Dosimetric and radiobiological parameters in brain cancers: A comparison of IMRT and VMAT techniques

This study aimed to perform a physics-driven comparison of volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) for brain cancers by integrating quantitative dosimetric indices derived from Monte Carlo–based dose calculation and radiobiological modeling. Plans prescribed at 50 Gy and 60 Gy were evaluated to investigate both physical dose distribution characteristics and predicted biological outcomes. Eighty-four computed tomography (CT) datasets of brain cancer patients (mean age, 51.9±12.8 years) were used for treatment planning. IMRT plans were generated using 7–9 non-coplanar fields, while VMAT plans employed a single full clockwise arc. Dose calculations were performed using a Monte Carlo algorithm within the treatment planning system to ensure accurate modeling of dose deposition in heterogeneous intracranial tissues. Quantitative dosimetric parameters, including minimum, mean, maximum doses and dose–volume metrics, were extracted. Conformity index (CI) and homogeneity index (HI) were calculated to assess plan quality from a physics standpoint. For radiobiological evaluation, dose–volume histograms (DVHs) were exported to Biosuit software to compute tumor control probability (TCP) using Niemierko’s EUD-based model and normal tissue complication probability (NTCP) for organs at risk (OARs) using the Lyman–Kutcher–Burman (LKB) model. VMAT demonstrated significantly shorter delivery times compared with IMRT (7.52±0.60 vs. 11.20±1.14 minutes; P=0.012) and required fewer monitor units per fraction, reflecting higher delivery efficiency. Quantitative dosimetric analysis revealed significant differences in D min , D2%, HI (0.12±0.07 for VMAT vs. 0.14±0.08 for IMRT; P=0.01), and CI (0.76±0.05 for VMAT vs. 0.72±0.05 for IMRT; P<0.001), indicating improved dose conformity and homogeneity with VMAT. Radiobiological modeling showed higher TCP for VMAT (0.83±0.07 vs. 0.80±0.06; P=0.04) and generally lower NTCP and EUD values for several OARs, although most NTCP differences were not statistically significant. Lower prescription dose (50 Gy) resulted in reduced OAR doses and NTCP values compared with 60 Gy. From a medical physics perspective, VMAT provides superior dosimetric performance and delivery efficiency compared with IMRT, while Monte Carlo–based dose calculation and radiobiological modeling suggest modest improvements in predicted tumor control and normal tissue sparing. The integration of advanced dose calculation algorithms with TCP/NTCP analysis enhances understanding of the physical–biological interplay in intracranial radiotherapy planning.