Protocol for X-ray dosimetry and exposure arrangements employed in studies of late somatic effects in mammals

A number of European laboratories studying the late effects of ionizing radiation in animals have established an effective cooperation within the European Late Effects Project Group (EULEP) since 1970. To facilitate the exchange of biological results several techniques, including quality control of the experimental animals, pathology and dosimetry, have to be standardized. The most important aspects of the procedures for X-irradiation and dosimetry of small animals are summarized. These include recommendations on irradiation conditions, dosimetry methods, characteristics of phantoms and factors affecting X-ray dosimetry. X-irradiation procedures employed by the participating institutes are described and the results of five X-ray dosimetry intercomparisons are reported. The introduction of a common dosimetry protocol has resulted in improvements in exposure arrangements and absolute dosimetry.     

The IAEA Radiotracer Biodistribution Template – A community resource for supporting the standardization and reporting of radionuclide pre-dosimetry data

Radionuclide absorbed-dose dosimetry is an active area of development and has the potential to positively impact molecular radiotherapies. At present, many of the operations required to perform dosimetry calculations are unstandardized and unestablished. While the current methodology allows reasonable dosimetry estimates to be derived and published, it can be difficult to understand, and reproduce, each others’ work. To help alleviate this we have identified the collection of biodistribution information as a key step in all internal dosimetry calculations, and present a template that can be used to standardize its documentation and reporting.A generalized biodistribution template entitled the IAEA Radiotracer Biodistribution Template (IAEA RaBiT) has been built and distributed for users performing biodistribution measurements in the community. The template enables robust recording of dosimetry-relevant information through standardization of details and their format. It has been designed to be simple and easy to use, and establish a structured recording of a common reference point in dosimetry operations – biodistribution data documentation. Improved documentation procedures may benefit organization of in house data, or be used to disseminate details throughout the community – for example to supplement dosimetry related publications. The standard format information may also enable the creation of new dosimetry related tools and protocols and support robust population databases.As dosimetry in nuclear medicine becomes more routinely applied in clinical applications, we need to develop the infrastructure for robustly handling large amounts of these data. Our IAEA RaBiT can be used as a standard format structure for data collection, organization, and dissemination.     

Personal dosimetry of exposure to mobile telephone base stations? An epidemiologic feasibility study comparing the Maschek dosimeter prototype and the Antennessa DSP‐090 system

The aim of our study was to test the feasibility and reliability of personal dosimetry. Twenty-four hour exposure assessment was carried out in 42 children, 57 adolescents, and 64 adults using the Maschek dosimeter prototype. Self-reported exposure to mobile phone frequencies were compared with the dosimetry results. In addition, dosimetry readings of the Maschek device and those of the Antennessa DSP-090 were compared in 40 subjects. Self-reported exposures were not associated with dosimetry readings. The measurement results of the two dosimeters were in moderate agreement (r(Spearman) = 0.35; P = .03). Personal dosimetry for exposure to mobile phone base station might be feasible in epidemiologic studies. However, the consistency seems to be moderate.     

The effect of changes in dosimetry on cancer mortality risk estimates in the atomic bomb survivors

In the spring of 1986 the Radiation Effects Research Foundation (RERF) received a new atomic bomb dosimetry system. This report presents the comparisons of leukemia and nonleukemia cancer mortality risk estimates under the old and new dosimetries. In terms of total kerma (essentially whole-body gamma plus neutron exposure), risk estimates for both classes of cancer are 75-85% higher with the new dosimetry. This and other summary comparisons allow for possible nonlinearity at high estimated doses. Changes are also considered in relation to organ doses and assumptions about the relative biological effectiveness (RBE) of neutrons. Without regard to RBE, the risk estimates for total organ dose are essentially unchanged by the dosimetry revision. However, with increasing assumed values of RBE, the estimated low-LET risk decreases much less rapidly under the new dosimetry, due to the smaller neutron component. Thus at an assumed constant RBE of 10, for example, the effect of the dosimetry revision is to increase organ dose risk estimates, relative to those based on the old dosimetry, by 30% for nonleukemia and 80% for leukemia. At an RBE of 20 these increases are 72 and 136%, respectively. A number of other issues are discussed. The city difference in dose is no longer statistically significant, even at an RBE of one. Estimation of RBE is even less feasible with new dosimetry. There is substantial question of the linearity in dose response, in the sense of a leveling off at higher doses. Finally, some indication is given of how risks estimated from this dosimetry and the current data may compare to widely used estimates based largely on the RERF data with the previous dosimetry.     

