title: Risks and benefits of reducing target volume margins in breast tangent radiotherapy.
abstract: This study investigates the potential benefits of planning target volume (PTV) margin reduction for whole breast radiotherapy in relation to dose received by organs at risk (OARs), as well as reductions in radiation-induced secondary cancer risk. Such benefits were compared to the increased radiation-induced secondary cancer risk attributed from increased ionizing radiation imaging doses. Ten retrospective patients' computed tomography datasets were considered. Three computerized treatment plans with varied PTV margins (0, 5 and 10 mm) were created for each patient complying with the Radiation Therapy Oncology Group (RTOG) 1005 protocol requirements. The BEIR VII lifetime attributable risk (LAR) model was used to estimate secondary cancer risk to OARs. The LAR was assessed for all treatment plans considering (a) doses from PTV margin variation and (b) doses from two (daily and weekly) kilovoltage cone beam computed tomography (kV CBCT) imaging protocols during the course of treatment. We found PTV margins from largest to smallest resulted in a mean OAR relative dose reduction of 31% (heart), 28% (lung) and 23% (contralateral breast) and the risk of radiation-induced secondary cancer by a relative 23% (contralateral breast) and 22% (contralateral lung). Daily image-guidance using kV CBCT increased the risk of radiation induced secondary cancer to the contralateral breast and contralateral lung by a relative 1.6-1.9% and 1.9-2.5% respectively. Despite the additional dose from kV CBCT for the two considered imaging protocols, smaller PTV margins would still result in an overall reduction in secondary cancer risk.
authors.affiliation: Department of Medical Physics and Radiation Engineering, The Canberra Hospital, Garran, Australia. Deepak.basaula@act.gov.au.|Ingham Institute of Applied Medical Research, Sydney, Australia. Deepak.basaula@act.gov.au.
authors.forename: Deepak
authors.identifier: http://orcid.org/0000-0001-5507-8380
authors.initials: D
authors.lastname: Basaula
authors.affiliation: Northern Sydney Cancer Therapy Centre, Royal North Shore Hospital, Sydney, Australia.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Quinn
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, Sydney, Australia.|Ingham Institute of Applied Medical Research, Sydney, Australia.|Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia.
authors.forename: Amy
authors.initials: A
authors.lastname: Walker
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, Sydney, Australia.|Ingham Institute of Applied Medical Research, Sydney, Australia.|University of New South Wales, Sydney, Australia.
authors.forename: Vikneswary
authors.initials: V
authors.lastname: Batumalai
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, Sydney, Australia.|Ingham Institute of Applied Medical Research, Sydney, Australia.|University of New South Wales, Sydney, Australia.
authors.forename: Shivani
authors.initials: S
authors.lastname: Kumar
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, Sydney, Australia.|Ingham Institute of Applied Medical Research, Sydney, Australia.|University of New South Wales, Sydney, Australia.
authors.forename: Geoff P
authors.initials: GP
authors.lastname: Delaney
authors.affiliation: Liverpool and Macarthur Cancer Therapy Centres, Sydney, Australia.|Ingham Institute of Applied Medical Research, Sydney, Australia.|University of New South Wales, Sydney, Australia.|Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia.|Institute of Medical Physics, University of Sydney, Sydney, Australia.
authors.forename: Lois
authors.initials: L
authors.lastname: Holloway
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D009928:Organ Specificity / Q000528:radiation effects; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D012307:Risk Factors
keywords: Breast radiotherapy; Imaging dose; Margin; Planning target volume; Secondary cancer risk