KEY POINTS
- This retrospective planning study included 14 patients previously treated with DIBH VMAT to the left breast or chest wall plus comprehensive regional nodal irradiation. Each patient generated 18 plans across TrueBeam, Halcyon and Versa HD, producing 252 plans comparing open-field versus aperture-restricted geometry and three optimizer convergence settings.
- All plans prescribed 40.05 Gy in 15 fractions and were normalized so that 95% of the breast/chest-wall PTV received 95% of prescription. Aperture restriction moved the deep tangential field border approximately 1–2 cm toward the isocenter, limiting direct beam entry through the heart while maintaining identical arc geometry.
- Mean heart dose fell significantly with aperture restriction for every linac and convergence mode. With the basic “Off” optimizer setting, it decreased from 4.20 to 2.71 Gy on TrueBeam, 3.32 to 2.58 Gy on Halcyon, and 3.97 to 2.84 Gy on Versa HD, all P<.001.
- The clinical planning threshold showed an even clearer difference: 33/126 open-field plans (26.2%) exceeded a 4-Gy mean heart dose versus only 3/126 aperture-restricted plans (2.4%). With “On” or “Extended” convergence, all aperture-restricted plans remained below 4 Gy; the lowest average heart dose was 2.19 Gy with Halcyon plus Extended optimization.
- Ipsilateral lung exposure also decreased. On TrueBeam with convergence Off, left-lung V17Gy dropped from 31.17% to 23.12% (P<.001); across the full dataset, all 126 aperture-restricted plans met the acceptable V17Gy ≤35% criterion compared with 107/126 open-field plans.
- Cardiac sparing came with a low-dose trade-off in the contralateral breast/chest wall. For example, TrueBeam-Off right breast/chest-wall V5Gy increased from 5.00% to 8.95%, Halcyon-Off from 4.11% to 8.69%, and Versa-HD-Off from 4.31% to 11.62%; right-lung V4Gy did not significantly differ between geometries.
- Aperture restriction increased modulation and monitor units, but high-MU plan QA remained acceptable: average gamma pass rates were approximately 98.9–99.9% across platforms. More extensive convergence further improved heart dose and hotspots but increased optimization time from about 6 minutes with Off to 18 minutes with On and 50 minutes with Extended.
CLINICAL TAKEAWAY
For comprehensive left-sided breast/chest-wall plus nodal VMAT, simply controlling the deep aperture can materially reduce cardiac and ipsilateral lung exposure without sacrificing target coverage. The strategy is technically attractive and reproducible across three linac designs, but the higher contralateral breast dose means its value should be individualized, particularly when an intact contralateral breast is present.