Different optimizing strategies based on spot scanning carbon ion therapy for non-small cell lung cancer

Abstract

Objective To evaluate the dose variation of target coverage and organs at risk (OARs) among four planning strategies using spot-scanning carbon-ion radiotherapy for non-small cell lung cancer (NSCLC). Methods Ten NSCLC patients utilizing gating motion control were selected to receive dose calculation over multiple acquired 4DCT images. Four optimizing strategies consisted of intensity-modulated carbon-ion therapy (IMCT-NoAS), IMCT combined with internal gross tumor volume (IGTV) assigned muscle (IMCT-ASM), single beam optimization (SBO)(SBO-NoAS) and SBO combined with IGTV assigned muscle (SBO-ASM). The initial plan was re-calculated after the 4DCT data were reviewed and then compared with the initial plan in the dosimetry. Results For re-calculation plans with two reviewing CTs, all four strategies yielded similar planning target volume (PTV) coverage. Merely IMCT-NoAS strategy presented with relatively significant variations in dose distribution. Dose variation for OARs between initial and re-calculated plans: for all four strategies, V20 of ipsilateral lung was increased by approximately 2.0 Gy (relative biological effective dose, RBE), V30 of heart was increased by approximately 1.0 Gy (RBE) for both IGTV assigned muscle strategies, whereas decreased by approximately 0.2 Gy (RBE) for both IGTV non-assigned muscle strategies. The maximum dose of spinal cord was changed by 2.5 Gy (RBE). Conclusions Carbon-ion radiotherapy is sensitive to the anatomic motion within the tumors along the beam path. When the tumor motion along the head-foot (H-F) direction exceeds 8 mm, SBO-ASM strategy provides better dose coverage of target. Strategies with IGTV assignment may result in dose overshoot to a position deeper than the initial planning dose distribution. Key words: Lung neoplasms/intensity-modulated carbon-ion therapy; Single beam optimization; Spot scanning carbon-ion; Plan evaluation