Dosimetry System Research Articles

Simulation-guided development of an optical calorimeter for high dose rate dosimetry.

Optical Calorimetry (OC) is based on interferometry and provides a direct measurement of spatially resolved absorbed dose to water by measuring refractive index changes induced by radiation. The purpose of this work was to optimize and characterize in software an OC system tailored for ultra-high dose rate applications and to build and test a prototype in a clinical environment.A radiation dosimeter using the principles of OC was designed in optical modelling software. Traditional image quality instruments, fencepost and contrast phantoms, were utilized both in software and experimentally in a lab environment to investigate noise reduction techniques and to test the spatial and dose resolution of the system. Absolute dose uncertainty was assessed by measurements in a clinical 6 MV Flattening Filter Free (FFF) photon beam with dose rates in the range 0.2-6Gy/s achieved via changing the distance from the source.Design improvements included: equalizing the pathlengths of the interferometer, isolating the system from external vibrations and controlling the system's internal temperature as well as application of mathematical noise reduction techniques. Simulations showed that these improvements should increase the spatial resolution from 22 to 35 lp/mm and achieve a minimum detectable dose of 0.2Gy, which was confirmed experimentally. In the FFF beam, the absolute dose uncertainty was dose rate dependent and decreased from 2.5 ± 0.8 to 2.5 ± 0.2Gy for dose rates of 0.2 and 6Gy/s, respectively.A radiation dosimeter utilizing the principles of OC was developed and constructed. Optical modelling software and image quality phantoms allowed for iterative testing and refinement. The refined OC system proved capable of measuring absorbed dose to water in a linac generated photon beam. Reduced uncertainty at higher dose rates indicates the potential for OC as a dosimetry system for high dose rate techniques such as microbeam and ultra-high dose-rate radiotherapy.

High-resolution three-dimensional dosimetry in clinically relevant volumes utilizing optically stimulated luminescence.

The continued development of new radiotherapy techniques requires dosimetry systems that satisfy increasingly rigorous requirements, such as high sensitivity, wide dose range, and high spatial resolution. An emerging requirement is the ability to read out doses in three dimensions (3D) with high precision and spatial resolution. A few dosimetry systems with 3D capabilities are available, but their application in a clinical workflow is limited for various reasons, primarily originating from their chemical nature. The search for a 3D dosimetry system with potential for clinical implementation is thusongoing. To demonstrate the capabilities of a novel optically-stimulated-luminescence (OSL)-based 3D dosimetry system capable of measuring radiation doses in clinically relevantvolumes. A laser-based readout system was used to measure dose distributions delivered by both photons and protons, utilizing the OSL from a mm YSO:Ce crystal. A homogeneous treatment plan consisting of two opposing photon fields was used to establish an inhomogeneity correction map of the crystal response and demonstrated the accuracy and precision of the system. The crystal was additionally irradiated with a photon treatment plan consisting of three overlapping mm fields delivered from different angles, and a proton treatment plan consisting of four pencil beams with energies 90 MeV ( ), 115 MeV, and 140 MeV. The system abilities were quantified by comparing the 3D-resolved measurements to Monte Carlosimulations. The dose map reproducibility of the system was found to be within 2% including both statistical and systematic errors. The measurements yielded integrated doses from a volume of mm with voxel volumes of just mm . An excellent agreement between the 3D-resolved measurements and the simulations was found for both photon- andproton-irradiation. The capabilities of the devised system for measuring clinically relevant fields of photons and proton pencil beams within a clinically relevant volume were demonstrated. The system poses as a promising candidate for clinical applications, and enables future research in the field of OSL-based tissue-equivalent 3Ddosimetry.

