The two articles have analysed the toxicity in a cohort given trastuzumab concurrently with RT. The first study is particularly pertinent for your patient. While skin and esophageal toxicity were not significantly increased, but the cardiac function is reduced more. So I would exercise caution if doing IMN radiation. Radiation pneumonitis is not significantly increased either. In addition this interesting rat model study also suggests there is little increase in late radiation pneumonitis. It is important to stress here that the first study was having a retrospective design for RT data collection. The 2nd study did not allow use of IMN (2% received it though) and though prospective was not designed to answer the question of increase/decrease toxicity with use of trastuzumab and herceptin.

However there are several pertinent issues that the authors of the 1st article pointed out with respect to concurrent use of Trastuzumab and RT in breast cancer patient with IMN reported by shaffer et al in a letter to the editor. The letter is available here and gives a nice highlight of the pertinent issues with shaffer's study which did show no increase in cardiotoxicity with the use of Trastuzumab concurrent with RT.