ESTRO 2024 - Abstract Book

S220

Brachytherapy - Gynaecology

ESTRO 2024

target. Complications like persistent diarrhoea, rectal bleeding, and fistula can severely compromise the quality of life. A Hydrogel spacer injected in the recto-vaginal space can push the rectum away and out of the high-dose field and potentially reduce the rate of development of late large bowel toxicities.

Material/Methods:

After institutional ethical committee clearance, this prospective study evaluated 83 consecutive patients with newly diagnosed locally advanced cervical cancer(FIGO 2009 stage I B to IV A) undergoing definitive pelvic chemoradiation and image-guided intra-cavitary brachytherapy(ICBT) between January 2019 and June 2019. On ICBT planning, if the cumulative 2Gy equi-effective(EQD2) rectal dose exceeded the institutional constraint of 70Gy, these patients were taken up for para-rectal hydrogel instillation. 31 patients were found to be eligible for the procedure. All patients received 46 Gy in 23 fractions of external beam radiation to the primary and regional sites by the 3DCRT technique along with concurrent weekly platin-based chemotherapy. After assessing the feasibility of intra cavitary brachytherapy, they underwent an ICBT procedure and 3D-volume-based planning. The prescription dose was 28Gy in 4 fractions delivered with at least a 6-hour gap between fractions. The high-risk clinical target volume(HRCTV) and organs-at-risk(OAR) were delineated according to GEC-ESTRO guidelines on the simulation (CT and MRI) images 2 . A conventional point-based plan for pre-hydrogel(HG) instillation simulated images was computed initially for all patients after ICBT application. If the cumulative EQD32 for 2cc of rectum exceeded 70Gy, these patients were taken up for a para-rectal hydrogel(30cc of Hydrogel-Hydroxypropyl methylcellulose) procedure for the temporary increase in recto-vaginal distance and were replanned. Every patient had four brachytherapy plans: Point-A and optimised plans for each pre-HG and post-HG instillation scenario for the same fraction.

The two-tailed paired T-test was used to compare the difference in dose distribution to OARs(bladder, rectum, and sigmoid) and HRCTV before and after the HG instillation.

Results:

The cumulative mean 2cc rectum dose on pre-HG simulated images when the prescription dose was normalised to Point-A was 76.96±4.5 Gy. The mean separation between the closest points of the rectum and HRCTV was 1.47±0.3 cm on the post-HG MRI. The mean ICBT 2cc rectal dose pre-HG and post-HG instillation were 67.31±9.025% and 47.56±9.029% of the prescription dose for the Point-A plan, respectively. With the aim of optimization to achieve 100% D90, mean 2cc optimized rectal doses were computed as 61.7±7.335% pre-HG and