title: Characterizing proton-activated materials to develop PET-mediated proton range verification markers.
abstract: Conventional proton beam range verification using positron emission tomography (PET) relies on tissue activation alone and therefore requires particle therapy PET whose installation can represent a large financial burden for many centers. Previously, we showed the feasibility of developing patient implantable markers using high proton cross-section materials ((18)O, Cu, and (68)Zn) for in vivo proton range verification using conventional PET scanners. In this technical note, we characterize those materials to test their usability in more clinically relevant conditions. Two phantoms made of low-density balsa wood (~0.1 g cm(-3)) and beef (~1.0 g cm(-3)) were embedded with Cu or (68)Zn foils of several volumes (10-50 mm(3)). The metal foils were positioned at several depths in the dose fall-off region, which had been determined from our previous study. The phantoms were then irradiated with different proton doses (1-5 Gy). After irradiation, the phantoms with the embedded foils were moved to a diagnostic PET scanner and imaged. The acquired data were reconstructed with 20-40 min of scan time using various delay times (30-150 min) to determine the maximum contrast-to-noise ratio. The resultant PET/computed tomography (CT) fusion images of the activated foils were then examined and the foils' PET signal strength/visibility was scored on a 5 point scale by 13 radiologists experienced in nuclear medicine. For both phantoms, the visibility of activated foils increased in proportion to the foil volume, dose, and PET scan time. A linear model was constructed with visibility scores as the response variable and all other factors (marker material, phantom material, dose, and PET scan time) as covariates. Using the linear model, volumes of foils that provided adequate visibility (score 3) were determined for each dose and PET scan time. The foil volumes that were determined will be used as a guideline in developing practical implantable markers.
authors.affiliation: The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX 77030, USA. Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Jongmin
authors.initials: J
authors.lastname: Cho
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Ibbott
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Kerr
authors.forename: Richard A
authors.initials: RA
authors.lastname: Amos
authors.forename: Francesco C
authors.initials: FC
authors.lastname: Stingo
authors.forename: Edith M
authors.initials: EM
authors.lastname: Marom
authors.forename: Mylene T
authors.initials: MT
authors.lastname: Truong
authors.forename: Diana M
authors.initials: DM
authors.lastname: Palacio
authors.forename: Sonia L
authors.initials: SL
authors.lastname: Betancourt
authors.forename: Jeremy J
authors.initials: JJ
authors.lastname: Erasmus
authors.forename: Patricia M
authors.initials: PM
authors.lastname: DeGroot
authors.forename: Brett W
authors.initials: BW
authors.lastname: Carter
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Gladish
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Sabloff
authors.forename: Marcelo F
authors.initials: MF
authors.lastname: Benveniste
authors.forename: Myrna C
authors.initials: MC
authors.lastname: Godoy
authors.forename: Shekhar
authors.initials: S
authors.lastname: Patil
authors.forename: James
authors.initials: J
authors.lastname: Sorensen
authors.forename: Osama R
authors.initials: OR
authors.lastname: Mawlawi
mesh_terms: D057918:Fiducial Markers; D006801:Humans; D008670:Metals; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography; D019736:Prostheses and Implants; D061766:Proton Therapy; D061089:Radiotherapy, Image-Guided / Q000592:standards*
chemical_list: D008670:Metals