Medical Dosimetry Research Articles

Surgeon Radiation Dose During Complex Endovascular Procedures

Surgeon radiation dose during complex endovascular procedures (CEPs) has not been well studied. We sought to characterize radiation exposure to surgeons during CEPs based on procedure type, operator position, level of operator training, upper vs lower body exposure, and the addition of protective shielding. Optically stimulable, luminescent nanoDot (Landauer Inc) detectors were used to measure radiation dose prospectively to surgeons during CEPs. NanoDot dosimeters were placed outside the lead apron of the primary and assistant operator at the left upper chest and left lower pelvis positions. For each case, procedure type, reference air kerma (RAK), kerma area product (KAP), the relative position of the operator, level of training of the fellow, and presence or absence of external additional shielding devices were recorded. Three positions were assigned on the right hand side of the patient in decreasing relative proximity to the flat panel detector (FPD) as A, B, and C, respectively. Position A (main operator) was closest to the FPD. Position D was on the left side of the patient at the brachial access site. NanoDots were read using a Microstar II medical dosimetry system (Landauer Inc) after every procedure. The nanoDot dosimetry system was calibrated for scattered radiation in an endovascular suite with a NIST-traceable solid state radiation detector (Piranha T20, RTI). Comparative statistical analyses of nanoDot dose levels between categories was performed using analysis of variance with Tukey pairwise comparisons. Bonferroni correction was used for multiple comparisons. There were 415 nanoDot measurements with the following case distribution: 16 thoracic endovascular aortic repairs or endovascular aneurysm repairs, 18 fenestrated endovascular aneurysm repairs (FEVARs), 13 embolizations, 41 lower extremity, 10 fistulograms, and 13 viscerals. The mean operator dose for FEVARs was statistically higher than for other case types (P < .03), 15 μSv at position A and 11 μSv at position B. For all case types, positions A (8.7 ± 2.7 μSv) and D (14.4 ± 7.8 μSv) received statistically higher effective doses than B (3.9 ± 2.7 μSv; P < .001 or C (0 mGy). However, the mean operator dose for position D was not statistically different from position A. The addition of the lead skirt significantly decreased the lower body dose (33 ± 3.4 μSv to 6.3 ± 3.3 μSv) but not the upper body dose (6.5 ± 3.3 μSv to 5.7 ± 2.2 μSv). The use of ceiling-mounted shielding did not affect the nanoDot dose. There was no difference in the operator dose observed based on level of training when the fellow was in position A. KAP was the better predictor of operator radiation dose compared with RAK. The mean KAP for all cases was 330 Gycm2, and the regression coefficient for operator dose to KAP was 0.021 ± 0.003 μSv/Gycm2 for position A and 0.015 ± 0.003 μSv/Gycm2 for B. Surgeon radiation dose during CEPs depends on case type, operator position, and table skirt use, but not on the level of fellow training. On the basis of this data, the primary operator could perform ∼12 FEVARs per week and have an annual dose of <10 mSv, which would not exceed lifetime occupational dose limits during a 35-year career. Excluding FEVARs with the above case mix, the primary operator could perform ∼40 CEPs per week and stay within regulatory limits. With practical case loads, operator doses are relatively low and unlikely to exceed occupational limits.

Characterisation of the thermoluminescence (TL) properties of tailor-made Ge-doped silica glass fibre for applications in medical radiation therapy dosimetry

We have investigated the characterisation of new fabricated material Ge doped silica glass thermoluminescence TL dosimeter (Photonic Research Centre, University of Malaya) for medical radiation dosimetry at therapy energy. Previously, the dosimeter has been studied to provide ideal dosimetry system, suitable to ensure an accurate delivery of radiation doses to tumour tissue while minimising the amount of radiation administrated to healthy tissue. Both energies of photon and electron were used in this experiment for a dose range of 1 to 5 Gy. The various sizes of core diameter Ge doped silica glass (120, 241, 362, 483 and 604 μm) were exposed by using linear accelerator at Pantai Medical Centre. For both energies, the optical fibres were found to produce a flat response to a fixed photon and electron doses to within 4% (S.D) of the mean of the TL distribution. In terms of dose response, the fibres provide linear response over the range investigated, from a fraction of 1-5 Gy. The finding shows 120 μm fibres have 1.82 greater dose response than 604 pm fibres irradiated at 6 MV photon with a fixed dose of 3 Gy. While for electron energy 12 MeV, the response shows 120 μm fibres have 1.58 greater dose response compared to 604 μm fibres. The good responses are suitable to make these tailor-made doped silica fibres a promising TL material for use as a dosimetric system in medical radiation therapy.

