ArticleBMC cancer2026
Spiral volumetric modulated arc therapy enhances peak-to-valley dose contrast for 3D-GRID radiotherapy compared to VMAT and tomotherapy.
Article in BMC cancer, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
purposeThree-dimensional GRID radiotherapy for bulky tumours requires high peak dose while effectively preserving a low-dose intratumoural valley, but this remains challenging with current linac-based techniques. Spiral volumetric modulated arc therapy (sVMAT) is an integrated delivery technique with synchronized longitudinal couch motion and gantry rotation that generates a spiral/helical beam trajectory, combining key advantages of volumetric modulated arc therapy (VMAT) and helical tomotherapy (TOMO). This study evaluated the dosimetric feasibility of sVMAT for single-fraction 3D-GRID radiotherapy and compared it with conventional VMAT and TOMO.
methodsTwenty patients with bulky tumours were retrospectively replanned. Cylindrical GRID peak structures with a diameter of 1.0 cm were generated within the GTV using a uniform 0.5-1.0 cm retraction from the GTV boundary and a 1.0 cm clearance from adjacent OARs; cylinders violating these spatial constraints were automatically truncated or excised. A single fraction of 18 Gy was prescribed to the virtual GRID peaks only, while dose to the intervening non-peak GTV valley was minimized as low as reasonably achievable rather than intentionally prescribed. For each patient, three plans were individually generated: VMAT, TOMO and sVMAT. sVMAT plans were created on the NeuRT Aurora platform using DeepPlan with synchronized gantry rotation and bidirectional couch translation. Dosimetric comparisons included gradient index (GI), peak-to-valley dose ratio using two definitions (PVDR
resultssVMAT showed the strongest overall dosimetric performance. sVMAT achieved the steepest dose gradient, with a lower GI than VMAT and TOMO (8.86 ± 2.00 vs. 14.93 ± 5.18 and 15.07 ± 5.97; both p < 0.001). PVDR1 was numerically highest with sVMAT (5.137 ± 2.325), compared with VMAT (4.692 ± 2.213) and TOMO (3.963 ± 2.288). PVDR2 was also highest with sVMAT (2.975 ± 0.470 vs. 2.604 ± 0.464 and 2.575 ± 0.567, respectively). All three techniques met single-fraction OAR constraints without clinically meaningful differences. Both MU and beam-on time for sVMAT were intermediate between VMAT and TOMO, with VMAT showing the lowest values and TOMO the highest; mean beam-on time was 1181 ± 512 s for sVMAT, versus 307 ± 30 s for VMAT and 1896 ± 1224 s for TOMO.
conclusionFor cylindrical 3D-GRID radiotherapy, sVMAT provided superior dose confinement and enhanced peak-to-valley dose contrast, while maintaining OAR sparing comparable to VMAT and TOMO. These findings support sVMAT as a promising platform for modern high-contrast 3D-GRID radiotherapy.
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