Optimizing Head and Neck Cancer Radiotherapy: A Dosimetric Comparison of FF and FFF Beams in VMAT
Abstract
Aim: Head and neck cancer (HNC) is a significant global health concern, with rising incidence rates and a high prevalence in South Asia, particularly in India. Radiation therapy, including advanced techniques like Volumetric-Modulated Arc Therapy (VMAT) and Intensity-Modulated Radiotherapy (IMRT), plays a crucial role in treating HNC. This study aims to compare the dosimetric and biological and second cancer risk estimation differences between flattened (FF) and flattening filter-free (FFF) beams in VMAT treatment plans for HNC, focusing on the impact of 6 MV and 10 MV energies.
Methods: Twenty HNC patients underwent replanning using VMAT on an ELEKTA VERSA HD linear accelerator with 6 MV FF, 6 MV FFF, 10 MV FF, and 10 MV FFF beams. Dosimetric parameters evaluated included dose distribution to planning target volumes (PTVs) and dose delivered to 98% of the target (D98), 50% (D50), and 2% (D2), as well as doses to organs at risk (OARs)., monitor units per segment (MU/Segment), number of MU/cGy, treatment delivery time, conformity index, and homogeneity index, also biological parameters (NTCP and EUD) and second cancer risk estimation were evaluated.
Results: The results showed that 6 MV FFF beams provided slightly better dose-sparing for OARs compared to 6 MV FF, with no significant differences in target volume coverage. Both FF and FFF beams demonstrated comparable conformity indices, but FF beams had better homogeneity indices. FFF beams required more monitor units (MUs) and segments but offered reduced treatment delivery times. For 10 MV beams, FFF showed marginal advantages in dose homogeneity and sparing of normal tissues at lower doses, though it required more MUs and segments, this study found that NTCP and EUD were largely comparable between FF and FFF types, with minor but statistically significant differences for the brainstem (favoring FFF) and heart. Second cancer risks varied slightly by energy and technique 6MV FFF reduced parotid risks (though increased larynx risk).
Conclusion: 6 MV beams, particularly FFF, showed slight advantages in sparing OARs and target volume coverage compared to 10 MV beams. This study highlights the dosimetric comparability of FF and FFF beams in HNC treatment, with FFF offering potential benefits in treatment efficiency and reduced delivery times. This study also shows that FF and FFF types yield comparable radiobiological outcomes, though 6MV FFF beams slightly reduce doses to critical organs without sacrificing efficacy. Both types perform similarly, with minor risk variations by energy.
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Copyright (c) 2025 Limam Ahmed Neya, Reham S Sherif , Ehab M Attalla, Reem H El-Gebaly, Ahmed M Abdelaal
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