ESTRO 2022 - Abstract Book

S1134

Abstract book

ESTRO 2022

three Point A based plans were evaluated: standard Point A, Point A with inverse optimization (Point A-IO), and Point A with dose shaping (Point A-DS). Two inverse optimization plans were evaluated: inverse plan with entire tandem length (IP-ETL) and inverse plan with modified tandem length to fit HR-CTV (IP-MTL). Priority for each treatment plan was HR-CTV coverage by prescribed dose (800 cGy). Secondary priority was organ at risk constraints (rectum D2cc < 470 cGy, bladder D2cc < 650 cGy). Target coverage, V100%, V150%, V200%, V250%, and OAR doses were compared for each plan. Results The table shows target coverage (%), HCD (V150%, V200%, V250%) and OAR doses for the five treatment plans for three target sizes. All five treatment plans were able to achieve adequate target coverage (98-100%) and OAR constraints for all three target sizes except the Point A plan for large target. Point A based plans had larger V100%, V150%, V200%, and V250% than the inverse plans, particularly for larger targets. IP-MTL plans had the smallest HCD volumes. However, volume of HCD (V150%, V200%, V250%) relative to volume of prescribed dose (V100%) was similar between all treatment plans and target sizes: 46-55% for V150%, 26-35% for V200% and 17-24% for V250%. Conclusion Adequate target coverage and OAR constraints can be achieved with both Point A based planning and inverse planning. Conventional Point A based plans have larger V100% and HCD volumes compared to more modern inverse planning. However, volume of HCD relative to volume of prescribed dose is similar in both Point A based and inverse plans. Therefore, selecting a target definition for ICBT is a personal choice. There is no data available which is the best Plan for high local control with low morbidities. Purpose or Objective Retrospective evaluation of the outcomes and late gastrointestinal (GI) and genitourinal (GU) toxicity regarding to dose reduction in curative chemoradiation of cervical cancer. Materials and Methods Between October 2002 and March 2017, 390 patients with FIGO stage IB2-IVA cervical cancer were treated with 45 or 50.4 Gy conventional three-dimensional conformal external beam radiation therapy (EBRT) and intracavitary high-dose-rate brachytherapy (BT) with doses either 3x7 Gy or 4x7 Gy. The predictors of treatment outcome were evaluated with Cox- regression, while logistic regression was used to determine the effect of the dose on late GI and GU toxicity. Results The median follow-up time was 54 months (range 2-204 months). The 10-year overall survival (OS), disease-free survival (DFS), locoregional relapse-free survival (LRFS) and metastases-free survival (MFS) were 39.4%, 39.5%, 40.3% and 40.4%, respectively. Patients with bulky primary tumour (>4 cm) and positive lymph node (pelvic with or without paraaortic) status treated with 50.4 Gy EBRT and 4x7 Gy BT showed better outcomes compared with the group of patients received 3x7 Gy BT: LRFS was 55.1% and 53.8% (p=0.0485), DFS was 52.8% vs. 47.9% (p=0.0026) and OS was 62.3% vs. 46.1% (p=0.0199) in 4x7 Gy versus 3x7 Gy BT groups. Cumulative grade 0 GI toxicity occurred in 65.1%, grade 1 in 13.3%, grade 2 in 12.4%, grade 3 in 7.6% and grade 4 in 1.6% of the patients. Small bowel resection was performed in 23 patients (5.8%) due to grade 3-4 toxicity. 7.9% of the survivors (36 patients) still have late grade 1-2 GI toxicity. Referring to late GU toxicity, 79.3% of the patients reported grade 0 toxicity, 8.1% of the patients had grade 1, 11.0% had grade 2 and 1.6% had grade 3 events. Grade 4 GU toxicity was not registered. Persistent grade 1-2 incontinence still occurs in 11% (32 patients) and one patient had grade 3 incontinence. Neither the dose of the EBRT, BT nor the equivalent dose at fractionation of 2 Gy took effect on the rate of the late GI and GU toxicity. Conclusion Treating with higher dose of brachytherapy resulted in significantly better outcomes only in the group of patients with bulky primary tumour and node positive cervical cancer, however our results did not show correlation between the dose of the radiotherapy and late toxicity. PO-1338 Is dose reduction feasible for better late toxicity in curative chemoradiation of cervical cancer? N. Nguyen Anhhong 1 1 National Institute of Oncology, Centre of Radiotherapy, Budapest, Hungary

PO-1339 Long- term outcomes after electronic brachytherapy in the adjuvant treatment of endometrial cancer.

M. Cerrolaza 1 , A. Mendez 1 , A. Miranda 1 , V. Navarro 1 , C. Escuin 1 , A. Campos 1 , S. Flamarique 1 , M. Gascon 1 , S. Lozares 2 , R. Ibañez 1 1 University Hospital Miguel Servet, Radiotherapy, ZARAGOZA, Spain; 2 University Hospital Miguel Servet, Physics, ZARAGOZA, Spain

Purpose or Objective