Source-surface distance and source-axis distance beam data acquisition.
Radiation beam characteristics are usually obtained by scanning in a water phantom. Central axis depth dose data, beam profiles, and isodose curves are derived from these measurements. Certain treatment planning systems require that beam profiles be scanned isocentrically rather than at a constant source-surface distance. We have looked at profiles taken both ways, with appropriate field-size correction, and find no significant difference between them. This should simplify data acquisition in many cases.
D011874:Radiometry / Q000379:methods*; D011878:Radiotherapy / Q000295:instrumentation*; D012542:Scattering, Radiation