Comparison of dosimetry in radiotherapy for prophylactic cranial irradiation for prophylactic cranial irradiation in small cell lung cancer

Abstract

Objective To compare the dosimetric differences among three-dimensional conformal radiotherapy(3D-CRT),intensity-modulated radiotherapy(IMRT)and RapidArc for prophylactic carnial irradiation(PCI)in small cell lung cancer(SCLC)patients.Methods Ten patients with SCLC were enrolled into this study.3D-CRT,9-field IMRT(IMRT)and double arc RapidArc plans were designed and optimized for each patient.The goal was to deliver 25 Gy to ≥ 95％ of the planning target volume(PTV)while the same normal-tissue dose constraints were achieved.The dose distribution and conformal index (CI),homogeneity index(HI)of target volume,the maximum dose(D2 ％),the minimum dose(D98 ％),target coverage of PTV(V95 and V100),and Dmean and Dmax of organs at risk(OAR)were analyzed by using the dose volume histogram(DVH).The monitor units and delivery time were also evaluated.Results All plans met the clinical requirements.PTV dosimetric parameters(CI,HI,D2％,D98％,V95 and V100)of RapidArc and IMRT were superior to those of 3D-CRT with significant difference(P＜0.05).The maximum doses to the optic nerves,brainstem and the mean dose to the parotid glands of the IMRT and RapidArc plans were all significantly lower than those of the 3D-CRT plan(P＜0.05),while 3D-CRT plan provided the lowest maximum doses and mean dose of the lens and eyes(P＜0.05).Compared with IMRT plan,no obvious advantage in PTV dosimetric parameters could be observed in RapidArc plans.In terms of organ sparing,no statistical difference was observed between IMRT and RapidArc plans.The number of monitor units for 3D-CRT,IMRT and RapidArc were 287.8,1388.8 and 346.6,respectively.Conclusions Compared with 3D-CRT,IMRT and RapidArc show better dosimetric quality.The 3D-CRT plan has a significantly lower dose on the lens and eyes,less MU and shorter delivery time than IMRT and RapidArc plans. Key words: Three-dimensional conformal radiotherapy; Intensity modulated radiotherapy; Prophylactic cranial irradiation; Dosimetry