Posterior Axillary Boost Indications?

[JayQuah]

I'm two weeks into my breast rotation and I figured its time for my first n00b question:
Do your institutions employ post. axillary boost field? What are the indications? Any data to support it?
As far as I can tell, it seems like we use it for everyone that is getting treated to the SCV nodes that has gross extanodal extension in the axilla...how say you?

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[Brim]

I'm not aware of any data supporting the use of PAB. Most studies looking into this suggest that having microscopic extranodal extension is a poor prognostic factor but it does not necessary portend for axillary failure and does not indicate a need for full axillary RT.

Many rad oncs would give full axillary RT for gross extranodal extension or in other circumstances where there is a high risk of having gross residual disease or microscopic disease remaining in the axilla. Again, I don't think there's any data to back up this practice.

There are a few times when I had patients I treated only the lymphatics using only anterior supraclav fields (no axillary boost) and they developed isolated axillary failures. These are times when I wish I could have gone back and treated with an axillary boost, although I'm not sure it would have always made a difference. In high risk patients, I'd rather risk a chance of lymphedema (which is manageable) than have cancer recurrence (which most often is not).

That being said, I don't use an axillary boost field routinely when I treat the supracalv, but only in instances where I feel there is a high risk of having untreated disease in the axillary nodes.

Also, it should be mentioned that a PAB field is not per se the ideal method of giving tumoricidal dose to the axillary nodes. A number of dosimetric studies challenge the use of the historic PAB fields and suggest other methods of giving adequate dose to the axilla.

A few references:
Pierce, PMID 7673012
Grills, PMID 12788171
Mignano, PMID 10506712

I'm two weeks into my breast rotation and I figured its time for my first n00b question:
Do your institutions employ post. axillary boost field? What are the indications? Any data to support it?
As far as I can tell, it seems like we use it for everyone that is getting treated to the SCV nodes that has gross extanodal extension in the axilla...how say you?

 

[G'ville Nole]

For many patients who meet the classical indications for full axillary RT (i.e. gross ECE, inadequate dissection, >50% LN+), a SCV field will provide an appropriate dose to the axillary calc point. I don't use a PAB on those patients. If the dose to the calc point is inadequate (I use 95% of Rx as a cut off), I'll use a PAB to flush in the missing dose.

To be clear, I don't use a PAB to give the level II lymphatics a higher dose than the rest of the SCV volume.

 

[medgator]

For many patients who meet the classical indications for full axillary RT (i.e. gross ECE, inadequate dissection, >50% LN+), a SCV field will provide an appropriate dose to the axillary calc point. I don't use a PAB on those patients. If the dose to the calc point is inadequate (I use 95% of Rx as a cut off), I'll use a PAB to flush in the missing dose.

agreed. Sometimes, in a big patient, you'll need a PA field to get adequate dose to the SCV. And sometimes, the classic PAB field doesn't even cover the axilla that well in some patients.