“…It has been used in many reported studies to investigate dose distributions for small stereotactic fields, 1-5 photon beam relative dosimetry, 6,7 and IMRT-QA. 8,9 Additionally, because of the reported energy independence, [10][11][12] it has found applications in low energy brachytherapy 13 and orthovoltage dosimetry, [14][15][16] and more recently, to quantify output, dose profiles, and depth dose for small ͑down to 1 mm͒ orthovoltage ͑40-225 kVp͒ fields for use in translational studies. 17,18 However, whereas reports published in 2005 and 2006 have shown at most weak ͑Ͻ10%͒ dependencies of response on energy, 10-12 more recent publications and measurements at our institution have indicated stronger ͑Ͼ20%͒ dependencies on energy, [19][20][21][22] which seems to be in direct contradiction.…”