Acuros xb

The current study recalculated the dose–volume metrics of the PTV, heart and lungs in the included 4F-3DCRT and SA-VMAT plans using the same dose calculation algorithm: Acuros XB version 15.6.05 (Varian Medical Systems). For recalculation, we used the originally calculated monitor units for clinical uses in 4F-3DRT and SA-VMAT. For the evaluation of the conformity and homogeneity of the PTV, the current study used the conformity index, which is equal to the volume of the body receiving at least 95% of the prescribed dose (V_95%) divided by the volume of the PTV (V_PTV) and the homogeneity index (HI) = (D_2% - D_98%)/D_50%, where D_X% represent the doses received by X% and PTV volumes, according to the International Commission on Radiation Units and Measurements 83. We then calculated the percentage volume receiving 30 Gy (V_{30 Gy}) of heart and the mean heart dose, V_{5 Gy}, V_{10 Gy}, V_{20 Gy} and V_{30 Gy} of lungs and the mean lung dose in both 4F-3DCRT and SA-VMAT.

Computed tomography data sets and target/OAR contours from the sixteen enrolled patients were transferred from the CK system to the Eclipse treatment planning system (version 15.5, Varian Medical System Inc.). The corresponding HA plans were then generated according to the corresponding CK treatment plan’s dose prescription and OAR constraints. The HA plans were designed using 6 MV flattening-filter-free photon beams and a 1400 MU/min dose rate from Varian TrueBeam (Varian Medical System Inc.) equipped with a high-definition 120-leaf multileaf collimator (with a dynamic beam aperture and a spatial resolution of 2.5 mm leaf width × 32 pairs at the center, 5 mm width × 28 pairs in the peripheral leaves, and maximum static field size 40 cm × 22 cm). The Eclipse system automatically arranged arc fields: one full or half coplanar arc with a couch rotation of 0° and up to three partial noncoplanar arcs with couch rotations of 315°, 45°, and 90° (or 270°)^{17 (link),19 (link)}. The collimator angle and field size were optimized to maintain the coverage of the targets and reduce the radiation dose to OARs. The photon optimization algorithm for the homogeneous delivery group and the inhomogeneous delivery group was SRS NTO and ALDO (version 15.5.11, Varian Medical System Inc.). The calculation algorithms of Acuros XB (version 15.5.11, Varian Medical System Inc.) were applied for all cases.

Each patient was immobilized in the supine position with a VacQfix Cushion (Qfix, Avondale, PA), after which a planning CT scan at slice intervals of 2 mm was performed. Tumor and organ delineation and radiotherapy planning were performed by using Eclipse (Varian Medical Systems, Palo Alto, CA). Gross tumor volume (GTV) was determined on the basis of the visible extent of the tumor on planning CT, and internal GTV was determined by using 4-D CT images. A planning target volume (PTV) was created by adding 5 mm around the internal GTV for inter- and intrafractional uncertainty. Twenty-eight or 30 Gy in 1 fraction, 48 Gy in 4 fractions or 60 Gy in 8 fractions was prescribed to cover 95% of the PTV by using 6 MV-FFF beams. The planning algorithm included an Acuros XB; in addition, the radiotherapy technique was volumetric modulated arc therapy, and the treatment machine was a TrueBeam STx (Varian Medical Systems, Palo Alto, CA).