Dosimetric Characterisation Research Articles

Commissioning, dosimetric characterisation and machine performance assessment of the AQURE mobile accelerator for intraoperative radiotherapy

Commissioning, dosimetric characterisation and machine performance assessment of the AQURE mobile accelerator for intraoperative radiotherapy

Physical and dosimetric characterisation of different Contrast-Enhanced digital mammographic systems: A multicentric study

PurposeContrast-enhanced digital mammography (CEDM) is a relatively new imaging technique recombining low- and high-energy mammograms to emphasise iodine contrast. This work aims to perform a multicentric physical and dosimetric characterisation of four state-of-the-art CEDM systems. MethodsWe evaluated tube output, half-value-layer (HVL) for low- and high-energy and average glandular dose (AGD) in a wide range of equivalent breast thicknesses. CIRS phantom 022 was used to estimate the overall performance of a CEDM examination in the subtracted image in terms of the iodine difference signal (S). To calculate dosimetric impact of CEDM examination, we collected 4542 acquisitions on patients. ResultsEven if CEDM acquisition strategies differ, all the systems presented a linear behaviour between S and iodine concentration. The curve fit slopes expressed in PV/mg/cm2 were in the range [92–97] for Fujifilm, [31–32] for GE Healthcare, [35–36] for Hologic, and [114–130] for IMS. Dosimetric data from patients were matched with AGD values calculated using equivalent PMMA thicknesses. Fujifilm exhibited the lowest values, while GE Healthcare showed the highest. ConclusionThe subtracted image showed the ability of all the systems to give important information about the linearity of the signal with the iodine concentrations. All the patient-collected doses were under the AGD EUREF 2D Acceptable limit, except for patients with thicknesses ≤35 mm belonging to GE Healthcare and Hologic, which were slightly over. This work demonstrates the importance of testing each CEDM system to know how it performs regarding dose and the relationship between PV and iodine concentration.

Universal evaluation of MLC models in treatment planning systems based on a common set of dynamic tests

PurposeTo demonstrate the feasibility of characterising MLCs and MLC models implemented in TPSs using a common set of dynamic beams. Materials and methodsA set of tests containing synchronous (SG) and asynchronous sweeping gaps (aSG) was distributed among twenty-five participating centres. Doses were measured with a Farmer-type ion chamber and computed in TPSs, which provided a dosimetric characterisation of the leaf tip, tongue-and-groove, and MLC transmission of each MLC, as well as an assessment of the MLC model in each TPS. Five MLC types and four TPSs were evaluated, covering the most frequent combinations used in radiotherapy departments. ResultsMeasured differences within each MLC type were minimal, while large differences were found between MLC models implemented in clinical TPSs. This resulted in some concerning discrepancies, especially for the HD120 and Agility MLCs, for which differences between measured and calculated doses for some MLC-TPS combinations exceeded 10%. These large differences were particularly evident for small gap sizes (5 and 10 mm), as well as for larger gaps in the presence of tongue-and-groove effects. A much better agreement was found for the Millennium120 and Halcyon MLCs, differences being within ± 5% and ± 2.5%, respectively. ConclusionsThe feasibility of using a common set of tests to assess MLC models in TPSs was demonstrated. Measurements within MLC types were very similar, but TPS dose calculations showed large variations. Standardisation of the MLC configuration in TPSs is necessary. The proposed procedure can be readily applied in radiotherapy departments and can be a valuable tool in IMRT and credentialing audits.

Dosimetric characterisation and application to radiation biology of a kHz laser-driven electron beam

Laser-plasma accelerators can produce ultra-short electron bunches in the femtosecond to picosecond duration range, resulting in very high peak dose rates in comparison with clinical accelerators. This unique characteristic motivates their possible application to radiation biology studies to elucidate the effect of high peak dose rates and peculiar temporal structures on the biological response of living cells, which might improve the differential response between tumour and healthy tissues. Electron beams driven by kHz laser systems are an attractive option among laser-plasma accelerators since the high repetition rate can boost the mean dose rate and improve the stability of the delivered dose in comparison with J-class laser accelerators running at few Hz. In this work, we present the dosimetric characterisation of a kHz, low energy laser-driven electron source and preliminary results on in-vitro irradiation of cancer cells. A shot-to-shot dosimetry protocol enabled monitoring of the beam stability and the irradiation conditions for each cell sample. Results of survival assays on HCT116 colorectal cancer cells are in good agreement with previous findings reported in the literature and validate the robustness of the dosimetry and irradiation protocol.

