Micro-Scale Dose Distribution of Microplanar X Rays from Synchrotron Radiation:Measurement and Monte Carlo Calculation

Knowledge of dose distribution with micron resolution is required in radiation therapy studies that use a spatially fractionated X-ray microbeam.However, the condition of the collimator affects the dose distribution.To estimate the performance of a modified collimator, the measured dose distribution was compared with that of a Monte Carlo PENELOPE calculation.The dose distribution for synchrotron radiation with an effective energy of 90 keV that passed through a single-slit collimator to produce a 25-m-wide beam was measured with a GafChromic HD-810 film and digital microscope.The calculated and measured doses did not agree in the slope because the measured dose distribution was partly enhanced by photons that were reflected from the collimator.In the other region, the doses agreed within 20%.Compared with a former multi-slit collimator, the single-slit collimator considerably reduced the scattered components and produced a lower dose in the valley, which approached the calculated dose.