OPTIMAL STRATEGY FOR PROPHYLACTIC CRANIAL IRRADIATION IN LIMITED STAGE SMALL CELL LUNG CANCER Patricia Tai 1, Avi Assouline 2,3, Kurian Joseph 4, Edward Yu 5 1 Saskatchewan Cancer Agency, Allan Blair Cancer Center, Regina, Canada 2 Service de Radiothérapie, Groupe Hospitalier Pitié Salpêtrière, Paris, France 3 Centre Clinique de la Porte de Saint Cloud, Boulogne-Billancourt, France 4 Dept of Radiotherapy, Cross Cancer Institute, University of Alberta, Canada 5 Dept of Radiotherapy, London Regional Cancer Center, U. of Western ON, Canada RESULTS 289 patients were treated with curative intent, of which 177/289 (61.2%) had PCI. For the whole group of 289 patients, PCI resulted in overall and cause-specific survival (OS and CSS) benefit (P= and , respectively) but not significant for the 93 IR patients (P=0.32 and 0.39). The timing of PCI was before chemotherapy completion in 78 patients versus 99 patients after chemotherapy, which did not significantly affect OS and CSS (P=0.41 and 0.33, respectively). The first site of metastases was in the brain for 12.5% vs 45.5% of complete responders with and without PCI (P=0.02); 6.1% vs 27.6% of incomplete responders with and without PCI (P=0.05), respectively. Medium time to first brain metastatic symptoms was 21.1 vs 12.4 months in complete responders (P<0.0001) and 18.5 vs 8.9 months in incomplete responders (P=0.03) with and without PCI, respectively. MATERIALS AND METHODS From our population-based provincial registry from 1981 through 2007, charts were identified and retrieved for review. Typical chest radiotherapy doses/fractionations were 45 Gy/25f/5 weeks, 50 Gy/25f/5 weeks, or 40 Gy/15f/3 weeks. Typical PCI dose-fractionation were: 2500 cGy/10 fractions/2 weeks, 3000 cGy/15 fractions/3 weeks, or 3000 cGy/10 fractions/2 weeks. PCI was given at different times from the start of chemotherapy. In this study, incomplete response was defined as response less than 100% to chemo- radiation radiologically. BACKGROUND Previous clinical studies often reported on a mixed patient population of limited and extensive stage small cell lung cancer (SCLC). Some gave PCI to complete response (CR) patients only while others gave it to both CR and partial response (PR) patients. It is not clear from the literature if partial responders of limited stage SCLC would benefit from PCI. Purpose: To resolve controversies regarding the optimal timing and case selection for prophylactic cranial irradiation (PCI) in limited stage small cell lung cancer. DISCUSSION PR patients benefit from PCI, in terms of reduced rate and delayed time for development of brain metastases, although without significant OS or CSS benefit in this study. As it is difficult to differentiate CR from PR patients accurately despite modern imaging, the authors recommend PCI to be given to both CR and PR patients. CONCLUSION The timing of PCI with respect to chemotherapy does not significantly affect patient survival. Incomplete responders benefited from PCI, with reduced rate and delayed time for development of brain metastases, although without significant OS or CSS benefit. PCI can be considered for incomplete responders soon after completion of chemo-radiation before brain metastases develop. Table 1. Overall rates of brain recurrence before death Table 2. Overall survival rates Fig.1. Cause-specific survival rate of whole group (289 patients)