How well does left chest wall electron chest wall RT compare with IMRT with with respect to heart and lung radiation doses?

The acute skin toxicity is high, as well as the late telangiectasias. There can also be substantial variation in the skin surface contour of the patient, so really only patients without reconstruction and relatively ‘flat’ profile are suitable. Some have mitigated that by building custom boluses that require even higher electron energies and time/expertise to set up. Also, the role of treating the chest wall only without RNI is quite limited at this point so this technique will not have wide use. It’s a good concept, but probably appropriately not preferred over other techniques.

There is a nice literature demonstrating that chest-wall electrons are a viable tx approach for PMRT (e.g. UFla has a nice series; Feigenberg et al., PMID 12788177). 

Like many things, the more you do it, the better you get (so maybe someone from UF can chime in). I have done this maybe 50 times (?), essentially only when I cannot get (partly)-wide tangents, or "tangents plus a medial chestwall/IMN electron field: to work well. I have done the medial chest electron strip many times (hundreds), and I have found that when I give 40-44 Gy electrons only, the patients generally have not developed telangiectasias; while at 50 Gy they often have developed telangiectasias. 

When I have done the electron-only technique to the whole chest wall, one almost always needs a few electron fields to address the large target volume, and the chest curvature. So, one needs to be careful with the match-lines between the fields (I used to routinely feather the junction). Some have suggested an electron-arc approach to address the chest-wall curvature (McNeely et al., PMID 3384727).    

If the chest wall is of relatively-uniform thickness, an electron-only technique for the chest wall is very good. When the chest wall is of non-uniform thickness, one can use different electron energies for the different parts of the target (e.g. a common thing is to use higher energy electrons medially to get to the IMN) and lower energy laterally. Similarly, for the medial chest, I have often split the field and used a higher energy superiorly and a lower energy inferior (where the IMNs are less often involved, and where the heart is nearby). I used to also use variable thickness of bolus to address the variable chest wall thicknesses (but this tends to increase skin doses). 

From a therapist's perspective, I am pretty confident that they find the multiple electron fields to me more challenging than the other approaches (e.g. multiple fields to match). Indeed, IMRT arc-based approaches have gotten pretty fast and easy. 

Nevertheless, for the right patient, an all-electron technique for the chest wall can be very good. 

A little history: It is worth remembering that in the Overgaard PMRT study, that we routinely quote to justify PMRT, many patients were treated using en-face electrons to the medial and central chest, and large APPA photons to the SC, axilla, and lateral chest wall (i.e. the "reverse hickey stick") (see Overgaard et al., PMID 3064776). 

It may offer heart and lung dose advantages in some scenarios but heterogeneous has dose distribution and most importantly, skin toxicity is also higher because of surface dose 
to circumvent that we do sometimes use medial electron matched to lateral photon tangent.

I sometimes use an electron field to cover as much of the anterior chest wall as possible and then match that with a lateral photon field with bolus. The photon field can be extended superiorly to cover the axilla and SCF if needed with a central block over the electron field.