ESTRO 38 Abstract book

S645 ESTRO 38

D.Y. Kim 1 , D.S. Heo 2 , B. Keam 2 , S. Ahn 3 , J. Kim 4 , K.C. Jung 5 , J.H. Kim 1,6,7 , H. Wu 1,6,7 1 Seoul National University College of Medicine, Radiation Oncology, Seoul, Korea Republic of ; 2 Seoul National University College of Medicine, Internal Medicine, Seoul, Korea Republic of ; 3 Seoul National University College of Medicine, Otorhinolaryngology, Seoul, Korea Republic of ; 4 Seoul National University College of Medicine, Radiology, Seoul, Korea Republic of ; 5 Seoul National University College of Medicine, Pathology, Seoul, Korea Republic of ; 6 Seoul National University, Cancer Research Institute, Seoul, Korea Republic of ; 7 Seoul National University, Institute of Radiation Medicine- Medical Research Center, Seoul, Korea Republic of Purpose or Objective To analyze the clinical outcomes in patients with metastatic carcinoma of cervical lymph nodes from an unknown primary (MUO) according to the radiation target volume, and suggest an optimal radiation field Material and Methods A total of 62 patients with MUO at Seoul National University Hospital between 1998 and 2016 were reviewed. We compared the overall survival (OS), locoregional recurrence (LRR) and primary site failure depending on radiation target volume. The target volume was classified according to whether the head and neck mucosal sites were included and whether the neck node was treated unilaterally or bilaterally. Results Median follow-up time was 44.1 months. 37.1 % (n=23) of patients received mucosa RT and 62.9% (n=39) didn’t. Mucosa RT showed no significant effect on OS and LRR. Though mucosa RT had borderline significance with primary site failure, only 4 patients (10.3%) who had not treated mucosa developed a subsequent mucosal head and neck carcinoma. Moreover, the location of primary site failure was found to be unpredictable and 75% of recurred patients received successful salvage therapies. When analyzing the unilateral (n=35) or bilateral neck irradiation (n=21), there were no significant differences in OS and LRR between the two radiation fields. When treated bilaterally, there were 2 patients who recurred at ipsilateral in-field and 1 patient found out recurrence at contralateral neck. In case of the unilateral irradiation, there were 4 recurrences at ipsilateral in-field and 2 cases at ipsilateral out-field, especially neck node level I. In addition, when treated both neck, more mucositis occurred significantly. Conclusion We found that there were no benefits in OS and LRR in patients with MUO when treating head and neck mucosal sites and bilateral neck node in radiation target volume. Primary site failure was hard to predict and salvage therapy could be performed in case of incidence of subsequent mucosal carcinoma. EP-1166 Optimal timing for salvage surgery after definitive radiotherapy in hypopharyngeal cancer. S. Chun 1 , B. Keam 2 , D.S. Heo 2 , K.H. Kim 3 , M. Sung 4 , E. Chung 4 , J. Kim 5 , K.C. Jung 6 , J.H. Kim 1 , H. Wu 1 1 Seoul National University Hospital, Department of Radiation Oncology, Seoul, Korea Republic of ; 2 Seoul National University Hospital, Department of Internal Medicine, Seoul, Korea Republic of ; 3 Bundang Jesaeng Hospital, Department of Otorhinolaryngology, Seongnam, Korea Republic of ; 4 Seoul National University Hospital, Department of Otorhinolaryngology, Seoul, Korea Republic of ; 5 Seoul National University Hospital, Department of Radiology, Seoul, Korea Republic of ; 6 Seoul National University Hospital, Department of Pathology, Seoul, Korea Republic of

oral mucositis and hypothyroidism were identified through a systematic literature review. The NTCP for these endpoints was estimated in a cohort of 33 OPC patients, of which 19 had HPV p16-positive tumors. NTCP estimates were based on delivered photon intensity-modulated radiation therapy (IMRT) plans, and comparative intensity- modulated PT (IMPT) plans generated from clinical protocols in a collaborating PT center. Equal target coverage and robustness optimization was used in PT plans to account for setup uncertainty. Latencies and durations of complications were modeled based on NTCP estimates while accounting for OPC-specific age-, sex-, and smoking status-adjusted conditional survival probability. The quality-adjusted life years (QALYs) lost attributable to each treatment complication were then calculated by assigning quality-adjustment factors based on severity of complications. Monte Carlo sampling 10,000 times for each patient case was done to account for the uncertainty in underlying modeling parameters and quality- adjustment factors. Results Mean age was 61y, 73% were male, 61% had stage IV disease and 70% had >10 pack-year smoking history. For all patients the average QALYs lost from all modeled complications were 1.52 with IMRT and 1.15 with IMPT, with average 0.37 QALYs spared with PT. The estimated QALYs spared varied considerably between patients and was significantly greater for patients with p16-positive tumors (0.45 vs. 0.25 QALYs, p=0.004). Estimated QALYs lost from each complication are shown in the figure for patients with p16-positive tumors, illustrating how long- term complications dysphagia and xerostomia dominate the QoL burden. The table shows estimated QALYs spared with PT for different levels of dose de-escalation to the primary disease for p16-positive tumors, assuming that treatment efficacy remains at the lower dose levels. The combination of dose de-escalation and IMPT results in the lowest estimated QALYs lost.

Conclusion The estimated QALYs spared with PT varies greatly even among p16-positive oropharyngeal cancer patients and identifying those who would benefit most using this data- driven approach could improve resource allocation and patient selection for PT. Since PT delivered with dose de- escalation protocols is estimated to have the least QoL burden it is imperative that this be tested prospectively, especially in regards to treatment efficacy. EP-1165 Failure Patterns of Cervical Lymph Nodes in Metastases of Unknown Primary according to Target Volume