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Figure 1. (Top) The tofu phantom and Zn/¹⁶O-water hydrogel in a syringe used in this research. (Bottom) Cross-section of the tofu phantom injected with Zn/¹⁶O water hydrogels.

 이 연구에서 개발된 마커가 주사를 통해 두부에 주입되었습니다. 두부의 절단면을 통해 주입된 마커가 보입니다.

Figure 2. (Top) PET/CT fusion images of the tofu phantom injected with 0.9 cm³ of Zn/¹⁸O-water hydrogels (10%/90% mass ratio) and irradiated by a proton beam (2 Gy) from the bottom. (Bottom) PET/CT fusion images of ¹⁶O-water hydrogels (1.8 cm³) and ¹⁸O-water hydrogels (0.9 cm³) irradiated (2 Gy) in the dry Petri dish environment.

두부와 주입된 마커가 양성자치료후 PET으로 스켄되었습니다. 마커가 선명하게 PET에 보입니다.

Abstract

Biocompatible/biodegradable hydrogel polymers were immersed in 18O-enriched water and 16O-water to create 18O-water hydrogels and 16O-water hydrogels. In both cases, the hydrogels were made of ~91 wt% water and ~9 wt% polymer. In addition, 5-8 μm Zn powder was suspended in 16O-water and 18O-enriched water and cross-linked with hydrogel polymers to create Zn/16O-water hydrogels (30/70 wt%, ~9 wt% polymer) and Zn/18O-water hydrogels (10/90 wt%), respectively. A block of extra-firm 'wet' tofu (12.3  ×  8.8  ×  4.9 cm, ρ  ≈  1.05 g cm-3) immersed in water was injected with Zn/16O-water hydrogels (0.9 ml each) at four different depths using an 18-gauge needle. Similarly, Zn/18O-water hydrogels (0.9 ml) were injected into a second tofu phantom. As a reference, both 16O-water hydrogels (1.8 ml) and 18O-water hydrogels (0.9 ml) in Petri dishes were irradiated in a 'dry' environment. The hydrogels in the wet tofu phantoms and dry Petri dishes were scanned via CT and images were used for treatment planning. Then, they were positioned at the proton distal dose fall-off region and irradiated (2 Gy) followed by PET/CT imaging. Notably high PET signals were observed only in 18O-water hydrogels in the dry environment. The visibility of the Zn/16O-water hydrogels injected into the tofu phantom was outstanding in CT images, but these hydrogels provided no noticeable PET signals. The visibility of the Zn/18O-water hydrogels in the wet tofu were excellent on CT and moderate on PET; however, the PET signals were weaker than those in the dry environment, possibly owing to 18O-water leaching out. The hydrogel markers studied here could be used to develop universal PET/CT fiducial markers. Their PET visibility (attributed more to activated 18O-water than Zn) after proton irradiation can be used for proton therapy/range verification. More investigation is needed to slow down the leaching of 18O-water. 

Author information

Cho J1, Campbell P, Wang M, Alqathami M, Mawlawi O, Kerr M, Cho SH.​

1Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.