title: Microscopic gold particle-based fiducial markers for proton therapy of prostate cancer.
abstract: OBJECTIVE
  We examined the feasibility of using fiducial markers composed of microscopic gold particles and human-compatible polymers as a means to overcome current problems with conventional macroscopic gold fiducial markers, such as dose reduction and artifact generation, in proton therapy for prostate cancer.
  
  
  METHODS
  We examined two types of gold particle fiducial marker interactions: that with diagnostic X-rays and with a therapeutic proton beam. That is, we qualitatively and quantitatively compared the radiographic visibility of conventional gold and gold particle fiducial markers and the CT artifacts and dose reduction associated with their use.
  
  
  RESULTS
  The gold particle fiducials could be easily distinguished from high-density structures, such as the pelvic bone, in diagnostic X-rays but were nearly transparent to a proton beam. The proton dose distribution was distorted <5% by the gold particle fiducials with a 4.9% normalized gold density; this was the case even in the worst configuration (i.e., parallel alignment with a single-direction proton beam). In addition, CT artifacts were dramatically reduced for the gold particle mixture.
  
  
  CONCLUSIONS
  Mixtures of microscopic gold particles and human-compatible polymers have excellent potential as fiducial markers for proton therapy for prostate cancer. These include good radiographic visibility, low distortion of the depth-dose distribution, and few CT artifacts.
authors.affiliation: Proton Therapy Center, National Cancer Center, Goyang, Gyeonggi, Korea.
authors.forename: Young Kyung
authors.initials: YK
authors.lastname: Lim
authors.forename: Jungwon
authors.initials: J
authors.lastname: Kwak
authors.forename: Dong Wook
authors.initials: DW
authors.lastname: Kim
authors.forename: Dongho
authors.initials: D
authors.lastname: Shin
authors.forename: Myonggeun
authors.initials: M
authors.lastname: Yoon
authors.forename: Soah
authors.initials: S
authors.lastname: Park
authors.forename: Jin Sung
authors.initials: JS
authors.lastname: Kim
authors.forename: Sung Hwan
authors.initials: SH
authors.lastname: Ahn
authors.forename: Jungwook
authors.initials: J
authors.lastname: Shin
authors.forename: Se Byeong
authors.initials: SB
authors.lastname: Lee
authors.forename: Sung Yong
authors.initials: SY
authors.lastname: Park
authors.forename: Hong Ryeol
authors.initials: HR
authors.lastname: Pyo
authors.forename: Dae Yong
authors.initials: DY
authors.lastname: Kim
authors.forename: Kwan Ho
authors.initials: KH
authors.lastname: Cho
mesh_terms: D016477:Artifacts; D005240:Feasibility Studies; D006046:Gold / Q000737:chemistry*; D006801:Humans; D008297:Male; D010316:Particle Size; D019047:Phantoms, Imaging; D011108:Polymers; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D019736:Prostheses and Implants; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D012542:Scattering, Radiation; D014057:Tomography, X-Ray Computed
chemical_list: D011108:Polymers; D006046:Gold