Characterization of the PTB ultra-high pulse dose rate reference electron beam

: Purpose. This investigation aims to present the characterisation and optimisation of an ultra-high pulse dose rate (UHPDR) electron beam at the PTB facility in Germany. A Monte Carlo beam model has been developed for dosimetry study for future investigation in FLASH radiotherapy and will be presented.Material and methods. The 20 MeV electron beams generated by the research linear accelerator has been characterised both in-beamline with profile monitors and magnet spectrometer, and in-water with a diamond detector prototype. The Monte Carlo model has been used to investigate six different setups to enable different dose per pulse (DPP) ranges and beam sizes in water. The properties of the electron radiation field in water have also been characterised in terms of beam size, quality specifierR50and flatness. The beam stability has also been studied.Results. The difference between the Monte-Carlo simulated and measuredR50was smaller than 0.5 mm. The simulated beam sizes agreed with the measured ones within 2 mm. Two suitable setups have been identified for delivering reference UHPDR electron beams. The first one is characterised by a SSD of 70 cm, while in the second one an SSD of 90 cm is used in combination with a 2 mm aluminium scattering plates. The two set-ups are quick and simple to install and enable an expected overall DPP range from 0.13 Gy up to 6.7 Gy per pulse.Conclusion. The electron beams generated by the PTB research accelerator have shown to be stable throughout the four-months length of this investigation. The Monte Carlo models have shown to be in good agreement for beam size and depth dose and within 1% for the beam flatness. The diamond detector prototype has shown to be a promising tool to be used for relative measurements in UHPDR electron beams

Metody pomiaru małych ładunków i prądów jonizacyjnych w ochronie radiologicznej i radioterapii

Artykuł jest streszczeniem rozprawy doktorskiej o tym samym tytule, która została obroniona przez autora na Wydziale Mechatroniki Politechniki Warszawskiej. W niniejszym artykule przedstawiono metody pomiaru małych prądów DC i ładunków elektrycznych, które są stosowane powszechnie w dozymetrii promieniowania jonizującego. Artykuł prezentuje ich zalety i wady w różnych aplikacjach z naciskiem na zastosowanie w systemach pomiarowych, wykorzystywanych na stanowiskach wzorców pierwotnych i wtórnych kermy w powietrzu i dawki pochłoniętej w wodzie

Use of a Keithley 6517A electrometer in the Townsend compensation circuit

W niniejszym artykule przedstawiono możliwość wykorzystania elektrometru firmy Keithley typ 6517A w metodzie zerowej, która jest najdokładniejszą z metod pomiaru małych prądów DC i ładunków elektrycznych. Metoda ta eliminuje główne źródła błędów jak prąd upływowy i zjawisko absorpcji dielektrycznej ładunku elektrycznego. W artykule przedstawiono i omówiono dokładnie metodę zerową. Metoda ta została porównana z innymi znanymi metodami pomiaru małych prądów DC i ładunków elektrycznych. Wyniki tych porównań zostały przedstawione i omówione w artykule. Dzięki zerowej metodzie można otrzymać względną niepewność standardową około 0,003% dla prądu o wartości 3 pA i stabilność długoterminową około 0,01%. Na podstawie uzyskanych wyników i doświadczeń budowane są obecnie systemy pomiarowe w Głównym Urzędzie Miar, np. systemy pomiarowe dla stanowisk wzorca pierwotnego dawki pochłoniętej w wodzie i kermy w powietrzu.A ionization chamber is the most widely used type of dosimeter for precise measurements. The typical values of charge or current to be measured by ionization chambers can be estimated from the fact that an exposure of 1 R (Roentgen is now a historical unit of the exposure dose) generates a charge of 2.58∙10-10 C in 1 cm3 of room temperature air at pressure 1 atm. In most practical cases, ionization currents are very small, in the range from 1 µA to 0.1 fA, so their measurement requires careful technique and appropriate instrumentation. Making a measurement with a ionization chamber requires a high-voltage power supply and an electrometer. The electrometer measures current or charge in the range 200 fA to 1 µA (current mode) and 2 pC to 10 mC (charge mode) with the maximum resolution of 1 fA or 10 fC and the accuracy better than 0.5%. Its long term stability is 0.1% per year. These parameters are insufficient for measurements in which there are used ionization chambers as the primary standard. There are also problems with the calibration of these electrometers on a satisfactory level. This paper presents the possibility of using a digital Keithley 6517A electrometer in the null method which is the most accurate method measuring very low DC currents and electrical charges. This method eliminates the leakage current and the capacitor dielectric absorption phenomenon. The null method is presented and discussed. This method is compared with the known measuring methods and the results of comparison are summarized and discussed. Thanks to the null method there can be achieved the relative standard uncertainty of 0.003% for the current about 3 pA and the long term stability about 0.01%. The results of the research are used at the Central Office of Measures in the Laboratory of Ionizing Radiation and Color Standards. Based on these studies new measuring systems are being built at the Central Office of Measures, e.g. a measuring system for the primary standards of absorbed dose to water and air kerma

Metrology for advanced radiotherapy using particle beams with ultra-high dose rates.

Dosimetry of ultra-high dose-rate (UHDR) beams is one of the critical components which is required for safe implementation of FLASH radiotherapy into clinical practice. In the past years several national and international programmes have emerged with the aim to address some of the needs that are required for translation of this modality to clinics. These involve the establishment of dosimetry standards as well as the validation of protocols and dosimetry procedures. This review provides an overview of recent developments in the field of dosimetry for FLASH radiotherapy, with particular focus on primary and secondary standard instruments, and provides a brief outlook on the future work which is required to enable clinical implementation of FLASH radiotherapy

The European Joint Research Project UHDpulse - Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates.

UHDpulse - Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates is a recently started European Joint Research Project with the aim to develop and improve dosimetry standards for FLASH radiotherapy, very high energy electron (VHEE) radiotherapy and laser-driven medical accelerators. This paper gives a short overview about the current state of developments of radiotherapy with FLASH electrons and protons, very high energy electrons as well as laser-driven particles and the related challenges in dosimetry due to the ultra-high dose rate during the short radiation pulses. We summarize the objectives and plans of the UHDpulse project and present the 16 participating partners