EPID-based in vivo dosimetry – new developments and applications

In vivo dosimetry has been shown to be a powerful quality assurance method in modern radiation therapy. The most common tool used for in vivo dosimetry is the electronic portal imaging device (EPID) which can quantitatively image the therapeutic beam fluence exiting the patient during treatment delivery. Since the last major literature review on this topic was published five years ago, the radiation oncology community has shown continued strong interest in this subject. Commercial options have become more widely available, with a related increase in validation efforts and sensitivity testing, while new applications continue to be explored. Work has been done to understand and increase the accuracy of the EPID for dosimetric applications, as well as continued efforts to provide practical, quantitative experiences from clinical implementation of in vivo dosimetry systems. This review examines the published literature related to in vivo EPID dosimetry from January 2017 to February 2022. The literature is classified into three main topical areas: (1) new or improved algorithmic developments including validation work, (2) applications of the in vivo EPID dosimetry method, and (3) error identification and error sensitivity analyses.

Comprehensive Shielding System Enhances Radiation Protection for Structural Heart Procedures

BackgroundThis study of radiation exposure (RE) to physicians performing structural heart procedures evaluated the efficacy of a novel comprehensive radiation shield compared to those of traditional shielding methods. A novel comprehensive shielding system (Protego, Image Diagnostics Inc) has been documented to provide superior RE protection during coronary procedures compared to that provided by a standard “drop down” shield. The purpose of this study was to assess the efficacy of this shield in transcatheter aortic valve replacement (TAVR) procedures, which are associated with disproportionate RE to operators. MethodsThis single-center, 2-group cohort, observational analysis compared RE to the primary physician operator performing TAVR using the Protego shield (n = 25) with that using a standard drop-down shield with personal leaded apparel (n = 25). RE was measured at both thyroid and waist levels with a real-time dosimetry system (RaySafe i3, RaySafe) and was calculated on a mean per case basis. Data were collected on additional procedural parameters, including access site(s) for device implantation, per case fluoroscopy time, air kerma, and patient factors, including body mass index. Between-group comparisons were conducted to evaluate RE by group and measurement sites. ResultsThe Protego system reduced operator RE by 99% compared to that using standard protection. RE was significantly lower at both the thyroid level (0.08 ± 0.27 vs 79.2 ± 62.4 μSv; P < .001) and the waist level (0.70 ± 1.50 vs 162.0 ± 91.0 μSv, P < .001). “Zero” total RE was documented by RaySafe in 60% (n = 15) of TAVR cases using Protego. In contrast, standard protection did not achieve zero exposure in a single case. ConclusionsThe Protego shield system provides superior operator RE protection during TAVR procedures. This shield allows operators to work without the need for personal lead aprons and has potential to reduce catheterization laboratory occupational health hazards.

Experimental study of dosimetric properties of thermoluminescent powder TLD-100

The creation of a scientifically substantiated quality assurance system for dosimetry and the optimization of medical exposure of the population of Ukraine during diagnostic and therapeutic procedures (and the possibility of dosimetric control and monitoring of emergency situations) falls within the field of the application of ionizing radiation sources (IRs). Trends in modern medicine in most countries, including Ukraine, prove a continued increase in the share of medical exposure. The main requirements and recommendations for the use of IRs for medical purposes while ensuring the radiation safety requirements for patients are provided in the documents of such International Organizations as the International Commission on Radiological Protection (ICRP), the International Atomic Energy Agency (IAEA), the World Health Organization (WHO) and the European Commission (EC).&#x0D; One of the key factors to ensure the quality of radiation therapy is metrological and dosimetric support. To enhance the effectiveness of radiation treatment and reduce the number of complications in the future, it is necessary to irradiate the local target within the patient’s body with a dose error of no more than 5%. Control of the radiation output of the therapeutic device, i.e., the calibration of the therapeutic beam used in the treatment process, is an essential element of radiation therapy.&#x0D; Radiation protection programmes are based on checking the accuracy of the calibration of remote radiotherapy devices using thermoluminescent dosimeters (TLDs) – small plastic capsules filled with thermoluminescent powder that are sent by post to radiology centres for exposure to a specific dose in a water phantom.&#x0D; Radiation therapy in Ukraine is primarily conducted using cobalt machines, X-ray therapy devices and linear accelerators.&#x0D; The results of the study include the examination of the dependency of measurement results on various exposure parameters using the automatic reader PCL-3, the determination of dosimetric characteristics of the thermoluminescent powder TLD-100, and the development of a calibration method for thermoluminescent dosimeters under standard irradiation conditions on a remote gamma therapy device.&#x0D; Therefore, the accuracy of beam calibration using TLD dosimeters has been studied, which will enable to timely detect errors in clinical dosimetry and reduce the number of cases of radiation-related complications for patients during their treatment.

