Evaluation of the activation of brass apertures in proton therapy using gamma-ray spectrometry and Monte Carlo simulations
- 23 June 2020
- journal article
- research article
- Published by IOP Publishing in Journal of Radiological Protection
- Vol. 40 (3), 848-860
- https://doi.org/10.1088/1361-6498/ab9f42
Abstract
Collimating apertures are used in proton therapy to laterally conform treatment fields to the target volume. While this is a standard technique in passive spreading treatment heads, patient-specific apertures can supplement pencil-beam scanning (PBS) techniques to sharpen the lateral dose fall-off. A radiation protection issue is that proton-induced nuclear reactions can lead to the formation of radionuclides in the apertures. In the experiments of the current study, cylindrical, thick brass targets were irradiated with quasi-monoenergetic proton fields of 100.0 MeV and of 226.7 MeV in PBS mode. The radioactivation of these two brass samples was characterized with a low-level gamma-ray spectrometer. The activation products were scored in a Monte Carlo simulation, too, and compared with the experimental activities. For the high-energy field, 63Zn, 60Cu, and 61Cu were the most important short-lived isotopes regarding the measured specific activity. After irradiation with the 100.0 MeV field, 62Cu, 63Zn, and 60Cu had the highest activity. Regarding long-lived isotopes, which determine the storage time of the used apertures, the isotopes 57Co, 65Zn, 54Mn, 56Co had the largest contribution to the activity. The relative difference of activities between simulation and experiment was typically between 10%-20% for short- lived nuclides and were up to a factor of five larger for long-lived nuclides. Summarizing experiments and simulations for both incident proton energies, 62Cu was the most important detected residual nucleus regardless if specific activity or equivalent dose is considered.Keywords
Funding Information
- Mercur (St-2019-0007)
This publication has 23 references indexed in Scilit:
- A Monte Carlo study on the collimation of pencil beam scanning proton therapy beamsMedical Physics, 2016
- A patient‐specific aperture system with an energy absorber for spot scanning proton beams: Verification for clinical applicationMedical Physics, 2015
- Potential Hazard Due to Induced Radioactivity Secondary to RadiotherapyHealth Physics, 2014
- Radiation Safety Considerations in Proton Aperture DisposalHealth Physics, 2014
- Evaluation of radioactivity induced by patient-specific devices in proton therapyJournal of the Korean Physical Society, 2012
- Pitfalls of tungsten multileaf collimator in proton beam therapyMedical Physics, 2011
- Commissioning of output factors for uniform scanning proton beamsMedical Physics, 2011
- Induced radioactivity in a patient-specific collimator used in proton therapyNuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2010
- Commissioning a passive-scattering proton therapy nozzle for accurate SOBP deliveryMedical Physics, 2009
- Experimental studies and nuclear model calculations on the formation of radioactive products in interactions of medium energy protons with copper, zinc and brass: Estimation of collimator activation in proton therapy facilitiesApplied Radiation and Isotopes, 1997