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Session chair: Lerch , Michael L. F. (University of Wollongong, Centre for Medical Radiation Physics, Wollongong, Australia); Sakata , Dousatsu (Department of Accelerator and Medical Physics, Institute for Quantum Medical Science, QST, Chiba, Japan)
Shortcut: N-04
Date: Tuesday, 19 October, 2021, 9:15 AM - 11:15 AM
Room: NSS - 4
Session type: NSS Session


Click on an contribution to preview the abstract content.

9:15 AM N-04-01

A 3D diamond dosimeter with graphitic surface connections (#1020)

A. L. Porter1, A. Oh1, K. Kanxheri2, I. Lopez Paz1, L. Servoli2, C. Talamoni3

1 University of Manchester, School of Physics and Astronomy, Manchester, United Kingdom
2 INFN Perugia, Perugia, Italy
3 University of Florence, Florence, Italy


Diamond detectors have a distinct advantage in dosimetry, as carbon is closer to tissue equivalence than other solid-state materials. Polycrystalline Chemical Vapour Deposition (pCVD) substrates have larger area and cheaper cost than other diamonds but have a relatively slow time response due to the higher concentration of charge-trapping defects. To mitigate these disadvantages, 3D sensor technology has been proposed. In contrast to planar detectors, 3D design has charge collecting electrodes as columns within the diamond bulk. The electrodes can be fabricated as graphitic paths by laser inscription. This electrode geometry decouples the charge collection distance from the substrate thickness, increasing the theoretical charge collection efficiency and reducing probability of charge trapping. These devices have the benefit of defining smaller active volumes, appropriate for radiotherapy applications such as small field dosimetry. Previous 3D diamond detectors used conventional surface metallisation to connect to the readout electronics. This work describes a new prototype with laser inscription extended to include graphitic surface connections in place of metallisation to obtain an all-carbon device. This innovative device will reduce the need for the application of correction factors during dosimetric measurements due to metallic components. The device was characterised using a laboratory x-ray tube and an Elekta Synergy SXVI LINAC the Florence University Hospital. The device was shown to have a dose linearity and dose rate independent response comparable to previous diamond dosimeters, and the improvement of the operational voltage range, which was measured to be as low as 6V. This has been attributed to the reduction of the electric field distortion within the detector’s active region at the diamond-metal interface. This work proposes the first implementation of a 3D all-carbon diamond dosimeter on a pCVD substrate for dosimetric purposes.

Keywords: Dosimetry, Diamond, Graphite, 3D, CVD
9:30 AM N-04-02

First Application of Silicon Carbide Detector in Synchrotron X-Ray radiation fields (#1435)

V. de Rover1, J. Paino1, 2, L. Moore1, A. Kok3, M. Petasecca1, 2, M. Pavoli3, L. Tran1, 2, I. Kolevatov4, A. Rozenfeld1, 2, M. Lerch1, 2

1 University of Wollongong, Centre for Medical Radiation Physics, Wollongong, Australia
2 University of Wollongong, Illawarra Health and Medical Research Institute, Wollongong, Australia
3 SINTEF, Oslo, Norway
4 University of Oslo, Department of Physics, Oslo, Norway


New detectors designed to have a radiation-stable, accurate and more human tissue-like response when measuring the radiation dose delivered in Synchrotron X-ray radiation fields is particularly important in Microbeam Radiation Therapy. This paper focusses on demonstrating an epitaxial silicon-carbide (EPI-SiC) detector specifically manufactured for such radiation fields. In particular, how the EPI-SiC detector responds to the intense radiation with applied bias and any measureable radiation damage effects that may impact on the ability of the EPI-SiC detector to accurately measure the radiation doses delivered. The EPI-SiC detector responds well to synchrotron X-ray broad beams generated at the Australian Synchrotron. In edge-on detector readout mode the sharp penumbra of the X-ray beam defined by a 0.532 mm wide rectangular beam aperture can easily be observed. At an applied reverse bias of 100 V, 65 nA of photocurrent is measured when the EPI-SiC detector is fully illuminated by the beam. With approximately 30,000 Gy delivered (60 times more than the peak dose typically delivered in MRT) we observe a 19.7% increase in the measured reverse bias dark current. These results are very encouraging, and indicate that the prototype EPI-SiC detectors are suitable for use in these intense synchrotron radiation environments. 

