ESTRO 2020 Abstract Book

S1100 ESTRO 2020

stenosis and dose to the RVRP. Finally, a shorter VRL is correlated with vaginal stenosis.

OC-1050 Characterization of intracavitary/interstitial brachytherapy using oblique needles in cervix cancer M. Serban 1 , L. Fokdal 1 , S. Kynde Nielsen 1 , S. Bjerre Hokland 1 , A. Hansen 1 , H. Spejlborg 1 , S. Rylander 1 , P. Petric 1 , J. Lindegaard 1 , K. Tanderup 1 1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark Purpose or Objective To characterize the performance of brachytherapy using intracavitary/interstitial (IC/IS) applicators including oblique needles in locally advanced cervical cancer (LACC). Material and Methods Out of 118 consecutive LACC patients treated with radiochemotherapy and image guided adaptive brachytherapy (IGABT) between Oct. 2013 – July 2016, 39(33%) were treated with IC BT and 79(67%) with IC/IS BT. 20/79 patients treated with IC/IS BT including oblique needles, relative to tandem direction (IC/IS-O BT), were evaluated in this analysis. IC/IS-O BT was applied with an in-house 3D printed vaginal template (ring) to steer the needles parallel (P) and obliquely (O) into the distal parametrial/vaginal tissues. Number of needles, depth/angle of needle insertion, relative needles/tandem/ring+packing dwell times (normalized to IC standard dwell time loading), and high dose volumes (150%, 200% and 300% (100% = 85Gy EQD2 10 )) were analyzed for the first BT fraction (BT1). Total (EBRT+BT) EQD2 doses for targets and OARs, and isodose surface volumes were evaluated. Furthermore, local control and grade 3/4 complications (CTCAE v3) were recorded retrospectively. Results In the 20 patients, median age was 62 years and local FIGO stage was IIB(15%), IIIA/IIIB(45%) and IVA(25%). 35%, 25% and 50% of patients had bladder, mesorectum/rectum wall and vaginal infiltration at diagnosis. Median GTV width at diagnosis was 53.5mm and BT1 CTV HR width was 49.3mm. CTV HR volume at BT1 was 44.9cm 3 . Median total/active number of needles implanted was 11/10, of which 36% were O-needles. Average O-needles length and angle was 3.3cm and 23°. Average dwell time loading weight (% of total TRAK) for tandem, ring+packing and IS needles was 31%, 25% and 44%, respectively. Normalized dwell times are given in Fig1. In IS needles, 72% of dwell positions within CTV HR had normalized dwell times <20%. 6% of IS needles dwell positions were loaded outside CTV HR , of which 99.8% had normalized dwell times <20%. Median V85Gy EQD2 10 was 85cm 3 , with 15% of this volume being located inside ring+packing. Volumes of 150% to 300% dose regions within CTV HR and targets/OARs doses are presented in Table1. 95%(80%) of patients had CTV HR D90% > 85(90)Gy while each OARs hard(soft) dose constraints (EMBRACE II) was met, on average, in 94%(81%) of patients. For a median follow-up time of 16 months, local control was achieved in 17/20(85%) and grade 3/4 toxicity observed in 2/20(10%) of patients.

Conclusion The use of O-needles in LACC patients with large/unfavourable residual tumour volumes at time of BT results in excellent target coverage and OARs sparing. V85Gy is comparable to those of standard loading, showing high dose conformity. Tandem and ring loading is reduced as compared to standard loading and shifted into needle loading. While needles carry on average almost half of total TRAK, this is achieved with gentle loading in the majority of dwell positions. Early clinical outcome in terms of local control and morbidity seems promising. M. Schmid 1 , C. Kirisits 1 , K. Tanderup 2 , C. Haie-Meder 3 , L. Fokdal 2 , A. Sturdza 1 , P. Hoskin 4 , U. Mahantshetty 5 , B. Segedin 6 , K. Bruheim 7 , F. Huang 8 , B. Rai 9 , R. Cooper 10 , E. Van der Steen-Banasik 11 , E. Van Limbergen 12 , B. Pieters 13 , L.T. Tan 14 , R. Nout 15 , A.A.C. De Leeuw 16 , N. Nesvacil 1 , I. Jürgenliemk-Schulz 16 , J.C. Lindegaard 2 , R. Pötter 1 , E. Collaborative Group 17 1 Medical University of Vienna, Department of Radiation Oncology, Vienna, Austria ; 2 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark ; 3 Institute Gustave-Roussy, Department of Radiotherapy, Paris, France ; 4 Mount Vernon Hospital, Mount Vernon Cancer Centre, Northwood, United Kingdom ; 5 Tata Memorial Hospital, Department of Radiation Oncology, Mumbai, India ; 6 Institute of Oncology Ljubljana, Department of Radiotherapy, Ljubljana, Slovenia ; 7 The Norwegian Radium Hospital - Oslo University Hospital, Department of Oncology, Oslo, Norway ; 8 Cross Cancer Institute and University of Alberta, Department of Oncology, OC-1051 Local failure in cervical cancer patients after MR image-guided adaptive brachytherapy