2398 Intensity Modulated Radiotherapy for Oral Cavity Cancer M. Yao, J. E. Bayouth, H. Tan, J. Wacha, K. J. Dornfeld, J. M. Buatti University of Iowa Hopsitals & Clinics, Iowa City, IA Purpose/Objective(s): Squamous cell carcinoma of oral cavity (OCSCC) has a worse among head and neck cancers treated with IMRT. To improve the treatment outcome, we reviewed our experience in IMRT treatment of OCSCC. Materials/Methods: From May 2001 to July 2005, 55 patients with OCSCC were treated with IMRT for curative intent. Fifty patients received postoperative IMRT; 3 of them also received concurrent chemotherapy. Five were treated primarily with definitive IMRT. Sites included were oral tongue, 20; floor of mouth, 15; buccal mucosa, 6; retromolar trigone, 6; alveolar ridge, 6; and lip, 2. Three target volumes CTV1, CTV2 and CTV3 were defined. The prescribed doses to CTV1, CTV2, and CTV3 in the definitive cohort were 70 Gy, 60 Gy and 54 Gy respectively. For high-risk postoperative IMRT, the prescribed doses to CTV1, CTV2, and CTV3 were 64 – 66 Gy, 60 Gy and 54 Gy respectively. For intermediate-risk postoperative IMRT, the prescribed doses to CTV1, CTV2 and CTV3 were 60 Gy, 60 Gy and 54 Gy. The failure patterns were determined by co-registration or comparison of the treatment planning CT to the CT or MRI obtained at the time of recurrence. Results: The median follow-up for all patients was 17.1 months (range, 0.27 - 59.3 months). The median follow-up for living patients was 23.9 months (range, 9.3 - 59.3 months). There were 9 patients with local-regional failures; 4 had local failures only, 2 had regional failures only, and 3 had both local and regional failures. There were 5 patients that failed distantly; 3 of them also had loco-regional failures. There were 3 with new primaries; 1 had oral tongue carcinoma in situ with microinvasion, 1 had lung squamous cell carcinoma, and 1 had acute myeloid leukemia. The 2-year overall survival, disease-specific survival, local recurrence free survival, loco-regional recurrence free survival, and distant disease free survival is 68%, 74%, 85%, 82% and 89%, respectively. The median time from treatment completion to local-regional recurrence was 4.1 months (range, 3.0 to 12.1 months). The local regional control is strongly correlated with extracapsular extension (ECE). The 2-year local regional control for patients with ECE is 54.5%, and 89.7% for those without ECE (p=0.0277). The local regional control is not correlated with T stage, N stage, AJCC stage, perineural invasion, lymphovascular invasion, or differentiation. For local failures, 3 failed in CTV1 that received 66 - 70 Gy; 2 failed in CTV2 that received 60 Gy; and 2 marginal failures. Both marginal failures failed in masticator space and infratemporal fossa due to perineural spread of the cancer. For regional failures, 2 failed in CTV1 that received 60 Gy and 66 Gy, respectively. Three failed in contralateral neck, 2 of them failed in CTV2 that received 60 Gy and one out of radiation field. One treatment death occurred in a patient who received postoperative radiation with concurrent chemotherapy. She had cardiac arrest 3 days after treatment completion with suspicion of aspiration. Conclusions: 1. For OCSCC with nerve involvement, the ipsilateral infratemporal fossa needs to be included in the radiation field. 2. The contralateral neck needs to be included particularly in oral tongue cancer. 3. For patients with ECE, postoperative radiation with concurrent chemotherapy is recommended. But such treatment has increases side effects. Excellent supportive care is necessary including airway protection with tracheostomy. Author Disclosure: M. Yao, None; J.E. Bayouth, None; H. Tan, None; J. Wacha, None; K.J. Dornfeld, None; J.M. Buatti, None. 2399 Differential Roles of 18F-FDG PET in Patients With Locoregionally Advanced Nasopharyngeal Carcinoma After Primary Curative Therapy: Response Evaluation and Impact on Management J. Chang, S. Chan, T. Yen, S. Ng, C. Lin, H. Wang, C. Liao Chang Gung Memorial Hospital, Taoyuan 33333, Taiwan Purpose/Objective(s): This prospective study is to compare the efficacy of whole body 18F-fluoro-2-deoxy-D-glucose positron emission tomography (18F-FDG PET) and conventional work-up (CWU) in evaluating treatment response for patients with locoregionally advanced nasopharyngeal carcinoma (NPC) after primary curative therapy and to investigate the impact of PET on patient management. Materials/Methods: Locoregionally advanced NPC patients (Stage III and IVa-b, diagnosed by 18F-FDG PET and CWU) who had completed primary curative therapy for 3 months were enrolled. The curative therapy consisted of concurrent chemora- diotherapy with/without induction chemotherapy. All these patients also received 18F-FDG PET and CWU to evaluate response. The residual criteria were based on pathology and/or subsequent follow-up for at least 6 months. Detection rates between 18F-FDG PET and CWU and impact on management were determined on a site and patient bases, respectively. Results: From January 2002 to August 2005, 131 NPC patients were eligible, including 71 stage III (group A) and 60 stage IVa-b (group B) patients. Twelve patients were proved to have residual tumors. 18F-FDG PET showed a higher sensitivity than CWU in group A (100% vs. 25%) and group B (91.7% vs. 58.3%). The specificity of PET was significantly higher than CWU in group B (97.6% vs. 91.7%, P = 0.019) but slightly lower in group A (95.7% vs. 96.7%). In group B, the overall accuracy of PET was also significantly higher (97.2% vs. 89.4%, P = 0.002) but similar to that in group A (95.8% vs. 95.3%). PET induced management changes in 11 patients (15.4%, 11/71) of group A, with positive and negative impacts on 3 and 8 of patients, respectively. In group B, management of 26 patients (43%, 26/60) was changed due to PET, including positive impacts on 23 patients and negative on 3. Conclusions: Our preliminary data indicate that 18F-FDG PET plays differential roles in stage III and IVa-b NPC patients after primary curative therapy. In stage IVa-b patients, PET demonstrates a higher sensitivity and specificity in evaluating response and positively modify management in 38% (23/60) of them. In stage III patients, the impact of PET is less prominent though it has a higher sensitivity. Author Disclosure: J. Chang, None; S. Chan, None; T. Yen, None; S. Ng, None; C. Lin, None; H. Wang, None; C. Liao, None. S431 Proceedings of the 48th Annual ASTRO Meeting