Abstract
PurposeVarian Halcyon linear accelerator version 2 (The Halcyon 2.0) was recently released with new upgraded features. The aim of this study was to report our clinical experience with Halcyon 2.0 for a dual‐isocenter intensity‐modulated radiation therapy (IMRT) planning and delivery for gynecological cancer patients and examine the feasibility of in vivo portal dosimetry.MethodsTwelve gynecological cancer patients were treated with extended‐field IMRT technique using two isocenters on Halcyon 2.0 to treat pelvis and pelvic/or para‐aortic nodes region. The prescription dose was 45 Gy in 25 fractions (fxs) with simultaneous integrated boost (SIB) dose of 55 or 57.5 Gy in 25 fxs to involved nodes. All treatment plans, pretreatment patient‐specific QA and treatment delivery records including daily in vivo portal dosimetry were retrospectively reviewed. For in vivo daily portal dosimetry analysis, each fraction was compared to the reference baseline (1st fraction) using gamma analysis criteria of 4 %/4 mm with 90% of total pixels in the portal image planar dose.ResultsAll 12 extended‐field IMRT plans met the planning criteria and delivered as planned (a total of 300 fractions). Conformity Index (CI) for the primary target was achieved with the range of 0.99–1.14. For organs at risks, most were well within the dose volume criteria. Treatment delivery time was from 5.0 to 6.5 min. Interfractional in vivo dose variation exceeded gamma analysis threshold for 8 fractions out of total 300 (2.7%). These eight fractions were found to have a relatively large difference in small bowel filling and SSD change at the isocenter compared to the baseline.ConclusionHalcyon 2.0 is effective to create complex extended‐field IMRT plans using two isocenters with efficient delivery. Also Halcyon in vivo dosimetry is feasible for daily treatment monitoring for organ motion, internal or external anatomy, and body weight which could further lead to adaptive radiation therapy.
Highlights
The Halcyon 2.0 (Varian Medical Systems, Palo Alto, CA, USA) became clinically available in the market since mid‐July 2018 with new upgraded features over the previous version (1.0)
As serving a high‐volume center for gynecological cancer treatments, we report our clinical experience with Halcyon 2.0 focusing on a dual‐isocenter intensity‐modulated radiation therapy (IMRT) planning and delivery for gynecological cancer patients and examine the feasibility of in vivo portal dosimetry
Our study demonstrated that daily treatment delivery verification using in vivo portal dosimetry based on treatment exit dose is feasible, while most published studies reported the use of portal dosimetry only for pretreatment verification.[15–17]
Summary
The Halcyon 2.0 (Varian Medical Systems, Palo Alto, CA, USA) became clinically available in the market since mid‐July 2018 with new upgraded features over the previous version (1.0). Halcyon linear accelerator is mainly designed for intensity‐modulated radiation therapy/volumetric modulated arc therapy (IMRT/ VMAT) delivery due to its unique features such as fast delivery via 4 RPM with a dose rate of 800 MU/s, FFF only beam, MLC characteristics, and automated daily IGRT workflow. The accuracy of IMRT/ VMAT planning and delivery depends on the quality of treatment planning system commissioning based on the beam data acquisition and modeling.[3–7]. The Halcyon linac is preconfigured with a reference beam model built in the Eclipse treatment planning system which the users cannot modify. Beam model parameters related to small fields and MLC dosimetry which typically are challenging for IMRT/VMAT commissioning can benefit in achieving good agreements between planning and delivery. Several studies have shown good agreements between measurements and calculated or reference values on Halcyon 1.0.8,9
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