Objective To investigate the prophylactic effect of silicone on radiodermatitis during the treatment of keloid by using ⁹⁰Sr-⁹⁰Y applicator.

Methods The clinical data of 175 patients who received ⁹⁰Sr-⁹⁰Y applicator for keloids at the Shanghai Sixth People's Hospital Affiliated to Shanghai Jiao Tong University School of Medicine from January 2019 to June 2021 were retrospectively analyzed. The patients included 81 males and 94 females, with ages of (27.2±3.7) years. The patients were divided into the control group (57 cases), the 1 mm-thick silicone protection group (55 cases), and the 2 mm-thick silicone protection group (63 cases) by using the envelope random grouping method. All the patients were treated with multiple small-dose radiation therapy by using a ⁹⁰Sr-⁹⁰Y applicator. The skin around the lesion was respectively protected with 1 mm- and 2 mm-thick silicone in the 1 mm-thick and 2 mm-thick silicone protection groups. Radidermatitis for the three groups of patients was graded using the radidermatitis grading criteria of the Radiation Therapy Oncology Group. The incidence and severity of radiodermatitis were compared among the groups. The effects of the treatment course and silicone protection on the occurrence of severe radidermatitis were analyzed. Independent sample t-test (equal variances assumed) was used to compare the two groups for the measurement data in accordance with normal distribution. One-way ANOVA was adopted to compare the three groups. The chi-squared test was conducted to compare the count data in the three groups. Lastly, the factors that affected the efficacy of the treatment were analyzed via univariate Logistic regression analysis.

Results No statistically significant difference was found in the incidence of radiodermatitis between the 1 mm-thick silicone protection group and the control group (83.6% vs. 89.5%, χ²=0.815, P=0.367). The incidence of radiodermatitis was significantly lower in the 2 mm-thick silicone protection group than in the control group and the 1 mm-thick silicone protection group (89.5% vs. 83.6% vs. 54.0%), and the differences were statistically significant (χ²=18.108, 11.738; both P<0.05). The severity of overall radiodermatitis was lower in the 1-mm thick silicone protection group than in the control group (1.05±0.65 vs. 1.37±0.75), and the difference was statistically significant (t=−2.409, P<0.05). The severity of radiodermatitis in the 2 mm-thick silicone protection group (0.63±0.66) was lower than that in the control group and the 1 mm-thick silicone protection group, and the differences were statistically significant (t=−5.749, −3.473; both P<0.05). The increase in the number of treatment courses augmented the risk of radiodermatitis (OR=2.348, 95%CI: 1.524–3.618, P<0.001). Meanwhile, the use of silicone with different thicknesses can reduce the risk of radiodermatitis (1 mm-thickness silicone: OR=0.273, 95%CI: 0.109–0.685, P<0.01; 2 mm-thickness silicone: OR=0.099, 95%CI: 0.034–0.293, P<0.001).

Conclusion During the treatment of keloid with ⁹⁰Sr-⁹⁰Y applicator, the use of 2 mm-thick silicone to protect the surrounding normal skin tissue can significantly reduce the incidence and severity of radiodermatitis.