Simulation of Hp(10) and effective dose received by the medical staff in interventional radiology procedures

Interventional radiology and cardiology are widespread employed techniques for diagnosis and treatment of several pathologies because they avoid the majority of the side-effects associated with surgical treatments, but are known to increase the radiation exposure to patient and operators. In recent years many studies treated the exposure of the operators performing cardiological procedures. The aim of this work is to study the exposure condition of the medical staff in some selected interventional radiology procedures. The Monte Carlo simulations have been employed with anthropomorphic mathematical phantoms reproducing the irradiation scenario of the medical staff with two operators and the patient. A personal dosemeter, put on apron, was modelled for comparison with measurements performed in hospitals, done with electronic dosemeters, in a reduced number of interventional radiology practices. Within the limits associated to the use of numerical anthropomorphic models to mimic a complex interventional procedure, the personal dose equivalent, Hp(10), was evaluated and normalised to the simulated Kerma-Area Product, KAP, value, indeed the effective dose has been calculated. The Hp(10)/KAPvalue of the first operator is about 10 μSv/Gy.cm2, when ceiling shielding is not used. This value is calculated on the trunk and it varies of +/−30% moving the dosemeter to the waist or to the neck. The effective dose, normalised to the KAP value, varies between 0.03 and 0.4 μSv/Gy.cm2. Considering all the unavoidable approximation of this kind of investigations, the comparisons with hospital measurement and literature data showed a good agreement allowing to use of the present results for dosimetric characterisation of interventional radiology procedures.

Simulation and experimental validation of a prototype electron beam linear accelerator for preclinical studies

PurposeMeasurements and Monte-Carlo simulations were carried out to model the dose distribution of a prototype electron beam linear accelerator (Kinetron LINAC) to determine the dose to organs in small animal irradiations experiments. Dose distributions were simulated using the GATE8.0/Geant4.10.3 Monte-Carlo platform, and measured in air and solid water phantoms using a commercial scintillating screen detector and new EBT-XD Gafchromic films. MethodsThe LINAC is able to produce 4.5 MeV electron beams at dose-rates ranging from Gy/min to thousands of Gy/s, and is used to study the radiobiological effects of very-high dose-rates that have been shown to protect normal tissues from radiation toxicity. Numerical simulations and experimental dosimetric characterisation of this electron accelerator were performed with the Monte-Carlo toolkit and various detectors. Absolute dose distributions in solid water were measured and compared with simulations. Realistic electron irradiation conditions were simulated in voxelised mice CT images. 3D dose distributions and dose-volume histograms in lungs of mice were simulated and analyzed. ResultsMeasured and calculated depth-dose profiles for several beam configurations (energy and dose-rate) were compared. Beam emittance was validated by comparing measured and calculated beam sizes along the central axis in air: the deviation for all conditions was less than 1 mm. A good agreement was obtained between experimental dose distributions and the results obtained with simulations (<2% dose differences for lateral and depth-dose profiles). ConclusionsThe method presented here, relying on few free parameters, can be adapted to very-high dose-rate electron irradiation to support the analysis of preclinical research experiments.

