Abstract Book

S795

ESTRO 37

delineation method and the maximal standardized uptake values (SUVmax) were calculated. The dose to rectum, mesorectum and pelvic lymph nodes was 45 Gy (1.8 Gy /fraction). A concomitant boost was delivered to GTV (defined on PET-0) +2 cm margin with a total dose of 50 Gy (2 Gy/fraction). A subsequent sequential boost was delivered to GTV (defined on PET1)+5mm margin with a total dose of 5 Gy in 2 fractions (2.5 Gy/fraction) for a total dose of 55 Gy. Pathological response was expressed based on pTNM and Dworak tumor regression grading and toxicities were scored according to the CTCAE v4.03 scale Results Nine patients (M/F: 8/1, median age 60 years) were enrolled. The median SUVmax of the rectal lesions was 12.9 (range: 5.6-45) at PET-0, 9.7 (range: 5.6-20.4) at PET-1 and 5.5 (range: 0-5.9) at PET-2, respectively. TV measured by PET was 28.1 mL (range: 1.2-90.9) at PET-0 and 11.6 mL (range: 0.7-62.4) at PET-1, respectively. Median SUVmax percent reduction and median TV percent reduction during RT was 33% (range: 0-54%) and 64% (0-86%), respectively. Among patients undergoing PET-2, median SUVmax percent reduction compared with PET-0 was 50% (range: 47%-100%) and 34% (range: 21%- 100%) compared with PET-1. The only patient with positive lymph-node at PET-0 responded completely to lymph-node at PET-1, while rectal lesion showed a stable uptake. PET-2 was completely negative. To date, this is the only resected patient (11 weeks after RT) with complete clinical response and pCR. No acute grade ≥ 3 toxicity was recorded Conclusion These preliminary results show that an adaptive strategy based on [18F]FDG-PET/CT can be feasible to reduce the target volume of a sequential boost EP-1464 Radical approach to primary unresectable rectal cancer–what is the optimal road? M. Kraszkiewicz 1 , J. Wydmanski 1 , W. Majewski 1 1 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Radiotherapy Department, Gliwice, Poland Purpose or Objective To compare the treatment outcome in patients with a primary unresectable rectal cancer treated with radical radiotherapy (RT) vs. radiochemiotherapy (RTCT). Material and Methods A total of 145 of patients (pts) with unresectable, locally advanced rectal cancer cT4, cN+/N0, M0 were treated between 2000 and 2016 in Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology Gliwice Branch. A total of 73 pts received RT and 72 pts received RTCT. The main intent of treatment was tumor downstaging allowing further resection. The median age in RT group was 63 years (range 33-84) in RTCT group it was 59 years (range 26 to 76) (p=0,045). Pts in RTCT group had sligtly better performance status than in RT group i.e., ZUBROD 0, 1, 2 was scored in 60% vs 44%, 40% vs 52%, 0% vs 6% pts, respectively (p=0.054). Other factors like: tumor volume and location, the rate of exploratory laparotomy and sex were not significantly different between the groups. In RT group hyperfractionation to the Total Dose (TD) of 66 Gy wih 1.5 Gy twice daily or conventional fractionation to TD of 60-66 Gy with 2 Gy once daily were used. In RTCT group TD of 54 Gy with 1.8 Gy once daily was applied along with two courses of 5-Fluorouracil (325

mg/m2 or 375 mg/m2)+Leucovorin ( 20mg/m2 ) in 1st and 5th week. The efficacy of the treatment was evaluated and compared in 4 endpoints:1) the rate of objective response (OR) i.e. the sum of complete and partial tumor regression that demonstrates early response to the treatment, 2) the rate of tumor resectability after RT or RTCT, 3) Local Control (LC) and 4) Overall Survival (OS). Results Objective response rate was higher in RTCT than in RT group: 75% vs 60%, respectively (p=0,065) . The resectability rate was also higher in RTCT than in RT group: 64% vs 37% (p=0,0012) . Five year LC rate was 68% in RTCT pts, while in RT group it was 34% (p=0,000) . One patient in RTCT group and 2 patients in RT group achieved a durable tumor regression despite the lack of a furher surgical resection and were scored as locally controlled at 5-years. No patient in RTCT group experienced a local recurrence after surgery as compared to 22% of local recurrences in RT group. The 5 year OS was 52% vs 25% respectively (p=0,002). Conclusion The study demonstarted statistically significant better outcome for patients treated with radiochemotherapy than treated with radiotherapy in the aspect of objective response, surgical resectability, local control, and overall survival. Radiochemotherapy remains the optimal choice for primary unresectable rectal cancer and should be offered to all suitable patients. EP-1465 Palliative RT: new score to estimate survival times of patients with gastrointestinal malignancies C. Kerger 1 , C. Straube 1 , A. Hapfelmeier 2 , S.E. Combs 1 , D. Habermehl 1 1 Technical University Munich, Department of Radiation Oncology- Klinikum rechts der Isar, München, Germany 2 Technical University Munich, Institute of Medical Informatics- Statistics and Epidemiology, München, Germany Purpose or Objective Physicians usually are overwhelmed when estimating the remaining survival time of palliative patients. This finding reaches major importance in patients undergoing RT because there is a variety of treatment schedules that can be used in the common palliative settings with different treatment durations. Usually radiation oncologists tend to overestimate life expectancy, so the ratio between treatment time and survival time often is inadequate. Therefore, we see a need for reliable models, that can support the decision making process. This study was performed to create a prognostic score to estimate survival time of patients with metastasized gastrointestinal malignancies undergoing palliative radiotherapeutic treatment schedules. Aim of the study was to identify individual and (radio-)therapy-related prognostic factors that predict the remaining survival time in this special patient subgroup Material and Methods A retrospective cohort study of 143 patients undergoing palliative radiotherapy (RT) at the Department of Radiation Oncology at the Klinikum rechts der Isar (Munich, Germany) was performed. The study included patients with diagnosed primary tumor sites of the oesophagus (18.9%), the stomach (20.3%), the colon/rectum (42%), the liver/biliary tract (6.3%) and the pancreas (8.4%). Patients underwent radiotherapy at the following sites: brain (25,5%), bone (26,8%), lung (20,4%), liver (7,6%), lymph nodes (10,2%), others (9,3%).