S500 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010

had a decreased risk of DM (HR 0.762; p\0.01). Multivariate analysis was carried out for RFS and only stage (HR 3.4; p\0.01)and pre trt SUV (HR 1.09; p = 0.032) remained statistically significant. Pts who developed relapse (n = 22) had a median SUV onpre trt scan of 7.65 vs. 4.15 for patients without relapse. Median time between baseline PET and start of SBRT was 22.5 days(range, 8-204). No correlation was found between PET timing and outcomes.

Conclusions: This study found that FDG PET and in particular pre trt SUVmax has a role in predicting risk of relapse followingSBRT in NSCLC. How inoperable early stage NSCLC pts with high SUV values should best be managed is yet to be determinedbut this may have implications for adjuvant trt.

Author Disclosure: K.L. Clarke, None; M. Taremi, None; M. Freeman, None; S. Fung, None; M. Dahele, None; A. Bezjak, None;A. Brade, None; J. Cho, None; A. Hope, None; A. Sun, None.

2662 Diagnostic Ability of Dual-time-point FDG PET/CT for Mediastinal Lymph Node Metastases in Non-small

Cell Lung Cancer Patients

M. Hu, J. Yu, L. Xing, A. Han, L. Kong

Shangdong Cancer Hospital and Institute, Jinan, China

Purpose/Objective(s): The purpose of this study was to determine the diagnostic ability of dual-time-point 18F-fluorodeoxyglu-cose positron emission tomography / computed tomography (FDG PET/CT) for mediastinal lymph node (LN) metastases inpatients with non-small cell lung cancer (NSCLC) and to assess the contribution for dual-time-point FDG PET/CT in NSCLCpatients and coexisting inflammatory lung disease.

Materials/Methods: One hundred two patients with NSCLC were examined. All patients were classified into two groups: Group 1(patients with pulmonary complications) and Group 2 (patients without pulmonary complications). FDG PET/CT imaging (wholebody) was performed at 1-h (early) post-FDG injection and repeated 2 h (delayed) after injection of 18F-fluorodeoxyglucose (FDG)in the thoracic area. The results of lymph node detection by single-time-point and dual-time FDG PET/CT imaging were evaluatedby comparing the results with the histopathological diagnoses.

Results: Four hundred twenty-seven mediastinal LN stations were resected and histologically examined. Ninety-four stations wereshown to be positive for malignancy. In Group 1, sensitivity, specificity, accuracy, PPV and NPV for detection of LN metastases onsingle-time-point FDG PET/CT were 67.4%, 75.0%, 73.3%, 43.7% and 88.9%, respectively, compared with 84.4%, 85.6%, 85.4%,62.9% and 95.1% on dual-time-point imaging (p = 0.051, 0.017, 0.002, 0.027, 0.053, respectively). The sensitivity, specificity, ac-curacy, PPV and NPV for detection of LN metastases on single-time-point FDG PET/CT were 81.3%, 89.0%, 87.3%, 67.2%, and94.5%, respectively. Those values on dual-time-point FDG PET/CT were 87.5%, 94.2%, 92.8%, 80.8% and 96.4%, respectively.The p values were 0.399, 0.081, 0.057, 0.108 and 0.387 after comparing these indexes between these two imaging, respectively.

Conclusions: Dual-time-point PET/CT imaging has advantages in the diagnosis of metastasis of mediastinal lymph nodes inNSCLC patients compared with single-time-point imaging and was more meaningful for patients with complications whose resultsfrom single-time-point imaging are positive.

Author Disclosure: M. Hu, None; J. Yu, None; L. Xing, None; A. Han, None; L. Kong, None.

2663 Definitive Radiotherapy for New Primary Tumors in the Lung: The Benefit of the Doubt

J. C. Jones, N. Trakul, W. Hara, J. A. Abelson, P. Maxim, S. Dieterich, Q. Le, M. Diehn, B. W. Loo

Stanford University Cancer Center, Palo Alto, CA

Purpose/Objective(s): As patients live longer with cancer, it is becoming more common for patients to present with a lung tumorthat could represent either a new primary malignancy or metastatic disease. The appropriate management of patients with synchro-nous lung tumors or with a new lung tumor in the setting of a previously treated malignancy is not well defined. Although definitivetreatment is generally reserved for early stage disease, diagnostic uncertainty leads to the consideration of definitive local treatmentapproaches, despite the possibility of systemic disease progression. We reviewed the outcomes of 20 patients with new primaryearly stage NSCLC versus metastatic disease who were given ‘the benefit of the doubt’ and treated definitively with stereotacticablative radiotherapy (SART).

Materials/Methods: A retrospective review of patients treated at Stanford University between 2006 and February 2010 identified20 patients (63-80 years old), who presented either with a new lung tumor after definitive treatment for a prior cancer or withsynchronous new lung tumors, and who were treated with definitive SART for the new T1-T2 NSCLC tumor sites. The patientswere considered poor surgical candidates or declined surgical treatment for these tumors. All patients had biopsy proven NSCLCwithout simultaneous extrapulmonary sites of disease. Most tumors were treated with either 50 Gy in 4 fractions or 25 Gy in 1fraction. In these 20 treatment courses, 32 tumors, including 11 synchronous pairs of tumors, were treated.

Results: The mean follow-up time was 13.2 months (median 11.2 months, range 2-26 months). The local control rate for thesetumor sites was 100%, and the overall survival (OS) by Kaplan-Meier analysis was 94% at 6 months and 87% at 2 years.Disease-free survival (DFS) was 89% at 6 months, 81% at 1 year, and 71% at 2 years. Three of four patients who developed met-astatic disease developed extrapulmonary sites of disease within one year. Antecedent advanced stage malignancy was associatedwith poorer DFS and OS after treatment. Patients with a history of stage III/IV disease were more likely to develop metastatic dis-ease than those with a history of stage I/II malignancy prior to the ‘new’ primary NSCLC (hazard ratio 16.8, p\0.001).

Conclusions: When evaluating patients with lung tumors in the setting of prior malignancies or synchronous tumors, it is oftendifficult to distinguish a new primary carcinoma from a metastatic lesion. Our results demonstrate that ‘the benefit of the doubt’may be warranted when considering treatment options, and further study is needed. Our outcomes for patients treated with SARTfor new primary lung tumors are similar to the outcomes reported for patients treated with surgical resection of second primary lungtumors, even when the possibility of metastatic origin of the new tumor cannot be excluded.

Author Disclosure: J.C. Jones, None; N. Trakul, None; W. Hara, None; J.A. Abelson, None; P. Maxim, None; S. Dieterich, None;Q. Le, None; M. Diehn, None; B.W. Loo, None.