Charge Collection and Radiation Hardness Properties of SOI Microdosimeters and their Application in Clinical LETd Verification for Proton Therapy
Linh Tran, Vladimir Pan
Centre for Medical and Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
Abstract: A charge collection efficiency (CCE) study is performed at the Australian Nuclear Science and Technology Organization (ANSTO) on a new batch of silicon on insulator (SOI) microdosimeters while also investigating their radiation hardness properties for medical, space and accident applications. SOI microdosimeters with an active layer thickness of 10, 20, and 50 μm have been investigated with a 24 MeV carbon ion beam as well as a Co-60 gamma source. A displacement current phenomenon was observed to be occurring in this batch of microdosimeters leading to undesirable effects. The radiation hardness study, which was performed with a fluence of ∼108 12C ions/cm2, showed a CCE deficit of approximately 2% at an operation bias of 10 V within the SVs. Results of the radiation hardness studies suggest that the SOI microdosimeter can tolerate total ionizing doses (TID) and displacement damage (DD) levels that are typical to annual quality assurance (QA) in particle therapy for several years, without any noticeable degradation. Following these findings, a first of its kind experimental verification of LETd optimized treatment plans for proton therapy have been carried out using an SOI microdosimeter at the Massachusetts General Hospital (MGH), Boston, USA. Three clinical treatment plans of a typical ependymoma structure set were designed using the standard clinical approach, the proposed protocol approach, and a one-field approach. The plans were then reoptimized to reduce the LETd-weighted dose in the brainstem. All six plans were delivered in a solid water phantom and the experimental yD was measured. Following LETd optimization, a reduction in yD was found within the brainstem by an average of 12%, 19% and 4% for the clinical, protocol and one-field plans respectively while maintaining adequate coverage of the tumor structure. The experimental LETd-weighted doses were in agreement with the TPS calculations and Monte Carlo simulations. The combination of the CCE and radiation hardness studies, along with the successful LETd-optimization verification, demonstrate the applicability of the SOI microdosimeter for clinical practices for QA and other treatment plan verifications.
Seminar takes place on Tuesday, April 2nd 2024 at 2:00 PM
in the IEAP meeting room, Praha 1, Husova 240/5.
| Ing. Bartoloměj Biskup, Ph.D. seminar organizer |
doc. Ing. Ivan Štekl, CSc. director of IEAP |
doc. Dr. André Sopczak IEEE CS - NPSS chair |
NUCLEAR & PLASMA SCIENCES SOCIETY CHAPTER
IEEE Czechoslovakia section
https://www.ieee.cz/main/section/nps/