CT beam dosimetric characterization procedure for personalized dosimetry

Personalized dosimetry in computed tomography (CT) can be realized by a full Monte Carlo (MC) simulation of the scan procedure. Essential input data needed for the simulation are appropriate CT x-ray source models and a model of the patient's body which is based on the CT image. The purpose of this work is to develop comprehensive procedures for the determination of CT x-ray source models and their verification by comparison of calculated and measured dose distributions in physical phantoms. Mobile equipment together with customized software was developed and used for non-invasive determination of equivalent source models of CT scanners under clinical conditions. Standard and physical anthropomorphic CT dose phantoms equipped with real-time CT dose probes at five representative positions were scanned. The accumulated dose was measured during the scan at the five positions. ImpactMC, an MC-based CT dose software program, was used to simulate the scan. The necessary inputs were obtained from the scan parameters, from the equivalent source models and from the material-segmented CT images of the phantoms. 3D dose distributions in the phantoms were simulated and the dose values calculated at the five positions inside the phantom were compared to measured dose values. Initial results were obtained by means of a General Electric Optima CT 660 and a Toshiba (Canon) Aquilion ONE. In general, the measured and calculated dose values were within relative uncertainties that had been estimated to be less than 10%. The procedures developed were found to be viable and rapid. The procedures are applicable to any scanner type under clinical conditions without making use of the service mode with stationary x-ray tube position. Results show that the procedures are well suited for determining and verifying the equivalent source models needed for personalized CT dosimetry based on post-scan MC calculations.Peer reviewe

Measurement and simulation of the neutron response of the Nordball liquid scintillator array

The response of the liquid scintillator array Nordball to neutrons in the energy range 1.5 < T_n < 10 MeV has been measured by time of flight using a 252Cf fission source. Fission fragments were detected by means of a thin-film plastic scintillator. The measured differential and integral neutron detection efficiencies agree well with predictions of a Monte Carlo simulation of the detector which models geometry accurately and incorporates the measured, non-linear proton light output as a function of energy. The ability of the model to provide systematic corrections to photoneutron cross sections, measured by Nordball at low energy, is tested in a measurement of the two-body deuteron photodisintegration cross section in the range E_gamma=14-18 MeV. After correction the present 2H(gamma,n)p measurements agree well with a published evaluation of the large body of 2H(gamma,p)n data.Comment: 20 pages 10 figures, submitted Nucl. Instr. Meth.

Citizen science’s transformative impact on science, citizen empowerment and socio-political processes

Citizen science (CS) can foster transformative impact for science, citizen empowerment and socio-political processes. To unleash this impact, a clearer understanding of its current status and challenges for its development is needed. Using quantitative indicators developed in a collaborative stakeholder process, our study provides a comprehensive overview of the current status of CS in Germany, Austria and Switzerland. Our online survey with 340 responses focused on CS impact through (1) scientific practices, (2) participant learning and empowerment, and (3) socio-political processes. With regard to scientific impact, we found that data quality control is an established component of CS practice, while publication of CS data and results has not yet been achieved by all project coordinators (55%). Key benefits for citizen scientists were the experience of collective impact (“making a difference together with others”) as well as gaining new knowledge. For the citizen scientists’ learning outcomes, different forms of social learning, such as systematic feedback or personal mentoring, were essential. While the majority of respondents attributed an important value to CS for decision-making, only few were confident that CS data were indeed utilized as evidence by decision-makers. Based on these results, we recommend (1) that project coordinators and researchers strengthen scientific impact by fostering data management and publications, (2) that project coordinators and citizen scientists enhance participant impact by promoting social learning opportunities and (3) that project initiators and CS networks foster socio-political impact through early engagement with decision-makers and alignment with ongoing policy processes. In this way, CS can evolve its transformative impact

Comparison of pencil-type ionization chamber calibration results and methods between dosimetry laboratories

Puikkokammiota on käytetty vuosikymmeniä tietokonetomografian annosmittauksissa. Viime vuosina tietokonetomografian menetelmien kehittyessä myös dosimetrisiä menetelmiä on arvioitu uudelleen. Tässä julkaisussa kuvataan vertailumittaus, jossa puikkokammio kalibroitiin kahdeksassa eri kalibrointilaboratoriossa Euroopassa käyttäen kolmea eri menetelmää. Käytettävät menetelmät olivat: ”kokonaissäteilytys (total irradiation)”, ”osittaissäteilytys (partial irradiation)” ja ”keskiarvoinen osittaissäteiltys (average parital irradiation)”. Viimeisenä mainittua menetelmää käytettiin vain osassa laboratorioista. Kalibroitavina suureina käytettiin ilmakermaa (K) ja sen pituuden tuloa (PKL). Suurin osa mittausvertailun kalibrointituloksista vastasi hyvin referenssiarvoa (> 99%), yhden labora-torion (VINCA) arvot olivat jonkin verran korkeammat kuin muiden. STUKin tulokset olivat erinomai-set. Esimerkiksi STUK:n En-arvo (taulukko 5), jolla mitattiin kalibrointikertoimen eroa kokonainaise-pävarmuuteen oli pieni (0.03-0.22). Jos En-arvo on pienempi kuin yksi voidaan todeta, että mittaustu-los ja mittauksen referenssiarvo ovat hyvin linjassa vastaavien epävarmuuksien kanssa. STUK:ssa ka-librointi tehtiin kahdella eri menetelmällä (kokonais- ja osittaissäteilytys), joiden tulokset olivat lähellä toisiaan (kuva 7), myös ilmakerman ja sen pituuden tulon vertailu (kuva 6) osoittaa STUK:n onnis-tuneen hyvin kalibroinnissa. STUK:n ilmoittamat epävarmuudet ovat keskimääräisiä epävarmuuksia hieman isommat, mutta eivät kuitenkaan poikkea oleellisesti muiden vertailulaboratorioiden ilmoit-tamista epävarmuuksista. Kaiken kaikkiaan STUK:n kalibrointiprosessin voidaan todeta toimivan luotettavasti. Mittausvertailussa osittaissäteilytys todettiin parhaaksi menetelmäksi ja tämän menetelmän käyt-töönotto on myös mahdollista STUKin kalibrointilaboratoriossa

Lessons learned from a HDR brachytherapy well ionisation chamber calibration error

The outcomes of a recent brachytherapy welltype ionization chamber calibration error are given in the hope that other brachytherapy treatment centres may better understand the importance of each entry stated in a well chamber calibration certificate. A Nucletron Source Dosimetry System (SDS) PTW well-type ionization chamber was sent for a biennial calibration in September 2010. Upon calibration of the chamber, it was discovered that the previous calibration (in July 2008) contained a +2.6% error in the chamber calibration coefficient. Investigation of the information on the 2008 well chamber calibration certificate indicated the source of the error, which could or should have been detected by both the calibration laboratory and/or the radiation therapy department upon return of the chamber. Consideration must be given to all values and conditions given on the calibration certificate when accepting a ionization chamber back from a calibration laboratory. The issue of whether the source strength from the source calibration certificate or the measured source strength from the calibrated ionization chamber should be entered into the treatment unit is also raised