Could the eventual results of the NSABP 39/RTOG 0413 trial for partial breast irradiation (PBI) be improved by combining spherical applicators and whole breast irradiation? Radiobiology suggests it may
There may be unacceptable risks associated with the relatively large single doses of irradiation prescribed over five days instead of over six weeks for three of the four trial arms of the NSABP39/RTOG 0413 clinical trial seeking to enlist 4,300 patients. The first arm prescribes 60 Gray (Gy) in two Gy fractions over six weeks, which is the present standard. The dose implications of the other three arms with reference to this standard were examined using the ID2 formalism. Particularly poor (non-homogeneous) dose distributions characterise spherical applicators like "MammoSite™" used as a sole device for accelerated partial breast irradiation (APBI).The alternative treatment, APBI done by 3-D conformal radiation, may also have a drawback, namely a sudden sharp cut-off in dose which may cause cosmetic problems due to circumscribed fibrosis and edema. Some recently published results from this trial reveal an alarming level of complications. The possible causes of these complications and poor cosmetic outcomes and how to avoid them are examined. An obstacle to the more widespread use of the "MammoSite™" type of device is that the device is not allowed closer than 5-7 mm from the skin or ribs; a possible remedy for this restriction is offered. It is also intended to make the relevant radiobiological principles usable for surgical oncologists.