A Method for Simultaneous Determination of Effective Removal Cross-section for Fast Neutrons and Mass Absorption Coefficient for Gamma Rays

The study of photon and neutron interactions with matter is an important issue for several applications, e.g. in industry, medical radiation dosimetry, security inspections, radiation shielding and nuclear engineering materials.

Medical radiation dosimetry—theory of charged particle collision energy loss by Brain McParland

Medical radiation dosimetry—theory of charged particle collision energy loss by Brain McParland

Evaluation of epitaxial silicon diodes as dosimeters in X-ray mammography

In this work we report on results obtained with 2 rad-hard n-type epitaxial silicon diodes in mammography X-ray dosimetry. One sample was not irradiated before using as a dosimeter, while the other received a 60Co gamma-ray pre-dose of 200 kGy. Both unbiased devices operated in a short-circuit mode as on-line radiation dosimeters for quality assurance in medical imaging dosimetry. The irradiation was performed using 28 kV and 35 kV X-ray beams from a Pantak/Seifert generator, previously calibrated by standardized ionization chamber. The dosimetric response of these devices was investigated with respect to the repeatability, long term stability, sensitivity dependence on energy and dose-rate, charge-dose linearity and directional response. The calibration coefficients of each diode, in terms of air kerma, were also determined. These dosimetric parameters of both diodes fully meet the requirements of IEC 61674 norm, confirming their use as a reliable alternative choice for mammography photon dosimetry within the dose range of 60 μGy-10 Gy (unirradiated EPI diode); for the pre-irradiated EPI diode upper limit of dose was not reached up to now. Nevertheless, it still remains to be investigated whether or not the pre-irradiation procedure influences on the response long-term stability of EPI devices. These studies are under way.

TLD Instrumentation: A Case Study of PC Controlled TL Reader

Thermoluminescence reader is an important tool and a requisite for a researcher to study and characterize Thermoluminescence (TL) materials in different forms. Requirement for a versatile PC Controlled TL Reader has been felt for quite some time globally. Nucleonix Systems, Hyderabad, India, have developed a PC Controlled TL Reader by integrating complete electronics hardware circuits (comprising of Power Electronics, Low/High voltage Supplies, Temperature Controller, Micro Controller based data acquisition circuits having serial counter, ADC, DAC, EEPROM, PMT, PMT housing, sample heating system, drawer assembly, etc.) in a single enclosure. The system also integrated with software to calculate the activation energy (E), frequency factor (S) and order of kinetics ‘1’ for the prominent glow peaks using different equations.This Integral TL Reader unit gets connected to the Personal Computer System through serial port RS232C/USB port. The user interface to the system is through front–end VB software defined Graphics User Interface (GUI). The system also contains some of the software features like glow curve acquisition, analysis, filing, printing, plotting, overlapping, maker data reporting, etc. Additionally, system facilitates single/two/three plateau heating with variable heating rates.The primary objective of this development is to bring out versatile TL instrumentation system and also to make it affordable to many of the researchers in the Universities and other areas, including Radio-therapist, Medical Physicists in Cancer Hospitals. This system has been evaluated for its performance with CaSO4: Dy discs, powder, as well as with LiF: Mg, Ti chips. Linearity and reproducibility have been found to be quite satisfactory also within +2%. This system is quite useful to study the TL of phosphor, minerals and characterization of various solid semiconducting materials, and also can be used in personal dosimetry measurements and research studies in medical dosimetry, environmental radiation monitoring, and host of other applications in R&amp;D Labs., etc.

Medical dosimetry using a RL/OSL prototype

A portable and robust instrument has been developed for the routine assessment of patient exposure to ionizing radiation during radiotherapy treatments. The design principles of hardware and software are described, along with preliminary measurements that illustrate the operation of the system and its capabilities. In this study the authors used radioluminescence (RL) and Optically Stimulated Luminescence (OSL) from Al2O3:C detectors coupled to a PMMA optical fibre to acquire dose in medical dosimetry. The RL/OSL prototype can provide two independent dose estimates from the same in vivo treatment: one integrated dose estimate (OSL) and one real-time dose estimate (RL), which can be compared to one another. The authors first characterized the dose–response to a calibration source (137Cs), analysing the OSL and the RL signal to doses from 0.5 to 3 Gy. Later the percentage dose depth from RL is presented for two gamma (6 and 15 MV) and two electron (6 and 12 MeV) medical beams.

