Vaginal Fistulas of the Bladder and Small Bowel After Two-Dimensional Intracavitary Brachytherapy in a Patient With Cervical Cancer.

Image-guided brachytherapy (IGBT) is commonly used for patients with cervical cancer, but two-dimensional intracavitary brachytherapy (2D-ICBT) is also still utilized for certain patients. We report a patient with cervical cancer who developed vaginal fistulas of the bladder and small bowel after chemoradiotherapy with 2D-ICBT. A 61-year-old woman with stage IIB cervical cancer underwent a combination of external beam radiotherapy (EBRT) at a dose of 50.4 Gy in 28 fractions and 2D-ICBT at a dose of 22 Gy in four fractions. As packs were well inserted around the uterus in all fractions of 2D-ICBT, the doses to the surrounding organs at risk (OAR) could be likely to be kept at low levels. She developed a huge fistula between the vagina and bladder approximately 2.5 years after radiotherapy (RT). She also developed a fistula between the vagina and small bowel approximately seven years after RT and underwent bypass from the small bowel to the transverse colon. The OAR were delineated using computed tomography for EBRT planning, and the cumulative dose of 2D-ICBT plus EBRT was evaluated as the source of toxicity. The cumulative dose converted to the equivalent dose in 2-Gy fractions (EQD2) was calculated using the linear-quadratic model with α/β = 3 for the OAR. The cumulative EQD2 values of the minimum dose to the most irradiated 2 cc (D2cc) of the bladder and small bowel were 90.2 Gy and 79.5 Gy, respectively. These values exceeded the upper limits of the dosimetric criteria of the OAR, suggesting an association with both vaginal fistulas. As the adoption of IGBT is too slow in some countries, it is noteworthy that a reduced bladder volume may result in a significant increase in the dose to the small bowel and bladder in 2D-ICBT.