S512 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010

Author Disclosure: M.A. Henderson, None; M.J. Stephens, None; D.J. Hoopes, None; C.T. Yiannoutsos, None; A.J. Fakiris, None;R.C. McGarry, None; J.W. Fletcher, None; R.D. Timmerman, None.

2688 PET/CT Simulation Driven Changes in Treatment Intent in Lung Cancer Patients Previously Staged

with PET/CT

G. A. Geiger, R. Rengan, S. Both, J. P. Plastaras

University of Pennsylvania, Philadelphia, PA

Purpose/Objective(s): PET/CT scanning is becoming increasingly prevalent for treatment planning in patients with non-small cell lung cancer (NSCLC) and dedicated PET/CT units are appearing in many radiation oncology departments.However, the vast majority of PET/CT treatment planning is performed with fusion of previously obtained PET orPET/CT scans and the interval between the acquisition of these scans and simulation CTs can vary from weeks to months.This investigation was performed to determine whether appropriately staged patients undergoing PET/CT simulations ona hybrid unit had either staging or treatment intent changes despite having PET/CT scans performed within the prior threemonths.

Materials/Methods: Fifty-four patients were simulated on a dedicated PET/CT scanner between 4/29/09-2/28/10 with the in-tent of treating non-metastatic NSCLC. All included patients had accompanying diagnostic nuclear medicine interpretations. Ofthese, 30 patients had previous PET/CTs in the three months immediately preceding their simulation and all had been appro-priately staged without any evidence of distant metastatic disease. Patients were analyzed for change in stage and/or treatmentintent with specific attention to the proximity of previous appropriate staging PET/CT scans. AJCC 2002 staging was used forall patients.

Results: A total of 30 patients were eligible for inclusion, of which 17 were males and 13 were females. The median agewas 70. Overall, 12 of 30 patients (40%) were found to have new nodal or metastatic disease. Of these, 8 (27%) hadevidence of metastatic disease with the remaining 4 (13%) diagnosed with nodal disease requiring substantial alterationof treatment fields (i.e., new N2 or N3 disease). Six patients (20%) were not treated with radiation and received systemictherapy alone. Two patients with oligometastatic disease were treated with definitive chemoradiation. The median intervalbetween PET/CT scans was 1.9 months in all patients and 1.5 months in patients found to have new nodal or metastaticdisease.

Conclusions: Radiation treatment planning with hybrid PET-CT scans repeated within 3 months of an initial staging PET/CTresulted in the identification of significant new findings that altered treatment intent. This study supports the notion that longerdurations between staging PET/CT and PET/CT treatment planning scans may be inadequate and diagnostic PET/CT scans shouldbe obtained as close to the initiation of treatment as possible in NSCLC.

Author Disclosure: G.A. Geiger, None; R. Rengan, None; S. Both, None; J.P. Plastaras, None.

2689 Substantial Dose is Incidentally Delivered to Mediastinal and Hilar Nodes during Stereotactic Body

Radiation Therapy for Peripheral NSCLCA

K. L. Martin, J. Gomez, D. P. Nazareth, G. W. Warren, A. K. Singh

Roswell Park Cancer Institute, Buffalo, NY

Purpose/Objective(s): To determine the amount of incidental radiation dose received by mediastinal and hilar nodes for patientswith non-small cell lung cancer (NSCLC) treated with stereotactic body radiation therapy (SBRT).

Materials/Methods: Fifty consecutive patients with NSCLC, treated using SBRT, were identified. Of these, 38 had a prescriptiondose of 60 Gy in 20 Gy fractions and were eligible for analysis. For each patient, upper (level 2) and lower (level 4) paratracheal,and hilar (level 10) nodal regions were contoured on the planning CT images. Using the clinical treatment plan, dose and volumecalculations were performed retrospectively for each nodal region.

Results: Lymph node dose was related to the location of the tumor. For all patients, the hilar lymph nodes received mean doses of18.55 Gy and maximum point dose of 69.1 Gy. The left and right lower paratracheal nodes received mean doses of 6.84 Gy andmaximum point dose of 17.3 Gy.