Biological and dosimetric characterisation of spatially fractionated proton minibeams

The biological effectiveness of proton beams varies with depth, spot size and lateral distance from the beam central axis. The aim of this work is to incorporate proton relative biological effectiveness (RBE) and equivalent uniform dose (EUD) considerations into comparisons of broad beam and highly modulated proton minibeams. A Monte Carlo model of a small animal proton beamline is presented. Dose and variable RBE is calculated on a per-voxel basis for a range of energies (30–109 MeV). For an open beam, the RBE values at the beam entrance ranged from 1.02–1.04, at the Bragg peak (BP) from 1.3 to 1.6, and at the distal end of the BP from 1.4 to 2.0. For a 50 MeV proton beam, a minibeam collimator designed to produce uniform dose at the depth of the BP peak, had minimal impact on the open beam RBE values at depth. RBE changes were observed near the surface when the collimator was placed flush with the irradiated object, due to a higher neutron contribution derived from proton interactions with the collimator. For proton minibeams, the relative mean RBE weighted entrance dose (RWD) was ~25% lower than the physical mean dose. A strong dependency of the EUD with fraction size was observed. For 20 Gy fractions, the EUD varied widely depending on the radiosensitivity of the cells. For radiosensitive cells, the difference was up to ~50% in mean dose and ~40% in mean RWD and the EUD trended towards the valley dose rather than the mean dose. For comparative studies of uniform dose with spatially fractionated proton minibeams, EUD derived from a per-voxel RWD distribution is recommended for biological assessments of reproductive cell survival and related endpoints.

EP-1510: Dosimetric characterisation of stereotactic cones by means of MC simulations

EP-1510: Dosimetric characterisation of stereotactic cones by means of MC simulations

Radiation response and basic dosimetric characterisation of the ‘Magic Plate’

Two Dimensional (2D) silicon diode arrays are often implemented in radiation therapy quality assurance (QA) applications due to their advantages such as: real-time operation (compared to the films), large dynamic range and small size (compared to ionization chambers). The Centre for Medical Radiation Physics, University of Wollongong has developed a multifunctional 2D silicon diode array known as the Magic Plate (MP) for real-time applications and is suitable as a transmission detector for photon flunce mapping (MPTM) or for in phantom dose mapping (MPDM). The paper focusses on the characterisation of the MPDM in terms of output factor and square field beam profiling in 6 MV, 10 MV and 18 MV clinical photon fields. We have found excellent agreement with three different ion chambers for all measured parameters with output factors agreeing within 1.2% and field profiles agreeing within 3% and/or 3mm. This work has important implications for the development of the MP when operating in transmission mapping mode.

National audit of a system for rectal contact brachytherapy

Abstract Background and purpose Contact brachytherapy is used for the treatment of early rectal cancer. An overview of the current status of quality assurance of the rectal contact brachytherapy systems in the UK, based on a national audit, was undertaken in order to assist users in optimising their own practices. Material and methods Four UK centres using the Papillon 50 contact brachytherapy system were audited. Measurements included beam quality, output and radiation field size and uniformity. Test frequencies and tolerances were reviewed and compared to both existing recommendations and published reviews on other kV and electronic brachytherapy systems. External validation of dosimetric measurements was provided by the National Physical Laboratory. Results The maximum host/audit discrepancy in beam quality determination was 6.5%; this resulted in absorbed dose variations of 0.2%. The host/audit agreement in absorbed dose determination was within 2.2%. The median of the radiation field uniformity measurements was 2.7% and the host/audit agreement in field size was within 1mm. Test tolerances and frequencies were within the national recommendations for kV units. Conclusions The dosimetric characterisation of the Papillon 50 was validated by the audit measurements for all participating centres, thus providing reassurance that the implementation had been performed within the standards stated in previously published audit work and recommendations for kV and electronic brachytherapy units. However, optimised and standardised quality assurance testing could be achieved by reducing some methodological differences observed.

PO-0792: Dosimetric characterisation of a commercial plastic scintillator detector for its application to QA in EBRT

PO-0792: Dosimetric characterisation of a commercial plastic scintillator detector for its application to QA in EBRT

Treatment planning comparison between high dose rate and intensity-modulated radiation therapy for prostate cancer as a means of boost dose

