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ESTRO 37

2 TATA MEMORIAL CENTRE, Medical Physics, Mumbai, India 3 TATA MEMORIAL CENTRE, Medical Oncology, Mumbai, India Purpose or Objective To evaluate loco-regional control and toxicities with dose escalation using IMRT in FIGO Stage IIB cervical cancer Material and Methods Histo-pathologically proven cervical cancer with FIGO Stage IIB who were planned for curative radio(chemo)therapy were randomly allocated to either study arm of IMRT or standard arm of Conventional/3D conformal radiotherapy. External radiation was delivered to whole pelvis using box-field (standard arm) or fixed- five field IMRT (Study arm) with concurrent cisplatin chemotherapy and high dose rate brachytherapy (HDR- BT). The standard arm was treated according to the Institutional guidelines of 40 Gy/20#/4 weeks (20Gy open fields and 20Gy with midline shielding), while the study arm received to a dose of 50 Gy/25# to pelvic planning target volume. In both the arms, all patients received HDR-BT to a prescription dose of 7 Gy to point A x 5# once weekly. Acute and late toxicities were graded according to CTCAE version 3.0 and RTOG criteria. Results Between February 2005 and June 2013, two hundred patients [median age 51years (31-65 years)] were randomized to either standard arm (n=101) or study arm (n=99). Ninety six percent of the patients in standard arm and 98% in study arm completed planned treatment. Treatment compliance, the external and BT doses radiation doses were compiled using EQD2 and a post-hoc analysis is done to compare loco-regional control, DFS and toxicities according to doses delivered. Mean (SD) Equivalent Dose at 2Gy per fraction (EQD2) doses to point A, ICRU rectal point and ICRU bladder point were 72.7Gy (+/- 8) and 98.2Gy (+/-5.5), 52.1Gy (+/-10.1) and 81.3Gy (+/-9.9), 54.3Gy (+/-14.9) and 83.2Gy (+/-16.1) in the standard arm and the study arm respectively. After a median follow-up of 62 months, there was no difference in loco-regional control (86.5% Vs 85.8%; p = 0.96) or disease-free-survival (74.3% vs 70.8%, p=0.99) between the standard arm and the study arm respectively. No significant difference was observed in acute grade 2 or more dermatitis (15.8% vs 25.3%, p=0.25), enteritis (15.8% vs 19.2%, p=0.79) and cystitis (2% vs 4%, p=0.58) between the standard arm and the study arm, respectively. Haematological toxicities (anaemia, leukopenia and thrombocytopenia) also were not significantly different between trial arms. Late rectal toxicity was significantly higher in study arm as compared to standard arm [Grade II: 14 Vs 0 (p<0.005); Grade III/IV: 15 Vs 2 (p<0.005)]. However, there was no significant difference in late bladder and bowel toxicities. Conclusion In FIGO Stage IIB cervical cancer patients, there is no significant difference in loco-regional control, disease free survival and acute toxicities with dose-escalation using IMRT. Late rectal toxicities are significantly higher in IMRT arm which is probably related to dose escalation including BT. OC-0391 Evolution of external beam radiotherapy in cervix cancer: from EMBRACE I to EMBRACE II T. Berger 1 , M. Sanggaard Assenholt 1 , Y. Seppenwoolde 2 , A. De Leeuw 3 , I. Jürgenliemk-Schultz 3 , N. Boje Kibsgaard Jensen 1 , R. Nout 4 , L.T. Tan 5 , J. Swamidas 6 , G. Lowe 7 , R. Hudej 8 , I. Dumas 9 , D. Georg 2 , C. Kirisits 2 , R. Pötter 2 , J. Lindegaard 1 , K. Tanderup 1 1 Aarhus University Hospital, Oncology, Aarhus C, Denmark 2 Medical University of Vienna / General Hospital of Vienna, Department of Radiation Oncology, Vienna,

Austria 3 University Medical Centre Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands 4 Leiden University Medical Center, Department of Radiation Oncology, Leiden, The Netherlands 5 Cambridge University Hospitals NHS Foundation Trust, Oncology Centre, Cambridge, United Kingdom 6 Tata Memorial Hospital, Department of Medical Physics, Mumbai, India 7 Mount Vernon Cancer Centre, Radiotherapy Physics, Northwood, United Kingdom 8 Institute of Oncology Ljubljana, Department of Radiophysics, Ljubljana, Slovenia 9 Gustave Roussy, Department of Radiotherapy, Villejuif, France Purpose or Objective To evaluate the evolution of external beam radiotherapy (EBRT) practice between EMBRACE I and the in itial phase of EMBRACE II and the consequences on irradiated volumes. Material and Methods The international prospective EMBRACE I study enrolled 1416 locally advanced cervical cancer (LACC) patients from 23 institutions from 2008 to 2015. EBRT was delivered as IMRT or conformal radiotherapy (CRT), and dose prescription ranged from 45-51Gy/25-30fx to the elective target. PTV margins were according to institutional practice. The elective target included pelvic, ±para-aortic (PAN), and ±inguinal Lymph Nodes (LN). In 1270 patients treated with pelvic±PAN irradiation (patients with inguinal irradiation were excluded), PTV volume and V43Gy were available. Among them, 448 patients with LN boosting had nodal PTV (PTV-N) volume and/or V57Gy available. Differences in PTV volume across centres were compared for centres which enrolled >15 patients: 18 centers for pelvic and 5 for PAN. The EMBRACE II study was initiated in 2016 and 3 centres enrolled 68 patients by 10-2017. EMBRACE II implies common contouring guidelines, IMRT, daily IGRT and a joint dose prescription protocol including 45Gy/25fx for the elective volume (pelvic±PAN) and 55/57.5Gy for simultaneously integrated LN boost with coverage probability planning. A 5mm PTV margin and a PTV constraint of V95%>95% were required. PTV and V43Gy were reported in 50 patients, V50Gy and PTV-N in 29 boosted patients. Results EMBRACE I: CRT was used in 60% of patients and IMRT in 40%. For pelvic irradiation (84%), median PTV (first - third quartile) was 1549 (1312-1807) cm 3 and V43Gy 2390 (2028-2799) cm 3 and for PAN patients (16%), 1924 (1663- 2175)cm 3 and 2909 (2528-3462)cm 3 , resulting in V43/PTV of 1.54 and 1.51, respectively. For pelvic patients treated with IMRT, V43/PTV was 1.31. Median institutional PTV varied at most by 745 for pelvic and 588cm 3 for PAN patients. In pelvic patients, median V43Gy was 513cm 3 larger with CRT as compared to IMRT, and 357cm 3 larger with ≥48Gy as compared to 45Gy, as showed in Figure 1. Median V57Gy for boosted patients was 98cm 3 and PTV-N 57cm 3 . EMBRACE II: For pelvic irradiation (66%), median PTV was 1350 (1206-1424) cm 3 and V43Gy 1409 (1278-1544) cm 3 and for PAN patients (34%), median PTV was 1803 (1735- 2038)cm 3 and V43Gy 1935 (1794-2109)cm 3 , resulting in V43/PTV of 1.04 and 1.07, respectively. Median institutional PTV varied at most by 217cm 3 for both pelvic and PAN patients. For boosted patients, median V50Gy was 67cm 3 and PTV-N 43cm 3 .