For early-stage tongue cancer, oropharyngeal cancer, or recurrent cases that are not suitable for surgery, brachytherapy is highly favored due to its highly conformal dose distribution. The 18G technology manual-type oral brachytherapy needle, as the core tool for achieving this high-precision dose delivery, demonstrates unique advantages in dosimetry and significantly improves the treatment ratio. This article will explore its specific performance in the treatment of tongue cancer and oropharyngeal cancer.

The High Conformality of Dose Distribution

1. Target area coverage: The tumor shapes in the tongue and oropharynx are irregular and are close to important organs such as the mandible and salivary glands. Using 18G needles for implantation, multiple needles can be flexibly arranged according to the three-dimensional shape of the tumor. Due to the thin diameter of the needles (18G), a dense needle array can be achieved without causing excessive trauma, thereby forming a "surrounding" high-dose area within the target area. After TPS optimization, more than 90% of the target volume can easily receive the prescribed dose of radiation.
2. Steep dose drop-off: The physical nature of close-range radiotherapy determines its characteristic of dose attenuation with the square of distance. The 18G needle, as the carrier of particles or radiation source, ensures that the radiation source is precisely located within the target area. This enables the high-dose area to closely surround the tumor, while the dose rapidly drops to a lower level outside the target area. For tongue cancer, this means that a radical dose (such as 60-80 Gy) can be given to the tumor, while the radiation dose to the contralateral mandible is controlled within the tolerable range (<50 Gy), significantly reducing the risk of radiation-induced bone necrosis.

Protection of Organs at Risk (OARs)

1. Mandible and Teeth: During traditional external beam radiotherapy for tongue cancer, the mandible often receives a relatively high scattered dose. The 18G needle implantation technique allows doctors to precisely place the needle within the tumor, away from the mandible. Through carefully designed needle paths and particle distribution, the maximum dose point in the mandible can be significantly lower than the external irradiation plan. This is crucial for preserving the patient's mandibular function and appearance.
2. Salivary Glands and Oral Mucosa: One of the most troublesome side effects in the treatment of oropharyngeal cancer is xerostomia. The precise implantation of the 18G needle enables most parotid and submandibular glands to be spared from high-dose irradiation. Although a portion of the oral mucosa inevitably receives irradiation, due to the steep dose gradient, the severity and duration of mucositis are usually better than those of conventional radiotherapy. The quality of life of the patients is significantly improved.
3. Spinal Cord and Brainstem: For lesions close to the base of the skull, protecting the spinal cord and brainstem is the top priority. The short-range effect of the 18G needle limits its dose influence to within a few centimeters. As long as the needle tip and particles do not approach these central nerve structures, nearly perfect protection can be achieved.

The Combined Application with Other Technologies

1. Synergistic with external irradiation: For locally advanced head and neck cancer, the common approach is to use external irradiation combined with brachytherapy. First, external irradiation is used to control the subclinical lesions, and then the 18G needle implantation technique is used to "supplement the dose" for the visible residual tumors. This combination can not only leverage the broad spectrum of external irradiation but also utilize the efficiency of brachytherapy, achieving an "1 + 1 > 2" effect.
2. Combined with chemotherapy or targeted therapy: The 18G needle implantation is minimally invasive and has a quick recovery, without affecting the continuation of systemic treatment. Patients can complete brachytherapy during the intervals of chemotherapy or targeted drugs, achieving concurrent or sequential comprehensive treatment.

Summary

The 18G technology manual-type oral brachytherapy needle, with its outstanding dosimetric advantages - highly conformal target coverage, steep dose decline, and effective protection of surrounding vital organs - has established its significant position in precise radiotherapy. It provides an effective and relatively low-toxic local treatment option for patients with head and neck tumors and is an indispensable part of the modern tumor comprehensive treatment system.