title: Relative biological effectiveness (RBE) and out-of-field cell survival responses to passive scattering and pencil beam scanning proton beam deliveries.
abstract: The relative biological effectiveness (RBE) of passive scattered (PS) and pencil beam scanned (PBS) proton beam delivery techniques for uniform beam configurations was determined by clonogenic survival. The radiobiological impact of modulated beam configurations on cell survival occurring in- or out-of-field for both delivery techniques was determined with intercellular communication intact or physically inhibited. Cell survival responses were compared to those observed using a 6 MV photon beam produced with a linear accelerator. DU-145 cells showed no significant difference in survival response to proton beams delivered by PS and PBS or 6 MV photons taking into account a RBE of 1.1 for protons at the centre of the spread out Bragg peak. Significant out-of-field effects similar to those observed for 6 MV photons were observed for both PS and PBS proton deliveries with cell survival decreasing to 50-60% survival for scattered doses of 0.05 and 0.03 Gy for passive scattered and pencil beam scanned beams respectively. The observed out-of-field responses were shown to be dependent on intercellular communication between the in- and out-of-field cell populations. These data demonstrate, for the first time, a similar RBE between passive and actively scanned proton beams and confirm that out-of-field effects may be important determinants of cell survival following exposure to modulated photon and proton fields.
authors.affiliation: Centre for Cancer Research and Cell Biology, Queen's University Belfast, Belfast, UK. k.butterworth@qub.ac.uk
authors.forename: Karl T
authors.initials: KT
authors.lastname: Butterworth
authors.forename: Conor K
authors.initials: CK
authors.lastname: McGarry
authors.forename: Ben
authors.initials: B
authors.lastname: Clasie
authors.forename: Alejandro
authors.initials: A
authors.lastname: Carabe-Fernandez
authors.forename: Jan
authors.initials: J
authors.lastname: Schuemann
authors.forename: Nicolas
authors.initials: N
authors.lastname: Depauw
authors.forename: Shikui
authors.initials: S
authors.lastname: Tang
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: McMahon
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Schettino
authors.forename: Joe M
authors.initials: JM
authors.lastname: O'Sullivan
authors.forename: Hsaio-Ming
authors.initials: HM
authors.lastname: Lu
authors.forename: Hanne
authors.initials: H
authors.lastname: Kooy
authors.forename: Harald
authors.initials: H
authors.lastname: Paganetti
authors.forename: Alan R
authors.initials: AR
authors.lastname: Hounsell
authors.forename: Kathryn D
authors.initials: KD
authors.lastname: Held
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Prise
mesh_terms: D002450:Cell Communication / Q000528:radiation effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D006801:Humans; D061766:Proton Therapy; D012062:Relative Biological Effectiveness; D012542:Scattering, Radiation