Risks and benefits of reducing target volume margins in breast tangent radiotherapy

  • Deepak BasaulaEmail author
  • Alexandra Quinn
  • Amy Walker
  • Vikneswary Batumalai
  • Shivani Kumar
  • Geoff P. Delaney
  • Lois Holloway
Scientific Paper


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.


Breast radiotherapy Planning target volume Margin Secondary cancer risk Imaging dose 



This work is supported by Cancer Australia and The National Breast Cancer Foundation Grant Project Number 1033237.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

The ethics was approved by the local institutional ethics board.


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Copyright information

© Australasian College of Physical Scientists and Engineers in Medicine 2017

Authors and Affiliations

  1. 1.Department of Medical Physics and Radiation EngineeringThe Canberra HospitalGarranAustralia
  2. 2.Northern Sydney Cancer Therapy CentreRoyal North Shore HospitalSydneyAustralia
  3. 3.Liverpool and Macarthur Cancer Therapy CentresSydneyAustralia
  4. 4.Ingham Institute of Applied Medical ResearchSydneyAustralia
  5. 5.University of New South WalesSydneyAustralia
  6. 6.Centre for Medical Radiation PhysicsUniversity of WollongongWollongongAustralia
  7. 7.Institute of Medical PhysicsUniversity of SydneySydneyAustralia

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