title: Verification procedure for isocentric alignment of proton beams.
abstract: We present a technique--based on the Lutz, Winston, and Maleki test used in stereotactic linear accelerator radiosurgery--for verifying whether proton beams are being delivered within the required spatial coincidence with the gantry mechanical isocenter. Our procedure uses a proton beam that is collimated by a circular aperture at its central axis and is then intercepted by a small steel sphere rigidly supported by the patient couch. A laser tracker measurement system and a correction algorithm for couch position assures precise positioning of the steel sphere at the mechanical isocenter of the gantry. A film-based radiation dosimetry technique, chosen for the good spatial resolution it achieves, records the proton dose distribution for optical image analysis. The optical image obtained presents a circular high-dose region surrounding a lower-dose area corresponding to the proton beam absorption by the steel sphere, thereby providing a measure of the beam alignment with the mechanical isocenter. We found the self-developing Gafchromic EBT film (International Specialty Products, Wayne, NJ) and commercial Epson 10000 XL flatbed scanner (Epson America, Long Beach, CA) to be accurate and efficient tools. The positions of the gantry mechanical and proton beam isocenters, as recorded on film, were clearly identifiable within the scanning resolution used for routine alignment testing (0.17 mm per pixel). The mean displacement of the collimated proton beam from the gantry mechanical isocenter was 0.22 +/- 0.1 mm for the gantry positions tested, which was well within the maximum deviation of 0.50 mm accepted at the Proton Therapy Center in Houston.
authors.affiliation: Proton Therapy Center, Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, U.S.A.
authors.forename: George
authors.initials: G
authors.lastname: Ciangaru
authors.affiliation: Proton Therapy Center, Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, U.S.A.
authors.forename: James N
authors.initials: JN
authors.lastname: Yang
authors.affiliation: Proton Therapy Center, Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, U.S.A.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Oliver
authors.affiliation: Proton Therapy Center, Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, U.S.A.
authors.forename: Martin
authors.initials: M
authors.lastname: Bues
authors.affiliation: Proton Therapy Center, Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, U.S.A.
authors.forename: Mengping
authors.initials: M
authors.lastname: Zhu
authors.affiliation: Power Systems Division, Hitachi America, Houston, Texas, U.S.A.
authors.forename: Fumio
authors.initials: F
authors.lastname: Nakagawa
authors.affiliation: Power Systems Division, Hitachi America, Houston, Texas, U.S.A.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Chiba
authors.affiliation: Power Systems Division, Hitachi America, Houston, Texas, U.S.A.
authors.forename: Shin
authors.initials: S
authors.lastname: Nakamura
authors.affiliation: Power Systems Division, Hitachi America, Houston, Texas, U.S.A.
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Yoshino
authors.affiliation: Power Systems Division, Hitachi America, Houston, Texas, U.S.A.
authors.forename: Mosumi
authors.initials: M
authors.lastname: Umezawa
authors.affiliation: Proton Therapy Center, Department of Radiation Physics, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, U.S.A.
authors.forename: Alfred R
authors.initials: AR
authors.lastname: Smith
mesh_terms: D002138:Calibration; D019544:Equipment Failure Analysis / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D010315:Particle Accelerators / Q000295:instrumentation* / Q000592:standards; D061766:Proton Therapy; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods / Q000592:standards; D016634:Radiosurgery / Q000295:instrumentation* / Q000592:standards; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D014481:United States; D011522:Protons
chemical_list: D011522:Protons