title: Microdosimetric measurements for neutron-absorbed dose determination during proton therapy.
abstract: This work presents microdosimetric measurements performed at the Midwest Proton Radiotherapy Institute in Bloomington, Indiana, USA. The measurements were done simulating clinical setups with a water phantom and for a variety of stopping targets. The water phantom was irradiated by a proton spread out Bragg peak (SOBP) and by a proton pencil beam. Stopping target measurements were performed only for the pencil beam. The targets used were made of polyethylene, brass and lead. The objective of this work was to determine the neutron-absorbed dose for a passive and active proton therapy delivery, and for the interactions of the proton beam with materials typically in the beam line of a proton therapy treatment nozzle. Neutron doses were found to be higher at 45° and 90° from the beam direction for the SOBP configuration by a factor of 1.1 and 1.3, respectively, compared with the pencil beam. Meanwhile, the pencil beam configuration produced neutron-absorbed doses 2.2 times higher at 0° than the SOBP. For stopping targets, lead was found to dominate the neutron-absorbed dose for most angles due to a large production of low-energy neutrons emitted isotropically.
authors.affiliation: Department of Medical Physics, University of Wisconsin, 1005 Wisconsin Institutes for Medical Research 1111 Highland Ave., Madison, WI 53705, USA. perezandujara@radonc.ucsf.edu
authors.forename: Angélica
authors.initials: A
authors.lastname: Pérez-Andújar
authors.forename: Paul M
authors.initials: PM
authors.lastname: Deluca
authors.forename: Allan F
authors.initials: AF
authors.lastname: Thornton
authors.forename: Markus
authors.initials: M
authors.lastname: Fitzek
authors.forename: Draik
authors.initials: D
authors.lastname: Hecksel
authors.forename: Jonathan
authors.initials: J
authors.lastname: Farr
mesh_terms: D003300:Copper / Q000737:chemistry; D006801:Humans; D007196:Indiana; D007854:Lead / Q000737:chemistry; D009502:Neutrons; D019047:Phantoms, Imaging; D020959:Polyethylene / Q000737:chemistry; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D014867:Water / Q000737:chemistry; D015032:Zinc / Q000737:chemistry
chemical_list: D014867:Water; C048399:brass; D007854:Lead; D003300:Copper; D020959:Polyethylene; D015032:Zinc