Bootstrap Framework 3.3.6

[surquhart]

Our patients  have, over the last 5-7 years, been asked to do the DIBH protocol out of an abundance of caution to protect the heart from coronary disease after RT based on clinical knowledge of post RT effects. Makes sense. Granted some folks can't do DIBH and others are not doing for other reasons. Initially we scanned patients with and without DIBH to see the necessity of the techniques for individuals. Now we seem to try it on most folks.

Good idea to make things simpler I suppose.

My question is this - why is it that when we plan these ladies, we look for mean dose to the whole organ (most of which is left out of the field) rather than dose to the apex of the ventricle which is closer and encompasses a lot of the LAD. Since the LAD artery is the most commonly occluded of the coronary arteries and it provides the major blood supply to the interventricular septum and thus bundle branches of the conducting system, wouldn't blockage of this artery due to coronary artery disease  lead to impairment or death (infarction) of the conducting system after RT? with the result being a "block" of impulse conduction between the atria and the ventricles known as "right/left bundle branch block." So why don't we contour that portion of the heart closest to the fields to get an idea of dose there instead of the "whole organ"? or at least look at max dose to the organ which would be closest to the fields? It is evident that perfusion decreases are shown most when the apex of the ventricle in is-field.

I am sure there is something I am missing or overthinking but I appreciate anything you can lend to this question.

[jason]

You make a good point about not relying on mean heart dose (MHD) to tell the entire story in breast DIBH. Many DIBH dosimetric studies do include contours for LAD and report on the dose to this region. It is important to review and report metrics other than MHD. While it may be easier for a planner to not include the additional contour, it does make sense to me to contour sensitive sub-volumes of the heart.

[david_grant]

I was considering making a change to our practice a while ago because I too was thinking that it was counter intuitive to contour whole heart volumes instead of the left ventricle or LAD.  I did some research and found that there are several papers that refer to the topic.  I think that there is enough evidence in those papers to conclude that the mean heart dose acts as a good surrogate for predicting CAD and LAD doses and is easier to contour consistently.

The recommended Mean heart dose constraints are proven evidence based doses that predict the risk of late side effects.

The following article is just one example of the work that has gone into this topic http://dx.doi.org/10.1016/j.prro.2012.06.007