Spectral-tracking characterization and wide-range monitoring of scattered and secondary radiation in proton therapy

Abstract In particle radiotherapy practice it is valuable to examine, accurately measure and monitor the secondary radiation fields produced during treatment. Measurements performed non-invasively and out-of-field avoid interfering with and modifying the delivered dose treatment. Use of a simplified and compact device is advantageous for reduced cost and effort of deployment and operation. For this purpose, we examine in detail the scattered beam particles and secondary radiation field produced well beyond even meters away from the irradiated area in proton therapy. We use the semiconductor pixel detector Timepix3 implemented as a miniaturized radiation camera which we mounted at the ceiling of the treatment room. The pixel detector provides high-resolution per-pixel spectrometry with time, position, directional and tracking response. Applying radiation imaging and particle tracking techniques together with extensive experimental calibrations in well-defined radiation fields, the single detector provides the composition and spectral-tracking characterization of the complex fields. In particular, the scattered proton field at the detector position is evaluated and unfolded into spectral-directional groups which serve to map and examine the characteristics and directional origin of the radiation out of field. Detailed particle fluxes and dose rates, total and partial, are measured out of field with sub-second time resolution. Deposited energy distributions in the detector sensor are derived in wide range. Verification and complementary information are provided by numerical Monte-Carlo (MC) simulations. The combined results and presented technique can be potentially used to inspect and systematically evaluate quality assurance irradiations and treatment plans.