A Unified Planning Platform Comparison of VMAT, Helical Tomotherapy, and IMRT in Nasopharyngeal Carcinoma: Dosimetric Superiority and Organ Sparing Analysis

Introduction This study aimed to perform a rigorous dosimetric comparison of three advanced radiotherapy techniques—Volumetric Modulated Arc Therapy(VMAT), Helical Tomotherapy (TOMO), and Intensity-Modulated Radiation Therapy(IMRT)—for nasopharyngeal carcinoma (NPC), with particular emphasis on target coverage homogeneity, organ-at-risk (OARs) sparing, and the impact of using a unified treatment planning system (TPS) to eliminate inter-platform biases. Methods A total of 62 non-metastatic NPC patients were included in this retrospective study. All plans were re-optimized and calculated using a single TPS (RayStation 10B) with identical dose calculation algorithms to ensure comparability. Each patient underwent planning with dual-arc VMAT, helical TOMO, and 9-field IMRT techniques. Plans were evaluated based on homogeneity index (HI), conformity index (CI), and dose-volume parameters for multiple serial and parallel OARs. Statistical analyses included ANOVA with post-hoc Tukey tests. Results All techniques achieved adequate target coverage. VMAT yielded significantly superior homogeneity across all target volumes (HI = 0.06 ± 0.01 for PGTV70, p < 0.05), with no significant differences in CI among techniques. Both VMAT and TOMO significantly reduced doses to serial OARs such as the brainstem and spinal cord compared to IMRT (p < 0.05). TOMO provided the best parotid glands sparing (mean dose 26.13 ± 1.76 Gy), outperforming both VMAT and IMRT (p < 0.01). VMAT achieved the lowest brainstem mean dose (21.43 ± 4.47 Gy), while TOMO excelled in reducing high-dose volumes for most parallel OARs. Conclusion VMAT offers superior dose homogeneity and reduced delivery time, making it a highly efficient and dosimetrically favorable option for NPC radiotherapy. TOMO demonstrates advantages in sparing critical OARs, particularly in high-dose regions. The use of a unified TPS platform confirms that observed differences are technique-derived rather than planning-system artifacts. These findings support technique selection based on institutional resources and clinical priorities.