Conclusions: Considerable incidental dose to mediastinal and hilar lymph nodes is delivered during SBRT. This incidental dose tothe lymph nodes is considerable enough to have therapeutic effect on subclinical disease.

Author Disclosure: K.L. Martin, None; J. Gomez, None; D.P. Nazareth, None; G.W. Warren, None; A.K. Singh, None.

2690 Stereotactic Lung Radiotherapy (SBRT) Associated with Improved Local Control Compared to

3-dimensional Conformal Radiotherapy (3DCRT) for Stage I Non-small Cell Lung Cancer (NSCLC)

M. Mislmani, I. S. Grills, J. M. Robertson, H. Ye, E. McInerney, S. Martin, L. L. Kestin

William Beaumont Hospital, Royal Oak, MI

Purpose/Objective(s): To compare lung SBRT with standard fractionated 3DCRT for treatment of early-stage NSCLC in terms oflocal control, overall survival, and associated toxicities.

Materials/Methods: One hundred thirty-five patients (136 lesions) with stage I NSCLC comprised two treatment modalitygroups; the 3DCRT group had 54 patients, consisting of T1N0M0: 65% and T2N0M0: 35%. The SBRT group had 81patients (82 primary lesions) consisting of T1N0M0: 70% and T2N0M0: 30%. The median patient ages were 76y, 75y

Proceedings of the 52nd Annual ASTRO Meeting S513

for SBRT, 3DCRT respectively; 57% were women for SBRT while 61% were women for 3DCRT (p = NS). More AfricanAmericans had SBRT (15% v 5%, p\0.01). All patients were medically inoperable. Median percentage predicted DLCOwas 53% and 42% (p\0.01) for 3DCRT and SBRT, respectively. There were no differences in percentage predicted FEV1between groups (62% SBRT v 59% 3DCRT). Although overall T-stages were similar between groups, 3DCRT patients hadlarger tumors with a median size of 2.7cm for SBRT v 3.6 for 3DCRT (p\0.01). The median dose for 3DCRT was 70 Gyin 35 fractions (54-79.2 Gy), and for SBRT was 48 Gy in 4 fractions (40-60 Gy). Follow-up was $2y in both groups.

Results: With a mean follow-up of 1.57 years, SBRT had a significantly lower rate of local recurrence (LR) at 2 years, 8%,compared to 21% with 3DCRT (p = 0.02). No statistically significant differences were identified, however, in the rates ofregional recurrence (RR) 12% SBRT v 9% 3DCRT (p = NS) or distant metastasis (DM) 19% in both groups. Disease-freesurvival was also similar in both groups, 49% in each. Although overall survival (OS) and cause-specific survival (CSS)were somewhat higher in the SBRT group, these differences did not reach statistical significance in this patient dataset. 2yOS was 65% after SBRT v 54% after 3DCRT (p = NS); 2y CSS was 91% after SBRT and 80% after 3DCRT (p = NS).The only statistically significant difference in treatment-related toxicity between the two groups was a higher rate of $ grade2 dermatitis after 3DCRT (11% v 1%, p = 0.02). Otherwise, the rates of $ grade 2 pneumonitis (6% SBRT v 5% 3DCRT),acute esophagitis (0% v 2%), chronic myositis (5% v 2%) and rib fracture (5% v 0%) were statistically similar. For all patients,no statistically significant predictor of LR could be identified other than 3DCRT. Only gender (Male) predicted RR (p\0.01) orDFS (p = 0.02).

Conclusions: In this dataset, online image-guided SBRT was associated with superior local control versus standard fractionation3DCRT for stage I NSCLC, but not a significant improvement in survival. Toxicity profiles were similar between the two groups.These findings support the continued use of hypofractionated SBRT.

Author Disclosure: M. Mislmani, None; I.S. Grills, None; J.M. Robertson, None; H. Ye, None; E. McInerney, None; S. Martin,None; L.L. Kestin, None.

