INTRODUCTION  The majority of clinical trials addressing outcomes in limited- stage small cell lung cancer (LS-SCLC) following definitive chemoradiotherapy have relied on 3D conformal radiotherapy (3DCRT) techniques.  Intensity modulated radiotherapy (IMRT) may decrease toxicity or facilitate dose escalation, but clinical data is lacking. RESULTS CONCLUSIONS OBJECTIVE  In our dataset, patients with more advanced stage were more likely to be treated with IMRT than 3DCRT.  Overall survival was significantly worse in the IMRT group, presumably due to higher disease stages represented in this group and unaccounted treatment variables. However, local control was not significantly different between the 3DCRT and IMRT-treated patients.  Despite larger treatment volumes, IMRT was associated with similar dosimetric parameters compared to 3DCRT, except for lower hotspots, higher lung volumes receiving low doses of RT (i.e., lung V5 and V10), and lower heart V30.  The rates of grade 2+ toxicity were comparable for IMRT vs. 3DCRT, except for worse fatigue in the IMRT group. This may be in part due to larger treatment volumes in the IMRT group.  Results from ongoing clinical trials may support dose escalation for LS-SCLC in the future. The enhanced conformality of IMRT may facilitate meeting dose constraints in this setting, and based on our retrospective experience, use of this radiation delivery technique does not appear to result in compromised local tumor control in the thorax. Intensity Modulated versus 3D Conformal Radiation Therapy for Limited Stage-Small Cell Lung Cancer Carmen A. Perez a,1, Amanda McLane a,1, Andreas Rimner a,1, Daphna Y. Gelblum a,1, Richard M. Gewanter a,1, Lee M. Krug b,1, Maria C. Pietanza b,1, Kenneth E. Rosenzweig a,2, Abraham J. Wu a,1 Department of Radiation Oncology a, Thoracic Oncology Service/Department of Medicine b, Mount Sinai School of Medicine 2, Memorial Sloan-Kettering Cancer Center New York, NY 1 To compare disease control outcomes, dosimetric parameters, and toxicity following either 3DCRT- or IMRT-based definitive chemoradiotherapy for LS-SCLC. METHODS I. Outcomes at median follow-up of 20 months p = % 36% 3DCRT N = 72 IMRT N = 77 Total N = 149 Deaths 46 (64%)53 (69%)99 (66%) Distant Failures (DF) 33 (46%)41 (53%)74 (50%) Locoregional Failures (LRF) 15 (21%) 20 (26%)35 (23%) Patient CharacteristicsTotal3DCRTIMRTp value (Pearson Chi- square) MEDICAL HISTORY Age (years)Median [range]64 [43-93]63 [45-84]66 [43-93]0.987 GenderMale43%44%42%0.722 Female57%56%58% Smoking HistoryPositive96%97%95%0.453 Weight loss >10lbYes17%20%16%0.527 KPSMedian [range]80 [60-100] STAGING PETYes93%89%97%0.038 Brain MRI/CTYes97%94%100%0.036 Stage Grouping (AJCC 7 th Ed.)I A2%3%0%<0.001 I B2% 3% II A11%19%6% II B9%11%7% III A54%50%57% III B22%15%27% TREATMENT SurgeryComplete Resection5%7%3%0.210 No/Incomplete95%93%97% Chemotherapy TimingConcurrent80%82%78%0.541 Sequential20%18%22% 4D-CT SimulationYes7% 8%1.000 RT fractionation: BIDBID53%60%47%0.113 Planned dose (cGy)Median [range]4500 [n/a] RT treatment breakYes14%12%17%0.429 RT fractionation: DailyDaily47%40%53%0.113 Planned dose (cGy)Median [range]5400 [ ]5400 [ ]5400 [ ]1.000 RT treatment breakYes23%24%22%0.128 PCIYes48%54%42%0.124 Statistics: Kaplan-Meier methods to estimate survival outcomes; Log-rank test to assess univariate associations; Mann-Whitney U test (nonparametric test) to compare the distribution of dosimetric data Retrospective Study Profile 149 LS-SCLC patients Diagnosed Treated at MSKCC with thoracic RT and platinum-based chemotherapy 72 treated with 3DCRT 70/72 (97%) completed intended RT dose 26/72 (36%) with retrievable dosimetric data 77 treated with IMRT 70/77 (91%) completed intended RT dose 76/77 (99%) with retrievable dosimetric data II. Dosimetric Parameters Stratified by Stage ParameterMean Values (range)p value 3DCRTIMRT Total PTV Volume (cc)520 ( )677 ( )0.053 Relative Dmax116% ( %)110% (97-127%)<0.005 Lung V552% (24-76%)59% (28-80%)0.009 Lung V1041% (21-60%)45% (22-67%)0.019 Lung V2029% (14-44%)30% (14-45%)0.546 Lung V3024% (7-37%)22% (7-32%)0.084 Lung Mean Dose (cGy)1559 ( )1540 ( )0.628 Heart Mean Dose (cGy)1637 ( )1443 ( )0.271 Heart V3027% (0-68%)17% (0-84%)0.031 Esophagus Dmax (cGy)5040 ( )5295 ( )0.094 Spinal Cord Dmax (cGy)3744 ( )3767 ( )0.779 III. Grade 2+ Toxicity 3DCRTIMRT Pneumonitis Esophagitis Fatigue % Incidence 8.8% 7% 34.1% 45.5% 17.1% 35.1% p = p = p = 0.04 IMRT vs. Images courtesy of Margie Hunt p = %, median 40m 45%, median 21m p = 0.499p = 0.062p = % 80% p = 0.118