Boost Use in Breast Conservation Radiotherapy

• Local failure of breast cancer at 72 month median follow-up and 10 year median follow-up for final analysis
  

• Local control translating to survival over 10 year median follow-up
  
• Quality of life at yearly intervals with reference to baseline
  
• Breast cosmesis - patient assessment and photos
  

A boost dose of radiation is commonly but not universally employed in breast conservation techniques.

The potential disadvantages when a boost is employed include:

• Increased complexity of treatment
• Increased duration of treatment
• Increased travel, social/employment dislocation
• Increased complications
• Worse cosmesis and/or increased breast discomfort
• Increased difficulty in detecting recurrence.
• Prolongation of gap or increased delay for chemotherapy if indicated

The potential advantages of a boost are the following:

• Reduced local failure rates
• Reduced local failure translating to improved survival
• Maximising cosmesis by reducing dose to larger breast volume

None of the potential advantages have been clearly demonstrated in a controlled fashion although there are sound theoretical reasons that a boost will improve local control. Holland's landmark paper using radiologic-pathologic correlation of mastectomy specimens, whilst finding residual foci beyond the boundaries of cosmetically acceptable resection margins, also found most of the residual tumour relatively close to the index mass. There is a known dose-response for control of breast cancer. Kurtz reported a doubling of the longterm recurrence rate when the dose to the tumour bed was less than 75 Gy or delivered at less than 8 Gy per week from 15% to 30% using telecesium following lumpectomy. Treating the entire breast to doses above 50 to 54 Gy in 5 weeks is associated with significantly worse cosmesis, hence the common use of a boost. There are as yet no controlled comparisons published however Beadle reported a 50% increase in the rates of poor cosmesis when a boost was employed. Borger has demonstrated that the risk of fibrosis increases fourfold with every 100 cm3 increase in boost volume. Accurate localisation of the tumour bed for boost delivery is difficult in the absence of radioopaque clips (uncommonly employed by our referral base). The use of electrons to deliver the boost has been reported to decrease the cosmetic outcome compared to I192 because of telangiectasia, although this is controversial with other reports indicating superior results with electrons, which is the modality available at St George and Wollongong. The latter avoids hospitalisation. There is at least one other randomised multicentre study being conducted testing the value of a boost by the EORTC in Europe but no results are yet available.

Comparisons: Patients will be stratified by chemotherapy (none, AC, non-AC) and within the non-AC arm will be randomised in respect to timing (pre, sandwich, concurrent) of radiotherapy. Randomisation to treatment will be - boost (45Gy 25# + 16Gy 8#) or no boost (50Gy 25#).