Accelerated Partial Breast Irradiation (APBI)

Accelerated partial breast irradiation includes a variety of intraoperative, brachytherapy or external beam techniques that treat a smaller part of the breast with an accelerated technique. There is no strong evidence for routine use in breast cancer, but for selected patients it may prove to be appropriate. ASTRO recommendations for patients suitable for APBI include:

  • Age > 60
  • T1, N0
  • Any grade
  • Not lobular carcinoma or non-epithelial carcinomas
  • No lymphovascular invasion
  • Margins > 2 mm
  • Unifocal unicentric
  • No pure DCIS or extensive intraductal component

Patients outside these criteria should be treated cautiously or not at all (eg. DCIS may be used with caution whereas closer margins should definitely not receive APBI).
There are several treatment techniques used. Most techniques have difficulty when the tumour is located close to the skin (< 7 mm) as skin toxicity is significantly increased in this setting.

External Beam Radiotherapy

This is either 3D conformal external beam radiotherapy, electron beam radiotherapy or IMRT.

Electron beam radiotherapy

One of the best randomised trials available randomised patients between whole breast radiotherapy and either interstitial brachytherapy or external electron beam radiotherapy if the brachytherapy was unsuitable. The electron beam treatment was delivered en face to the tumour bed with a 2 cm margin (PTV). A dose of 50 Gy in 25 fractions was used, and therefore this qualifies more as 'partial breast irradiation' rather than APBI. The electron beam patients had similar control rates and cosmetic outcomes to whole breast radiotherapy whereas the interstitial patients had a better cosmetic outcome (see below).

Photon beam radiotherapy

Photon beam radiotherapy is the subject of a large randomised controlled trial of APBI. Current evidence is only from large case series (eg. Berrang //et al//). The CTV is the seroma with a 1 - 1.5 cm expansion; the PTV expansion was a further 1 cm expansion. The expansions were limited to 0.5 cm from skin. Dose was delivered in 35-38.5 Gy over 10 fractions, 2 fractions per day (ie. completed within one week).
IMRT is not frequently used, particularly 7- or 9- field techniques as opposed to tangential IMRT.

Brachytherapy

Intracavitary Brachytherapy

This has been popularised by the MammoSite device which is inserted intraoperatively. Other devices exist using multiple channels. The limitation of the intracavitary devices is that shaping of dose gradients is limited by the number of channels and their position within the device. Best outcomes are seen when the tumour cavity is > 7 mm from the skin surface.

Interstitial Brachytherapy

This technique involves placing remote afterloading catheters through the CTV. The number of catheters required depends on the size of the tumour bed; they are spaced with 1 cm margins. Dose is delivered over 1 week. Interstitial brachytherapy has the potential advantage of better dose conformality for irregularly shaped cavities. There is some concern regarding poor cosmetic outcomes due to the needles but this has only been seen on older studies.

Intraoperative Radiotherapy

Intraoperative radiotherapy is given with superficial x-rays or localised electrons. Similar control rates to other methods of APBI have been shown. Example trials include TARGIT-A which has shown equivalent outcomes to WBRT in a randomised study.

Summary

APBI is infrequently used in Australia. It may be suitable for patients with very low risk disease (eg. age > 60, tumour size < 2 cm, no lymphovascular invasion, no extensive DCIS component, unifocal/unicentric with clear margins by 2 mm). Further randomised evidence with long term follow up is required before it can be considered standard of care for early stage breast cancer.


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