S462 I. J. Radiation Oncology d Biology d Physics Volume 72, Number 1, Supplement, 2008

Materials/Methods: Twenty consecutive L-SCLC patients treated from April 2006 to March 2008 at the H. Lee Moffitt CancerCenter with definitive intent were retrospectively analyzed. The prescription dose was 4,500 cGy in traditional BID fractionation.Two patients who did not undergo a staging PET/CT were excluded from analysis. Four additional patients who presented withperipheral tumors involving only hilar nodes were also excluded, leaving 14 patients in the present analysis. Tumor volumeswere contoured using a combination of PET/CT and CT data. For dosimetric analysis, bilateral supraclavicular, mediastinal andhilar nodal stations were contoured on the planning CT as per previously-published guidelines.1 For each patient, every nodal sta-tion was classified into one of four bins: treated nodes (ITV encompassed all or part of the nodal station); 1 echelon away; .1echelon away within the mediastinum; or untreated contralateral hilum/supraclavicular fossae. The minimum, maximum, andmean doses were recorded for each nodal station in every patient. Pair wise t-tests were performed to compare the doses of thetreated nodal bin to those of the other three nodal bins.

Results: For the ‘‘1 echelon away’’ nodal bin, the maximum dose was statistically equivalent to the treated nodes (p = 0.58). Themean dose was statistically lower (p\0.01), at 2,997 cGy. Maximum dose to the remaining nodes within the mediastinum (3188cGy) was statistically significantly lower (p\0.01). The mean dose to the contralateral hilum and supraclavicular fossae was 395cGy.

Conclusions: For limited-stage SCLC patients with bulky mediastinal disease, incidental radiation dose to uninvolved mediastinalnodes is not necessarily insignificant. By using improved imaging techniques, dose can be tailored to areas of gross disease, sparingregions uninvolved by tumor. With smaller treatment fields, patient morbidity might be lessened, even when allowing for furtherdose escalation in these patients, 36% of whom fail locally.2

References:1. Chapet O, Kong FM, Quint LE, et al., Int J Radiat Oncol Biol Phys 2005;63(1):170–178.2. Turrisi AT, Kim K, Blum R, et al., New Engl J Med 1999;340:265.

Author Disclosure: I.M. Ahmed, None; M. DeMarco, None; C.W. Stevens, None; T.J. Dilling, None.

2655 Metabolic Tumor Volume Predicts Overall Survival in Lung Cancer Patients Treated Definitively

P. Lee1, J. G. Bazan1, D. K. Weerasuriya1, P. W. Lavori2, A. Quon3, Q. Le1, B. W. Loo, Jr.,1

1Stanford University, Department of Radiation Oncology, Stanford, CA, 2Stanford University, Department of Health Researchand Policy, Stanford, CA, 3Stanford University, Division of Nuclear Medicine, Stanford, CA

Purpose/Objective(s): In lung cancer, stage has classically been the most important prognostic factor for disease progression andsurvival. However, stage may be simply a surrogate for underlying tumor burden. The purpose of this study was to assess the prog-nostic value of pre-treatment tumor volume as measured by FDG-PET imaging with a focus on lung cancers treated with a definitiveintent.

Materials/Methods: Between January 2003 and June 2005, 325 patients with lung cancer were evaluated at our institution withdiagnostic PET-CT scans; of these 66 had an initial staging PET-CT scan performed prior to initiation of therapy (surgery, chemo-radiotherapy, or chemotherapy). 64 of 66 patients had follow-up and formed the cohort of this study (61 NSCLC, 3 SCLC). Of the64 patients, 41 patients (39 NSCLC, 2 SCLC) were treated with definitive intent. Follow-up was complete to the time of progres-sion for 45 of 64 patients (23 of 41 in the definitive subgroup), and to the time of death for 42 of 64 patients (20 of 41 in the definitivesubgroup). The median follow-up was 18.2 months overall, and 24.5 months for the subgroup treated definitively. We used customsoftware to segment metabolically active tumor regions semi-automatically on PET scans. We determined the relationship betweentime to progression (TTP) and overall survival (OS) and MTV, defined as the total volume of the metabolically active region mea-sured in mL. Other prognostic factors evaluated were stage, treatment intent, age, Karnofsky performance status (KPS), and weightloss.

Results: The median TTP for the cohort was 9.5 months, and the 6 month freedom from progression (FFP) was 70%, and for thedefinitive subgroup 19.1 months and 88%, respectively. The median OS for the cohort was 18.9 months with a 6 month OS of 78%,and for the definitive subgroup was 37.8 months and 90%, respectively. The median MTV was 29.9 mL (range, 0.5 - 545.3 mL)overall, and 14.1 mL (range, 0.5 - 297.4 mL) for the definitive subgroup. In the definitive intent subgroup, on multivariate Coxproportional hazards regression analysis, an increase in MTV of 41 mL (the difference between the 75th and 25th percentiles)was associated with a 33% increase in hazard of progression (hazard ratio 1.33), with a p value of 0.062 after adjusting for stage,age, KPS, and weight loss. Similarly, an increase in MTV of 41 mL was associated with a 48% increase in the hazard of death (HR1.48), with an adjusted p value of 0.032.

Conclusions: High tumor burden assessed by PET MTV is a poor prognostic feature in lung cancer in general as well as in patientstreated definitively independent of classic prognostic variables. This may be a promising tool for stratifying patients for risk-adap-ted therapies. These results will need to be validated in larger cohorts with longer follow-up, as well as evaluated prospectively.

Author Disclosure: P. Lee, None; J.G. Bazan, None; D.K. Weerasuriya, None; P.W. Lavori, None; A. Quon, None; Q. Le, None;B.W. Loo Jr., None.

2656 The Prognostic Value of 18F-FDG Uptake by using Serial PET/CT in Patients with Local Advanced

Non-small Cell Lung Cancer

X. Xu1, J. Yu1, L. Kong1, X. Sun1, G. Yang2, Z. Fu2, A. Han2, J. Zheng2

1Departments of Radiation Oncology, Shandong Cancer Hospital and Institute, Jinan, China, 2Departments of NuclearMedicine, Shandong Cancer Hospital and Institute, Jinan, China

Purpose/Objective(s): To determine the prognostic value of standardized uptake value (SUV) of F-18 fluorodeoxyglucose(18F-FDG) by serial positron emission tomography and computed tomography (PET/CT) in NSCLC.