Abstract Book

S638

ESTRO 37

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 independently 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

5 weeks, delivered by 3-D conformal technique on linear accelerator. Acceleration consisted of a sixth 2 Gy fraction on Saturday. Primary end point was to assess feasibility and toxicity. Patients were reviewed weekly during RT and monthly thereafter, using Radiation Therapy Oncology Group (RTOG) criteria. Analysis of acute and late toxicity is presented. Survival analysis was done by Kaplan-Meier method and all events were calculated from the date of registration. Results Forty patients were accrued. Patient characteristics are mentioned in figure 1. The median surgery-RT start time was 6.6 weeks (range 4.1-14.4). Grade 3 mucositis, pharynx/esophageal toxicity and skin toxicity were seen in 77.5%, 25% and 17.5% respectively. Two patients had grade 4 mucositis. Progression of acute toxicities over time is presented in figure 2. No other grade 4 toxicity was seen. 23 patients received intra-venous fluid support and 57.5% were on Ryle’s tube support during RT. All the patients were taken off Ryle’s tube within 4 weeks of RT completion. Median RT completion time was 36 days (range 33-41). 97.5% completed RT doses as planned. Three patients had treatment interruptions. The median weight loss was 5.8% (range 1-9). At last follow-up, grade 3 subcutaneous toxicity and xerostomia were documented in 5% and 2.5% respectively. The median follow-up was 21.2 months (range 5.4–29). The 2-year loco-regional control rate was 87%. There were two distant failures. 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.

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.