High-dose hypofractionated pencil beam scanning carbon ion radiotherapy for lung tumors: Dosimetric impact of different spot sizes and robustness to interfractional uncertainties

PurposeThe robustness against setup and motion uncertainties of gated four-dimensional restricted robust optimization (4DRRO) was investigated for hypofractionated carbon ion radiotherapy (CIRT) lung tumors.MethodsCIRT plans 9 patients were optimized using 4DRRO strategy with 3 mm errors, 3% density errors breathing phases related to the gate window. The prescription 60 Gy(RBE) in 4 fractions. Standard spots (SS) compared big (BS). Plans recalculated on multiple 4DCTs acquired within weeks from treatment simulation rigidly registered planning images bone matching. Warped dose distributions generated deformable image registration accumulated 4DCTs. Target coverage (D98%, D95% V95%) evaluated distributions.ResultsComparable target obtained both spot sizes (p = 0.53 D95%). mean increased 0.6 BS 0.0078), still respecting constraint a 4-fraction stereotactic risk radiation pneumonitis. Statistically significant differences found 0.048 p 0.024), showing be more robust. Using BS, average degradations D98%, V95% doses −2.7%, −1.6% −1.5%.ConclusionsGated highly uncertainties. healthy tissues but than SS. selected settings guaranteed adequate during simulated course acceptable toxicity.