Breast Boost

Rationale

The largest study is the EORTC Boost Trial, which randomised close to 5,600 patients between whole breast radiotherapy (50 Gy) with or without a 16 Gy boost. With 10 year follow up, local control improved from 90% to 94%; the largest benefit was seen in younger women and the least benefit in older women (but benefit existed in all groups). There was a higher rate of adverse events (1% up to 4%).
The Lyon Boost Trial was run on a smaller number of patients and had much shorter follow-up; local recurrence was reduced by 1% in the 10 Gy boost arm.
Regarding boost technique, Oh et al demonstrated geographical miss of up to 50% when only the scar was used to determine the field size; it is recommended to use a combination of the scar, surgical reports and CT imaging of the surgical bed to determine the appropriate field size and energy.

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Technique

Boosting of the tumour bed is somewhat controversial; there is evidence that most (70-80%) recurrences occur in close proximity to the tumour bed. Older studies are confounded by poor pathological examination of tumour margins following surgery and the main debate is whether patients with well clear margins need boosting of their tumour bed at all. Most departments continue to use a 10 - 14 Gy boost in 2 Gy fractions.
Electron boost is the most commonly utilised technique.

  • The patient is positioned so that the scar, tumour bed and overlying tissue lie in a plane perpendicular to the vertical.
  • The scar or tumour bed is included in the field with a 2 cm margin
  • An electron cutout is used to prevent dose to other areas of the breast
  • Beam energies depend on the depth of the tumour bed and the chest wall, usually 9 MeV - 16 MeV is used.

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