ESTRO 2021 Abstract Book

S845

ESTRO 2021

Conclusion The parotid glands and submandibular glands significantly reduced in volume during the course of radiotherapy, which was correlated to cumulative dose and patient weight loss. Moreover, we observed significant migration of the parotids. This forms the rationale for regular adaptive re-planning during treatment, to avoid excessive irradiation of the salivary glands. The impact on xerostomia is currently under investigation in a prospective study. PO-1016 External validation of a nomogram for chemoirradiation in stage 2 nasopharyngeal carcinoma with IMRT P.L. Yip 1 , P. Chan 2 , K. Cheung 2,3 , C. Chow 3 , W. Lai 4 , H. Lee 5 , K. Lam 6 , C. Chiang 6 , C. Wong 7 , M. Poon 8 , M. Tong 9 , K. Au 3 , W. Ng 6 , K. Ngan 6 , A. Lee 6 , Y. Tung 2 1 Tuen Mun Hospital , Department of Clinical Oncology, Hong Kong, Hong Kong (SAR) China; 2 Tuen Mun Hospital, Department of Clinical Oncology, Hong Kong, Hong Kong (SAR) China; 3 Queen Elizabeth Hospital, Department of Clinical Oncology, Hong Kong, Hong Kong (SAR) China; 4 Princess Margaret Hospital, Department of Clinical Oncology, Hong Kong, Hong Kong (SAR) China; 5 Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, Department of Clinical Oncology, Hong Kong, Hong Kong (SAR) China; 6 Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, Department of Clinical Oncology, Hong Kong, Hong Kong (SAR) China; 7 Pamela Youde Nethersole Eastern Hospital, Department of Clinical Oncology, Hong Kong, Hong Kong (SAR) China; 8 Hong Kong Sanatorium & Hospital, Hong Kong, China., Comprehensive Oncology Centre, Hong Kong, Hong Kong (SAR) China; 9 Prince of Wales Hospital, Hong Kong, Department of Clinical Oncology, Hong Kong, Hong Kong (SAR) China Purpose or Objective Optimal treatment for stage II nasopharyngeal carcinoma (NPC) in the intensity-modulated radiotherapy (IMRT) era had been controversial. Newly released ESMO/EURACAN and CSCO/ASCO guidelines in the late 2020 recommended decision on concurrent chemoirradiation (CCRT) to be based on radiotherapy technique and risk assessment, respectively. Recently a nomogram was published by Sun et al. to predict overall survival (OS) and the additional benefit of CCRT vs. radiotherapy (RT) alone on stage II NPC previously treated with conventional RT. We carried out this study to evaluate the association between clinical parameters in the nomogram with OS and externally validate the nomogram in the IMRT era. Materials and Methods We retrospectively reviewed data from the HKNPCSG 1301 study (Treatment outcomes of NPC in the modern era after IMRT in Hong Kong: A report of 3328 patients) and selected patients with 1. stage II (AJCC 7 th ) NPC, 2. Aged 70 or below, 3. WHO II or III histology subtypes who underwent RT alone or CCRT with radical intent. Clinical parameters were studied and applied to the nomogram under study to predict OS. Nomogram predicted and actual 5-year OS were compared. Results 331 patients were included. Median follow up was 83.8 months (IQR [67.8, 101.9]). In univariable analysis, within T category, N category, TN category, age, gender, and treatment group (RT alone vs. CCRT), only increasing age (p=0.03) was predictive of inferior OS. In Cox proportional hazards model, none of the clinical parameters used in the nomogram were significant predictors for OS (Table 1). The nomogram yielded a concordance index of 0.553 (95% CI [0.466, 0.64]) in predicting 5-year OS, which lacked clinically meaningful