ObjectiveTo analyze the influencing factors of tumor volume, body immunity, and poor prognosis after125I particle therapy for differentiated thyroid cancer.MethodsA total of 104 patients with differentiated TC who were treated with125I particles during January 2020 to January 2021 was picked. These subjects were graded as low-dose group (80Gy-110Gy) and high-dose group (110Gy-140Gy) according to the minimum dose received by 90% of the target volume (D90) after surgery. The tumor volume before and after treatment was compared, and fasting venous blood was collected before and after treatment. The content of thyroglobulin (Tg) was detected by electrochemiluminescence immunoassay. The levels of absolute lymphocyte count (ALC), lymphocytes, neutrophils, and monocytes were detected on automatic blood cell analyzer. The lymphocyte to monocyte ratio (LMR), neutrophil to lymphocyte ratio (NLR) and platelet to lymphocyte ration (PLR) were calculated. The changes in the condition of patients were closely observed, and the occurrence of adverse reactions in the two groups were compared. The risk factors influencing the efficacy of125I particle therapy for differentiated TC were analyzed through multivariate logistic regression analysis.ResultsThe total effective rate of patients in the low- and high-dose groups was 78.85% and 82.69%, respectively (P> 0.05). Compared with the pretreatment period, the tumor volume and Tg level in both groups were much lower (P< 0.05), and the differences in tumor volume and Tg level had no statistically significant difference between the two groups before and after treatment (P> 0.05). At 1 week of the treatment, the total incidence of adverse reactions such as nausea, radiation gastritis, radiation parotitis, and neck discomfort was obviously higher in the high-dose group than in the low-dose group (P< 0.05). At 1 month of treatment, the incidence of adverse reactions such as nausea was markedly higher in the high-dose group than in the low-dose group (P< 0.05). After treatment, serum NLR and PLR contents were memorably elevated and LMR level was sharply decreased in both groups, and serum NLR and PLR contents were higher and LMR content was lower in the high-dose group than in the low-dose group (P< 0.05). Multivariate logistic regression analysis showed that the pathological type of follicular adenocarcinoma, tumor size ≥ 2 cm, clinical stage of III~IV, distant metastasis, and high TSH level before125I particle treatment were all risk factors related to the efficacy of125I particle treatment of TC (P< 0.05).ConclusionThe efficacy of low-dose and high-dose125I particles in the treatment of differentiated thyroid cancer is comparable, among which low-dose125I particles have fewer adverse effects and have less impact on the immunity of the body, which is well tolerated by patients and can be widely used in clinical practice. In addition, the pathological type of follicular adenocarcinoma, tumor size ≥ 2 cm, clinical stage III~IV, distant metastasis, and high TSH level before125I particle treatment are all risk factors that affect the poor effect of125I particles on thyroid cancer treatment, and early monitoring of the above index changes can help evaluate the prognosis.