Hydrogel spacer injection to the meso-sigmoid to protect the sigmoid colon in cervical cancer brachytherapy: A technical report

Purpose:
The use of a hydrogel spacer inserted into recto-vaginal fossa is a valuable strategy to mitigate radiation exposure to the rectum during radiation therapy for female pelvic malignancies. However, when the sigmoid colon is in proximity to the cervix, radiation exposure to the sigmoid colon cannot be adequately mitigated with a hydrogel spacer injected into the recto-vaginal fossa. Here, we presented a case, in which a hydrogel spacer was injected into the meso-sigmoid to protect the sigmoid colon.

Material and methods:
A 73-year-old female diagnosed with T3b stage IIIC2r uterine cervical cancer (FIGO 2018) underwent high-dose-rate interstitial brachytherapy consisting of 24 Gy in 4 fractions, following concurrent chemoradiotherapy with external beam radiation therapy of 50 Gy in 25 fractions of whole pelvic radiation therapy. In the initial brachytherapy, the sigmoid colon was in close contact with the uterine cervix. In the second brachytherapy, attempts to create a space between the sigmoid colon and uterine cervix using injected artificial ascites were unsuccessful due to rapid absorption of fluid. In the third and fourth brachytherapy fractions, 5 mL of hydrogel was injected into the meso-sigmoid through a pouch of Douglas under trans-rectal ultrasonography guidance. Dose ratio of sigmoid colon D_2cc and high-risk clinical target volume (HR-CTV) D₉₀ of each brachytherapy were evaluated.

Results:
Dose ratio of the sigmoid colon D_2cc to HR-CTV D₉₀ was 1.03, 0.43, 0.56, and 0.47 in each respective brachytherapy session, indicating dose escalation to HR-CTV whilst achieving acceptable sigmoid dose with hydrogel spacer injected into the meso-sigmoid.

Conclusions:
The dose ratio of the sigmoid colon to HR-CTV D₉₀ was decreased by introducing a hydrogel spacer into the meso-sigmoid. In cases where the sigmoid colon is in proximity to the cervical tumor, this novel technique can be considered to achieve better clinical outcomes.