[Dosimetric comparison of different techniques for external beam accelerated partial breast irradiation]

The aim of this article is to evaluate and compare four different radiotherapy techniques of accelerated partial breast irradiation (APBI) considering planning quality, dosimetric and practical aspects. The investigated techniques are three dimensional conformal radiotherapy (3D-CRT), "step and shoot" (SS) and "sliding window" (SW) intensity-modulated radiotherapy, intensity-modulated arc therapy (RA). CT scans of 10 patients previously treated with APBI were selected for the study. Surgical clips were placed on the borders of the tumour bed during breast conserving surgery. Target volume (PTV) was defined as enlarged CTV, which was created from the tumour bed through volume expansion using individual margins. Planning objectives were set up according to the international recommendations. Non-coplanar fields were used only for the 3D-CRT plans. For each plan homogeneity, conformity and plan quality indices were calculated from volumetric and dosimetric parameters of target volumes and organs at risk. The total monitor units and feasibility were also investigated. There was no significant difference in the coverage of the target volume by the prescribed dose between the techniques. SW plans were significantly more homogeneous (HI=0.033) than the 3D-CRT (HI=0.057) and the RA (HI=0.073) plans. The homogeneity of the SS technique (HI=0.053) did not differ significantly compared to others. The conformity of the 3D-CRT technique was significantly worse (CN=0.62) than that of SS (CN=0.85), SW (CN=0.85) and RA (CN=0.86) plans. There was a significant difference between RA (29.4%) and 3D-CRT (44.1%) and SW (35.6%) plans in the V50% of the ipsilateral breast. Mean V10% of the ipsilateral lung in 3D-CRT (10.1%) plans was significantly lower than in SS (34.3%), SW (34.3%) and RA (35.3%) plans. 3D-CRT technique provided the best heart protection. The shortest treatment times were achieved with RA technique. Good target volume coverage and tolerable dose to the organs at risk are achievable with all four techniques. Taking into account all the aspects, we recommend the sliding window IMRT technique for accelerated partial breast irradiation.