Results and analysis of an intercomparisons study for individual monitoring services of Latin American and Caribbean regions.

The aim of this paper is to present the results obtained by the Latin-American and Caribbean personal dosimetry services that participated, with the support of IAEA, in the 2020-Eurados whole-body dosemeter intercomparison for photon radiation. All participant services in this study use thermoluminescent dosimetry (TLD) systems except one that uses optically stimulated luminescence (OSL) dosemeters. Data analysis shows that 93.4% of the results are within the acceptance range, according to International ISO Standard ISO 14146: 2018. The evaluation of the trumpet curves shows that only three laboratories presented a few dosemeters results outside the limits of acceptability. Participation in this Eurados intercomparison exercise gave the Latin American and Caribbean laboratories the opportunity to show compliance with their own quality management system, to compare results with other participants and to develop plans for improving their dosimetry systems. It also gave the assurance that occupational doses are being measured properly and following the international standards in the regions.

Analysis of EURADOS neutron intercomparison results according to new ISO standards criteria.

The European Radiation Dosimetry Group has carried out several different types of intercomparison (IC) exercises in the past that qualify as proficiency tests for different dosimetry systems and types of radiation. The first neutron dosemeter IC was held in 2012 (IC2012n) and was followed by a second in 2017/2018 (IC2017n). In sum, 31 Individual Monitoring Services (IMSs) entered 34 dosimetry systems in IC2012n, and 32 IMSs entered 33 dosimetry systems for IC2017n. Such exercises provided a rare opportunity to see how neutron dosemeters perform. For the IC2012n exercise, there were no applicable performance standards for neutron personal dosemeters. ISO/TC85/SC2 updated the ISO Standard 14146 in 2018 (ISO 14146:2018. Radiation protection-Criteria and performance limits for the periodic evaluation of dosimetry services) to include neutron dosimetry. It was thus possible to analyse the IC2017n exercise in accordance with the requirements given by this new standard. It is now of interest to reanalyse the results of IC2012n to quantify any modifications to the conclusions.

EURADOS whole-body dosemeters intercomparisons: lessons learnt from individual results.

Every 2years since 2008, Eurados WG2 has organised a whole-body dosemeters intercomparison (IC) in photon and beta fields. This paper presents the information that individual participants can extract from their results. The irradiation plan of each IC was designed to allow participants check the performance of some important characteristics of their dosimetry systems, in particular: linearity, angular response, energy response and response to mixed fields. The analysis of anomalous responses indicates that many systems can reduce the number of outliers by improving their calibration procedures.

CIEMAT participation in the seven EURADOS intercomparisons for whole-body dosemeters in photon and beta fields (2008-20).

Regular participation in intercomparisons (ICs) is an excellent way to test the reliability of results in laboratories. This work presents the analysis and conclusions of the results obtained by the CIEMAT dosimetry system in the last seven EURADOS ICs of whole-body dosemeters in fields of photons and beta radiation. Compliance with the criteria established in the ISO14146 standard, as well as the behavior of the CIEMAT personal dosemeters in all these ICs, has provided the necessary confidence for its use in the individual monitoring of workers during these years.

EURADOS intercomparisons on whole-body dosemeters for photons from 2008 to 2020: analysis and comparison of general results.

