A Dosimetric Comparison of Volumetric-Modulated Arc Therapy to Intensity-Modulated Radiation Therapy in the Treatment of Locally Advanced Rectal Carcinoma

Introduction: The study was conducted to compare volumetric-modulated arc therapy (VMAT) with intensity-modulated radiation therapy (IMRT) in patients with locally advanced rectal cancer (LARC). Material and Methods: Ten computed tomography (CT) scans were selected and for each CT scan, two plans were created (IMRT and VMAT). The average cumulative dose-volume histograms (DVH) of VMAT plans for the planning target volumes (PTVs), organs at risk (OARs), and normal tissues were calculated and compared with those reported for the corresponding IMRT technique. Results: Target coverage was equivalent for both techniques. For primary PTV, the average homogeneity index (HI) of IMRT was significantly lower than the VMAT plans (0.10±0.04 vs. 0.11±0.03; P<0.0001). The average conformity index (CI) values for IMRT and VMAT were 1.21 and 1.12, respectively, with a nonsignificant trend for better results with VMAT (P=0.1). For the PTV boost, there was a nonsignificant trend for better results with VMAT in average HI and CI. The VMAT was superior to IMRT in OAR sparing. For monitor units (MUs), VMAT plans required 70% less MUs than IMRT. Conclusion: For LARC patients, VMAT was able to deliver treatment plans dosimetrically equivalent to IMRT in terms of PTV coverage. The VMAT provided better OAR sparing and significant reduction of MUs in comparison to IMRT.