Radiobiological Comparison of Intensity-modulated Radiotherapy Using Cobalt-60 and 6 MV Linear Accelerator in Head and Neck Cancers

A BSTRACT Purpose of the Research: This study aims to compare the radiobiological effectiveness of intensity-modulated radiotherapy (IMRT) plans generated using the eclipse treatment planning system (TPS) with 6 MV X-rays from a linear accelerator (Linac) against equivalent plans developed for a Cobalt-60 (Co-60) unit in head and neck cancer patients. Materials and Methods: Twenty-five head and neck cancer patients were planned using IMRT with Eclipse TPS for 6 MV X-rays. Equivalent Co-60 plans were generated for comparison. Dose-volume histogram (DVH) data were analyzed using BIOPLAN software and Brenner’s analytical model to calculate tumor control probability (TCP) and normal tissue complication probability (NTCP) for optic nerves and spinal cord. Results: The average TCP values were significantly higher for 6 MV Linac plans (60.2%) compared to Co-60 (46.5%) using BIOPLAN ( P < 0.001). Brenner’s model showed a 76.1% increase in TCP. NTCP values were significantly lower for Linac plans for both optic nerves (0.062% vs. 0.279%) and spinal cord (0.008% vs. 0.085%) with NTCP reductions of 76.6% and 90.3%, respectively. A strong negative correlation was observed between delivered dose and NTCP values. Conclusion: IMRT plans using 6 MV Linac provide superior tumor control with significantly reduced toxicity to critical organs compared to Co-60. Radiobiological evaluation offers a more comprehensive and predictive assessment than DVH-based metrics and should be integrated into clinical practice to enhance treatment quality and patient outcomes.