SU‐E‐J‐17: A Study of Accelerator‐Induced Cerenkov Radiation as a Beam Diagnostic and Dosimetry Tool

Purpose:To investigate accelerator‐induced Cerenkov radiation imaging as a possible beam diagnostic and medical dosimetry tool.Methods:Cerenkov emission produced by clinical accelerator beams in a water phantom was imaged using a camera system comprised of a high‐sensitivity thermoelectrically‐cooled CCD camera coupled to a large aperture (f/0.75) objective lens with 16:1 magnification. This large format lens allows a significant amount of the available Cerenkov light to be collected and focused onto the CCD camera to form the image. Preliminary images, obtained with 6 MV photon beams, used an unshielded camera mounted horizontally with the beam normal to the water surface, and confirmed the detection of Cerenkov radiation. Several improvements were subsequently made including the addition of radiation shielding around the camera, and altering of the beam and camera angles to give a more favorable geometry for Cerenkov light collection. A detailed study was then undertaken over a range of electron and photon beam energies and dose rates to investigate the possibility of using this technique for beam diagnostics and dosimetry.Results:A series of images were obtained at a fixed dose rate over a range of electron energies from 6 to 20 MeV. The location of maximum intensity was found to vary linearly with the energy of the beam. A linear relationship was also found between the light observed from a fixed point on the central axis and the dose rate for both photon and electron beams.Conclusion:We have found that the analysis of images of beam‐induced Cerenkov light in a water phantom has potential for use as a beam diagnostic and medical dosimetry tool. Our future goals include the calibration of the light output in terms of radiation dose and development of a tomographic system for 3D Cerenkov imaging in water phantoms and other media.

SU-E-T-194: From Dicom-RT to Radiobiological Dose Metrics in 5 Minutes

Purpose: To develop a flexible and standalone framework for batch calculation of radiobiological dose metrics from Dicom-RT. Methods: Software has been developed which allows (1) The calculation of DVH data from DICOM dose and structure files (DVHgenerator), (2) Calculation of a wide range of radiobiological metrics from this data (CompPlanGui). Both these tools are run via graphical user interface (GUI), making them fast and simple. Part 1 is a new tool which has not previously been published, whilst part 2 is a GUI overlay for the previously published software ‘Comp-Plan’ (Holloway et. al., Medical Dosimetry, 2012), previously reliant on command line interface. The time taken for an experienced user to evaluate a test case of 6 plans with and without CompPlanGUI was quantified. Results: The DVH-generator has been found to be faster, more robust and require far less physical memory then using alternative software solutions for the same purpose. The Comp Plan GUI significantly reduces the amount of time required to set up a base directory, eliminates code crashes arising from typographical errors, and renders the code far more accessible to non-expert users. It took an experienced user of the code around 3 minutes to set up a base directory of 6 plans compared around 8 minutes without, indicating that using CompPlanGUI reduced setup time by over 50%. Conclusion: A standalone GUI based framework has developed which allows for the batch calculation of radiobiological dose metrics directly from Dicom-RT files. As with the original code, this work will be made freely available on request, as well as via matlab file exchange.

SU‐E‐I‐24: Design and Fabrication of a Multi‐Functional Neck and Thyroid Phantom for Medical Dosimetry and Calibration

Purpose:The purpose of this study is the design and fabrication of a multipurpose anthropomorphic neck and thyroid phantom for use in medical applications (i.e. quality control of images in nuclear medicine, and dosimetry).Methods:The designed neck phantom is composed of seven elliptic cylindrical slices with semi‐major axis of 14 and semi‐minor axis of 12.5 cm, each having the thickness of 2cm. Thyroid gland, bony part of the neck, and the wind pipe were also built inside the neck phantom.Results:The phantom contains some removable plugs,inside and at its surface to accommodate the TLD chips with different shapes and dimensions, (i.e. rod, cylindrical and cubical TLD chips)for the purpose of medical dosimetry (i.e. in radiology, radiotherapy, and nuclear medicine). For the purpose of quality control of images in nuclear medicine, the removable thyroid gland was built to accommodate the radioactive iodine. The female and male thyroid glands were built in two sizes separately.Conclusion:The designed phantom is a multi‐functional phantom which is applicable for dosimetry in diagnostic radiology, radiotherapy, and quality control of images in nuclear medicine.