AbstractPurposeThe main objective of this study was to compare dosimetric characterisation of high-dose-rate brachytherapy (HDR-BT) with external beam intensity-modulated radiation therapy (EX-IMRT) as a means of delivering boost dose.Materials and methodsFive HDR patients were selected for IMRT planning. Patients underwent ultrasound-guided catheter placement for HDR. Computed tomography (CT) images were obtained and imported into the Nucletron PLATO Brachytherapy system. The prostate, urethra, bladder and rectum were contoured on axial slices. The dose was calculated and optimised by graphical optimisation. The CT images of these structures were exported from the PLATO to Eclipse workstation for IMRT planning. For each patient, the dose–volume histogram (DVH) of HDR and IMRT plans were generated, drawn on the same scale and compared.ResultsThe dose distribution in HDR plans was non-uniform and conformed peripherally inside the planned target volume (PTV). A small volume of the prostate received a very high dose from HDR.In IMRT plans, a uniform dose distribution was observed. The DVH curves for PTV dropped sharply and reached to a zero volume of the prostate at about 6·4 Gy. In HDR plans, the DVH curves for PTV showed a long tail up to a very high dose. About 10% of the prostate received about 13·3 Gy, which is 222% of the prescribed dose (6 Gy) in HDR plans. In contrast, the same volume in IMRT plans received &lt;6 Gy (100%). The average dose for V90 was about 6·3 Gy for HDR and 5·8 Gy for IMRT plans. At a prostate volume of V100 level, the average dose in all plans was 5·0 Gy from HDR and 5·4 Gy from IMRT plans. In HDR plan, the V100 dose for urethra varied from 0·6 to 3·0 Gy (average 1·8 Gy). The range in IMRT plans varied from 3·6 to 6 Gy with an average of 4·7 Gy. At V90 level, the dose range in HDR and IMRT plans varied from 2·5 to 4·7 Gy (average 3·8 Gy) and 4·8 to 5·4 Gy (average 5·3 Gy), respectively. In general, the dose to the bladder and rectum was comparatively lower in HDR than in IMRT plans.ConclusionsHDR brachytherapy may reduce normal tissue toxicities in prostate boost treatments, even though the dose homogeneity inside the PTV is far worse than in IMRT treatments. Another advantage of HDR over IMRT is that the organ motion is not a significant concern as in IMRT.

Dosimetric assessment and characterisation of the neutron field around a Howitzer container using a Bonner sphere spectrometer, Monte Carlo simulations and the NSDann and NSDUAZ unfolding codes

The Neutron Measurements Laboratory at the Nuclear Engineering Department of the Polytechnic University of Madrid consists of a bunker-like room and was built for neutron dosimetry research purposes and measurements. The facility includes a 74-GBq ²⁴¹Am-Be neutron source placed inside a neutron Howitzer container. The source can be moved to the irradiation or to the storage position. In this work, a Bonner sphere spectrometer (BSS) was used to measure the neutron fluence spectra with the source in both positions. Ambient dose equivalent rates, *(10), were measured using a calibrated neutron area monitor LB6411 (Berthold). The measured count rates were used as input to the NSDann and NSDUAZ unfolding programs to obtain the neutron fluence spectra and *(10). Monte Carlo (MC) simulation methods were used to model the system and to calculate the neutron fluence rate and the ambient dose equivalent rate at the measurement points. The comparison between NSDUAZ and NSDann resulted in relative deviations up to 6.87 % in the total neutron fluence rate and 7.18 % in *(10) values, despite the differences in the shape of the spectra obtained for the irradiation position. Comparing with the measured values, the *(10) values obtained with the unfolding programs exhibit a maximum relative deviation of 12.19 %. Taking into account the associated uncertainties, MC simulations seem to be in reasonable agreement with measurements. A maximum relative deviation of 15.65 % between computed and measured *(10) values was obtained. The computed count rates were applied to the unfolding programs to calculate the total neutron fluence rate and a maximum deviation of 12.83 % was obtained between the original values calculated by NSDann. A sensitivity test showed that the NSDann unfolding program is very sensitive to the uncertainties of the BSS count rates.

Lactose and sucrose aqueous solutions for high-dose dosimetry with 10-MeV electron beam irradiation

In the present study, dosimetric characterisation of aqueous solutions of lactose and sucrose was analysed by UV spectrometry following irradiation using 10-MeV electron beam at doses between 0.5 and 10.5 kGy. As a dosimetric index, absorbance is selected at 256 and 264 nm for lactose and sucrose aqueous solutions, respectively. The intensity of absorbance for irradiated solutions depends on the pre-irradiation concentration of lactose and sucrose. The post-irradiation stability of both solutions was investigated at room temperature for a measurement period of 22 d.

