment accessibility, minimally invasive nature, and dose optimization.

The selection of the needle length aims to achieve precise path coverage from the puncture point on the body surface to the tumor target area. This requires comprehensive consideration of tumor depth, anatomical path, and treatment techniques. For permanent particle implantation in prostate cancer, a transperineal puncture template guidance is typically used. The needle length must be sufficient to penetrate the soft tissues of the perineum, the prostate, and possibly reach the peritoneal membrane on the opposite side of the prostate to ensure uniform particle distribution in three-dimensional space. Common needle lengths range from 15 to 20 centimeters, which are sufficient for most patients' anatomical structures. For intracavitary combined interstitial implantation in cervical cancer or endometrial cancer, the treatment needle needs to be punctured through the vaginal fornix to enter the cervix or adjacent tissues. At this time, the needle length must be individually selected based on the tumor size, vaginal length, and the position of the uterus, as too short a needle length will not cover the target area, and too long a needle length may increase unnecessary tissue damage and operational risks. In breast cancer surgery or postoperative accelerated partial breast irradiation (APBI), the needles used for placing balloon applicators or for multi-catheter implantation have lengths that depend on the volume of the breast and the position of the surgical cavity.

The tube diameter, usually denoted by "G" (the smaller the number, the larger the inner diameter), is crucial in balancing treatment requirements and the concept of minimally invasive procedures. The common specifications for close-range treatment needles range from 14G (coarse, approximately 2.1mm outer diameter) to 21G (fine, approximately 0.8mm outer diameter). The main advantage of the thicker needles (such as 14G-16G) lies in their strong structural rigidity and larger inner cavity. The high rigidity ensures that when puncturing dense tissues (such as the breast or fibrotic tissues after treatment) or when requiring a longer path to be crossed, the needle body is less likely to bend, allowing it to faithfully follow the preset needle insertion direction and depth, which is crucial for achieving precise dose distribution. The larger inner cavity can accommodate various specifications of radiation sources or allow for more flexible adjustment of the post-placement position of the source within the needle tube, suitable for high-dose rate (HDR) post-treatment, where it may be necessary to quickly exchange different activity source stepping devices. However, a thicker needle diameter implies greater tissue trauma, a higher risk of bleeding, and potential pain.

The thinner needles (such as 17G - 21G) represent the trend of extreme minimally invasive and precise implantation, and are widely used in permanent particle implantation. For example, the needles used for implanting iodine-125 particles are usually around 18G. The puncture channels created by the fine needles are smaller, significantly reducing the risks of bleeding, hematoma, and infection, and enabling patients to recover faster and experience less pain after the operation. In aesthetic sensitive areas such as the head and neck, breast, etc., the scars left by the fine needle puncture are also less noticeable. More importantly, the fine needles allow for more dense and flexible needle placement, enabling the creation of more complex target area shapes and achieving highly conformal dose distribution. However, the challenge of fine needles lies in their relatively weak rigidity, higher technical requirements for the operator, and smaller inner cavity, which have strict limitations on the size of the radiation source or implant device.

The innovation of the manufacturer lies in not only offering various specifications, but also enhancing the performance of each specification through needle tip design and structural optimization. For instance, designing needle tips with optimized cutting surfaces enables excellent puncturing performance even with finer specifications, reducing tissue compression. Some needle devices adopt ultra-thin wall designs, ensuring sufficient rigidity while maximizing the inner cavity size or minimizing the outer diameter. For template-guided techniques that require multiple needles to be implanted simultaneously, the manufacturer ensures that needles of different lengths and specifications within the same product series have excellent dimensional consistency and interchangeability, which is crucial for precise parallel implantation using templates with fixed pitch.

Therefore, the design of the close-range treatment needle is a precise science that integrates anatomy, radiation physics, and clinical experience. Manufacturers use a carefully planned specification system to convert the abstract requirements for dose distribution into specific and operational instrument parameters. Radiation oncologists and physicists can, based on the location, size of the tumor, the relationship with adjacent organs at risk, and the selected treatment technique (HDR temporary implantation vs. LDR permanent implantation), choose the treatment needle with the length and diameter that best match, just like choosing the most suitable surgical knife. This in-depth understanding and refined provision of specifications ensures that regardless of where the tumor is hidden in the body or its irregular shape, there will be a set of appropriately designed instruments that can achieve the maximum tumor dose coverage and the optimal protection of normal tissues through the least invasive path, truly embodying the individualized essence of precise radiotherapy.