ESTRO 2021 Abstract Book

S1007

ESTRO 2021

Kaplan Meier and long Rank, T-student, Chi square. RESULTS: Mean follow-up: 40.15 months (6-99). In 35 evaluable patients who underwent surgery, T downstaging was presented in 16 p. (45%) and pathological complete response in 9 p. (25.7 %). Five-year OS, LRFS, NRFS and DMFS were 43%, 81%, 69.4 % and 51% respectively. Pathological pT3-4 stages were associated with a low 5-y NRFS (42% vs 86% for pT0-2; p=0.04). There was a trend to a worse 5-y NRFS in patients with cT3-4 stages (58% vs 100% for cT1-2; p=0.06) Worse 5-y OS was observed for pT3-4 stages (25% vs 73% for pT0-2; p=0.009); and T downstaging (31.7 % vs 75 % for no T downstaging; p=0.002). Distant metastasis were most frequent in cT3-4 (5-y DMFS of 36% vs 89% for cT1-2; p=0.03), pT3-4 (5-y DMFS of 21% vs 77% for pT0-2; p=0.02) and positive pN stage (5-y DMFS of 15% vs 69% for pN0; p=0.04). Most frequent toxicities were haematological and gastrointestinal tract: leukopenia 25p. (62,5%), G≥2 20p (50%); neutropenia 17 p. (42.5%), G≥2 17 p. (100%); thrombocytopenia 14 p. (35%), G≥2 4 p. (10%); anemia 12 p. (30%), G≥2 3 p. (7%); dysphagia 19 p. (47,5%), G≥2 16 p. (40%); nausea and/or vomiting 10 p. (25%), G≥2 7p. (18%).

Conclusion Neoadjuvant chemo-radiotherapy for esophageal cancer achieves good survival and locoregional control with aceptable toxicities. Distant metastasis were frequent in high risk patients (cT3-4, pT3-4 and pN+) suggesting that more aggressive systemic therapy should be considered in future studies. PO-1217 Clinical outcomes after stereotactic ablative radiotherapy in locally advanced cholangiocarcinoma A.U. Larsen 1 , E.S. Worm 2 , E.M. Tabaksblat 1 , M. Høyer 3 , B. Weber 4 , H.R. Mortensen 3 1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 3 Aarhus University Hospital, Danish Center of Particle Therapy, Aarhus, Denmark; 4 Aarhus University Hospital , Department of Oncology and Danish Center of Particle Therapy, Aarhus, Denmark Purpose or Objective Cholangiocarcinoma (CC) is a rare, aggressive malignancy with a poor prognosis. The only curative treatment is surgical resection, however most patients (70%) are unresectable at the time of diagnosis. Stereotactic Ablative Body Radiotherapy (SABR) is feasible in carefully selected patients and might be an alternative to palliative chemotherapy or best supportive care in fragile patients. Materials and Methods Between 2009-2018, 41 patients with unresectable locally advanced CCs were treated with SABR at our institution and retrospectively analyzed. Data were retrospectively obtained from patient files and the treatment planning system. The prescribed clinical target volume (CTV) mean radiation dose ranged from 42 Gy to 60 Gy in 3 or 6 fractions, delivered with 2-3 fractions per week. The CTV and PTV were enclosed by the 95% and 67% isodose surfaces, respectively. Constraints to organs at risk were based on local guidelines. From 2015 and forward, neo-adjuvant or adjuvant chemotherapy was a treatment option for suitable patients. The primary endpoint was overall survival and secondary endpoints were local control, progression-free survival and toxicity. Results The study included 41 patients, with a mean age of 69 years (range 39-82); 63% were male. 17% had a Charlson Comorbidity Score ≥3 and 27% a performance status ≥2. The median CTV diameter was 3.6 cm (2-7.4 cm) and the most frequently used radiotherapy schedule was 48 Gy in 6 fractions used in 11 patients (27%). Only 7 patients received chemotherapy and the most common reasons not to receive chemotherapy were poor performance status and/or comorbidity. The median follow-up time was 9.5 months and 9 patients (22%) were lost to follow-up. Median overall survival was 11.8 months and 2-year overall survival was 19.5%. The 1-year local control rate was 67.7% and median time to progression 5.7 months. In univariate analysis, shorter overall survival was associated with extrahepatic disease (p=0,049) and presence of any grade of toxicity (p=0,011). 32 patients (78%) were followed for at least 3 months after SABR. Acute toxicity occurred in 21