Enhanced 3D-GRID radiotherapy on helical tomotherapy via personalized geometric optimization: A comparative study
Purpose:
This study developed and evaluated a personalized cylindrical 3D-GRID radiotherapy strategy adapted to helical tomotherapy (TOMO) for large-volume tumors, and compared it with intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT).
Methods:
Fifteen patients with large-volume tumors (GTV > 150 cm3) were retrospectively included. Anatomy-constrained cylindrical GRID volumes were generated within the GTV with predefined OAR clearance. Paired IMRT, VMAT, and TOMO plans were created using identical GTV and GRID-volume prescription objectives, and dosimetric, integral-dose, OAR-dose, and delivery-efficiency metrics were compared using the same patient-specific GRID geometry for all patients.
Results:
GTV lower-dose coverage metrics (D90 %, D95 %, and D98 %) did not differ significantly among techniques (all p > 0.05). For IMRT, VMAT, and TOMO, respectively, PVDR1 was 1.953 ± 0.159, 1.983 ± 0.164, and 2.229 ± 0.128, and PVDR2 was 2.466 ± 0.166, 2.474 ± 0.187, and 2.752 ± 0.144 (both omnibus p < 0.001). The higher PVDR values with TOMO were mainly driven by higher D5 % and D10 %, not lower D90 % or D95 %. TOMO also showed higher gradient index and Body-GTV integral dose, indicating less favorable dose fall-off and broader dose spread, whereas VMAT required the fewest MUs and shortest beam-on time. No evaluated OAR endpoint differed significantly among techniques or exceeded its corresponding five-fraction constraint.
Conclusion:
Personalized cylindrical 3D-GRID planning is dosimetrically feasible on TOMO and may serve as a platform-adapted option for TOMO-only or TOMO-dominant centers. Higher DVH-derived PVDR or AVF values should be interpreted with dose fall-off, integral dose, OAR dose, and delivery efficiency rather than as evidence of TOMO superiority.
