J.C. Lin

PO-0675: Post-radiation adjuvant chemotherapy with oral tegafur-uracil in high-risk nasopharyngeal carcinoma

& G2 (2)). Dice similarity coefficients (DSC) were used to compare G1 and G2 spatial similarity. G1 and G2 defined structures were subsequently analysed for planned dose discrepancy. 1. Christianen ME, Langendijk JA, WesterlaanHE, et al. Delineation of organs at risk involved in swallowing for radiotherapy treatment planning. Radiother Oncol 2011;101:394-402. 2. Levendag PC, Teguh DN, Voet P, et al. Dysphagia disorders in patients with cancer of the oropharynx are significantly affected by the radiation therapy dose to the superior and middle constrictor muscle: a dose-effect relationship. Radiother Oncol 2007;85:64-73. Results: Differences in G1 and G2 delineation guidelines reported DSC values less than 0.5, indicating poor spatial correlationSPCM (DSC=0.09±0.09, range of 0.02-0.22), MPCM (DSC=0.47±0.16, range:0.26 to 0.63), IPCM (DSC=0.34±0.12, range: 0.19 to 0.49), CP (DSC=0.33±0.12,range: 0.12 to 0.41), and OI (DSC=0.15±0.13, range: 0 to 0.31). This difference in delineation led to dose differences for each structure (Dmean), shown inTable I, with some structures impacted by up to 13.9 %. Such variation is indicative of the variable proximity of the pharyngeal axis to areas of steep dose heterogeneity. In general, the range of per-structure dose differences across all patients was large, showing that indicated complication probability can be highly dependent upon which guideline is chosen for clinical use. Table 1. Dose difference of Dmean between structures delineated with G1 and G2 guidelines