ESTRO 2024 - Abstract Book

S245

Brachytherapy - Gynaecology

ESTRO 2024

794

Proffered Paper

Clinical outcomes of 3 vs 4 Fractions of MRI-guided brachytherapy in cervical cancer

Elizabeth Chuk 1 , Candice Yu 1 , Aba Anoa Scott 1 , Zhihui Amy Liu 2 , Michael Milosevic 1 , Jennifer Croke 1 , Anthony Fyles 1 , Jelena Lukovic 1 , Alexandra Rink 1 , Akbar Beiki-Ardakani 1 , Jette Borg 1 , Jason Xie 1 , Kitty Chan 1 , Heather Ballantyne 1 , Julia Skliarenko 1 , Jessica L. Conway 1 , Robert A. Weersink 1 , Kathy Han 1 1 Princess Margaret Cancer Centre, University Health Network, Radiation Medicine Program, Toronto, Canada. 2 Princess Margaret Cancer Centre, University Health Network, Biostatistics, Toronto, Canada

Purpose/Objective:

MRI-guided brachytherapy (MRgBT) is an essential component in the management of locally advanced cervical cancer that has significantly improved local control and toxicity. However, MRgBT is also resource intensive. Our objective was to compare disease and toxicity outcomes in locally advanced cervical cancer patients treated with a less resource intensive regimen of 24 Gy/3 fractions (Fr) versus the conventional 28 Gy/4Fr.

Material/Methods:

This retrospective study included consecutive patients with FIGO 2018 stage IB-IVA cervical cancer treated with definitive chemoradiation between April 2014 - March 2021 at a large academic cancer centre. Patients with histologies other than squamous cell carcinoma, adenocarcinoma or adenosquamous carcinoma; those who did not receive cisplatin; or those who received palliative intent treatment were excluded. MRgBT fractionation transitioned gradually during the study period from 28 Gy/4Fr to 24 Gy/3Fr due to resource constraints and to improve patient experience. Patient, tumour and treatment parameters, disease status and treatment-related toxicities were extracted from medical records. Continuous variables were compared using Wilcoxon’s rank sum test; categorical variables, using Chi-squared test. Disease-free survival (DFS) was estimated using the Kaplan-Meier method and compared using the log rank test. Cumulative incidence of local failure (LF), and grade 2+ gastrointestinal (GI), urinary (GU) and vaginal toxicity were estimated using the cumulative incidence function with death as a competing risk, and compared using the Gray’s test. For LF, distant metastasis was also counted as a competing risk. Statistical analyses were performed in R version 4.0.2. All tests were two sided, and p values < 0.05 were considered statistically significant.

Results:

Of the 241 patients included for analysis, 101 (42%) received 24 Gy/3Fr and 140 (58%) received 28 Gy/4Fr. There were no significant differences in the distribution of histology, T category, or FIGO 2018 stage between the 2 groups (see Table). The 24 Gy/3Fr group was older, had smaller tumor size at diagnosis and smaller CTV HR at brachytherapy. The CTV HR D 90% were similar between the 2 groups. The 24 Gy/3Fr group had significantly lower rectal D 2cm3 , small bowel D 2cm3 , bladder D 2cm3 and ICRU rectovaginal point dose compared to the 28 Gy/4Fr group. With a median follow up of 3.2 (range 0.2-9.2) years, there were 14 local, 41 regional nodal and 51 distant failures in 63 (26%) patients (simultaneous failures at different sites included). There were no significant differences between the 24 Gy/3Fr vs 28 Gy/4Fr group in 3-year DFS (77% vs 68%, p = 0.21), 3-year cumulative incidence of LF