Starting in 2008 the European Dosimetry Group (EURADOS) has been performing international intercomparisons (ICs) on photon whole-body dosemeters for individual monitoring services. These ICs have been organized (on a biennial basis) starting 2008 up to 2020 now, each time with a similar set-up but with small alterations in the subsequent irradiation plans. The response for Hp(10) and Hp(0.07) was tested for different radiation qualities, angles of incidences (0°-60°) within a wide range of dose values (0.5-500mSv), to check energy and angular response, linearity, reproducibility and mixed-field response. Within the last 12years almost 15 000 whole body dosemeters have been irradiated and the corresponding response values evaluated. With an increasing number of participants and participating systems (from 62 to 132), this IC program has become an important tool for individual monitoring services to test their whole-body dosimetry systems, compare their results with other services or systems and to improve the quality of their dosimetry. The paper presents and compares the general results of these seven ICs and analyses the dosimetric results for the participating system types.

Revision of the 21909 standard on passive personal neutron dosemeters.

Since 2012, International Standardization Organization TC85/SC2 Working Group 19 dealing with 'Individual monitoring for external radiations' has been conducting important work revising the 21909 standard on passive personal neutron dosemeters. A consensus in the community acted that the 2005 version( 1) needed to be revised for two main reasons: (1) to achieve a document applicable to all systems irrespectively to the considered techniques and (2) to reach harmonisation between performance tests and conditions of use at the workplaces. The document was completely rewritten to be binding enough to ensure that any neutron dosimetry system fulfilling the criteria would be reliable in most of the usual work situations, in terms of dose level, energy and direction distributions of the neutron fluence. This paper explains the reasons behind the revision and the new philosophy of the series published in 2021, so that Individual Monitoring Services may better understand how to apply the requirements in practice.

EURADOS intercomparison IC2020ph on whole body dosemeters for photons.

The European Dosimetry Group has been organising international intercomparisons (ICs) for personal dosemeters on a regular basis. The IC announced in 2020 was postponed to the end of 2020 and the beginning of 2021 due to coronavirus (COVID-19) restrictions. The irradiation plan consisted of nine irradiation setups with five different photon radiation qualities (S-Cs, S-Co, N-150, W-60, W-80) and two different angles of irradiation incidence (0o and 60o). A total of 112 monitoring services from 50 countries with 132 dosimetry systems participated. The present work describes and analyses the individual results for the personal dose equivalent quantities Hp(10) and, if submitted, Hp(0.07) for all participating systems. It also presents the organisational details and the difficulties arising from the COVID-19 crisis during the IC. The statistical results showed a satisfactory performance with the medians of all Hp(10) and Hp(0.07) response values very close to unity. However, there are few individual monitoring services with significant large variations.

Assessment of the impact on a PADC neutron dosimetry system of the new operational dose quantities proposed in ICRU report 95.

The International Commission on Radiation Units and Measurements, ICRU, have recommended, in ICRU Report 95, the adoption of new operational quantities for use in radiation protection monitoring. Their implementation will pose problems for instrument manufacturers supplying area dosemeters and for individual monitoring services providing personal dosemeters for radiation workers. The problems arise for photon, neutron and beta dosimetry, but this paper deals solely with neutron personal dosemeters based on poly-allyl diglycol carbonate (PADC) plastic. It presents information on the problems to be expected based on data from calibrations of actual personal neutron dosemeters in terms of the existing dose quantities.

INVESTIGATION ON THE USE OF FRICKE DOSIMETRY FOR COSMIC RADIATION

The dosimetry of cosmic radiation outside Earth's atmosphere is a significant challenge due to the high complexity of radiation fields encountered in Low Earth Orbit (LEO) and interplanetary space, in addition to the constraints imposed by instrument spaceflight. The Fricke dosimeter is a water-based (96% by mass) chemical dosimetry system that offers the potential to measure the absorbed dose in water in an arbitrary geometry, for doses of up to 400 Gy, for different energy spectra. The LCR/UERJ was part of the Cubes in Space project. The main goal of this work was to obtain absorbed doses in water at different altitudes in the atmosphere using rocket and balloon systems sent by NASA's space station, using the Fricke dosimeter. For each project, 10 polyethylene bags with the Fricke dosimeter were made. The dosimeters were sent on a 20-cubic-meter helium balloon to a target altitude of at least 36.5 km, where they experienced conditions close to space. The average dose in the Fricke solution in the balloon was 9.3 ± 1.5 Gy and in the rocket was 20.4 ± 1.4 Gy. The maximum altitude reached by the balloon is 36.5 km, with a flight duration of approximately 12 hours. On the other hand, the rocket reaches a maximum altitude of 120 km, but it remains in flight for only a few minutes. The 54% difference in the absorbed dose can be explained by the different particles that are responsible for the cosmic radiation in different altitudes. Cosmic radiation increases with altitude in the atmosphere and can vary from hour to hour. The Fricke dosimeter has proven to be effective for aerospace dosimetry, as it was utilized according to the presented boundary conditions. Gathering more technical flight information can lead to future results with greater precision and lower uncertainties.

