Versa hd linear accelerator

A Versa HD linear accelerator (Elekta AB, Stockholm, Sweden) was used to produce a 4× 4 cm field using a nominal beam energy of 6 MV and a source‐to‐surface distance of 90 cm. EBT3 films were positioned one by one at 10 cm depth in a 30×30×30 cm Gammex solid water phantom (Sun Nuclear, Melbourne, FL, USA). Absorbed dose to water was determined in the same phantom setup using a PTW 30006 Farmer chamber (PTW, Freiburg, Germany) in a 10× 10 cm field following TRS‐483.¹⁸, ¹⁹ The phantom dose conversion factor was previously determined to be unity with an uncertainty of 0.1%. The number of MUs to deliver 1–6 Gy in 1 Gy steps in the 4× 4 cm field was calculated based on the determination of absorbed dose in the 10× 10 cm field considering the field output factor of the 4× 4 cm field of 0.879. Experiments were carried out in service mode manually defining leaf and jaw position. The output factor was measured with a Semiflex TM31010 (PTW, Germany), which does not require a correction for small field effects for this field size.¹⁸

The fixed-field IMRT plans were done in the Monaco 5.11 planning system and used 6 MV x-ray of a versa HD linear accelerator (Elekta Ltd., Crawley, UK). FF-IMRT plans were generated using nine evenly distributed coplanar fields with the gantry angles of 200°/240°/280°/320°/0°/40°/80°/120°/160°, and 25 control points were set in each beam. All FF-IMRT plans were calculated using Monte Carlo algorithm and the DMLC (sliding window) technique.

17 patients were treated with a Versa HD linear accelerator (Elekta Medical Systems Co., Stockholm, Sweden) of 6 MV photon beams. The VMAT plan of a 360^o full bow with 2 arcs was designed for every patient based on Smart Arc inverse optimization. The objective functions were shown in Table 1. The doses were calculated with the Collapsed Cone Convolution (CCC) algorithm [18 (link)]. The planning prescription setting was as follows: the PTV prescription being 45.0–50.0Gy/25 fractions, and the PGTV prescription being 60.0–62.5Gy/25 fractions.
Table 1

Dose-volume criteria used in the cervix cancer VMAT plans

Volume of interest	Dose-volume criteria (cGy)
PGTV	MinD = 95%PD, VPD ≥ 95%, MaxD = 107%PD
PTV	MinD = 95%PD, VPD ≥ 95%, MaxD = 107%PD
Rectum	V40 < 60%, D33% < 45Gy
Bladder	V40 < 40%, D33% < 45Gy
L-Femur	V45 < 5%, V30 < 30%
R-Femur	V45 < 5%, V30 < 30%
Intestine	V30 < 30%
Cord	MaxD = 45Gy

Note: PD is the prescribed dose

All VMAT physical schemes were designed with Pinnacle TPS (version 9.10). When the default value was DCGS = 4.0 mm, the planners optimized and adjusted the treatment plans for cervical cancer patients based on their own previous experience. After all the indicators of the plans met the clinical requirements, changed the DCGS (from 2.0 mm to 5.0 mm) and recalculated dose in the target volumes and OARs.

Clinical manual VMAT plans (MP) were optimized according to Institutional protocol dose tolerances PTV V_95% > 97%, acceptable > 95%, D_1% < 107%; rectum D_50% < 44.7 Gy; bladder D_50% < 57.3 Gy; small bowel V_45Gy < 195 cm³; femoral heads D_5% < 44.7 Gy [25 –28 (link)]. All plans were optimized with Monaco TPS (version 5.51.10) using a 6 MV-coplanar dual 330°-arc (165–195°) with up to 150 control points (CP), and sequencing parameters such as 1 cm-minimum segment width (SW), and highly smoothed fluence. The parameters of the Monte Carlo calculation were a 3 mm-dose grid and 1%-statistical uncertainty per plan. Patients were treated using an Elekta VersaHD linear accelerator equipped with the Agility Multileaf Collimator (MLC, 160 leaves, 5 mm thickness, up to 6.5 cm/sec), with the Monitor Unit (MU) calibration of 1 MU = 1 cGy with the reference field at the reference depth. The clinical objectives were accounted for in the a-priori MCO of the clinical Monaco^™ TPS, as comprehensively treated described in Trivellato et al. [21 (link)]. Final normalization of dose distribution to achieve minimum PTV coverage or to satisfy small bowel constraints has been allowed. Whenever it was not possible to respect the above constraints for PTV or at least one OAR, minor or major deviations were discussed with and accepted by the approving clinician.

Colorectal cancer cell lines were grown as monolayers or spheroids in 35-mm dishes and cells were grown for 4–7 days. Afterwards, cells were irradiated with 1, 4, and 10 Gy using an Elekta Versa HD Linear Accelerator (6 MV, gantryi angle 0°, fieldsize 25 cm × 25 cm, focus-to-skin distance of 95 cm). Cell growth was monitored daily under a microscope (Olympus CKX41) using bright field imaging with 10× magnification. Images were obtained before irradiation and 4–6 days after irradiation using an F-View Soft Imaging System.

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).