Evaluation of using the Doppler shift effect of prompt gamma for measuring the carbon ion range in vivo for heterogeneous phantoms

Carbon ion therapy is an advanced radiation treatment modality considering its distinct dose distribution and high biological effectiveness. However, carbon ion therapy has become more sensitive to the range uncertainty comparing to the traditional x-ray radiotherapy because of its steep dose distribution near the Bragg peak, which makes the benefits not been fully utilized. Prompt gamma (PG) spectroscopy is one of the potential choices to achieve the range verification in carbon ion therapy. In this paper, we describe that the Doppler shift effect causes the energy shift of PG (4.44 MeV) produced by the de-excitation of the flying ¹²C*, which makes PG spectroscopy an alternative method for range verification. In order to prove its feasibility of applying this method during patient treatment, Monte Carlo simulation and analytical calculation are compared to verify the accuracy with different materials and non-uniform geometry model. The proposed method is applied to range measurement in the homogeneous phantom filled with different materials (polyethylene, water, and adipose) and the Chinese hybrid radiation phantom with two different irradiated positions (chest and abdomen). Results show that the difference value is less than 2.1% for three homogeneous phantoms. Moreover, good conformance is obtained when using the Chinese hybrid radiation phantom in both irradiated positions. These results prove the feasibility of using the proposed method in a more complicated heterogeneous human model.