# Clinical Outcomes and Individualized Seed Implantation Planning for Iodine-125 Seeds Brachytherapy in Lymph Node Metastases

## TL;DR

This study shows that using iodine-125 seed brachytherapy for lymph node metastases can improve treatment response when a specific radiation dose threshold is met.

## Contribution

The study identifies a specific D90 dose threshold (102.7 Gy) that significantly improves treatment response without increasing complications.

## Key findings

- An overall objective response rate of 71.6% and local control rate of 96.3% were achieved with iodine-125 seed brachytherapy.
- A D90 threshold of 102.7 Gy was found to significantly increase the objective response rate (81.54% vs. 31.25%).
- Tumor size was identified as an independent factor influencing treatment efficacy.

## Abstract

Lymph node metastasis (LNM) critically influences cancer prognosis and treatment. This study explored the efficacy and prognostic factors of CT-guided radioactive iodine-125 (¹²⁵I) seed brachytherapy (RISB) for LNM and optimized the therapeutic dosage.

We conducted a single-center retrospective cohort study analyzing 81 cases with histologically confirmed LNM (≤ 5 cm) from diverse primary cancers treated with CT-guided RISB. Postoperative dosimetric parameters (D90, D100, V90, V100, V150, V200) were assessed. Treatment response was evaluated at 6 months using RECIST 1.1, calculating the objective response rate (ORR) and local control rate (LCR). Patients were categorized into objective response and non-objective response groups based on treatment efficacy, and factors influencing treatment efficacy were identified through logistic regression analysis. Based on the ROC curve, the Youden index method was used to determine the dose optimization cutoff value.

The overall ORR was 71.6%, and LCR was 96.3%. The complication rate was 3.7%. Tumor size was an independent influencing factor for efficacy. Higher postoperative dosimetric parameters were associated with efficacy but were not independent influencing factors. ROC analysis identified the optimal D90 threshold as 102.7 Gy. The ORR in patients who achieved D90 > 102.7 Gy (n = 65, ORR = 81.54%) was significantly higher than in patients with D90 ≤ 102.7 Gy (n = 16, ORR = 31.25%) (p < 0.01). Complication rates did not differ between dose groups.

Patients with LNM undergoing RISB can achieve a significantly higher ORR by ensuring a postoperative D90 > 102.7 Gy, without increasing the risk of complications. This dose threshold serves as a practical reference for clinical dose planning. Tumor size independently influences better response, guiding patient selection.