title: Monte Carlo simulations of the dosimetric impact of radiopaque fiducial markers for proton radiotherapy of the prostate.
abstract: Many clinical studies have demonstrated that implanted radiopaque fiducial markers improve targeting accuracy in external-beam radiotherapy, but little is known about the dose perturbations these markers may cause in patients receiving proton radiotherapy. The objective of this study was to determine what types of implantable markers are visible in setup radiographs and, at the same time, perturb the therapeutic proton dose to the prostate by less than 10%. The radiographic visibility of the markers was assessed by visual inspection of lateral setup radiographs of a pelvic phantom using a kilovoltage x-ray imaging system. The fiducial-induced perturbations in the proton dose were estimated with Monte Carlo simulations. The influence of marker material, size, placement depth and orientation within the pelvis was examined. The radiographic tests confirmed that gold and stainless steel markers were clearly visible and that titanium markers were not. The Monte Carlo simulations revealed that titanium and stainless steel markers minimally perturbed the proton beam, but gold markers cast unacceptably large dose shadows. A 0.9 mm diameter, 3.1 mm long cylindrical stainless steel marker provides good radiographic visibility yet perturbs the proton dose distribution in the prostate by less than 8% when using a parallel opposed lateral beam arrangement.
authors.affiliation: Department of Radiation Physics, The University of Texas M D Anderson Cancer Center, Houston, TX, USA. wnewhaus@mdanderson.org
authors.forename: Wayne
authors.initials: W
authors.lastname: Newhauser
authors.forename: Jonas
authors.initials: J
authors.lastname: Fontenot
authors.forename: Nicholas
authors.initials: N
authors.lastname: Koch
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.forename: Andrew
authors.initials: A
authors.lastname: Lee
authors.forename: Yuanshui
authors.initials: Y
authors.lastname: Zheng
authors.forename: Laurie
authors.initials: L
authors.lastname: Waters
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
mesh_terms: D006801:Humans; D008297:Male; D008670:Metals / Q000737:chemistry; D015233:Models, Statistical; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011522:Protons; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D011878:Radiotherapy / Q000379:methods; D013193:Stainless Steel; D014025:Titanium / Q000737:chemistry; D014965:X-Rays
chemical_list: D008670:Metals; D011522:Protons; D013193:Stainless Steel; D014025:Titanium