S487
Clinical - Gynaecological
ESTRO 2026
demonstrated high long-term overall survival and an excellent safety profile in surgically treated intermediate-risk cervical cancer, supporting the feasibility of pelvic treatment- volume de-escalation for these patients. These findings contribute to the growing evidence supporting personalized adjuvant radiation strategies aimed at morbidity reduction without compromising oncologic outcomes. References: 1. Ohara K, Tsunoda H, Satoh T, et al. Use of the small pelvic field instead of the classic whole pelvic field in postoperative radiotherapy for cervical cancer: reduction of adverse events. Int J Radiat Oncol Biol Phys. 2004; 60(1): 258–264, doi: 10.1016/j.ijrobp.2004.02.023, indexed in Pubmed: 15337564.2. Hong JH, Tsai CS, Lai CH, et al. Postoperative low-pelvic irradiation for stage I-IIA cervical cancer patients with risk factors other than pelvic lymph node metastasis. Int J Radiat Oncol Biol Phys. 2002; 53(5): 1284–1290, doi: 10.1016/s0360- 3016(02)02831-6, indexed in Pubmed: 12128131. Keywords: Cervical cancer, Adjuvant radiotherapy, Smallfield Digital Poster Highlight 4816 Clinical Impact of Inter-fraction Dose Accumulation in Image-Guided Radiotherapy of Carcinoma Cervix Deepanjali Patel, Hirak Vyas, Shankar Vangipurum Department of Radiation oncology, Geetanjali Medical College and Hospital, Udaipur, India Purpose/Objective: Image guided radiation therapy (IGRT) integrated with IMRT/VMAT is increasingly used for managing carcinoma cervix. Dose Volume Histograms (DVHs) estimate doses delivered to organs at risk (OAR), but interfractional organ motion and volume changes can alter actual delivered doses. This
study aimed to calculate accumulated doses to the bladder and rectum using daily Cone Beam CT (CBCT) scans during treatment and to assess their clinical impact. Material/Methods: After ethical approval, 36 patients with histologically confirmed squamous cell carcinoma of the cervix were prospectively enrolled over 18 months. All underwent CT simulation using a vacuum cushion with a moderately full bladder and empty bowel protocol. Patients were treated with radical radiotherapy using the VMAT technique in 25 fractions as per institutional protocol. Daily pre-treatment CBCT scans (total 900) were acquired at 125 kV, 80 mA, and 28 mAs. For each patient, dose accumulation was performed by deformably registering CBCTs to the planning CT, generating DVHs for each fraction, and summating them. Acute toxicities were assessed using RTOG criteria post-treatment. Statistical analysis was performed using paired t-tests and regression models. Results: The median age was 51 years; 52% had Stage IIIB and the remainder Stage II disease. Comparison between cumulative CBCT and planning CT revealed higher accumulated mean doses. The mean rectal dose increased from 46.85 Gy (plan) to 50.25 Gy (CBCT) (p < 0.001), and bladder mean dose increased significantly as well. The proportion of bladder volume receiving 45 Gy (V45) rose from 67% (planned) to 77% (accumulated) (p < 0.001), while rectal V45 increased from 80% to 84%. Clinically, five patients developed grade 2 or higher genitourinary toxicity, while 16 exhibited grade 2 or higher gastrointestinal toxicity. Linear regression revealed bladder V45 as an independent predictor of genitourinary toxicity (p = 0.038), but no correlation was observed between rectum V45 and gastrointestinal toxicity. Conclusion: This is the first reported study to use deformable registration of daily CBCTs for cumulative dose estimation to bladder and
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