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Purpose <p>Three-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.</p> Methods <p>Twenty patients with bulky tumours were retrospectively replanned. Cylindrical GRID peak structures with a diameter of 1.0&#xa0;cm were generated within the GTV using a uniform 0.5–1.0&#xa0;cm retraction from the GTV boundary and a 1.0&#xa0;cm clearance from adjacent OARs; cylinders violating these spatial constraints were automatically truncated or excised. A single fraction of 18&#xa0;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<sub>1</sub>=D<sub>10%</sub>/D<sub>90%</sub> and PVDR<sub>2</sub>=D<sub>2%</sub>/D<sub>50%</sub>), and OAR sparing. Delivery efficiency was evaluated using monitor units (MU) and beam-on time.</p> Results <p>sVMAT 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 <i>p</i> &lt; 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&#xa0;s for sVMAT, versus 307 ± 30&#xa0;s for VMAT and 1896 ± 1224&#xa0;s for TOMO.</p> Conclusion <p>For 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.</p>

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Spiral volumetric modulated arc therapy enhances peak-to-valley dose contrast for 3D-GRID radiotherapy compared to VMAT and tomotherapy

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月24日

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  • Wu Weiwei,
  • Zhiwei Liu,
  • Li Weizhi,
  • Li Zhenghuan,
  • Dai Zhitao,
  • Wang Chuangao

摘要

Purpose

Three-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.

Methods

Twenty 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 (PVDR1=D10%/D90% and PVDR2=D2%/D50%), and OAR sparing. Delivery efficiency was evaluated using monitor units (MU) and beam-on time.

Results

sVMAT 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.

Conclusion

For 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.