ESTRO 37 Abstract book

S638

ESTRO 37

The 2-year progression free survival and 2-year overall survival rates were 83.5% and 85%, respectively. There were three cancer-related deaths and 3 patients died of other comorbidities.

dently based on MR, CT and FDG-PET/CT was validated with cross-sectional specimen via comparing the volume, overlap volume and volume difference ratio (VDR) during the GTVs. Results For the VX2 tumors in 6 rabbits, no significant difference (P>0.7) was observed between average GTVs delineated at cross-sectional autopsy (8.11 cm 3 ) with CT (8.02 cm 3 ), MR (7.89 cm 3 ) and PET/CT (8.65 cm 3 ), respectively. However, a significant difference (P=0.023) was showed during average overlap volume of GTV SA and GTV CT (OV CT , 5.57 cm 3 ), overlap volume of GTV SA and GTV MR (OV MR , 6.51 cm 3 ) and overlap volume of GTV SA and GTV PET/CT (OV PET/CT , 6.7683 cm 3 ). Average OV CT was smaller, but no significant difference (P=0.502) was seen between average OV MR and OV PET/CT . In addition, a significant difference (P=0.032 and P=0.047, respectively) was observed between average VDR of GTV CT (VDR CT , 0.2970) and VDR of GTV MR (VDR MR , 0.1800) and VDR of GTV PET/CT (VDR PET/CT , 0.1877), respectively. But no significant difference (P=1.000) was discovered between average VDR MR and VDR PET/CT . Conclusion In six rabbits of which the cross-sectional specimens were available, GTVs at CT, MR imaging, FDG-PET/CT and cross-sectional autopsy were similar, whereas FDG- PET/CT and MR were found to be more accurate modality. However, the GTV delineation of FDG-PET/CT in head and neck cancer is not superior to MR. EP-1134 significant risk factors in surgically resected oropharyngeal cancers according to p16 status T.J. Han 1 , H. Bae 2 , K.J. Kim 3 , M.Y. Lee 2 , H. Kim 4 , T. Koo 5 1 KangDong Sacred Heart Hospital, Radiation Oncology, Seoul, Korea Republic of 2 Hallym University Sacred Heart Hospital, Radiation Oncology, Anyang, Korea Republic of 3 Kangnam Sacred Heart Hospital, Radiation Oncology, Seoul, Korea Republic of 4 Dongtan Sacred Heart Hospital, Radiation Oncology, Hwaseoung, Korea Republic of 5 Chuncheon Sacred Heart Hospital, Radiation Oncology, Chuncheon, Korea Republic of Purpose or Objective To identify pathological risk factors for disease-free survival (DFS) in patients with p16-negative and p16- positive oropharyngeal cancer Material and Methods We analyzed 94 patients with oropharyngeal squamous cell carcinoma who had received radical surgery and adjuvant radiotherapy with or without concurrent chemotherapy at kangdong sacred heart hospital during 2004 Sep to 2017 Mar. Test for p16 status was done in 53 patients using PCR and human papilloma virus DNA microchip. Among of them, 23 patients were proven their positivity for p16. DFS was estimated using Kaplan Meier method and difference of survivals according to individual risk factors were analyzed by Log-rank test. Results Median duration of follow-up was 40 months. Five year DFS was 73.2% for overall patients, 66.5% for p16- negative patients, and 81.6% for p16-positive patients, respectively. Depth of invasion >2cm ( P =0.032), pathological extranodal extension ( P =0.014, Fig.1), 4 or more lymph node involvement ( P <0.001), greatest dimension of lymph node >3cm ( P =0.006), contralateral and/or bilateral lymph node involvement ( P =0.005) and level IV lymph node involvement ( P <0.001) were significantly associated with worse DFS for p16-negative patients. For p16-positive subgroup, contralateral and/or bilateral lymph node involvement ( P =0.001) were significantly associated with worse DFS, however, pathological extranodal extension ( P =0.490, Fig.2), 4 or more lymph node involvement ( P =0.382) and greatest dimension of lymph node >3cm ( P =1.000) were not.

Conclusion Reducing overall treatment time using postop erative PM-AFRT is feasible and tolerable. Although the acute mucositis rates were higher, all toxicities were manageable with vigilant follow-up during RT and supportive care. Longer follow up of our study cohort would better discern late toxicity and clinical outcomes. EP-1133 Validation of GTV delineation based on MRI, CT or FDG-PET/CT in head and neck cancer. Z. WANG 1 , X. Wang 1 , X. Zheng 2 , Z. Wu 3 1 Department of Oncology, The First Affiliated Hospital of Guangdong Pharmaceutical University, Guangzhou, China 2 Department of Radiation Oncology, Nanfang Hospital of Southern Medical University, Guangzhou, China 3 Department of Radiology, The First Affiliated Hospital of Guangdong Pharmaceutical University, Guangzhou, China Purpose or Objective To compare F-18-fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET)/computed tomography (CT), magnetic resonance (MR) and CT alone which based on the measurements of tumor volume in rabbits bearing head-and-neck cancer (HNC) with a cross-sectional autopsy that to validate the gross tumor volume (GTV) delineation based on above three imaging methods. Material and Methods Twelve HNC models were established in New Zealand rabbits with transplantation of VX2 cell line. Modeling was successful in nine rabbits. Each rabbit received FDG- PET/CT, MR and CT scan in the same immobilization and position within 24 hours. Then all rabbits were sacrificed and cryopreserved, which underwent the cross-sectional autopsy in the same position of imaging scan with a sectional thickness of 4.0 mm. Autopsying was successful in six rabbits. The GTV was delineated based on FDG- PET/CT, MR, CT and cross-sectional autopsy as GTV PET/CT , GTV MR , GTV CT and GTV SA , respectively. After three- dimensional coregistration, the GTV defined indepen-