Comparison Of Dosimetry In Whole Brain Radiation Therapy For Small Cell Lung Cancer Between Three-dimensional Conformal Radiotherapy And Volumetrically Modulated Arc Therapy

Objective: A treatment planning comparison study was performed toevaluate the dosimetric differences of three-dimensional conformalradiotherapy(3D-CRT) with volumetrically modulated arc therapy(RapidArc)for prophylactic cranial radiation(PCI) in small cell lung cancer(SCLC)patients.Materials and methods: Ten patients with SCLC were enrolled into thisstudy.3D-CRT and RapidArc plans were designed for each patient. Theprescribed dose was30Gy in15fractions. Plans were compared in terms ofconformity index, homogeneity index of target volume and receiving dose tocritical organs by analysis of dose-volume histogram.Results：The CI was0.49±0.11and0.92±0.01（t=8.71, P <0.05）, and HIwas1.07±0.01and1.05±0.01（t=-3.16, P <0.05） for3D-CRT and RapidArc,respectively. Compared with3D-CRT plan, the maximum, mean, minimumdose of PTV was elevated by1.0Gy，1.2Gy，18.6Gy(t=7.25,10.06,15.62, P<0.05). The mean dose to the external auditory canal, parotid, V20of the scalpand parotid of RapidArc were all significantly lower than those of3D-CRT（P<0.05）, while3D-CRT plan reduced the mean dose of the lens and internalauditory canal with significant differences（P <0.05）.Conclusion: RapidArc provides significant improvement in target coverage and homogeneity,so does in the sparing of the scalp, parotid glandsand external auditory canal.