A Feasibility Study of Fricke Dosimetry as an Absorbed Dose to Water Standard for 192Ir HDR Sources

High dose rate brachytherapy (HDR) using ¹⁹²Ir sources is well accepted as an important treatment option and thus requires an accurate dosimetry standard. However, a dosimetry standard for the direct measurement of the absolute dose to water for this particular source type is currently not available. An improved standard for the absorbed dose to water based on Fricke dosimetry of HDR ¹⁹²Ir brachytherapy sources is presented in this study. The main goal of this paper is to demonstrate the potential usefulness of the Fricke dosimetry technique for the standardization of the quantity absorbed dose to water for ¹⁹²Ir sources. A molded, double-walled, spherical vessel for water containing the Fricke solution was constructed based on the Fricke system. The authors measured the absorbed dose to water and compared it with the doses calculated using the AAPM TG-43 report. The overall combined uncertainty associated with the measurements using Fricke dosimetry was 1.4% for k = 1, which is better than the uncertainties reported in previous studies. These results are promising; hence, the use of Fricke dosimetry to measure the absorbed dose to water as a standard for HDR ¹⁹²Ir may be possible in the future.     

Three-dimensional quality assurance of IMRT prostate plans using gel dosimetry

Intensity modulated radiotherapy (IMRT) is one of the most modern radiation therapy treatment techniques. Although IMRT can deliver high and complex conformational doses to the tumor volume, its implementation requires rigorous quality assurance (QA) procedures that include a dosimetric pre-treatment verification of individual patient planning. This verification usually involves measuring a small volume of absolute dose with an ionization chamber and checking bi-dimensional fluency with an array of detectors. The planning technique has tri-dimensional characteristics, but no tridimensional dosimetry has been established in the clinical routine. One strategy to perform three-dimensional dosimetry is to use polymeric gels associated with magnetic resonance imaging to evaluate dose distribution. Here, we have compared the results of conventional QA procedures involving one- and two-dimensional dosimetry to the results of three-dimensional dosimetry conducted with MAGIC-f gel in 10 cases of prostate cancer IMRT planning. More specifically, we used the gamma index (3%/3 mm) to compare the results of three-dimensional dosimetry to the expected dose distributions obtained with the treatment planning system. Except for one IMRT treatment plan, the gel dosimetry results agreed with the conventional quality control and provided an overview of dose distribution in the target volume.     

Computational radiofrequency electromagnetic field dosimetry in evaluation of biological effects

Given growing computational resources, radiofrequency electromagnetic field dosimetry is becoming more vital in the study of biological effects of non-ionizing electromagnetic radiation. The study analyzes numerical methods which are used in theoretical dosimetry to assess the exposure level and specific absorption rate distribution. The advances of theoretical dosimetry are shown. Advantages and disadvantages of different methods are analyzed in respect to electromagnetic field biological effects. The finite-difference time-domain method was implemented in detail; also evaluated were possible uncertainties of complex biological structure simulation for bioelectromagnetic investigations.     

In vivo dosimetry for lung radiotherapy including SBRT

SBRT for lung cancer is being rapidly adopted as a treatment option in modern radiotherapy centres. This treatment is one of the most complex in common clinical use, requiring significant expertise and resources. It delivers a high dose per fraction (typically ∼6–30 Gy/fraction) over few fractions. The complexity and high dose delivered in only a few fractions make powerful arguments for the application of in vivo dosimetry methods for these treatments to enhance patient safety. In vivo dosimetry is a group of techniques with a common objective – to estimate the dose delivered to the patient through a direct measurement of the treatment beam(s). In particular, methods employing an electronic portal imaging device have been intensely investigated over the past two decades. Treatment verification using in vivo dosimetry approaches has been shown to identify errors that would have been missed with other common quality assurance methods. With the addition of in vivo dosimetry to verify treatments, medical physicists and clinicians have a higher degree of confidence that the dose has been delivered to the patient as intended.In this review, the technical aspects and challenges of in vivo dosimetry for lung SBRT will be presented, focusing on transit dosimetry applications using electronic portal imaging devices (EPIDs). Currently available solutions will be discussed and published clinical experiences, which are very limited to date, will be highlighted.     

