Hd 120

The treatment was planned within the 50% phase, used as a reference scan, and in the Pinnacle 9.10 TPS, with two partial dynamic conformal arcs, from 0° to 179.9°, where the multileaf collimator (MLC) was fitted to target each 5°. The treatment field size was 5 cm × 5 cm, created with an MLC (HD 120, with leaves of 2.5 mm in the center and 5 mm in the periphery) of the TrueBeam Novalis STx (Varian Medical Systems, Palo Alto, CA, USA). After that, the target was surrounded by secondary collimating jaws to reduce interleaf leakage.
The dose was calculated using the collapsed cone convolution algorithm, with a grid size of 2 mm, 6 MV beams, and a dose rate of 600 monitor unit (MU)/min. For all patients, the dose regimen of 60 Gy in 4#s over 1 week was prescribed. The prescription was normalized to 80% isodose lines. The planned dose to the moving GTV was 16.21 ± 0.46 Gy per fraction, delivered at 890 ± 10 MU.

The 76 plans of the 46 patients were exported from RayStation and then imported into Elements MBM v.4.0. The treatment plans were replanned using a demonstration protocol with a single isocenter using the DCA technique. The VMAT technique is available for one target among multiple targets in this machine, but was not used in this study. The protocol was modified for irregular dose fractionation. D₉₈ for the TV was used in MBM calculations, despite this differing from CK planning, because it is recommended in the protocol that we plan to use in clinical practice. The treatment beams were equipped with flattening filter free 6 MV photon beams (1200 MU/min). The number of arcs was determined automatically depending on the spatial distribution of the metastases. The arc consisted of at least one coplanar arc and 3 non-coplanar arcs with couch angles of 0, 45, 135 and 270°. The resolution of the multileaf collimator was 2.5 mm (HD 120, Varian Medical Systems, Palo Alto, CA, USA). Pencil Beam Convolution was used for inverse planning with a dose grid resolution of 2.0 mm. The treatment plans were automatically adapted to adjusted target dose homogeneity and dose constraints of the target and organs at risk based on the clinical treatment protocol.