Development of a NaI-based prompt gamma-rays detection system for proton range verification

Tzu-Hsiang Lin^1*, Hui-Yu Tsai¹, Ming-Wei Lin¹

¹Institute of Nuclear Engineering and Science, National Tsing Hua University, HSINCHU, Taiwan

* Presenter:Tzu-Hsiang Lin, email:thlin@m109.nthu.edu.tw

The sharp distal falloff of the proton dose distribution allows the proton therapy to directly deliver doses to tumor cells without causing external radiation damage to healthy tissues nearby. However, the expected proton range may be shifted due to the calibrating data from computed tomography and the errors of patient positioning, such that a in vivo estimation of proton range is needed to avoid overdose to normal tissues or underdose to target tumor. This study focuses on developing a NaI-based prompt gamma (PG)-rays detection system for proton range verification, which is composed of a 2-inches NaI detector and a slit collimator with a width of 2 mm.[1] When a 30-MeV, 1.5-nA proton beam irradiates a PE or a PMMA phantom, the intensity distributions of 4.4-MeV and 6.13-MeV PG-rays along the proton path are sampled by the collimator and recorded by the NaI detector toward the depth of 11 mm. By incorporating the number density distribution of protons in a target simulated by a Monte Carlo model and the prompt gamma-rays yield cross section, an analytical model is developed in conjunction with a dedicated deconvolution algorithm to retrieve the distribution of PG-rays emission in a target and consequently contribute to the estimation of proton range. For 30-MeV protons, the estimated proton ranges of 8.01 mm in a PE targe and of 6.88 mm in a PMMA target are reasonably close to the values of 7.94 mm and 7.04 mm verified by Monte Carlo simulations. These results demonstrate that a NaI-based system with a collimator can effectively resolve the spatial variation of prompt gamma-rays emission along the proton path and exhibits the potential for verifying proton range in a relatively simple and reliable manner.

REFERENCES
[1] J. M. Verburg, K. Riley, T. Bortfeld, and J. Seco, “Energy- and time-resolved detection of prompt gamma-rays for proton range verification,” Phys. Med. Biol., vol. 58, no. 20, pp. L37–L49 (2013)

Keywords: Proton therapy, Prompt gamma-rays, Range Verification, Radiation measurement