Radiation therapy typically employs high energy photon beams because the low absorption coefficient at these energies
minimizes skin dose with a conventional, unfocused beam. At orthovoltage energies less than 150 keV, the maximum
dose for a single beam occurs very close to the skin surface. However a well-focused beam of low energy x rays can
provide much higher flux at the target depth while sparing dose to the skin. The measured focal spot size for the
polycapillary optic was 0.2 mm and was found to remain unchanged through 50 mm of phantom thickness. The
calculated depth-dose curve was found to peak several centimeters below the surface with 25-40 keV radiation.
Modeling indicates that the tumor dose would remain much higher than
the skin dose even after scanning to cover a 1 cm<sup>3</sup> tumor.
Focusing x-ray optics can be used to increase the intensity onto small samples, greatly reducing the data collection time for powder diffraction. Typically, the beam convergence is restricted to avoid loss of resolution since the focused beams broaden the resulting powder diffraction rings. However, the resolution, as defined by the uncertainty in peak location, can be much less than the peak width. Two types of x-ray optics, polycapillary and doubly curved
crystals, were used to focus x rays onto standard inorganic powder diffraction samples. Comparisons were made of system resolution and diffracted beam intensity using low power microfocus sources.