ESTRO 2025 - Abstract Book

S829

Clinical - Gynaecology

ESTRO 2025

Purpose/Objective: Tumor response can vary significantly in cervical cancer patients [1]. Therefore, personalized treatments are needed to take this variability into account, especially during radiotherapy. This study evaluates the tumor volume evolution as a potential prognostic factor for treatment response throughout the radiotherapy in cervical cancer women treated with the Unity® 1.5T MR-Linac system (Elekta). Material/Methods: Between July 2021 and December 2023, 18 women underwent radiotherapy alone on the Unity® MR-Linac or with weekly concurrent chemoradiotherapy (Cisplatin 40 mg/m2). Seven patients who had an exclusive boost irradiation or a recurrence, and 1 patient who had an incomplete treatment for psychological reasons were excluded. Thus, 10 patients were included in this retrospective study. IMRT was used to deliver 45Gy in 25 fractions or 45Gy with an integrated boost at 55Gy if pelvic nodes invasion was present. Clinical data, including age, histology, FIGO stage, HPV status, chemotherapy cycles, radiotherapy dose, and nodal involvement, were collected. The GTVs were delineated on T2-MRI sequences at each treatment fraction and were validated by 2 radiation oncology experts in cervical cancer. Changes in tumor volume were evaluated over the radiotherapy treatment, with correlations drawn to final response. Statistical analysis, including descriptive statistics and correlation tests, was performed using IBM SPSS Statistics (version 30, IBM Corp., Armonk, NY, USA). Results: Patients’ and tumors’ characteristics are presented in Table 1. Figure 1 shows tumor volume shrinkage throughout the irradiation for each patient. The median [range] initial and final tumor volumes were 25.4 [3.4–78.8] cc and 1.1 [0 - 6.6] cc, respectively. The average±SD initial and final tumor volumes were 29.2±23.8 cc and 1.5±1.8 cc, respectively. Patients with more than 50% tumor reduction by fraction 10 showed a high probability of achieving 90% reduction by the end of radiotherapy treatment. Pearson correlation analysis showed a strong association between tumor reduction at fraction 10 and fraction 25 (r = 0.867, p < 0.01). Patients 2, 5, 7 and 9 who didn’t achieve this tumor reduction either had a FIGO IIIC or <5 cures of chemotherapy.