ESTRO 2021 Abstract Book

S24

ESTRO 2021

Conclusion An advanced analysis of the dosimetric impact on CTV and main OARs from the DUPROTON clinical robustness evaluation protocol was made for clinical neuro IMPT treatments, suggesting that current treatment planning is conservative and there is room to increase CTV coverage if needed. Patient-specific SRs based on PCE evaluation results may improve grip on trade-offs in treatment planning.

Poster highlights: Poster Highlights 2: Head and neck 1

PH-0048 Pattern of failure after curative (C-)RT in HNSCC: data from the phase III DAHANCA19 study M.H. Kristensen 1 , C.R. Hansen 2 , R. Zukauskaite 2 , A.I.S. Holm 3 , E.S. Hinsby 4 , C. Maare 5 , J. Johansen 2 , H. Primdahl 3 , Å. Bratland 6 , C.A. Christensen 7 , M. Andersen 8 , J. Overgaard 9 , J.G. Eriksen 10 1 Aarhus University Hospital , Dept of Experimental Clinical Oncology, Aarhus, Denmark; 2 Odense University Hospital, Dept of Oncology, Odense, Denmark; 3 Aarhus University Hospital, Dept of Oncology, Aarhus, Denmark; 4 Zealand University Hospital, Dept of Oncology, Næstved, Denmark; 5 Herlev Hospital, Dept of Oncology, Herlev, Denmark; 6 Oslo University Hospital , Dept of Oncology , Oslo, Norway; 7 Copenhagen University Hospital, Dept of Oncology, Copenhagen, Denmark; 8 Aalborg University Hospital, Dept of Oncology, Aalborg, Denmark; 9 Aarhus University Hospital, Dept of Experimental Clinical Oncology, Aarhus , Denmark; 10 Aarhus University Hospital, Dept of Experimental Clinical Oncology, Aarhus, Denmark Purpose or Objective Recurrent head and neck squamous cell carcinoma (HNSCC) often has a poor prognosis. Aim of the current study was to evaluate the recurrence pattern according to RT dose levels from patients (pts) treated in a randomized trial. Materials and Methods Data was prospectively collected in the randomized multicenter phase III study DAHANCA19. According to DAHANCA guidelines pts received 66-68Gy in 33-34fx, 6 fx/wk; concomitant weekly cisplatin (40mg/m 2 ) if UICC stage III/IV (7 th ed.) and the hypoxic sensitizer nimorazole. Pts were randomized to either the EGFR-inhibitor zalatumumab or placebo and no effect on 5-year survival was found. For pts with persistent (never tumor-free 3 months after end of RT) or recurrent disease (recurrence after complete remission was obtained) available post-treatment scans and treatment RT-plans were collected and analyzed. Recurrences were contoured and recurrence scans and treatment plans were deformable co- registered. Recurrences were evaluated for visual overlay with original GTV. For pts with more than one local recurrence, any recurrence with significant overlay with GTV was considered to originate from within the high dose target. Results Within 3 months after end of RT, 41 of 608 evaluable pts were diagnosed with persistent disease. Among the remaining 567 pts, 146 (26%) were registered with recurrent disease in the 5 year follow-up period. Of those 126 pts were registered within the first 3 years of follow-up. Median time to any recurrence was 12 [3-60] months. Distribution of recurrences according to site was: 82 T-site, 53 N-site (8 outside elective volume) along with 56 distant metastases of which 27 had simultaneous loco-regional recurrences (Figure 1). Of the 53 pts with nodal recurrences, 43 had initial N2/3 disease, 8 had primary N1-disease while only 2 had N0-disease according to the IUCC 7 th ed. Distant metastases were located in lungs (n=40), bone (n=20), lymph nodes below the clavicles (n=19), liver (n=8), CNS (n=3), soft tissue (n=2) and in other organs (n=5). Of 117 pts with T- and/or N-site recurrences, scans were available for 58 pts. Number of T- and N-site recurrences for individual pts ranged between 1 to 5 with 36 (62%) pts having only one site of recurrence. Target dose analyses showed that 40 pts (69%) had recurrences with significant overlay with GTV while only one pt had a single recurrence outside the elective volumes. The remaining 17 pts (29%) had recurrences within the elective radiation target area. Conclusion The majority of loco-regional recurrences (69%) were related to initial high dose GTV after curative (C-)RT. This indicates, that failures were sufficiently covered by prescribed dose and that other causes of failure, e.g. the biology of the tumor must be considered.