In silico comparison of photons versus carbon ions in single fraction therapy of lung cancer.

Purpose: Stereotactic body image guided radiation therapy (SBRT) shows good results for lung cancer treatment. Better normal tissue sparing might be achieved with scanned carbon ion therapy (PT). Therefore an in silico trial was conducted to find potential advantages of and patients suited for PT.

Methods: For 19 patients treated with SBRT, PT plans were calculated on 4D-CTs with simulated breathing motion. Prescribed single fraction dose was 24Gy and OAR constraints used for photon planning were respected. Motion was mitigated by rescanning and range-adapted ITVs. Doses were compared to the original SBRT plans.

Results: CTV coverage was the same in SBRT and PT. The field-specific PTV including range margins for PT was 1.5 (median, 25-75% 1.3-2.1) times larger than for SBRT. Nevertheless, maximum point dose and mean dose in OARs were higher in SBRT by 2.8 (1.6-3.7) Gy and 0.7 (0.3-1.6) Gy, respectively. Patients with a CTV >2.5cc or with multiple lung lesions showed larger differences in OAR doses in favor of PT.

Conclusions: Patients receive less dose in critical OARs such as heart, spinal cord, esophagus, trachea and aorta with PT, while maintaining the same target coverage. Patients with multiple or larger lesions are particularly suited for PT.