On the re-calibration process in radiochromic film dosimetry

PurposeThe accuracy and precision of the dose estimates obtained with radiochromic film dosimetry are investigated in a clinical environment. The improvement in the accuracy of dose estimates reached with corrective methods is analyzed. Two novel re-calibration algorithms for radiochromic film dosimetry are presented.MethodsTwo different EBT3 lots are evaluated in two different centres. They are calibrated in Varian linacs and read in two different EPSON scaners. Once the lots are calibrated, three films per lot are considered and divided into stripes that are exposed to known doses. Several dosimetry protocols usually employed in radiochromic film dosimetry are used to convert film responses to absorbed doses. These protocols are characterized by different choices of the film responses or different sensitometric curves. Finally, the accuracy and reproducibility of the dose estimates is investigated with and without the corrective methods.Results and ConclusionsThe variabilities that affect radiochromic film dosimetry, such as intra-lot variability, inter-scan variability, post-exposure time and film autodevelopment may give rise to inaccuracies in the dose estimates. However, the implementation of re-calibration methods leads to more accurate dose estimates. All the investigated protocols showed more accurate and reproducible results when the re-calibrated methods were employed. So, the novel re-calibration methods may be applied in order to improve the accuracy and reproducibility of radiochromic film dosimetry.     

光动力学疗法剂量学的研究进展

随着光动力学疗法 ( photodynamic therapy,PDT ) 基础研究的不断深入和临床应用的广泛开展,如何精确量化光动力剂量,并根据患者的个体差异进行剂量的实时调整和优化已成为亟待解决的挑战性难题,属PDT研究的前沿热点．综述了现有PDT剂量学研究方法及其相应检测技术的研究进展,其中包括：a．测定光通量密度、光敏剂浓度和氧分压;b．测量光敏剂的光漂白速率和光致产物;c．监测PDT前后组织的光生物学响应;d．检测单态氧在1 270 nm的近红外发光．同时,还分析了这些PDT剂量学方法的优点和局限性．最后,讨论了PDT剂量学研究中所面临的挑战．     

Polarized dosimetry method for Gafchromic EBT3

PurposeTo analyze the changes in the polarization state of the flatbed scanner light caused by the EBT3 films and to propose a new method for correcting the lateral effects.Methods and materialsThe polarization changes induced by radiochromic films are analyzed using linear polarizing film. Based on the results, the linear polarizing films are used in the scanning process of the EBT3 films. This method is tested against the conventional EBT3 dosimetry using a series of simple regular beams and 21 cases of IMRT.ResultsThe mean results are statically different from the conventional dosimetry with EBT3. Depending on the transmission axis of the polarizing sheet, the results are better or worse compared to conventional dosimetry EBT3 film. When the transmission axis of the polarizing sheet is parallel to the coating direction, the dosimetry results are better and its variability is smaller. However, when the polarizer transmission axis is perpendicular to the coating direction, results are worse as well as its variability.ConclusionUsing a polarized film with the polarization axis parallel to the coating direction of the radiochromic film, and preferably above it, significantly improves the dosimetry results and is an easy and inexpensive way to correct the lateral artifacts of the conventional EBT3 dosimetry.     

Comparison of dosimetric characteristics of physical wedge and enhanced dynamic wedge in inhomogeneous medium using Monte Carlo simulations

BackgroundWidely used physical wedges in clinical radiotherapy lead to beam intensity attenuation as well as the beam hardening effect, which must be considered. Dynamic wedges devised to overcome the physical wedges (PWs) problems result in dosimetry complications due to jaw movement while the beam is on. This study was aimed to investigate the usability of physical wedge data instead of enhanced dynamic wedge due to the enhanced dynamic wedge (EDW) dosimetry measurement hardships of Varian 2100CD in inhomogeneous phantom by Monte Carlo code as a reliable method in radiation dosimetry.Materials and methodsA PW and EDW-equipped-linac head was simulated using BEAMnrc code. DOSXYZnrc was used for three-dimensional dosimetry calculation in the CIRS phantom.ResultsBased on the isodose curves, EDW generated a less scattered as well as lower penumbra width compared to the PW. The depth dose variations of PWs and EDWs were more in soft tissue than the lung tissue. Beam profiles of PW and EDW indicated good coincidence in all points, except for the heel area.ConclusionResults demonstrated that it is possible to apply PW data instead of EDW due to the dosimetry and commissioning hardships caused by EDW in inhomogeneous media.     

