Dosimetric comparison between single-channel vaginal cylinder and free-hand interstitial needles in vaginal brachytherapy of gynecological cancers.

Purpose: To compare the dosimetric differences in vaginal brachytherapy (VBT) using single-channel vaginal cylinder (SCVC) and free-hand interstitial needles (FIN).

Material and methods: Twenty-two women with malignant gynecologic tumors were prospectively treated with image-guided high-dose-rate (HDR) brachytherapy after surgery and external beam radiation therapy (EBRT). All HDR treatments were delivered using FIN implant technique. For dosimetric comparison purposes only, SCVCs of 2.5 cm diameter were placed in all patients. No sources were dwelled in cylinder applicator during clinical treatment. CT-guided brachytherapy treatment planning was performed according to GEC-ESTRO guidelines, with high-risk clinical target volume (HR-CTV) delineated based on clinical exams and MRI T2 sequences. Dose-volume parameters to HR-CTV and surrounding organs at risk (OARs) from interstitial plans were compared with those achieved from cylinder plans.

Results: Compared with SCVC group, FIN group showed the same HR-CTV coverage. FIN group had higher V_150% and V_200% (p < 0.05). In addition, it had lower HI (p < 0.05). However, doses to the rectum D_0.1cc (538.5 ±119.8 cGy), D_1cc (415.4 ±73.3 cGy), D_2cc (355.7 ±66.6 cGy), and D_mean (162.8 ±43.7 cGy) as well as the bladder D_0.1cc (516.1 ±85.2 cGy) and D_1cc (392.9 ±59.8 cGy) were lower in FIN group than in SCVC group (p < 0.05).

Conclusions: FIN technique can be a dosimetrically preferable alternative to the commonly used SCVC for HDR VBT boost in patients with gynecological malignancies. It provides adequate coverage of target volumes, with minimal radiation dose to surrounding organs at risk.