ESTRO 38 Abstract book

S87 ESTRO 38

while vaginal and uterine involvement did not. Median number of implanted/active P and P&O needles at first implant was 8/7 and 12/10, respectively. Individualized 3D printing was used in 13 (57%) patients of the P&O group. Embrace II hard constraints were fulfilled in 95% (Table 1). With a median follow-up time of >18 months, local control was obtained in 56 (95%) and grade ≥3 radiation related complications observed in 3 pts (5%). Conclusion The use of 3D printed TNT for IGABT in LACC is promising. It allows for successful management of extensive local disease even in narrow vaginal conditions. 3D printing enables full and affordable control of the production process with the possibility for treatment individualisation and one-time use of the BT template.

OC-0175 3D-printed tandem-needle-template for image guided adaptive brachytherapy in cervical cancer P. Petric 1 , L.U. Fokdal 1 , A. Traberg Hansen 1 , S. Kynde Nielsen 1 , K. Tanderup 1 , J.C. Lindegaard 1 1 Aarhus University Hospital, Department of Oncology, Aarhus C, Denmark Purpose or Objective Intracavitary/interstitial (IC/IS) image guided adaptive brachytherapy (IGABT) is being increasingly employed for locally advanced cervical cancer (LACC). However, narrow vagina and/or extensive local disease may compromise the use of tandem-ring or tandem-ovoid IC/IS applicators. We describe our experience with novel 3D printed vaginal tandem-needle templates (TNT) for insertion of needles in parallel (P) or parallel and oblique (P&O) direction. Material and Methods Fifty-nine consecutive patients treated with TNT from Jan 2015 - Jan 2018 were included. External beam radiotherapy (EBRT) consisted of 45 Gy/25 fx +/- nodal boost and concomitant cisplatin. Decision to use TNT and pre-planning of its optimal geometry were made after 4-5 weeks of EBRT, based on gynaecological examination and MRI with tandem-ring applicator in situ. Subsequently, TNT was 3D-printed in house, using biocompatible autoclavable material (Figure 1). TNT consisted of a 32- or 36-mm vaginal ring without a ring channel and with P and O holes for guidance of plastic needles. Standard (12 P needles or 8 P plus 7 O needles) or personalized TNT (individualized needle insertion points and angles) was printed. Following EBRT, 2 implants and 2 fractions of PDR IGABT were delivered about 1 week apart. TNT was fitted over commercially available uterine tandem. Plastic needles were placed through the guiding holes to pre- planned depths. The source was not in direct contact with the TNT. Dwell-positions in P needles were used to simulate the ring channel. Planning aims were based on the Embrace II protocol. TNT was discarded after single use. Results Patients selected for TNT were characterised by a median age of 69 years. Performance status (WHO) was > 0 in 49% and 56% of the patients had noteworthy co-morbidity. FIGO stage distribution was: IB 2%, IIB 48% and III-IV 50%. Median tumour width was 60 mm. Patients with P&O implants (n=32) had significantly larger tumours and more extensive parametrial involvement at diagnosis and BT when compared with P group (n=27). Bladder and rectum invasion also predicted for the use of P&O technique,

OC-0176 A systematic analysis of delineation performance seen in EMBRACE-II brachytherapy quality assurance S. Duke 1 , R. Pötter 2 , A. Sturdza 2 , M. Schmid 2 , T. Rumpold 2 , U. Mahantshetty 3 , N. Nesvacil 2 , A. De Leeuw 4 , C. Kirisits 2 , K. Tanderup 5 , R. Nout 6 , J. Lindegaard 5 , I. Jurgenliemk-Schulz 4 , L. Tan 1 1 Cambridge University Hospitals, Department of Oncology, Cambridge, United Kingdom; 2 Medical University of Vienna, Department of Radiotherapy, Vienna, Austria; 3 Tata Memorial Centre, Department of Radiation Oncology, Mumbai, India ; 4 University Medical Center, Department of Radiation Oncology, Utrecht, The Netherlands ; 5 Aarhus University Hospital, Department