An estimate of the magnitude of random errors in the DS86 dosimetry from data on chromosome aberrations and severe epilation

An analysis of the proportion of cells with chromosome aberrations in cultured blood lymphocytes from A-bomb survivors in Hiroshima and Nagasaki reveals that the dose-response relationship using DS86 assigned dose is significantly steeper in the subsample of individuals who reported severe epilation after the bombings than in those who did not report severe epilation. This effect is due either to random errors in the DS86 dose assignments or to individual differences in sensitivity to radiation, or to both. In this paper, working within a class of dosimetry error models, we estimate the magnitude of random dosimetry errors which would be required to account for all of the difference in the observed dose response between people who did and did not report severe epilation under the assumption that random dosimetry error is the only cause of the effect. We conclude that random dosimetry errors in the range 45 to 50% of true dose are necessary to explain completely the difference in dose response between the two epilation groups. We discuss evidence that the contribution of individual differences in radiation sensitivity to the observed epilation effect is likely to be small, so that random dosimetry errors may be the major cause of this effect.     

Validation of Dolphin dosimetry in three dimensional patient-specific quality assurance programme

AimThe aim of this study is to commission and validate Dolphin-Compass dosimetry as a patient-specific Quality Assurance (QA) device.BackgroundThe advancement of radiation therapy in terms of highly conformal delivery techniques demands a novel method of patient-specific QA. Dolphin-Compass system is a dosimetry solution capable of doing different QA in radiation therapy.Materials and methodsDolphin, air-vented ionization detector array mounted on Versa-HD Linear Accelerator (LINAC) was used for measurements. The Compass is a dose computation algorithm which requires modelling of LINAC head similar to other Treatment Planning Systems (TPS). The dosimetry system was commissioned after measuring the required beam data. The validation was performed by comparison of treatment plans generated in Monaco TPS against the measurement data. Different types of simple, complex, static and dynamic radiation fields and highly conformal treatment plans of patients were used in this study.ResultsFor all field sizes, point doses obtained from Dolphin-Compass dosimetry were in good agreement with the corresponding TPS calculated values in most of the regions, except the penumbra, outside field and at build-up depth. The results of gamma passing rates of measurements by using different Multi-leaf Collimator patterns and Intensity Modulated Radiation Therapy fluence were also found to be in good correlation with the corresponding TPS values.ConclusionsThe commissioning and validation of dosimetry was performed with the help of various fields, MLC patterns and complex treatment plans. The present study also evaluated the efficiency of the 3D dosimetry system for the QA of complex treatment plans.     

Radiation dose verification of an X-ray based blood irradiator using EBT3 radiochromic films calibrated using Gamma Knife machine

AimBlood irradiators (BI) initial acceptance testing and routine annual dosimetry checks require radiation dose measurements in order to comply with regulatory requirements.BackgroundTraditionally thermo-luminescence dosimeters (TLD) have been used to measure the dose. The EBT3 film is reported to be a better dosimeter for low energy X-rays than its predecessors EBT2 and EBT. To the best of our knowledge, the use of EBT3 films to perform dosimetry on X-ray based BI has not been reported yet.Materials and methodsWe performed routine radiation dosimetry checks using EBT3 films on a new X-ray based BI and compared the results with TLD dosimetry. Calibration films were irradiated with radiation beam from a Co-60 Gamma Knife (GK) radiosurgery machine and, alternatively, using an Ir-192 high dose rate (HDR) brachytherapy device. The films were calibrated to cover a wide dose range from 1 to 40 Gy. Such a wide dose range has not been reported yet in BI film dosimetry.ResultsWe obtained a relative difference of about 6.6% between doses measured using TLD and those measured using EBT3 films. Both irradiation methods using GK or HDR were found to be adequate for the calibration of the EBT3 Gafchromic films.ConclusionsWe recommend the use of EBT3 films in routine X-ray based BI dosimetry checks. The presented method takes advantage of available radiotherapy equipment that can be efficiently used for EBT3 films calibration. The method is fast, reproducible and saves valuable medical physicist's time.     

Measurement of dose rate at the interface of cell culture medium and glass dishes by means of ESR dosimetry using thin films of alanine.

