Normal lung tissue complication probability in MR-Linac and conventional radiotherapy

Purpose: To study normal lung tissue (NLT) complications in magnetic resonance (MR) image based linac and conventional radiotherapy (RT) techniques. Materials and Methods: The Geant4 toolkit was used to simulate a 6 MV photon beam. A homogenous magnetic field of 1.5 Tesla (T) was applied in both perpendicular and parallel directions relative to the radiation beam. Analysis of the NLT complications was assessed according to the normal lung tissue complication probability (NTCP), the mean lung dose (MLD), and percentage of the lung volume receiving doses greater than 20 Gy (V₂₀), using a sample set of CT images generated from a commercially available 4D-XCAT digital phantom. Results: The results show that the MLD and V₂₀ were lower for MR-linac RT. The largest reduction of MLD and V₂₀ for MR-linac RT configurations were 5 Gy and 29.3%, respectively. Conclusion: MR-linac RT may result in lower NLT complications when compared to conventional RT.