Is it still necessary to perform measured based pre-treatment patient-specific QA for SRS HyperArc treatments?

The Mobius3D system was validated as a modern secondary check dosimetry system. In particular, our objective has been to assess the suitability of the M3D as pre-treatment patient-specific Quality Assurance (QA) tool for Stereotactic Radiosurgery (SRS) HyperArc (HA) treatments. We aimed to determine whether Mobius3D could safely replace the measurements-based patient-specific QA for this type of treatment. 30 SRS HA treatment plans for brain were selected. The dose distributions, calculated by Mobius and our routinely used algorithm (AcurosXB v.15.6), were compared using gamma analysis index and DVH parameters based on the patient's CT dataset. All 30 plans were then delivered across the ionization chamber in a homogeneous phantom and the measured dose was compared with both M3D and TPS calculated one. The plans were delivered and verified in terms of PSQA using the electronic portal imaging device (EPID) with Portal Dosimetry (PD) and myQA SRS (IBA Dosimetry) detector. Plans that achieved a global gamma passing rate (GPR) ≥ 97% based on 2%/2mm criteria, with both Mobius3D and the conventional methods were evaluated acceptable. Finally, we assessed the capability of the M3D system to detect errors related to the position of the Multi-Leaf Collimator (MLC) in comparison to the analyzed measurement-based systems. No relevant differences were observed in the comparison between the dose calculated on the CT-dataset by M3D and the TPS. Observed discrepancies are imputable to different used algorithms, but no discrepancies related to goodness of plans have been found. Average differences between calculated (M3D and TPS) vs measured dose with ionization chamber were 2.5% (from 0.41% to 3.2%) and 1.81% (from 0.66% to 2.65%), for M3D and TPS, respectively. All plans passed with a gamma passing rate>97% using conventional PSQA methods with a gamma criterion of 2% dose difference and 2mm distance-to-agreement. The average gamma passing rate for the M3D system was determined to be 99.4% (from 97.3% to 100%). Results from this study also demonstrated Mobius has better error detectability than conventional measurement-based systems. Our study shows Mobius3D could be a suitable alternative to conventional measured based QA methods for SRS HyperArc treatments.

Интеграция моделей oir мкрз в дозиметрическую систему idose 2

Introduction: The iDose 2 dosimetry system is a tool for assessing the doses of internal irradiation of workers under the current individual dosimetry control (IDC). In this system, according to a series of measurements of the activity of radionuclides in biological objects (including those not exceeding the detection limit of the measurement technique) and information on contact times and types of compounds, estimates of the committed effective dose equivalent (CEDE) of internal irradiation, as well as their uncertainties, are made based on the Bayesian approach. It is possible to integrate practically any biokinetic models of the behavior of radionuclides in the human body, presented in the form of a system of ordinary differential equations (ODEs) with constant transition coefficients between compartments, into the iDose 2 dosimetry system without changing the source code. Purpose: Integration of new combined biokinetic models for the list of radionuclides: H-3, Sr-90, Cs-137, Pu-238, Pu-239 and Am-241 from Publications 100, 130, 134, 137 and 141 of the ICRP (conventionally called the series Occupational Intakes of Radionuclides (OIR)), for ingestion and inhalation routes of intake with AMAD = 1 and 5 microns. Material and methods: For each variant of the biokinetic model, the functions of retention/removal of radionuclides were found through the eigenvectors and eigenvalues of the matrix describing the ODE system. Results: A total of 65 new biokinetic models and 180 functions of radionuclide retention/removal in the form of a sum of exponents were integrated and quality control was carried out.