Keywords: Silicon Carbide detector, synchrotron radiation, dosimetry
9:45 AM N-04-03

Absorbed Dose Estimation of 177Lu-DOTA-TATE using 68Ga-DOTA-TATE (#312)

Y. Zheng1, Y. Huh2, K. Vetter1, Y. Seo2, 1

1 University of California, Berkeley, Department of Nuclear Engineering, Berkeley, California, United States of America
2 University of California, San Francisco, Department of Radiology and Biomedical Imaging, San Francisco, California, United States of America


Ga-68 labeled DOTA-TATE (68Ga-DOTA-TATE) is a radiolabeld somatostatin analog that could be used to detect neuroendocrine tumors. Its theranostic pair, Lu-177 labeled DOTA-TATE (177Lu-DOTA-TATE) is used for targeted radiopharmaceutical therapy. Although Lu-177 emits low intensity (10.36%) gammas as well as therapeutic β-particles, it is not preferred for diagnostic imaging because of suboptimal imaging characteristics. By co-injecting 68Ga-DOTA-TATE and 177Lu-DOTA-TATE simultaneously, we investigate the relationship between the uptake of 68Ga-DOTA-TATE and 177Lu-DOTA-TATE in organs and tumors, and use the percent of injected activity (%IA) values of 68Ga-DOTA-TATE at 0 hr and 4 hr to correlate with the time-integrated activity coefficients (TIACs) of 177Lu-DOTA-TATE, which could be then used to estimate the organ- and tumor-based doses of 177Lu-DOTA-TATE. The results show that the TIACs of 177Lu-DOTA-TATE are linearly correlated with the mouse total mass times the %IA of 68Ga-DOTA-TATE at 4 hr in tumors and the other organs, the extrapolated clearance time of 68Ga-DOTA-TATE in kidneys, the mouse total mass times the triangle areas of the %IA values of 68Ga-DOTA-TATE in the whole body. Although preliminary, with measurements of 68Ga-DOTA-TATE at the two time points, it is possible to estimate the absorbed doses of 177Lu-DOTA-TATE prospectively to plan the therapy.

Keywords: 68Ga-DOTA-TATE, 177Lu-DOTA-TATE, radiation dosimetry estimation
10:00 AM N-04-04

An idea for preparing the stabilized optically stimulated luminescence (OSL) dosimeters having smaller signal depletion (#131)

S. Goto1, 2, H. Yamaguchi2, M. Shimizu2, H. Hayashi1, H. Sekiguchi3, R. Akino3

1 Kanazawa University, Division of Health Sciences, Graduate School of Medical Sciences, Kanazawa, Japan
2 National Institute of Advanced Industrial Science and Technology, National Metrology Institute of Japan, Tsukuba, Japan
3 Nagase LANDAUER LTD., Tsukuba, Japan

This study is a collaborative study carried out with Kanazawa University, AIST and Nagase Landauer, Ltd. The microSTARii reader and nanoDotTM OSL dosimeter used in this study were loaned to us by Nagase Landauer, Ltd.


In radiotherapy, it is important to manage the absorbed dose to water in a high-energy photon beam from a clinical linear accelerator (linac). Optically Stimulated Luminescence (OSL) dosimeters can be mass-produced at a low cost, and there is the possibility of supplying to many facilities. Therefore, we focused our attention on OSL dosimetry for evaluating delivered using a linac. In a previous study, it has been reported that variation in sensitivity of commercially available reading devices is one of the main uncertainty components. We consider that the variation can be easily corrected when preparing a stabilized dosimeter. In the general reading procedure, an electron found in various energy traps are read out using a weak LED light. Because electrons at the shallow energy trap (SET) level are easily released, the signal value is depleted by multiple readings. In this study, we proposed a novel idea to reduce signal depletion related to multiple readings; the number of electrons at the SET level is reduced by bleaching an irradiated dosimeter for a few seconds. We performed experiments to verify this idea. 4 OSL dosimeters were irradiated at 50 Gy with a high-energy photon beam using medical linac. Then, the irradiated dosimeter was exposed to white LED light with a bleaching time of 10, 30 and 60 seconds. After bleaching treatments, the dosimeter was consecutively read out 25 times using a commercial reader, and the reduction rate was analyzed. The signal of dosimeter irradiated with 50 Gy was about 2.0×106 counts, and the signal depletion was evaluated and found to be -0.16 % / 1 reading. On the other hand, signal depletions with bleaching times of 10, 30, and 60 seconds showed results of -0.02 %, -0.01 %, and 0.01 %, respectively, while the corresponding signals decreased to 4.4×105, 8.9×104, and 3.0×104 counts, respectively. There is the possibility that OSL dosimeters can be prepared by exposing to visible light with a high-dose irradiated dosimeter.

