ESTRO 37 Abstract book

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ESTRO 37

OC-0073 Isodose surface volume in cervix brachytherapy: dependence on image guided adaptation and applicator M. Serban 1 , C. Kirisits 2 , K. Nkiwane 2 , I. Dumas 3 , J. Swamidas 4 , A. De Leeuw 5 , R. Hudej 6 , G. Lowe 7 , N. Nesvacil 2 , R. Pötter 2 , J. Lindegaard 1 , K. Tanderup 1 1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark 2 Medical University of Vienna / General Hospital of Vienna, Department of Radiation Oncology, Vienna, Austria 3 Gustave-Roussy Institute, Department of Radiotherapy, Paris, France 4 Tata Memorial Hospital, Department of Radiation Oncology, Mumbai, India 5 University Medical Centre Utrecht, Department of Radiotherapy, Utrecht, The Netherlands 6 Institute of Oncology Ljubljana, Department of Radiotherapy, Ljubljana, Slovenia 7 Mount Vernon Hospital, Cancer Centre, London, United Kingdom Purpose or Objective To investigate the isodose surface volumes (ISVs) for 85, 75 and 60 Gy EQD2 for locally advanced cervix cancer patients enrolled in the multi-institutional EMBRACE clinical trial. The hypothesis of this analysis was that individualized Image Guided Adaptive Brachytherapy (IGABT) in conjunction with the use of combined intracavitary/interstitial brachytherapy (IC/IS-BT) leads to improved dose conformity and an overall reduction of the ISVs as compared to standard loading, point A based BT. Material and Methods 1201 patients accrued in the EMBRACE study were analysed. EBRT with concomitant chemotherapy was followed by MR based IGABT. Different EBRT/BT fractionation schedules, BT dose rates (HDR/PDR), applicator designs (T&O, T&R, moulds, etc) and implant types (IC or IC/IS) were used. For the ISV calculation of the standard loading systems, 85, 75 and 65Gy EQD2 Point A-prescribed plans were produced in Oncentra treatment planning system for different sized commercial T&R and T&O applicators, including tandem lengths from 4–6 cm, ring diameters of 26, 30 and 34 mm and ovoid inter-channel spacing of 15, 20 and 25 mm. The EMBRACE EQD2 ISVs were calculated for both a/b 10 Gy (tumor) and 3 Gy (late adverse effects) using a predictive model based on Total Reference Air Kerma (TRAK). ISVs and conformity index (CI) were evaluated for IC and IC/IS BT using T&R or T&O applicators.

Results Median CTV HR

D 90%

and CTV HR

volume were 89.9 Gy and

28.4 cm 3 , respectively. The median CTV HR volume treated with IC/IS-BT was 38.0 cm 3 versus 23.6 cm 3 for IC-BT. Median EQD2 10 V85Gy , V75Gy and V60Gy were 71 cm 3 , 99 cm 3 and 230 cm 3 , respectively, and depended on CTV HR volume (Table 1). Median V85Gy was 24% smaller than in standard 85 Gy Point A prescription. 37% of patients were treated with ISVs similar to standard loading with 75 – 85 Gy Point A prescription (Figure 1). 42% of patients were treated with V85Gy smaller than with standard 75 Gy at Point A, proving volume de-escalation with IGABT (Figure 1). 21% of patients, of which two thirds had large CTV HR (> 35cm 3 ), were treated with V85Gy larger than in standard 85 Gy Point A prescription to ensure adequate target coverage (Figure 1). T&R was more conformal than T&O with CI being 23% and 16% smaller for T&R in the IC and IC/IS groups, respectively. CI was 9% and 17% smaller for IC/IS than for IC in T&R and T&O groups, respectively. For the same treated V85Gy for EQD2 10 , the corresponding V85Gy for EQD2 3 were, on average, 30% larger for HDR and 14% for PDR. Conclusion The MR-IGABT led to improved target coverage/conformity while the irradiated volumes on average were reduced compared to standard plans. The ISVs depended strongly on CTV HR volume proving dose adaptation according to individual response. Dose conformity increased with the use of T&R and with more frequent application of IC/IS implants. OC-0074 Image-guided brachytherapy in cervical cancer: Total Reference Air Kerma predicts bowel toxicity S. Bockel 1 , A. Escande 2 , E. Manea 1 , M. Khettab 1 , F. Busato 1 , T. Kumar 1 , L. Laurans 1 , I. Dumas 1 , R. Mazeron 1 , I. Lazarescu 1 , E. Deutsch 1 , C. Haie-Meder 1 , C. Chargari 1 1 Institut Gustave Roussy, Radiotherapy, Villejuif, France 2 Oscar Lambret Comprehensive Cancer Center, Radiotherapy, Lille, France

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