2691 Prediction of Radiation-induced Pulmonary Function Loss in Post-operative Radiotherapy for Non-small

Cell Lung Cancer Using a Fibrosis Volume Model

O. Noh, H. Jang, Y. Oh, K. Park, K. Park, M. Kim, M. Chun

Ajou University Hospital, Suwon 433-721, Republic of Korea

Purpose/Objective(s): To evaluate radiation-induced pulmonary function loss in post-operative radiotherapy (PORT) for non-small cell lung cancer (NSCLC) using the volume of radiation-induced pulmonary fibrosis.

Materials/Methods: Patients with NSCLC who were treated with PORT were enrolled in this investigation. Pulmonary functiontests (PFTs) were determined pre-operatively, pre-PORT, and . 6 months after PORT. Pre-PORT PFTs were also estimated frompreoperative PFTs using a quantitative CT method. The volume of radiation-induced pulmonary fibrosis (Vf) was evaluated onchest CT scan . 6 months after the completion of PORT. The correlations among the dosimetric parameters of the lung, Vf,and radiation-induced pulmonary function loss were analyzed.

Results: Between January 2003 and January 2007, 48 patients were treated with conformal radiotherapy. The mean values ofFEV1 were 2.16 L pre-operatively, 1.65 L pre-PORT; 1.61 L estimated pre-operatively, and 1.59 L during follow-up PFTs.PORT showed no additional decline in FEV1 (estimated pre-PORT FEV1 vs. follow-up FEV1 [1.63 L vs. 1.59 L]; p = 0.48).The radiation-induced pulmonary function loss was well-correlated with the dosimetric parameters (V25; r = -0.734; p \ .01),as well as the Vf (r = -0.695; p \ .01).

Conclusions: The degree of radiation-induced pulmonary function loss can be predicted by the dosimetric parameters of the lung inpatients with NSCLC who underwent surgical resection followed by PORT. Radiation-induced fibrosis volume can be used asa quantitative imaging marker in assessment of radiation-induced pulmonary injury.

Author Disclosure: O. Noh, None; H. Jang, None; Y. Oh, None; K. Park, None; K. Park, None; M. Kim, None; M. Chun, None.

2692 Heterogeneity Corrections Alters the Delivered Dose, Potentially Impacting Complications in Patients

Treated with Stereotactic Body Radiotherapy (SBRT) of the Lung

C. E. Rutter1, S. A. Naqvi1, B. Zhang2, K. Marter2, M. Koshy1, A. Dhople1, S. J. Feigenberg1, W. D. D’Souza1

1University of Maryland, School of Medicine, Baltimore, MD, 2University of Maryland Medical Center, Baltimore, MD

Purpose/Objective(s): SBRT using heterogeneity corrections is not widely used in North America, but may have an impact oncomplications and local control on tumors treated in the lung. This study evaluated the impact of patient and tumor related factorson dose to the tumor and surrounding normal structures with and without heterogeneity correction.

Materials/Methods: Fifty-one consecutive patients treated with SBRT for malignant lung tumors between September2005 and December 2008 were examined. SBRT treatments were delivered using RTOG 0236 guidelines, withoutheterogeneity corrections. Using the same beam arrangement and monitor units used for the actual treatment, thedose distributions were recomputed using heterogeneity correction. Dose-volume histograms were generated for the in-ternal target volume (ITV) with and without heterogeneity corrections. The percent differences in dose to 5% (hot spot),50%, and 95% of the ITV (D5, D50, D95) between homogenous dose calculation and heterogeneity correction werecomputed. Correlation analysis and independent samples t-tests were used to identify significant differences in thesestatistics based on tumor distance from the chest wall, lobe involved, ITV volume, GTV volume and the body massindex (BMI).

Results: On average, the use of heterogeneity correction resulted in increases in D95 (3.8%; range -7.7% to 11.2%), D50 (7.0%;range -3.0% to 15.3%), and D5 (8.7%; range -14.4% to 17.6%). Tumors greater than one centimeter away from the chest wallwere associated with a significantly larger increase in D5 (10.1% vs. 7.4%, p = 0.046). The magnitude of increase in D95 wascorrelated to ITV volume (R = 0.277, p = 0.049). ITV volume greater than the median value (13.9 cm3) resulted in a larger increase