Abstract # 2508 Intensity-modulated Radiation Therapy (IMRT) for Non-small Cell Lung Cancer (NSCLC): Treatment Outcomes from a Small, Elderly Cohort

Presenter: Scarbrough, Todd

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See Figure 1 for the overall patient schema (all figures are shown in the attached poster PDF). The 24 patient cohort is the focus of this retrospective analysis. Patient characteristics are shown in Table 1. (Due to a median overall survival followup of only 16 months, we have restricted our estimated survival and failure statements at 2 years.) Patients were treated to a high dose (mean: 71.5 Gy/ 35 fx). All plans were normalized such that 95% of the planning target volume (PTV) received 100% of the prescribed dose, resulting in a mean prescribed isodose line of 94%. All plans were calculated and optimized using tissue inhomogeneity (modified Batho). All plans were performed using the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA; see Figure 2). Inverse optimization was used for every IMRT plan. All patients received pre- and post-treatment PET scans. The primary tumor and involved nodes (as defined by PET and CT) were the clinical target volume (CTV) in all cases. The PTV consisted of the CTV plus an expansion margin of 5–15 mm (mean: 9 mm).

All patients were attempted to be simulated using the Varian RPM gating system. Some patients’ breathing patterns were not amenable to gating; these patients were then attempted to be simulated using a deep inspiratory breath holding (DIBH) technique with verification of reproducibility and maintenance of DIBH using the gating system and surface infrared markers. For patients not candidates for gating or DIBH, simulation was accomplished using a slow-acquisition CT scan during free breathing (FB). There were 7 patients treated using infrared analysis of DIBH or gated breathing and 17 patients treated in FB. Some patients judged not to have significant tumor and/or mediastinal motion with breathing (as visualized on the gated CT simulation scan) were treated in FB.

Beam energy was 6 MV in all cases. For patients treated with DIBH, beam on times were kept to 15 seconds or less. Gating patients were treated in the 40-60% phase (50% correlates to end-expiration by Varian’s RPM convention). Gating/DIBH patients were treated with a 600 MU/min dose rate, FB patients with 300 MU/min dose rate. Kilovoltage X-ray analysis of setup error, with on-line correction of any setup error, was employed for every fraction of treatment using the Varian On-board Imager. Sliding window IMRT was used for every treatment. Concurrent chemotherapy was carboplatin (AUC = 2) and paclitaxel (50-80 mg/m2) weekly for all patients. All patients received amifostine 500 mg SQ (as tolerated) ~30 min prior to every RT fraction.

Kaplan-Meier overall survival (OS) and freedom from progression (FFP) curves were compared using the Mantel-Cox logrank test (the Cox F-test was used for situations in which there were no uncensored observations). FFP was defined as a lack of any locoregional thoracic progression on CT or PET. Survival was calculated from date of diagnosis. FFP was calculated from date of chemoradiation completion. Cox proportional hazard modeling was used for univariate/multivariate analysis.

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