Dosimetry of a set-up for the exposure of newborn mice to 2.45-GHZ WiFi frequencies

This work describes the dosimetry of a two waveguide cell system designed to expose newborn mice to electromagnetic fields associated with wireless fidelity signals in the frequency band of 2.45 GHz. The dosimetric characterisation of the exposure system was performed both numerically and experimentally. Specific measures were adopted with regard to the increase in both weight and size of the biological target during the exposure period. The specific absorption rate (SAR, W kg(-1)) for 1 W of input power vs. weight curve was assessed. The curve evidenced an SAR pattern varying from <1 W kg(-1) to >6 W kg(-1) during the first 5 weeks of the life of mice, with a peak resonance phenomenon at a weight around 5 g. This curve was used to set the appropriate level of input power during experimental sessions to expose the growing mice to a defined and constant dose.

Preliminary dosimetric characterisation of thermoluminescent materials for beta radiation monitoring at nuclear medicine services

Beta emitters are widely used in nuclear medicine for diagnostic and therapeutic purposes. The critical groups exposed to a radioactive patient include the staff, other patients and members of the public accompanying the patient. The aim of this work is to characterise thermoluminescent (TL) materials for the staff monitoring of nuclear medicine services that manipulate beta radiation solutions of (153)Sm. This study was performed using CaSO(4):Dy + Teflon pellets, produced at IPEN, with different dimensions. For the dosimetric characterisation, these TL dosemeters were exposed to gamma source ((60)Co) and to beta sealed sources ((90)Sr + (90)Y, (204)Tl and (147)Pm) and to a non-sealed source ((153)Sm). Results were obtained related to reproducibility, lower detection limits, calibration curves, angle and energy dependence of response. All tested materials show usefulness for monitoring of workers exposed to beta radiation.

Inter-comparison among different TLD-based techniques in a standard multisphere assembly for the characterisation of neutron fields

In the framework of collaboration among the ENEA Radiation Protection Institute (Bologna), the ENEA Fusion Department (Frascati) and the INFN-LNF-Radiation Protection Group (Frascati), an experimental campaign was organised on the usage of thermoluminescence dosemeters (TLDs) for the dosimetric and spectrometric characterisation of neutron fields. Commercially available TLDs of different material and different sensitivity to photons and thermal neutrons were selected, namely TLD600H and TLD700H from Harshaw, GR206 and GR207 from SSDML (China), MCP-6s from TLD Poland. The detectors were first calibrated in standard fields of photons ((60)Co) and thermal neutrons at the ENEA-IRP Secondary Standard Calibration Laboratory of Bologna, then exposed in fast neutron standard fields of different energy, using a standard multisphere moderating assembly. The paper compares the dosimetric characteristics of the studied TL detectors, underlining the (n-gamma) discrimination capability, and discusses their spectrometric performances addressed to radiation protection applications.

252 poster A novel, rigorous approach to dosimetric characterisation of CCD-based electronic portal imaging devices

252 poster A novel, rigorous approach to dosimetric characterisation of CCD-based electronic portal imaging devices

Dosimetric Analysis and Characterisation of Radioactive Seeds Produced by the Sol-Gel Method

Dosimetric Analysis and Characterisation of Radioactive Seeds Produced by the Sol-Gel Method

In vitro cell irradiation systems based on [formula omitted] alpha source: construction and characterisation

One way of studying the risk to human health of low-level radiation exposure is to make biological experiments on living cell cultures. Two 210 Po α -particle emitting devices, with 0.5 and 100 MBq activity, were designed and constructed to perform such experiments irradiating monolayers of cells. Estimates of dose rate at the cell surface were obtained from measurements by a PIPS α-particle spectrometer and from calculations by the SRIM 2000, Monte Carlo charged particle transport code. Particle fluence area distributions were measured by solid state nuclear track detectors. The design and dosimetric characterisation of the devices are discussed.