Figure 2. Dose distributions and DVHs for the upfront 15-fraction stereotactic radiosurgery.

The images show (A, B) representative isodose distributions superimposed onto axial contrast-enhanced T1-weighted image and (C) DVHs.

(A, B) Nine representative isodose lines are shown to characterize the dose gradients mainly outside (A) and inside (B) the gross tumor boundary, along with the relevant BEDs based on the linear-quadratic formula with an alpha/beta ratio of 10 (BED₁₀). The 52.1 Gy isodoses are shown in both, although the colors are different. The sufficient GTV coverages with 52.1-57.9 Gy are compromised near the brainstem (arrows in A, B). (C) The BED₁₀s of 43.3 Gy, 47.6 Gy, and 52.4 Gy are 55.8 Gy, 62.7 Gy, and 70.7 Gy, respectively. The 52.4 Gy isodose is 73% relative to the maximum dose of the GTV.

DVH: dose-volume histogram; BED: biologically effective dose; GTV: gross tumor volume; GTV + 2/3 mm: a structure generated by adding an isotropic 2/3 mm margin to a GTV boundary; D_99%: a minimum dose encompassing at least 99% of the target volume