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. 2019 Nov;20(11):111-120.
doi: 10.1002/acm2.12747. Epub 2019 Oct 29.

Early clinical experience with varian halcyon V2 linear accelerator: Dual-isocenter IMRT planning and delivery with portal dosimetry for gynecological cancer treatments

Hayeon Kim  1 , M Saiful Huq  1 , Ron Lalonde  1 , Christopher J Houser  1 , Sushil Beriwal  1 , Dwight E Heron  1
Affiliations

Early clinical experience with varian halcyon V2 linear accelerator: Dual-isocenter IMRT planning and delivery with portal dosimetry for gynecological cancer treatments

Hayeon Kim et al. J Appl Clin Med Phys. 2019 Nov.

Abstract

Purpose: Varian 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.

Methods: Twelve 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.

Results: All 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.

Conclusion: Halcyon 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.

Keywords: Halcyon 2.0; In vivo portal dosimetry; dual-isocenter; extended-field IMRT; gynecological cancer.

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Conflict of interest statement

The authors have no conflict of interest to declare.

Figures

Figure 1
Figure 1
Interfractional exit dose change using in vivo dosimetry.
Figure 2
Figure 2
Comparison of cone beam computed tomography images for fraction 1 and fraction 24.
Figure 3
Figure 3
(a) Dose distribution at the two isocenters. (b). Dose distribution in the treatment field and junction area.
Figure 4
Figure 4
In vivo portal dosimetry comparison.
See this image and copyright information in PMC

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