[Conventional 2D and monoisocentric 3D techniques in breast and lymphatic irradiation: a dosimetric comparison]

The activity of our radiation oncology department mainly relies on breast pathology. Since July 2009, all the irradiations delivered simultaneously to the breast (CTV1), the surgical bed (CTV2), the internal mammary chain and the supra- and infraclavicular areas have been carried out using a mono-isocentric technique. This study aimed to compare dosimetric results between conventional 2D and mono-isocentric 3D techniques with or without optimization.

From January to August 2009, 20 patients with breast cancer in whom irradiation of the CTV1, CTV2, internal mammary chain and supra- and infraclavicular areas was retained, were included in a specific cohort. In each case, we have compared dosimetric results obtained with the conventional technique and with a mono-isocentric 3D technique, either with manual field in the field segmentation or with automatic segmentation (Oncentra Masterplan(®) from Nucletron(®), Optimizer(®) solution). Selected criteria were as follows: V95, V107 and mean dose (Dmean) to the target volumes, V20 and V30 to the ipsilateral lung, V35 and mean dose to the heart and maximal dose (Dmax) to the spinal cord.

Supra- and infraclavicular areas irradiation was significantly better using the mono-isocentric 3D technique (V95 %: 89.7 % vs. 77.1 %; P=0.001) as well as dose homogeneity (Dmean: 46.3 Gy vs. 45.1 Gy; P=0.008). No statistical difference was observed for the other target volumes. Heart and spinal cord protection were better with the mono-isocentric 3D technique (respectively Dmean: 8.4Gy vs. 11.1 Gy; P<0.0001 and Dmax: 29.2 Gy vs. 35.8 Gy; P=0.0003).

Mono-isocentric irradiation of the breast and lymphatic areas is a modern technique that benefits from imaging and computer progresses while being simple to carry out using standard planning system and linear accelerators. Mono-isocentric 3D irradiation with manual segmentation of the breast and the nodal areas provides a target volume irradiation comparing with conventional technique 2D and a better protection of the heart and of the spinal cord.