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Plan Uncertainty Study: Use of Carbon Ion Beam for Non-Small Cell Lung Cancer

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x liu

x liu*, K Shahnazi , Y Sheng , w wang , W Hsi , Shanghai proton and heavy ion center, Shanghai, shanghai


SU-I-GPD-T-175 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: to evaluate a robust plan for carbon ion therapy (CIT) of non-small cell lung cancer (NSCLC) , and protect the organs at risk (OAR) using 4D CT and gating for motion control.

Methods: particle beam is sensitive to tumor motion, density change, and they can cause target to have under dose or overdose due to irregular motions. Ten lung patients diagnosed with NSCLC were selected, and prescription was for 60Gy (RBE) to clinical target volume (CTV) in 15 fractions. Planning target volume (PTV) is designed based on target motion. Somatom definition AS (Siemens CT) and Syngo® RT Planning VC11B was used for treatment planning. Four optimized methods are: intensity modulated carbon therapy (IMCT); IMCT and assign IGTV to muscle; single beam optimization (SBO); SBO and assign IGTV to muscle. Plans were generated on identical average gating phases. Same gating widow were also acquired for CT reviews, and MIM was used to adaptive re-contour all structures into new CT set. Based on bone registration, plans were recalculated.

Results: typically 99% of PTV volume is covered by 95% of prescription dose for initial plans of four strategies. For the second and third CT, all four strategies have 95% dose coverage for PTV, IMCT with largest variation. The dose for contralateral lung, heart and esophagus change by about 5%, dose for the ipsilateral lung is increased almost 5%, spinal cord maximum dose has largest variation in this study of about 7%.

Conclusion: when tumor motion within 5mm, no obvious difference between four strategies, but when tumor motion larger than 8 mm, with use of SBO and assign IGTV to muscle will help plans to be more robust, Potentially these can cause dose overshoot.

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