Influence of head position on radiation dose distribution in whole brain volume-modulated arc therapy / 中华放射肿瘤学杂志

ABSTRACT

Objective To explore the intensity of coplanar arc-adjusted radiotherapy with volume-modulated arc therapy (VMAT) and whether the position of the head tilt influences the distribution of radiotherapy dose.Methods From 2015 to 2017,500 patients underwent radiotherapy of the head and kept their head tilted.The simulated non-inclined CT images were obtained by rotating the original CT images.The protocol of the coplanar VMAT whole brain irradiation was 30 Gy and the maximum dose of planning target volume in the hippocampus was limited to 16 Gy.The doses of the optic nerve,optic chiasm and eyeball were lower than 37.5 Gy.The dosimetric parameters of two different protocols were statistically compared by paired t-test.Results The average head tilt angle was (11.12°±0.68°).The homogeneity and the conformal index in the tilted and non-tilted positions were decreased by (8.3±9.6) ％(P=0.033) and (5.2±4.1)％(P=0.009).The dose of hippocampus in the tilted position of the head was decreased by (13.6±6.2) ％ on average compared with that in the non-inclined position (P=0.004).The dose of the lenses was decreased by (15.5±11.1)％(P=0.008) on average.The doses of optic nerve and eyeball were declined by (6.8±5.6) ％(P=0.013) and (8.6±6.5) ％(P=0.016).Conclusions By tilting the head at an appropriate angle during VMAT whole-brain radiotherapy,the radiation dose distribution of the target volume can be significantly improved and the radiation dose in the hippocampus and visual system can be reduced simultaneously to maintain the therapeutic effect and minimize the effect upon the cognitive and memory function of patients.