Keywords: OSL dosimeter, QA/QC, High-energy photon beam, Development dosimetry, Radiotherapy
10:15 AM N-04-05

First results of an oncological brachytherary fiber dosimeter (#949)

A. Giaz1, M. Martyn3, S. Cometti1, W. Kam2, S. Lomazzi1, R. Santoro1, M. Caccia1, S. O'Keeffe2

1 Università dell'insubria, DISAT, Como, Italy
2 Univerisity of Limerick, Optical Fibre Sensors Research Centre, Limerick, Ireland
3 Galway Clinic, Galway Clinic, Galway, Ireland

This contribution is submitted on the behalf of ORIGIN project.


The ORIGIN project aims to deliver photonics- enabled, adaptive, and more effective diagnostics-driven brachytherapy for cancer treatment through advanced real-time radiation dose imaging and radioactive source localization. This goal will be achieved by developing a 16 to 32 optical-fiber-based system where scintillating light is detected by Silicon Photomultiplier. This work reports the results achieved in laboratory and hospital conditions with single-sensor prototypes for low and high dose rate brachytherapy, requiring different specifications. The former requires high sensitivity and low minimum detectable signal, whereas an extended linearity range is crucial for the latter. Laboratory activities were essential to identify the optimal detector. Preliminary tests, performed at the hospital premises for both treatments, assessed the viability of the proposed solution. The first results were also relevant to identify the ASIC-based readout system that will allow the project to reach the final goal of engineering a multi-fiber real-time dosimetry imager.

Keywords: brachytherapy, dosimetry, SiPMs
10:30 AM N-04-06

Silicon based microdosimeter for variable LETD determination in proton radiotherapy planning (#868)

L. Tran1, B. James1, D. Bolst1, D. Wagenaar2, M. - J. Goethem2, S. Both2, M. Lerch1, M. Petasecca1, S. Guatelli1, M. Povoli3, A. Kok3, M. Jackson4, A. Rosenfeld1

1 University of Wollongong, Centre for Medical Radiation Physics, Wollongong, Australia
2 University of Groningen, Department of Radiation Oncology, Groningen, Netherlands
3 SINTEF, Oslo, Norway
4 University of New South Wales, Sydney, Australia


Variations in proton relative biological effectiveness (RBE) with dose averaged linear energy transfer (LETD) remain one of the largest sources of uncertainty in proton radiotherapy. Biological robust LETD based optimization has been introduced into some clinical treatment planning systems (TPS) to avoid normal tissue toxicity (Monte Carlo (MC) based calculation RaySearch commercial TPS). This work aims to introduce a new single cylindrical sensitive volume (SV) SOI microdosimeter modelling a biological cell using a 3D detector technology and can be operated in high intensity pencil beam scanning (PBS). The microdosimeter was applied for LETD verification computed in a MC dose engine of RaySearch TPS. Various treatment plans were generated in a research version of RayStation v6R TPS using pencil beam scanning at University Medical Center Groningen facility, the Netherlands. Two plans were created consisting of a single pristine Bragg peak of 70 MeV and 130 MeV in a homogeneous water phantom and three PBS treatment plans were created to treat a spherical target with a 5cm diameter with uniform dose coverage, in the CIRS 731- HN anthropomorphic head and neck phantom. The silicon microdosimeter system was used to measure these plans and to compare with Geant4 simulation for the same configuration and setup. Based on measured microdosimetric quantity, the dose mean lineal energy (yD), an additional dose for each plan was obtained. It has been observed that additional dose could increase up to 47% compared to prescribed physical dose assuming constant RBE of 1.1. Good agreement was observed between additional dose obtained based on measured yD and calculated LETD by RaySearch TPS. This work has demonstrated that the single SV silicon microdosimeter system developed by CMRP and fabricated at SINTEF is a very useful and unique tool to validate LETD computed in RaySearch TPS and will allow new quality assurance for biologically optimized proton therapy planning.

