ESTRO 2021 Abstract Book

S837

ESTRO 2021

therapy (p<0.001). In all participants, median baseline fat-free mass index (FFMI) was 18.1 (14-24.7) kg/m² and decreased to 17.8 (13.4-21.6) kg/m² till the end of therapy (p<0.001). Compliant patients with a BMI <22 kg/m² presented with less weight loss in the intervention group compared to the control (p=0.015, CI: 0.33- 2.95). At baseline, MUST was the only screening-test which showed both good sensitivity (86%) and specificity (88%) in detecting malnutrition. Median follow-up was 15 (1-26) months and is still ongoing. 2-year overall survival rate was 70% in the control and 79% in the intervention group (log-rank p=0.79). Pretherapeutic phase angle, posttherapeutic FFMI and albumin level were prognostic indicators for overall survival (log-rank p=0.002, p=0.008 and p=0.016). Conclusion Malnutrition has a negative impact on oncologic outcome. Baseline phase angle, posttherapeutic FFMI and serum albumin level may act as reliable indicators for overall survival. PO-1007 Radiotherapy with delayed accelerated hyperfractionated boost for node negative hypopharynx cancer T. Fujisawa 1 , A. Motegi 1 , S. Zenda 1 , H. Hojo 1 , M. Nakamura 1 , Y. Hirano 1 , H. Hirata 1 , R. Vijay Parshuram 1 , K. Matsuura 2 , T. Shinozaki 2 , R. Hayashi 2 , T. Akimoto 1 1 National Cancer Center Hospital East, Radiation oncology, Kashiwa, Japan; 2 National Cancer Center Hospital East, Head and Neck Surgery, Kashiwa, Japan Purpose or Objective Patients with hypopharyngeal cancer tend to have potential cervical lymph nodes metastasis even in the clinically node negative, indicating the necessity of prophylactic nodal irradiation. It has been also reported that accelerated radiotherapy (RT) contributes to improved local control of head and neck cancer. To achieve both prophylactic nodal irradiation of the cervical lymph nodes and improvement of local control by accelerated RT, we initiated definitive accelerated RT with prophylactic nodal irradiation for clinically nodes negative hypopharyngeal cancer. The purpose of this study is to evaluate the efficacy of the definitive RT for clinically node negative hypopharyngeal cancer using prophylactic nodal irradiation combined with accelerated local boost technique (Delayed Accelerated Hyperfractionated Boost: DAHB). Materials and Methods We retrospectively reviewed patients who received DAHB for clinically node-negative hypopharyngeal cancer from January 2010 to December 2019. The fraction schedule of DAHB consisted of prophylactic nodal irradiation with conventional fractionation at doses of 40–46 Gy/20–23frac. followed by a boost with accelerated RT at doses of 24–30 Gy/16–20frac. (1.5 Gy/fr, twice daily). Intensity-modulated radiotherapy or 3-dimensional conformal radiotherapy was used. Local control rate (LCR), overall survival (OS), progression- free survival (PFS), adverse events (AEs), and patterns of recurrence were analyzed. OS and PFS were calculated by the Kaplan-Meier method. AEs were evaluated based on the Common Terminology Criteria for Adverse Events version 4.0. Results In total, 34 patients were included this study. The patient characteristics were as follows; Male /female; 33/1, the median age; 71 (range: 51-79), TNM category; Tis or T1/ T2/ T3/T4: 8 (24%)/ 29 (69%)/ 3(7%)/ 2(5%), respectively. All patients completed planned DAHB without interruption. At the median follow-up duration of 45 months (range: 8-127 months), the 3-year LCR, OS and PFS were 85% (95%CI: 68-94%), 82 ％ (95 ％ CI ： 61-92 ％ ) and 73 ％ (95 ％ CI:52-86 ％ ), respectively. Initial complete response was achieved in 31 of all patients (91%). Regarding the recurrence pattern, no patient developed regional lymph node metastasis. Six (18%) patients developed local failure (residual disease and local recurrence) and 1 developed lung metastasis. Grade 0-2 mucositis, dermatitis, xerostomia and dysgeusia were 28 (82%), 34 (100%), 14 (41%), and 15 (44%), respectively. Grade 3 AEs, all of which were pharyngeal mucositis, were observed in 6 patients (18%), and no patient experienced grade 4-5 AEs. Conclusion DHAB for clinically node negative hypopharyngeal cancer showed excellent clinical outcomes with no regional lymph nodes recurrence, and was feasible with acceptable toxicities. PO-1008 Lymph node ratio dependent utilization of postoperative radiotherapy in T1-2N1 oral cavity carcinoma J. Wang 1 1 National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Department of Radiation Oncology, Beijing, China Purpose or Objective Oral cavity squamous cell carcinoma (OCSCC) patients with pathological T1-2N1 (pT1-2N1) diseases are generally not considered postoperative radiotherapy (PORT) candidates in current clinical practice. However, regional recurrence rate after postoperative observation for pT1-2N1 OCSCC is quite variable, justifying PORT in subgroup with high-risk of recurrence. In addition, the identification of AJCC N1 classification is apt to be influenced by the qualities of both neck dissection and pathological examination. Lymph node ratio (LNR) is defined as the ratio of positive lymph node to the total number of lymph node yield, aiming to compensate for the potential bias of the sampling and examining methods. No LNR-based prognosis stratification and PORT decision-making has been reported in pT1-2N1 patients with OCSCC. This study aimed to investigate the prognostic value of LNR and to further examine the clinical validity of LNR-dependent stratification in guiding PORT in pT1-2N1 OCSCC patients. Materials and Methods OCSCC patients who received surgery with at least 3 cervical lymph nodes dissection were extracted from Surveillance, Epidemiology and End Results (SEER) database between 2010 and 2015. Additive Cox model was implemented to examine the correlation between the continuous LNR and survival outcomes. Time-dependent