ESTRO 2021 Abstract Book

S494

ESTRO 2021

Triple-negative breast cancer (TNBC) cells are sensitive to PARP1 inhibitors in vitro. The combination of Olaparib and radiotherapy for TNBC is currently evaluated in the phase I RADIOPARP trial. During the dose- escalation portion of this study, Olaparib was escalated to 200 mg twice a day, corresponding to the target dose, without dose-limiting toxicities. The one-year toxicity profile of this combination is reported. Materials and Methods RADIOPARP is a monocentric prospective open-label phase I dose-escalation trial evaluating the combination of breast radiotherapy and Olaparib in TNBC patients with inflammatory, locoregionally advanced or metastatic disease, or with residual disease after neoadjuvant chemotherapy. Olaparib was orally given at increasing dose levels (50mg, 100mg, 150mg or 200mg twice a day); radiotherapy consisted of 50 Gy to the breast or chest wall with or without lymph node irradiation. Treatment-related toxicity was graded according to the CTCAE (version 4.03). Results Twenty-four TNBC patients were enrolled between 09/2017 and 11/2019. Olaparib was escalated to 200 mg twice a day without dose-limiting toxicities. At one-year follow-up, no treatment-related grade ≥3 toxicity was observed (Table 1). Three patients had persistent grade 2 adverse events (breast pain, fibrosis and deformity). There were no cardiac, pulmonary or digestive toxicity.

Adverse events/Grade

1

2

3

4

Pain

3

1

0

0

Fibrosis

0

1

0

0

Deformity

0

1

0

0

Skin hyperpigmentation

3

0

0

0

Telangiectasia

1

0

0

0

Lymphedema

1

0

0

0

Table 1 : One-year treatment-related adverse events (CTCAE version 4.03)

Conclusion the one-year follow-up report of the RADIOPARP phase I trial, evaluating Olaparib associated with breast radiotherapy in TNBC patients, demonstrated an acceptable toxicity profile of this combination with few low- grade adverse events.

Proffered papers: Proffered papers 38: Treatment planning: applications

OC-0631 Proton and photon treatment planning comparison for oesophageal cancer between six European centres L. Hoffmann 1 , H. Mortensen 2 , M. Berbee 3 , N. Bizzocchi 4 , R. Bütof 5 , R. Canters 6 , G. Defraene 7 , M.L. Ehmsen 2 , G.V. Freixas 3 , K. Haustermans 8 , E.W. Korevaar 9 , S. Makocki 5 , C.T. Muijs 10 , M. Nordsmark 11 , M. Thomas 12 , E.G. Troost 13 , S. Visser 10 , D.C. Weber 14 , D.S. Møller 1 1 Aarhus University Hospital, Department of Oncology, Section for Medical Physics, Aarhus, Denmark; 2 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark; 3 Maastricht University Medical Centre, GROW School for Oncology, Department of Radiation Oncology (Maastro), Maastrict, The Netherlands; 4 Center for Proton Therapy, Paul Scherrer Institut, Villigen, Switzerland; 5 Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Department of Radiotherapy and Radiation Oncology and OncoRay - National Center for Radiation Research in Oncology, Dresden, Germany; 6 Maastricht University Medical Centre, GROW School for Oncology, Department of Radiation Oncology (Maastro), Maastrict, The Netherlands; 7 KU Leuven, Department of Oncology – Laboratory of Experimental Radiotherapy, Leuven, Belgium; 8 University Hospitals Leuven and KU Leuven, Department of Radiation Oncology, Leuven, Belgium; 9 University of Groningen, University Medical Center Groningen, Department of Radiation Oncology, , Groningen, The Netherlands; 10 University of Groningen, University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands; 11 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 12 University Hospitals Leuven, Department of Radiation Oncology, Leuven, Belgium; 13 Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Department of Radiotherapy and Radiation Oncology and OncoRay - National Center for Radiation Research in Oncology, Dresden, Germany; 14 Paul Scherrer Institut, Center for Proton Therapy, Villigen, Swaziland Purpose or Objective Proton therapy (PT) may significantly reduce dose to organs at risk (OARs) compared to photon therapy (XT). A European randomized phase III trial (PROTECT) will investigate the effect of PT for oesophageal cancer patients. In preparation of the trial, we have compared doses and robustness in treatment plans calculated at each of six European centres. All plans should comply with strict QA guidelines for treatment planning, robustness evaluation and adaptive strategies. Materials and Methods Anonymized planning 4DCT scans of four patients were distributed to the centres, and targets and OARs were delineated in the mid-ventilation (mv) phase. All centres calculated one nominal PT and XT plan each, for all patients using the iCTV (sum of CTV in all respiratory phases) for optimization, total dose 50.4Gy in 28 fractions. For PT, beam directions should be between 140-220 degrees, for XT (IMRT or VMAT), no restrictions were set. Constraints for the iCTV and OARs should be respected, e.g. for the lungs: mean lung dose MLD<20Gy, V20Gy<35% and V5Gy<70%. Robustness towards respiration was evaluated by recalculating the