Keywords: Proton therapy, Relative biological effectiveness, SOI microdosimeter, LET, Microdosimetry
10:45 AM N-04-07

New arrays of 3D microdetectors for dosimetry and beam commissioning (#865)

D. Bachiller-Perea1, C. Guardiola1, M. Zhang1, C. Fleta2, D. Quirion2, F. Gómez3

1 IJCLab (CNRS, Université de Paris, Université Paris-Saclay), Orsay, France
2 Instituto de Microelectrónica de Barcelona (IMB-CNM, CSIC), Barcelona, Spain
3 Department of Particle Physics, Universidade de Santiago de Compostela, Santiago de Compostela, Spain


New detection devices based in 3D silicon-detectors with micrometric dimensions and specifically customized for microdosimetry in hadron therapy have been developed and tested. We have designed and fabricated different types of arrays of microdetectors (pixel-type, pad-type and strip-type) to allow different possibilities of spatial resolution, detection surface, and accumulated statistics. In this work, we present the first microdosimetry measurements comparing the performance of four systems covering surfaces of several square centimeters and based in the three types of arrays. Irradiations with protons at several energies in the range of 6-24 MeV have been carried out at a tandem accelerator to characterize, test and calibrate the new systems. The results presented here show the good performance of these novel devices to characterize the intensity of ion beams and to measure microdosimetric quantities with a resolution of 200 µm. The microdetector systems can be used for radiobiology experiments, hadron-therapy treatment planning, and other irradiation applications.

AcknowledgmentThis work was supported by the CNRS-Momentum fellow and the European Union’s Horizon 2020 Research and Innovation program under the Marie Sklodowska-Curie Grant Agreement no. 745109 and the G. A. no. 654168.
Keywords: Silicon detectors, proton therapy, microdosimetry, radiobiology, beam commissioning
11:00 AM N-04-08

Thermoluminescence glow curve study of beta irradiated germanium doped fibre with different dopant concentrations (#766)

C. Termsuk1, S. J. Sweeney1, C. Shenton-Taylor1

1 University of Surrey, Department of Physics, Surrey, United Kingdom


This study presents the effect from adding different Ge dopant concentrations into commercial optical fibre, exploring the glow curve and Thermoluminescence (TL) dosimeter response. Four commercial fibres consisting of 4% and 6% weight Ge doped multimode fibres, 17%Ge1%B (GeB) single mode and undoped silica fibres were exposed to beta irradiation (90Sr/90Y), followed by heating from room temperature to 400 °C after twenty-four hours post irradiation. The 6% Ge fibre showed superior sensitivity to 4 % Ge-doped and GeB fibres by factors of 9.2 and 1.3 respectively, whereas the undoped silica fibre had no response to radiation under this condition. The TL glow curves were analysed by MATLAB fitting and indicated that increasing the Ge concentration from 4 to 17% changed the peak maximum intensity position from 317 to 249 °C. Trap depth of these materials were further studied using Chen peak shape compared to TolAnal software analysis. The methods revealed five-deconvoluted peaks underneath a broad curve from the Ge doped glass fibres, this contributed to the presence of energy trap distribution between 0.63 -1.54 eV. The area under the peak from both methods supported that increasing Ge concentration shifted the dosimetric peak location to lower temperature. This may be of benefit to improve optical fibre dosimetry at lower temperature readout by increasing of dopant concentration, however degradation of TL sensitivity should be taken into account.

AcknowledgmentThe authors would like to thank Dr.Annika Lohstroh, Sarah Heisig, John-William Brown, Physics Department and Mechanical Engineering Science Department at the University of Surrey, as well as Fibercore, UK for supporting glass fibre samples. C.T.’s scholarship is supported by the Royal Thai Government.
Keywords: Dosimetry, Thermoluminescence, Optical fibre

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