LAUSR

Dosimetry in pediatric radiology is essential since children present greater radiosensitivity in relation to adults. The dose is estimated from the entrance skin dose calculated from air kerma and backscatter factor (BSF). However, the backscatter factors presented in guidelines for use in pediatric radiology were calculated for adults [1] . The purpose of this work is to calculate backscatter factors for children and adults, comparing the influence of patient dimensions on dose estimation in pediatric radiology. Monte Carlo simulation was used for calculations, using the PENELOPE 2014 code with the penEasy 2015 extension. The geometric model consists of a box simulating the chest with dimensions 30 × 30 cm2 and 10 cm thick for a newborn child and 15 cm thick for an adult, with homogeneous composition: soft tissue and PMMA. An ionization chamber was modeled as an air volume with dimension 2.5 × 3.8 × 2.5 cm3. Monoenergetic beams with energy between 10 and 100 keV and polyenergetic beams with a tube potential between 50 and 130 kV were simulated. Three field areas were used 10 × 10, 20 × 20 and 25 × 25 cm2. The code was modified to provide the entrance skin dose and incident air kerma. The BSF were determined from the ratio between these quantities. The BSF values obtained in this work were compared with values from the literature, showing differences smaller than 4%. For monoenergetic beam, BSF increases with energy increasing up to approximately 60 keV, where a maximum value is observed. For the polyenergetic beam, BSF increases monotonically with the tube potential. The BSF for acrylic are around 9% higher than for soft tissue, due to its higher density and effective atomic number. BSF increases up to 20% with field size. It is observed that the BSF values calculated for the adult are up to 15% higher than those calculated for children. These results point to the need for using appropriate BSF for children’s dimensions.