A liquid fiducial marker for image-guided proton beam therapy of abdominal tumors.

Purpose

This study compared a liquid to solid fiducial markers regarding visibility, artifact characteristics on X-ray imaging and dose perturbation for image-guided proton therapy (IGPT) of abdominal tumors. Additionally, the radio-opaque composition of the liquid fiducial marker was optimized, and the chemical stability after proton beam irradiation was analyzed. MATERIAL AND

Methods

The fiducial markers inserted into an anthropomorphic abdominal phantom were exposed to X-ray, single-energy computed tomography (SECT), dual-energy CT (DECT) and cone-beam CT (CBCT) to determine contrast-to-noise ratios (CNR) and artifacts. Proton dose perturbation estimations were performed using a Monte Carlo dose algorithm. Chemical stability following proton beam irradiation was assessed with biophysical and optical methods.

Results

The CNR of the liquid marker with a volume ≥ 100 μl (CNR ≤ 2.69) on 2D X-ray images was superior to the solid markers (CNR ≤ 1.72). The artifact areas (A) and severity in the CT modalities were more pronounced for the solid (e.g. , SECT A ≤ 279.4 mm3) than for the liquid fiducial marker (A ≤ 30.5 mm3). Dose mitigation of ≥ 50% in a proton beam was calculated for solid fiducial markers, while the liquid marker less influenced the dose distribution. Increasing radio-opaque content in the liquid prototypes improved visibility (CNR ≤ 2.97) without significantly increasing artifact volume (SECT: A ≤ 40.5 mm3) or dose perturbation. No degradation of the liquid fiducial marker's chemical composition was observed.

Conclusion

The liquid fiducial marker demonstrated comparable visibility and chemical stability with reduced artifact generation and dose perturbation compared to solid markers, indicating superiority for IGPT of abdominal tumors. Optimization of the liquid marker composition may be considered.