Agility mlc

A standard plan and a DP plan were developed for each patient in RayStation. To overcome the absence of computed tomography (CT) data in the public dataset, water-equivalent density overrides were assigned to the brain (1.04 g/cm³) and the skull (1.61 g/cm³). Both plans were created as volumetric modulated arc therapy with two 6 MV full arcs from an Elekta Versa HD with Agility MLC (5 mm leaf size). For the standard plan, an isodose of 60 Gy delivered in 30 daily fractions was assigned to the PTV. Dose constraints to OARs were set according to EORTC guidelines.^{31 ,32 (link)} For the DP plan the inverse dose prescription map previously imported into RayStation was assigned to a mock treatment plan. DP plans were generated using an approach previously described by Arnesen et al.³⁵ The optimization was performed in dose summation mode, where the mock plan containing the inverse DP prescription was assigned as a pretreated plan. As optimization targets minimum dose of 76.8 Gy to GTV, minimum dose of 61.2 Gy to CTV, minimum dose of 60.6 Gy to PTV, and maximum dose of 77.5 Gy to PTV were used to allow the optimizer to create the prescribed DP dose distribution within the PTV for the actual plan (Supplementary Fig. S1). Fractionation and dose constraints to OARs were set as per the standard plans.

A total of 52 patients were imaged with both FI and IECT. Treatment localizations were lung (39 patients, 12 in the upper lobe, 11 in the medial lobe, and 16 in the lower lobe) and liver (13 patients). All the patients were scanned and treated with their arms around the head, lying over a foam cradle and with a body mask performing abdominal compression.
Due to difficulties to locate tumors during daily treatment verification with CBCT, two to three 8‐shaped platinum pushable coils (Boston Scientific, Marlborough, MA, USA) were placed to liver patients inside or close to the tumor as fiducial markers. The markers were then used as tracking target in FI.
Treatments were planned with a Pinnacle 16.0 (Philips) treatment planning system (TPS). 3D conformal radiotherapy technique (3DCRT) was used for lung tumors except for the cases requiring a VMAT technique. This last technique was employed on all of the liver tumors. The Planning Target Volume encloses the ITV with a 5 mm margin. An Elekta (Elekta, Crawley, UK) C‐arm linac with an Agility MLC was used for treatment delivery.

VMAT plans were generated using a 6 MV photon beam, with the clinical Monaco Version 5.11.01 TPS (Elekta AB, Stockholm, Sweden) and the Agility MLC. For all patients included in this study a VMAT plan using two coplanar arcs was calculated using a Monte Carlo algorithm, with a calculation grid size of (0.3 cm)³ and a statistical uncertainty during dose prediction of 1%. These plans were delivered clinically.

Three different institutions with Elekta linacs (two VersaHD and one Synergy) equipped with the Agility MLC (Elekta AB, Stockholm, Sweden) and the RayStation TPS (RaySearch Laboratories, Stockholm, Sweden) participated in this study, using the 6 MV flattened beam. The Agility MLC uses a flat slightly non-target pointing surface [14] (link), [15] (link). The tilted leaf side is cut by the rounding of the leaf tip, reducing the maximum extension of the tongue-and-groove into the open region with a progressive increase of tongue-and-groove shadowing as far as 20 mm from the leaf tip end [7] (link).

Measurements were performed on a VersaHD linear accelerator (Elekta AB, Stockholm, Sweden) equipped with an Agility MLC (5 mm leaf width). Also available was the MV imaging acquisition software iViewGT™ (Elekta AB, Stockholm, Sweden) with an amorphous silicon EPID (PerkinElmer XRD 1642 AP) which is situated at 160 cm distance from the linac target. The EPID panel has a detection area of 41 × 41 cm² (1024 × 1024 pixels). Treatment plans with all available energies (6 MV, 10 MV, 6 MV FFF, and 10 MV FFF) were generated with Pinnacle V9.10 (Philips Medical Systems, Eindhoven, The Netherlands).