Planning of helical tomotherapy,intensity modulation radiation therapy and 3-dimensional conformal radiation therapy for cerebral metastatic cancer:A dosimetric study

Objective To provide the scientific evidence for the selection of helical tomotherapy（TOMO）,intensity modulation radiation therapy（IMRT） and 3-dimensional conformal radiation therapy planning（3D-CRT） for cerebral metastatic cancer by assessing their dosimetric characteristics. Methods Ten patients with 1,2,3 and more foci of cerebral metastatic cancer respectively on CT/MRI images were selected.Their target areas and normal organs were underlined and transmitted to the Precise,Pinancle and TOMO planning systems.Prescribed dose for the whole brain（PTVwb） was 40Gy/20F,while doses for the cerebral metastases（pGTVs） were boosted to 60Gy/20F.Treatment plans for the cerebral metastatic cancer were made with the 3D-CRT,IMRT and TOMO planning systems,respectively.Homogeneity index,heterogeneity index,dose coverage of targets,dose volume histograph（DVH）,and other dosimetric index were compared according to the RTOG 02-25 standards and organs at risk（OAR）.Maximum tolerant dose and average dose for normal organs were assessed. Results The three plans could meet the needs of prescribed doses and the limit of acceptable doses for the involved organs.The dose distribution,conformity,uniformity of TOMO plan were better than those of IMRT and 3D-CRT plans（P＜0.05）.The TOMO plan was better for the protection of lenses in patients with over 3 cerebral metastases than the IMRT and 3D-CRT plans（P＜0.05）,for the protection of optic nerves in patients with 1-2 metastases in middle and inner ears,and for the protection of brain stem in patients with more than 3 metastases than the 3D-CRT plan（P＜0.05）.The dose distribution,conformity,uniformity of PTVwb of IMRT plan were better than those of 3D-CRT plan（P＜0.05）.The 3D-CRT plan was better for the protection of optic nerves in middle ear of patients with 1-2 metastases and brain stem of patients with over 3 metastases,especially for the protection of brain stem of those with over 3 metastases than the IMRT plan（P＜0.05）,for the protection of eyes and lenses of patients with 1-2 metastases than the TOMO and IMRT plans（P＜0.05）. Conclusion The TOMO plan has better dose uniformity and conformality than the IMRT plan for cerebral metastases,and the IMRT plan is better than the 3D-CRT plan for cerebral metastases,especially for those with over 3 metastases.