Blood dosimetry during volumetric modulated arc therapy for non-small cell lung cancer: A time-resolved model of circulating particles.

INTRODUCTION: Volumetric modulated arc therapy (VMAT) for non-small cell lung cancer (NSCLC) may result in radiation-induced haematological toxicities. To estimate the dose received by circulating blood particles, we implemented a four-dimensional dose delivery algorithm into a stochastic simulation of blood dynamics. METHODS: The treatment data of NSCLC patients who received VMAT between 2018 and 2024 were considered. The prescribed dose was 60 Gy/55 Gy/50 Gy delivered in 30/20/25 fractions. To estimate the blood dose, the doses at each control point calculated with the BeamSplitter were used in the Haematological Dose software (HEDOS). The blood dose metrics D98%/mean dose/D2% were calculated and compared with the four-dimensional algorithm (variable dose rates) and the original algorithm (constant dose rates). The main organs contributing to the blood dose were reported. RESULTS: The cohort consisted of 115 treatments of 98 patients. As compared with constant dose rates, the population blood D98% decreased (median ΔD98% = -0.1 Gy, p-value < 0.001) with variable dose rates, whilst blood D2% increased (median ΔD2% = 0.1 Gy, p-value < 0.001). The mean blood doses were similar in both calculations (median mean blood dose = 5.4 Gy, p-value = 0.3). At the population level, the largest change in blood D2% was 0.38 Gy. The main organs contributing to the blood dose were lungs (25%), brachiocephalic veins (14%), and aorta (12%). CONCLUSIONS: VMAT for NSCLC induced a larger blood D2% and a smaller blood D98% as compared with constant delivery.