Purpose:In this paper,we report the results of our investigation into whole brain radiotherapy(WBRT)using linear accelerator(Linac)-based intensity-modulated radiation therapy(IMRT)and volumetricmodulated arc therapy(VMAT)in lung cancer patients with a high risk of metastasis to the brain.Materials & Methods:We assessed the absorbed dose and the rate of adverse effects for several organs at risk(OAR),including the hippocampus,according to the tilt of a patient's head.We arbitrarily selected each five WBRT cases where measurements were made with the patients' heads tilted forward and without such tilt.Using the dose-volume histogram(DVH),we calculated and compared the effective uniform dose(EUD)and normal tissue complication probability(NTCP)of the OAR.In order to compare the extent of hippocampal sparing,we also analyzed the mean and the maximum doses.Results:When a patient received coplanar(non-coplanar)IMRT with the head tilted forward,the EUD and NTCP values for the hippocampus decreased by 13%(2%)and 81%(15%),and the mean dose and maximum dose decreased by 8%(2%)and 7%(4%),respectively.For coplanar(non-coplanar)VMAT treatment,the EUD values decreased by 20%(14%),the NTCP values decreased by 92%(81%),and the mean dose and the maximum dose decreased by 10%(14%)and 13%(10%),respectively.Conclusion:If the patient tilted the head forward when receiving the Linac-based treatment,for the same treatment effect in the PTV,we confirmed that a lower dose entered the OAR,such as the hippocampus,eye,lens,and cochlea.Moreover,the damage to the hippocampus was expected to be the least when receiving coplanar VMAT with the head tilted forward,and we showed that damage to OAR,including the hippocampus,was the least overall when the head was tilted forward.Accordingly,if patients tilt their heads forward when undergoing Linac-based WBRT,we anticipate that a smaller dose would be transmitted to the OAR,resulting in better quality of life following treatment.