Pilot scale validation campaign of gel dosimetry for pre-treatment quality assurance in stereotactic radiotherapy

PurposeComplex stereotactic radiotherapy treatment plans require prior verification. A gel dosimetry system was developed and tested to serve as a high-resolution 3D dosimeter for Quality Assurance (QA) purposes. Materials and MethodsA modified version of a polyacrylamide polymer gel dosimeter based on chemical response inhibition was employed. Different sample geometries (cuvettes and phantoms) were manufactured for calibration and QA acquisitions. Irradiations were performed with a Varian Trilogy linac, and analyses of irradiated gel dosimeters were performed via MRI with a 1.5 T Philips Achieva at 1 mm3 or 2 mm3 isotropic spatial resolution. To assess reliability of polymer gel data, 54 stereotactic clinical treatment plans were delivered both on dosimetric gel phantoms and on the Delta4 dosimeter. Results from the two devices were evaluated through a global gamma index over a range of acceptance criteria and compared with each other. ResultsA quantitative and tunable control of dosimetric gel response sensitivity was achieved through chemical inhibition. An optimized MRI analysis protocol allowed to acquire high resolution phantom dose data in timeframes of ≈ 1 h. Conversion of gel dosimeter data into absorbed dose was achieved through internal calibration. Polymer gel dosimeters (2 mm3 resolution) and Delta4 presented an agreement within 4.8 % and 2.7 % at the 3 %/1 mm and 2 %/2 mm gamma criteria, respectively. ConclusionsGel dosimeters appear as promising tools for high resolution 3D QA. Added complexity of the gel dosimetry protocol may be justifiable in case of small target volumes and steep dose gradients.

Dosimetry Reconstruction in Radiopharmaceutical Therapy Using a Sparse Network of External γ-Sensors

Radiopharmaceutical therapy (RPT) has demonstrated promise in the treatment of neuroendocrine and prostate cancer. Due to the highly varied biodistribution and non-homogeneity of total integrated dose across cancer patients, a system for real-time dosimetry based on continuous measurement is desirable to deliver sufficient dose for tumor ablation while preventing toxicity from off-target uptake by organs at risk (OAR). Single time point imaging (mostly SPECT)-based dosimetry offers a snapshot of the body-wide dose distribution at a given time point, but even single SPECT imaging is generally limited in availability, often leading to significant inaccuracies in estimating total integrated dose. Therefore, accurate personalized dosimetry in RPT is an unmet need and requires continuous dosimetry measurements of tumors and OARs across multiple half-lives of the therapeutic radiopharmaceutical. Using a priori knowledge of tumor and OAR locations from pretherapy imaging, we have developed a novel algorithm that utilizes a network of custom uncollimated, optical fiber-based γ-counting probes to isolate the real-time in vivo tumor and OAR uptake in 177Lu-PSMA-617 and 225Ac-MACROPA-YS5 therapy. The proposed system was successfully validated in athymic mice models bearing varying numbers of tumors from two human prostate cancer cell lines (PC3-pip, PC3-flu). Uncollimated γ counts using the developed probes were acquired outside of the mice for 10 minutes, starting at 0 hr, 6 hrs, 12 hrs, 24 hrs, and 48 hrs after the injection of 177Lu-PSMA-617. The percent injected activity per mL of tissue (%IA/mL) of each tumor and OAR was reconstructed at every time point and compared to the %IA/mL extracted from SPECT/CT immediately after the recording. The developed system's %IA/mL reconstruction in PC3-pip tumors, PC3-flu tumors, kidneys, and bladders is highly correlative with the %IA/mL extracted from state-of-art in vivo dosimetry techniques, with %IA/mL ranging from 0.1% to 160% assuming a 29.6 MBq 177Lu-PSMA-617 administration. The least squares linear regression fit between the reconstructed activity and the activity measured from SPECT/CT is given by Estimated %IA/mL = 0.91 x SPECT %IA/mL, with an R2 of 0.991, and Pearson's r of 0.9975. There is a nearly 1:1 mapping between the proposed model and SPECT/CT. A novel dose reconstruction algorithm for personalized dosimetry in RPT that utilizes a sparse set of external γ-counters and a priori knowledge of tumor and OAR locations was developed and validated in in vivo human prostate cancer murine models. The proposed system enables continuous dosimetry measurements of multiple tumors and OAR noninvasively, with high accessibility, high temporal resolution, and across multiple classes of ɑ and β-based RPT. Similar experiments using 225Ac-MACROPA-YS5 are ongoing and additional results will be reported.

