Spatial Dosimetry Verification of Conformal Beams in Proton Radiotherapy by Spectral-Sensitive Imaging

Particle radiotherapy with conformal beams aims to tailor the delivered radiation and dose with spatial customization. For treatments using beam shaping collimators it is desired to verify the delivered doses and examine the characteristics of the produced fields with imaging response. For this purpose, we use the semiconductor pixel detector Timepix which provides time-resolved spectral-and imaging response with high spatial resolution and particle-type resolving power. Precise measurements are performed in-field at the isocenter on selected regions (≤14 mm) of delivered beams of low intensity (≤pA). Detailed information in wide dynamic range is produced in the form of field composition (particle-type species), spectral (deposited energy, linear-energy-transfer spectra) and spatial dose distribution at the sub-mm scale (≈200 μm spatial resolution). Results are presented for measurements of two conformal beam collimators used for eye treatment with 55 MeV protons. The produced 2-D maps and 1D profile distributions can be used for experimental verification of spatially fractionated radiation therapy (grid therapy), and in particle therapy for verification of Monte Carlo transport calculation, including LET distribution at the target isocenter position.