EP-1684: Optimization of a VMAT technique for three dose level irradiation of head and neck cancer

Material and Methods: From September 2010 to March 2014, 69 patients were treated for left breast (PTV-breast) cancer with SIB at surgical bed (PTV-boost) in 25 fractions: the prescribed doses (Dp) were 50 Gy and 60 Gy, respectively. All plans were generated with Varian EclipseTM v.10.0.28 TPS, using 5-7 IMRT sliding-window fields equally spaced along a 190° arc, with 6MV photon beams and a Varian Millenium120TM multileaf collimator. Dose computation were performed by AAA algorithm, with a 2.5 mm grid size. The first 41 patients were planned by fixing a null collimator rotation, and by leaving the optimizer Varian DVOTM v.10.0.28 free to search for the optimal setting of the jaws (IMRT-A). In the next 28 patients the arrangement of the two outermost tangential fields were set to maximally spare the heart and the left lung. In details, the collimator was rotated so as to align the medial jaw with the projection of the chest wall (IMRT-B). Further, for the most lateral field the jaws were collimated to the lateral and central portions only of the PTV-breast. The remaining 3-5 fields covered entire target according the BEV projection of the target. By selecting the Fixed Jaws Parameter of the two outermost fields into DVO the same jaws aperture defined in BEV were assured during optimization process. Plans aimed to cover at least 95% of the PTVs volume with a dose 3 95% of the Dp (V95% 395%), with V107%<2%, for PTV-boost. Hearth volume receiving more then 20 Gy (V20)<10%. Left lung V20<20%. Right breast mean dose (Dmean)<2Gy and right lung Dmean<3Gy. By hypothesis testing, several dose-volume metrics were then compared across the two groups of plans.