Comparison of dosimetric and radiobiological plans in intensity-modulated radiotherapy for oropharyngeal cancers

Objective: The aim is to evaluate and compare VMAT treatment plans dosimetrically and radiobiologically in patients diagnosed with oropharyngeal cancer within the head and neck patient group. Dosimetric analysis will focus on dose homogeneity in the target tumor region, dose distribution to healthy tissues, and assessment of side effects. Radiobiological analysis will assess the effectiveness of radiation dose in tumor cell killing and healthy tissue preservation. Method: CT images of 10 male patients diagnosed with oropharyngeal cancer were re-contoured for PTV54, PTV60, PTV70, and OARs. Treatment plans were generated using the Elekta Monaco treatment planning system with a prescribed radiation dose of 70 Gy, planned in three sequential phases using the VMAT technique. In addition to standard VMAT plans, new sequential plans were created by incorporating the biological α parameter with values of 0.5, 0.75, and 1. EUD equivalents were calculated using a software application, and TCP and NTCP analyses were performed. Results: VMAT and VMAT-α plans were compared in terms of dose distribution and critical organ sparing for different PTV volumes. While VMAT plans generally provided higher 95% coverage values and more homogeneous dose distribution, similar results were obtained with VMAT-α plans, particularly for α=1. In Dmin, Dmax, and Dmean dose analyses, VMAT-α plans exhibited lower Dmin values in certain volumes; however, these differences were balanced in terms of overall PTV70 coverage. Regarding critical organ doses, VMAT-α plans demonstrated lower doses for structures such as the brainstem, spinal cord, and larynx. Biological evaluations conducted using RADBIOMOD software indicated that VMAT and VMAT-α plans provided comparable efficacy in tumor control. Conclusion: Similar dosimetric outcomes were achieved with the VMAT technique commonly used in radiotherapy for oropharyngeal cancer and VMAT plans prepared using biological parameters.