Feasibility of EPID Based In Vivo Dosimetry for On-Couch Adaptive Radiotherapy

CBCT-based online adaptive radiotherapy allows treatment plans to be tailored to the anatomy of the day. For this purpose, dose optimization and computation are performed on a synthetic CT (sCT), i.e., a density map of the planning CT deformably registered onto the acquired CBCT. Plan-specific quality assurance of adaptive treatment sessions is currently limited to the vendors own secondary dose calculation on the sCT. The use of EPID recordings promises to detect deviations in beam delivery or patient position, incorrect sCT data and anatomical changes. The purpose of this research was to evaluate the feasibility of using a new commercial technology available for in-vivo dose reconstruction based on EPID exit beam measurements. EPID images were recorded from on-couch adapted, hypofractionated treatment plans created for a prostate patient. Secondary dose calculation of the adapted plan and 3D reconstructions from EPID images of the absolute dose delivered to the patient were performed with the in-vivo dosimetry system. Comparison of reconstructed and planned delivery was conducted by means of gamma analysis and DVH metrics. Comparisons of the intended plan to a second volumetric check (collapsed cone - CC algorithm), and to the EPID in-vivo calculation, produced gamma passing rates averaged over the 7 fractions of 98.3% and 88.8% at TG-218/219 recommended criteria (Table 1). DVH metrics showed average deviations of -2.9% / -3.3% for PTV D95% and -1.2% / -0.2% for PTV D50% between intended dose and secondary / EPID in-vivo dose. The pronounced discrepancies for fraction 3 in terms of both reduced gamma passing rates and increased deviations for the EPID reconstructed dose coincide with a large air cavity in the rectum showing up in the patient's CBCT prior to treatment. Secondary dose calculation based on the density information of the CBCT as an additional option for QA confirmed origin and magnitude of this effect. In-vivo EPID dosimetry of adaptive clinical plans is feasible. It was shown exemplary that it reveals fractions with noticeable anatomical changes between the sCT and the patient anatomy during treatment. As new recommendations were published on in-vivo dosimetry through TG 307, the development of new clinical tools and evaluation of existing commercial solutions is essential, also in the context of the growing use of on-couch adaptive technology.

Reference Materials of Absorbed Dose: Expanding Dynamic Range and Improving Measurement Accuracy

Establishment and control of metrological characteristics of measurements of absorbed ionizing radiation doses in the range of 0.01 and 200 kGy by reference materials is an urgent task due to their wide application in various industries. The most convenient means of metrological support for transferring a unit of absorbed dose rate of intense photon, electron, and beta radiation to measuring instruments in radiation technologies are reference materials with established metrological traceability to the International System of Units (SI). In the present study, a method for expanding the dynamic range of measuring the absorbed dose of high-intensity ionizing radiation by radiochromic film dosimetry systems was considered and tested. The accuracy (uncertainty) of dose measurements was estimated depending on the initial optical density of the radiation-sensitive layer of the radiochromic composition. The possibility of expanding the dose characteristics and improving the metrological characteristics of the existing reference materials of absorbed dose (in water) for use as secondary standards (Measures) of the absorbed dose of ionizing radiation reproducing and (or) storing one or more points of the selected measurement scale of the absorbed dose with increased accuracy (uncertainty) of the measured values of the absorbed dose (in water) in an extended dynamic range was shown.