Figure 10. Another alternative plan with dose escalation to the gross tumor for 15-fr radiosurgery combined with simultaneously integrated reduced-dose whole-brain irradiation.

The images show (A, B) the dose distributions superimposed onto CT images, (A) an axial image, (B) a coronal image and (C) DVHs.

(A-C) In the alternative plan, 62 Gy/15 fr is assigned to the D_99% of the GTV. The BED₁₀ of 62 Gy/15 fr is 87.6 Gy, almost equivalent to a single dose of 25 Gy (BED₁₀ 87.5 Gy). The cumulative BED₁₀s of the GTV D_99% in the original and alternative plans are 102.6 Gy and 87.6 Gy (14.6% reduction), while the total treatment duration is reduced by approximately one-third with the alternative plan. The cumulative BED₂s of the GTV D_99% in the original and alternative plans are 195.2 Gy and 190.1 Gy (2.6% reduction), respectively. The cumulative BED₂s of the GTV + 3 mm D_99% in the original and alternative plans are 157.1 Gy and 143.9 Gy (8.4% reduction), respectively.

D_99%: a minimum dose encompassing at least 99% of the target volume; GTV: gross tumor volume; GTV + 3 mm: GTV plus a uniform 3-mm margin; CT: computed tomography; DVH: dose-volume histogram; fr: fraction(s); BED_10/2: a biologically effective dose based on the linear-quadratic formula with an alpha/beta ratio of 10/2