Abstract
We tested whether an ionization chamber array (ICA) and a one‐dimensional water scanner (1DS) could be used instead of a three‐dimensional water scanning system (3DWS) for acceptance testing and commissioning verification of the Varian Halcyon–Eclipse Treatment Planning System (TPS). The Halcyon linear accelerator has a single 6‐MV flattening‐filter‐free beam and a nonadjustable beam model for the TPS. Beam data were measured with a 1DS, ICA, ionization chambers, and electrometer. Acceptance testing and commissioning were done simultaneously by comparing the measured data with TPS‐calculated percent‐depth‐dose (PDD) and profiles. The ICA was used to measure profiles of various field sizes (10‐, 20‐, and 28 cm2) at depths of dmax (1.3 cm), 5‐, 10‐, and 20 cm. The 1DS was used for output factors (OFs) and PDDs. OFs were measured with 1DS for various fields (2–28 cm2) at a source‐to‐surface distance of 90 cm. All measured data were compared with TPS‐calculations. Profiles, off‐axis ratios (OAR), PDDs and OFs were also measured with a 3DWS as a secondary check. Profiles between the ICA and TPS (ICA and 3DWS) at various depths across the fields indicated that the maximum discrepancies in high‐dose and low‐dose tail were within 2% and 3%, respectively, and the maximum distance‐to‐agreement in the penumbra region was <3 mm. The largest OAR differences between ICA and TPS (ICA and 3DWS) values were 0.23% (−0.25%) for a 28 × 28 cm2 field, and the largest point‐by‐point PDD differences between 1DS and TPS (1DS and 3DWS) were −0.41% ± 0.12% (−0.32% ± 0.17%) across the fields. Both OAR and PDD showed the beam energy is well matched to the TPS model. The average ratios of 1DS‐measured OFs to the TPS (1DS to 3DWS) values were 1.000 ± 0.002 (0.999 ± 0.003). The Halcyon–Eclipse system can be accepted and commissioned without the need for a 3DWS.
Highlights
The newly designed Halcyon linear accelerator (Linac; Varian Medical Systems, Palo Alto, CA) has a single‐energy 6‐MV flattening filter‐ free photon beam with maximum field size of 28 × 28 cm[2] at the isocenter
For the profiles measured with the ionization chamber array (ICA), our results demonstrated that the ICA‐measured profiles matched very well with treatment planning system (TPS) and 3D water scanning system (3DWS) data in high‐dose, low‐dose tail, and penumbra regions
We demonstrated that a 2D detector array and 1D water scanner system can be used for acceptance and clinical verification of the Halcyon‐Eclipse TPS static beam data, and the resulting beam data match those of the TPS and a 3DWS
Summary
The newly designed Halcyon linear accelerator (Linac; Varian Medical Systems, Palo Alto, CA) has a single‐energy 6‐MV flattening filter‐ free photon beam with maximum field size of 28 × 28 cm[2] at the isocenter. The gantry is enclosed and the machine does not have isocenter lasers or a light field but does have external setup lasers outside of the bore. The external lasers are used for initial patient (or phantom) setup outside the bore, and the patient can be loaded to the isocenter position through predefined couch shifts from the initial position to the isocenter position. The single‐energy Halcyon Linac is tightly matched with a treatment planning system (TPS) beam model that is predefined by Varian. The universal beam model in the Eclipse TPS for all Halcyon Linacs cannot be modified by the user and the TPS has no adjustable beam‐modeling tools. Because of this, commissioning verification was based on AAPM Medical Physics Practice Guideline for Commissioning and QA of External Beam Planning Systems (MPPG5.a).[1]
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