FIGURE 3. Results of phantom measurements. (A) Dependence of half-dose depth on mean positron energy measured with radiation-sensitive MD-55 Gafchromic films in water bath. Linear function is described by d = 0.024 + 1.045 E_mean. (B) Dose-over-depth functions calculated from phantom measurements. Curves are normalized to dose of 20 Gy at 1 mm distance from balloon surface. Only ¹⁵O and ⁶⁸Ga have acceptable dose distribution due to sufficient positron energy.