First Dosimetric and Biological Verification for Spot-Scanning Hadron Arc Radiation Therapy With Carbon Ions

Spot-scanning hadron arc radiation therapy (SHArc) is a novel delivery technique for ion beams with potentially improved dose conformity and dose-averaged linear energy transfer (LET_d) redistribution. The first dosimetric validation and in vitro verification of carbon ion arc delivery is presented.

Intensity-modulated particle therapy (IMPT) and SHArc plans were designed to deliver homogeneous physical dose or biological dose in a cylindrical polymethyl methacrylate (PMMA) phantom. Additional IMPT carbon plans were optimized for testing different LET_d-boosting strategies. Verifications of planned doses were performed with an ionization chamber, and a clonogenic survival assay was conducted using A549 cancer lung cell line. Radiation-induced nuclear 53BP1 foci were assessed to evaluate the cellular response in both normoxic and hypoxic conditions.

Dosimetric measurements and clonogenic assay results showed a good agreement with planned dose and survival distributions. Measured survival fractions and foci confirmed carbon ions SHArc as a potential modality to overcome hypoxia-induced radioresistance. LET_d-boosted IMPT plans reached similar LET_d in the target as in SHArc plans, promising similar features against hypoxia but at the cost of an increased entrance dose. SHArc resulted, however, in a lower dose bath but in a larger volume around the target.

The first proof-of-principle of carbon ions SHArc delivery was performed, and experimental evidence suggests this novel modality as an attractive approach for treating hypoxic tumors.