Exposure of remote organs and associated cancer risks from tangential and multi-field breast cancer radiotherapy.

PurposeWith the ever-increasing cure rates in breast cancer, radiotherapy-induced cancers have become an important issue. This study aimed to estimate secondary cancer risks for different treatment techniques, taking into account organs throughout the body.Material and methodsOrgan doses were evaluated for atangential three-dimensional conformal (3D-CRT) and amulti-field intensity-modulated radiotherapy (IMRT) plan using avalidated, Monte Carlo-based treatment planning system. Effects of wedges and of forward versus inverse planning were systematically investigated on the basis of phantom measurements. Organ-specific cancer risks were estimated using risk coefficients derived from radiotherapy patients or from the atomic bomb survivors.ResultsIn the 3D-CRT plan, mean organ doses could be kept below 1Gy for more remote organs than the lung, heart, and contralateral breast, and decreased to afew cGy for organs in the lower torso. Multi-field IMRT led to considerably higher mean doses in organs at risk, the difference being higher than 50% for many organs. Likewise, the peripheral radiation burden was increased by external wedges. No difference was observed for forward versus inverse planning. Despite the lower doses, the total estimated secondary cancer risk in more remote organs was comparable to that in the lung or the contralateral breast. For multi-field IMRT it was 75% higher than for 3D-CRT without external wedges.ConclusionRemote organs are important for assessment of radiation-induced cancer risk. Remote doses can be reduced effectively by application of atangential field configuration and alinear accelerator set-up with low head scatter radiation