A Comparative Dosimetric Analysis of Volumetric Modulated Arc Therapy (VMAT) Versus Intensity-Modulated Radiation Therapy (IMRT) for Head and Neck Cancer in an Indian Population

Background Radiotherapy is a primary treatment for head and neck cancers (HNC). Intensity-modulated radiation therapy (IMRT) is the standard, but volumetric modulated arc therapy (VMAT) has emerged as a faster alternative. This study compares the dosimetric and planning parameters of IMRT and VMAT for HNC patients in an Indian population. Aims To prospectively compare IMRT and VMAT plans for HNC patients, focusing on planning target volume (PTV) coverage, dose to organs at risk (OARs), conformity index (CI), homogeneity index (HI), monitor units (MUs), and treatment time. Methods This prospective observational study included 30 patients with HNC. For each patient, both a seven-field sliding window IMRT plan and a double-arc VMAT plan were generated. Dosimetric parameters for PTVs (66 Gy, 60 Gy, and 54 Gy) and OARs (spinal cord, brainstem, mandible, and parotids) were compared using paired statistical tests. Results Both techniques produced clinically acceptable plans. IMRT plans demonstrated statistically superior PTV coverage, with better D95% and D98% values across all target volumes (p < 0.01 for PTV66 D95% and D98%). IMRT also yielded slightly better conformity for the PTV66 (CI 95%: 0.98 vs. 0.97 for VMAT, p < 0.01). VMAT plans provided significantly better sparing of the parotid glands (p ≤ 0.01). While IMRT resulted in a lower maximum dose to the brainstem (40.88 Gy vs. 48.74 Gy, p < 0.01), doses from both plans were within tolerance. VMAT plans were significantly more efficient, reducing the mean number of MUs by 58.5% (1342.79 vs. 556.50) and the mean treatment time by 58.6% (3.67 min vs. 1.52 min) (p < 0.01 for both). Conclusion VMAT provides comparable, clinically acceptable plans to IMRT while offering superior parotid sparing and a significant reduction in treatment time and MUs. These efficiencies make VMAT a highly advantageous technique, particularly in high-volume cancer centres.