Previous studies on human cervical cancer cells (NHIK 3025) have indicated that the cells, when X-irradiated in suspension, appeared to be more radiosensitive than when they were irradiated attached to glass dishes. However, this result depends on dosimetry, which is difficult in the situation where cells are attached to glass dishes due to backscattering electrons at the glass-liquid interface. Recently developed dosimetry that is based on detection of radiation-induced stable radicals in alanine and uses ESR spectroscopy offers a possibility for more relevant dosimetry at the glass-liquid interface than the previous estimates of doses based on Fricke dosimetry. Thin alanine films (>/=10 microm) were used to measure dose at the interface by irradiating the films while they were placed tightly against the bottom of dishes and covered with 1 mm of wax simulating the medium above cells. Fricke dosimetry was also performed, with different depths of Fricke solution in the dishes, to elucidate the contribution to the dose delivered by backscattering electrons at the glass-liquid interface. A dose rate of 1.9 Gy/min was measured with a thin layer (0.2-0.3 mm) of Fricke solution in petri dishes made of glass. However, this estimate appears to be too high, due to a contribution to dose by short-ranged electrons generated when the X rays passed through a steel lid 4.5 cm above the dishes. Dosimetry using alanine films resulted in dose rates of 1.15 and 0.87 Gy/min at the interfaces of glass-liquid and plastic- liquid, respectively. Hence there is a significant contribution to dose from backscattering electrons on dishes made of glass. The reason for our previous observation of a difference in radiosensitivity between cells irradiated in suspension and cells irradiated attached to glass appears to be a lack of accurate dosimetry at the glass-liquid interface.     

EFOMP survey results on national radiotherapy dosimetry audits

PurposeThe Council Directive 2013/58/EURATOM entered into force in 2014, and its transposition into national legislations became applicable in 2018. The Council Directive 2013/58/EURATOM strengthened the importance of clinical audits, and stated that Member States should ensure dosimetry audit compliance in accordance with national procedures. Therefore, the purpose of this work was to picture the status of the implementation of dosimetry audits in European countries. Methods: A questionnaire was designed to describe dosimetry audit standards in radiotherapy across European countries. The questionnaire was sent to 33 EFOMP National Member Organizations (NMO). Results: Nineteen NMOs responded to the survey (14 EU members). For 58% of the participating countries national regulations required dosimetry audits in radiotherapy departments. In 37% of the participating countries there were implemented regulations for independent/secondary dose verification, and in 21% of the participating countries similar procedures for dose verification were already implemented although not regulated by law. In 42% of the participating countries there were implemented mechanisms to review updates and advances in the field of radiotherapy.ConclusionsThe transposition and further implementation of the Council Directive 2013/59/EURATOM was scarce, leading to heterogeneities in national policies about dosimetry audits.     

A dosimetry method in the transverse plane of HDR Ir-192 brachytherapy source using gafchromic EBT2 film

Radiochromic film dosimetry is increasingly used in brachytherapy applications for its higher resolution ability as compared to other experimental methods. The present study was aimed to assess the accuracy and suitability of use of the improved radiochromic film model, Gafchromic EBT2, to evaluate the dose distribution in the transverse plane of microselectron HDR ¹⁹²Ir source.A specially designed and locally fabricated Polymethyl methacrylate (PMMA) phantom was used in this work for the experimental measurement of dose distribution around the source in its transverse plane. The AAPM TG-43U1 recommended radial dose function, g (r), and dose rate constant, Λ, for the source were measured using Gafchromic EBT2 film and thermoluminescent dosimeters (TLD). The EBT2 film measured dosimetric quantities were validated against their values obtained from the TLD measurements and previously published values for the same source available in literature.The dose rate constant and radial dose function for microselectron HDR ¹⁹²Ir source obtained from Gafchromic EBT2 film measurements are in agreement with their TLD measured results within 3.9% and 2.8% respectively. They also agree within the accepted range of uncertainty with their experimental and Monte Carlo calculated results reported in literature.This work demonstrates the suitability of using Gafchromic EBT2 film dosimetry in characterization of dose distribution in the transverse plane of HDR Ir-192 source. This is a more efficient method than TLD dosimetry at discrete and distant positions. Relative to TLD dosimetry, it is found to be better reproducible, easy to use and a less expensive method of dosimetry.     

Standards for intravascular brachytherapy dosimetry.

The dosimetry of intravascular brachytherapy sources is quite difficult due to the small size of the sources and the close proximity at which measurements are necessary. The development of National Standards for the dosimetry of these sources is described in this paper as well as predictions of how these standards will be changed and improved upon in the future.