Dosimetric evaluation of glioblastoma (GB) radiotherapy with tomotherapy

In this study, 3 individual therapy planning and dose verification including single phase, hypofractional and double phase with Tomotherapy capable for Intensity Modulated Radiation Therapy (IMRT) by using section images of Computed Tomography (CT) taken before the therapy for 9 patients diagnosed with Glioblastoma (GB) were performed. The prescribed doses were to PTV total dose of 60 Gy at 2 Gy per daily fraction in single and double phase therapy; total dose of 40 Gy at 2,66 Gy per daily fraction in hypofractional therapy. For single phase therapy, when compared with 2,5 cm jaw width, maximum dose received by target volume decreased by 1,3% whereas minimum dose increased by 9,3% in planning done with 1 cm jaw width. Critical organ doses were decreased 5.00% for brain stem, 7,67% for optic chiasm, 31,70% for right optic nerve, 15,17% for left optic nerve, 29,47% for right lens, 23,10% for left lens at maximum dose and 33,93% for right eye, 19,63% for left eye at mean dose. Therapy period increases by 103% in mean when 1 cm jaw width was used instead of 2,5 cm jaw width. In double phase therapy; when compared with 2,5 cm jaw width, maximum dose for target volume in planning dose with 1 cm jaw width decreased 1,3% for phase 1, 3,5% for phase 2 whereas minimum dose for such target volume increased by 14,1% for phase 1 and 16,4% for phase 2; and better dose homogeneity was provided. Critical organ doses were decreased 13% for brain stem, 5,1% for optic chiasm, 31,4% for right optic nerve 35,5% for left optic nerve, 21% for right lens, 48,1% for left lens at maximum dose and 30,1% for right eye, 66,5% for left eye at mean dose. In spite of that, there is an increase in therapy periods by 128% for phase 1, 125% for phase 2. In hypofractional therapy both were reduced number of fractions and therapy periods by planning with 2,5 cm jaw width. Homogeneity index value for target volume is 1.05. Because total dose value was 40 Gy, critical organ dose values were below tolerance values. Therapy planning should be testes for compatibility to the therapy in tomotherapy. Data for planning were compared with measurement data. In all sections, median compatibility was obtained by 98% for single phase therapy, 96% for hypofractional therapy, 97% for the first phase and 98% for the second phase in double phase therapy. For all therapy options in GB treatment, although more homogenous dose for target organ and less critical organ dose was achieved with jaw width of 1 cm, a jaw width of 2.5 cm is an appropriate jaw width because of therapy period.