SU‐E‐T‐471: Potential of Using Simultaneous Integrated Boost (SIB) to Significantly Improve the Normal Tissue Sparing For Advanced Staged Non‐Small Cell Lung Cancer(NSCLC)

Purpose: To investigate advantages of SIB technique using IMPT for advanced stage NSCLCMethod: The 4DCT data sets were randomly selected from 9 patients with stage III NSCLC. The SIB volume (SIBV) was defined as GTV with 3mm expansion to account for uncertainties. PTV was defined as CTV with 5mm expansion. Conventional IMPT plan delivering 74Gy/37Fractions to at least 95% of PTV and IMPT SIB plans delivering 72Gy (BED:89.3Gy), 78Gy (BED:98.3Gy) and 84Gy (BED:107.5Gy) in 30 fractions to at least 95% of SIBV as well as 60 Gy to at least 95% of PTV were designed for each patient using robust optimization. TCP and NTCP were calculated and worst case robustness was analyzed for one patient. Results: The NTCP for lung and esophagus were 0.02 and 0.38 respectively for IMPT SIB 72Gy, 0.1 and 0.32 lower than those for IMPT 74Gy respectively, while TCP of PTV and SIBV are 0.87 and 0.9 for IMPT 74Gy, and 0.89 and 0.9 for IMPT SIB 72Gy respectively. The dose coverage of CTV and GTV in worst scenario was at least 95% of prescribed dose for both IMPT SIB 72Gy and IMPT 74Gy plans. The comparison of IMPT SIB plans showed no significant differences of normal structures sparing at different escalation dose level, such as percentage lung volume received 20Gy (V20, 29%) and mean dose (20Gy), esophagus V60 (16%), and maximum cord dose (36Gy). Our results suggest that dose escalation to SIBV only (TCP of SIBV are 0.9, 0.93 and 0.95 for SIB dose level 72Gy, 78Gy and 84Gy) in IMPT SIB technique will have minimal impact for normal structures sparing. Conclusion: IMPT SIB showed significantly advantages in target dose escalation with minimal impact on normal structures sparing. We are currently testing the impact of IMPT SIB on patient outcome in a prospective trial.