Evaluate the impact of the thyroid capsule on radiofrequency ablation efficacy in papillary thyroid carcinoma

Objective To evaluate the safety and efficacy of radiofrequency ablation（RFA）in the treatment of papillary thyroid microcarcinoma（PTMC）near and remote from the thyroid capsule. Methods The clinical data，ultrasound images，ablation parameters and postoperative follow-up metrics were prospectively collected from 130 patients with pathologically confirmed PTMC in the Second Affiliated Hospital of Xi'an Jiaotong University who underwent RFA treatment between January 2023 and December 2024. According to whether the nodule margin was ≤ 2 mm from the thyroid capsule，the patients were divided into the subcapsular group（60 cases）and the remote from the capsule group（70 cases）. The clinical data，ablation parameters，complication rate，absorption of ablation lesions，tumor recurrence and metastasis were compared between the two groups. Results The success rates of RFA in both groups were 100%. There was a statistically significant difference between the two groups at baseline in the location of nodules（χ²=13.266，P=0.001）. After 12 months of routine follow-up，the incidence of complications was 5.00%（3/60）in the subcapsular group and 1.43%（1/70）in the remote from the capsule group，all complications recovered within 1 month，with no statistically significant difference（P=0.407）. There were no significant changes in thyroid function［including free triiodothyronine（FT3），free thyroxine（FT4）and thyroid-stimulating hormone（TSH）］before and one month after RFA in the two groups（all P>0.05）. A statistically significant difference in the volume reduction rate（VRR）between the two groups was observed only when maximum diameter ≤ 5 mm at the 1st and 3rd months（all P<0.05）. For the remaining postoperative follow-up periods，there were no statistically significant differences in ablation zone volume or VRR between the two groups（all P>0.05）. At the final follow-up，for lesions with maximum diameter ≤ 5 mm，the tumor disappearance rate was 100% in both the subcapsular and remote from the capsule groups. For lesions with maximum diameter >5 mm，the rates were 78.4%（29/37）and 89.7%（26/29）in the respective groups，with no statistically significant difference between the two groups（χ² = 1.489，P =0.222）.There was no local tumor progression，lymph node metastasis or distant metastasis in either group. Conclusions RFA is a safe and effective treatment for subcapsular PTMC，demonstrating comparable efficacy to that for PTMC located remote from the thyroid capsule.