Simultaneous integrated boost technique by helical tomotherapy for the treatment of glioblastoma multiforme with ¹¹C-methionine PET: report of three cases

We performed hypofractionated high-dose irradiation of a patient’s residual glioblastoma multiforme using a simultaneous integrated boost (SIB) technique with helical tomotherapy system (HT) planning. The gross tumor volume (GTV)-1 was defined as the area of intensive ¹¹C-methionine (MET) uptake and GTV-2 was defined as the area of moderate MET uptake. The planning target volume (PTV)-1 encompassed GTV-1 plus a 5 mm margin, and PTV-2 encompassed GTV-2 plus a 2 mm margin. SIB with HT was performed in eight fractions, planning the dose for GTV-1 at 68 Gy (biologically effective dose: BED = 126 Gy), PTV-1 at 56 Gy (BED = 95 Gy), and PTV-2 at 40 Gy (BED = 60 Gy). In each of the target areas, the uptake value on ¹¹C-methionine positron emission tomography (MET-PET) was considerably decreased following SIB, although no remarkable changes were demonstrated on magnetic resonance imaging (MRI). These cases demonstrate that SIB with HT planning using MET-PET offers excellent target coverage and uniformity. In addition, SIB with HT planning using MET-PET is organ sparing and MET-PET has great efficacy for monitoring treatment response after SIB. To more clearly define the impact of SIB with HT planning using MET-PET, further investigations are required.