S455
Clinical - Gynaecological
ESTRO 2026
Material/Methods: Patients treated between 2016–2021 in EMBRACE-II from two centres were included. All received highly conformal image-guided intensity-modulated radiotherapy/volumetric arc therapy, chemotherapy, coverage probability planning simultaneously integrated nodal boosts, and MRI-guided adaptive brachytherapy. EBRT prescription dose was 45Gy and 55-57.5Gy in 25 fractions for elective and pathologic lymph node (LN) targets, respectively. The WP, LSS, LARS
(14.0% vs 13.3%). In Mumbai cohort, incidence of Grade ≥ 2 back pain was higher in pelvis + para-aortic than pelvis-only irradiation (52.3% vs 10.9%, p<0.001)(Figure 2).
(iliocostalis, longissimus, multifidus, quadratus lumborum, interspinales,
intertransversarii), and psoas were contoured on planning CTs. Dose-volume parameters were compared between EBRT-field groups (LN-negative pelvis-only, LN-positive pelvis- only, LN-positive pelvis + para-aortic) and between centres. In EMBRACE-II, back pain was recorded using CTCAE v3.0. Categorical variables were compared using Fisher’s Exact test. Continuous variables were compared using Mann-Whitney U test. Statistical significance was set at p ≤ 0.05. Results: Overall, 139 patients were analysed (Mumbai, India, n=67; Aarhus, Denmark, n=72). Para- aortic nodal (PAN) irradiation was delivered to 31.3% and 20.8% patients in Mumbai and Aarhus, respectively. Mumbai cohort had smaller anatomical bone/muscle volumes(cc) than Aarhus, and median(IQR) volumes(cc) were 641(589-717) vs 875(779-948), 393(355- 426) vs 499(445-551), 165(139-198) vs 236(179-277), 431(362-478) vs 481(382-571) for WP, LSS, Psoas, LARS, respectively. LN boosting in patients receiving pelvis-only irradiation did not increase mean dose to bone/muscle structures. Para-aortic irradiation led to higher mean dose across all structures except WP (p<0.001, Figure 1). Mumbai patients received higher mean dose to bone/muscle structures across all EBRT- fields compared to Aarhus (p<0.05). In Aarhus cohort, there was no difference in incidence of Grade ≥ 2 back pain between pelvis-only and pelvis + para-aortic irradiation
Conclusion: Mean radiation doses to LSS, LARS and psoas increased when PAN was included in elective EBRT field. In Aarhus cohort PAN radiation did not impact rates of late grade ≥ 2 back pain, whereas in Mumbai cohort back pain increased markedly. The reason might be caused by smaller bone/muscle anatomical volumes in Mumbai cohort. In pelvis-only
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