Development and characterization under large area intensity modulated radiotherapy beam of a bidimensional dosimeter made with p-type epitaxial silicon

Intensity modulated radiotherapy poses specific constraints in dosimetry due to the occurrence of: small radiation fields with high dose gradients; variation in space and time of the dose rate; variation in space and time of the beam energy spectrum. Our goal is to develop a silicon device adequate for coping these strict conditions. To this purpose we have studied various Si materials in terms of their thickness, resistivity and conductivity type, to determine the best radiation tolerant material. Independence on accumulated dose, ensuring radiation tolerance and thus needing no recalibration, was achieved both with thin and epitaxial Si diodes. A monolithical device designed and manufactured by us on epitaxial p-type silicon has been characterized under an IMRT field for prostate treatment. Our device is characterized by much larger spatial resolution than conventional ones and ability to directly measure temporal variations in dose modulation during plan verification.