Design and clinical application of intracavitary-interstitial brachytherapy applicator template in locally advanced cervical cancer / 中华放射肿瘤学杂志

ABSTRACT

Objective:To design and evaluate the application value of intracavitary-interstitial brachytherapy (IC-ISBT) applicator template for locally advanced cervical cancer.Methods:MRI data of 100 patients with ⅡB-ⅣA stage cervical cancer (International Federation of Gynecology and Obstetrics 2018 staging system) before and after external beam radiation therapy (EBRT) admitted to Sun Yat-sen University Cancer Center from March 2019 to September 2020 were collected. The range of primary cervical lesions was retrospectively analyzed and compared. Based on the residual mass of patients, the corresponding high-risk clinical target volume (HR-CTV) was delineated, and the IC-ISBT applicator template was designed and initially applied to cervical cancer patients. Dosimetry analysis and efficacy evaluation were compared between the applicator template-guided ( n=37) and free-hand implantation groups ( n=63). Chi-square test or Fisher exact test was performed for categorical variables, and t-test or U-test for continuous variables. Results:The median distance between the residual tumor margin (clockwise 3, 6, 9, 12 o'clock) and the center of 100 patients with ⅡB-ⅣA stage cervical cancer after EBRT was 16.5, 14.0, 17.0 and 13.0 mm, respectively. The corresponding HR-CTV was superimposed to reconstruct the three-dimensional diagram, and the cylindrical IC-ISBT applicator template with mushroom-like head was designed and manufactured: the longest and shortest diameter of the head was 35 and 20 mm, respectively; the central channel was adapted to the uterine tube, the C1-C12 channels was arranged in inner circle, and the peripheral B1-B5 and A1-A4 pin channels were expanded bilaterally. In terms of dose coverage, there was no significant difference between the HR-CTV D 90% [(635.12±22.65) vs. (635.80±25.84) cGy], bladder D 2 cm3 [(473.79±44.78) vs. (463.55±66.43) cGy)], rectum D 2 cm3 [(396.99±73.54) vs. (408.00±73.94) cGy] and sigmoid colon D 2 cm3 [(293.07±152.72) vs. (311.31±135.77) cGy] between the template-guided and free-hand implantation groups (all P>0.05), but the HR-CTV D 98% was significantly higher [(544.78±32.07) vs. (536.78±32.04) cGy, P=0.007] and the rectum D 1 cm3 and D 0.1 cm3 were significantly lower [(438.62±69.65) vs. (453.97±67.89) cGy, P=0.016; (519.46±70.67) vs. (543.82±81.24) cGy, P=0.001] in the template-guided implantation group. In addition, there was no significant difference in the complete response rate between two groups (86% vs. 83%, P>0.05). Conclusions:This IC-ISBT applicator template is reasonably designed, and the therapeutic efficacy of the template-guided implantation is equivalent to that of free-hand implantation. The dose coverage of the target area meets the clinical demand with a better protection of the organs at risk. The applicator template has the potential to be widely used as a conventional template in clinical practice as the applicator-guided implantation is convenient to operate and repeat.