Prone Whole Breast Radiotherapy

Rationale

Standard breast radiotherapy has the patient lying supine on an incline with lateral and medial tangential fields. This set up involves treatment of some underlying lung tissue, as well as the heart when the tumour is located on the left. Prone patient positioning has been postulated to reduce the dose to these deeper structures. Other techniques, such as forward planned IMRT, use of higher energy photons, inframammary support, or thermoplastic shell, have also been used.
Prone positioning is thought to be particularly useful for patients with pendulous breasts, which often displace laterally and inferiorly when the patient lies supine. This increases the separation and may require more posterior placement of the lateral field edge in order to cover the tissue completely. When the patient is placed prone, the breast is displaced anteriorly away from the chest wall, often reducing the separation. There is single institution data supporting that this technique leads to decreased lung and heart dose.
The main concerns regarding prone positioning are:

  • Decreased patient comfort
  • Less accurate set up
  • Inadequate coverage of the chest wall - this is of particular concern as all the major breast conservation studies have used supine techniques which treated the chest wall more extensively than is seen with the prone technique. Whether this coverage is needed is unclear
  • Lack of long term data demonstrating improved outcomes over conventional supine techniques

Technique

The patient lies on a custom made support with a space at the level of the breast. The breast is allowed to hang through this space and then CT simulation is performed. Opposed tangents are still used and treatment planning is similar. The breast tissue needs to be palpated clinically to determine the extent of the tangents. Isocentric techniques are difficult due to collisions between the machine and the patient support.

Opinion: Prone whole breast radiotherapy seems to have similar outcomes to supine treatment. It may be appropriate for a small group of women with pendulous breasts who receive suboptimal dose distribution from supine treatments. However, the difficulty in developing a custom made device for all breast patients (and several devices may be needed for each linear accelerator), together with concerns about treatment positioning, mean that I do not favour this approach and would prefer other methods of optimising dose distribution (eg. inframammary support) where possible.


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