13 - S494 I J Radiation Oncology d Biology d Physics Volume...

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2527 FDG Uptake at Sequential Intervals After Radiotherapy (RT) or RTof Chemo-Radiotherapy (CT+RT) and its Predictive Value for Tumor Control Probability (TCP) of Metastatic Lung Cancer in Regional Lymph Nodes N. C. Choi, T. Chun, M. Ancukiewicz, A. Niemierko, P. Fidias, A. Fischman Massachusetts General Hospital, Boston, MA Purpose/Objective(s): Biomarkers measurable in vivo non-invasively and capable of directing boost dose of radiation to residual cancer in regional lymph nodes is highly desired for individualized radiation dose schedule. Such optimized RT with timely and sensitive biomarker for tumor response, unavailable at this time, is likely to increase the rate of tumor control and survival while treatment related toxicities are reduced. The goals of this study are: (1). To determine FDG (2-±uoro-2-deoxy-D-glucose) uptake at sequential intervals after RT for met- astatic or recurrent lung cancer involving regional lymph nodes, (2). Determine the relationship between residual FDG uptake after RT and clinical outcome at 12 months (m), (3). Determine the levels of residual FDG uptake 10–12 days after RT that correlate with $ 95%, 90%, 50% probability of tumor control at 12 m (TCP-12 m). Materials/Methods: Patients (pts) with inoperable stage I-III lung cancer were enrolled into this prospective study in which 18F- FDG PET was obtained before (S1 [study #1]), 10–12 days (S2 [study #2]), 3 months (m) (S3), 6 m (S4) and 12 m (S5) after RT or RT of CT + RT. We measured FDG uptake with the simpli²ed kinetic method (SKM). The maximal value of FDG uptake measured with SKM was used for correlation with clinical outcome. The relationship between residual FDG uptake at S2–S5 and tumor control probability at 12 m was determined by ²tting the weighted logistic regression model. Results: We have entered 110 pts with stage I-IIIB lung cancer into this prospective study. 28 patients (7 with only metastatic regional nodal disease) with 45 involved regional lymph nodes met the study endpoints and were eligible for the analysis. Thus, 45 regional lymph nodes involved with metastatic lung cancer are the basis for the report. The baseline median value of maximum FDG uptake was 0.21 m mol/min/gm, and it was decreased to 0.10, 0.08, 0.08, and 0.08 m mol/min/gm at S2-5 respectively. FDG uptake for patients with nodal tumor control vs. nodal failure was 0.09 vs. 0.10 ( p = 0.63), 0.07 vs. 0.11 ( p = 0.004), and 0.08 vs. 0.20 ( p = 0.004) m mol/min/gm at S2 to S4 respectively. An inverse dose-response relation- ship was found between residual FDG uptake after RT and the probability of nodal tumor control at 12 m. From this relationship,
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13 - S494 I J Radiation Oncology d Biology d Physics Volume...

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