MO‐E‐17A‐12: Direct Realization of the CT Dose to Phantom: Energy to Heat Conversion in Polyethylene Using Calorimetry

Purpose:To develop a primary reference standard for absorbed dose to phantom for medical CT dosimetry. CT dosimetry relies on the implementation of the CTDI standard based on air kerma. We are taking a step toward an absorbed dose to water standard by first investigating the dose in a solid phantom. By directly measuring the heat converted from the incident radiation, the absorbed dose in the phantom at a point can be assessed with primary methods without relying on indirect conversions.Methods:The calorimeter contains two small thermistors embedded in a removable PE “core” inserted into the cylindrical HDPE phantom. A core made with polystyrene (PS) was also tested because of its purportedly negligible heat defect. Measurements were made using the two cores and with a calibrated ionization chamber in a CT beam. The air chamber values were converted to the dose to medium using appropriate stopping‐power ratios from the literature, and then compared to the thermal data.Results:The PS core data yielded a dose of 1.3 times (4‐run average, 3% std. dev.) higher than the converted chamber value, whereas the PE core data were inexplicably higher. The possible systematic errors include 1) excess heat from the thermistors, 2) in PE the exothermic chemical reactions, 3) uncertainties of the specific heat capacities of the materials, 4) thermal drift, and 5) theoretical conversion of chamber values. Monte Carlo simulations and finite element heat transfer calculations were performed to address some of these issues. The general validity was assessed in a 6 MV photon beam with an entirely different calibration scheme.Conclusion:This study demonstrates the feasibility but also revealed the difficulty in developing a new primary reference standard for absorbed dose to material for CT. Additional experimental and theoretical work is planned to achieve our goal.

Synthesis and thermoluminescence characterization of Na6Mg(SO4)4:RE (RE = Ce, Tb) phosphors

Thermoluminescence (TL) properties of sulfate-based phosphors activated by different rare earths have received tremendous attention to the field of radiation dosimetry. Those TL materials based on CaSO4 have been widely applied for medical and environmental dosimetry. Taking this fact into account we have synthesized Na6Mg(SO4)4 doped with Ce and Tb by wet chemical method. The prepared phosphor was characterized by XRD, FTIR, photoluminescence (PL) and thermoluminescence. For TL study, the phosphor is irradiated with γ-rays from 60Co source. For studying luminescence properties, the prepared phosphor was annealed at different temperatures and effects of these annealing temperatures on Na6Mg(SO4)4 samples are investigated and quantified. The changes in the glow curve and PL emission spectrum are also investigated as a function of annealing temperature and the annealing temperature was optimized. For calculation of trapping parameters various methods such as peak shape (PS) method, initial rise (IR) method, various heating rate (VHR) method, and computerized glow curve deconvolution (CGCD) are employed.

State of art: Optically stimulated luminescence dosimetry – Frontiers of future research

Since the commercial adoption of the optically stimulated luminescence (OSL) technique in dosimetry, almost 20 years ago, we have seen major advances in the deployment of OSL dosimeters in different areas, including personal, medical, and space dosimetry. The objective of this paper is to provide a critical overlook at the OSL technique from three different points of view: strengths, challenges and opportunities. We discuss factors that made the OSL technique successful: its simplicity, accuracy, wide dynamic range of measured dose, ease for automation, re-read capability, ability to perform imaging, and the availability of diverse instruments and materials. We look into problems that were overcome and others that remain in several areas of new applications into which OSL has expanded in the past 10 years, such as medical, space, neutron and accident dosimetry. Finally, we discuss unexplored possibilities, new driving forces, and open questions. We hope the broad overview presented here will encourage more discussion and stimulate the research that will advance our fundamental understanding of the OSL process.

High sensitivity flat SiO2 fibres for medical dosimetry

We describe investigation of a novel undoped flat fibre fabricated for medical radiation dosimetry. Using high energy X-ray beams generated at a potential of 6MV, comparison has been made of the TL yield of silica flat fibres, TLD-100 chips and Ge-doped silica fibres. The flat fibres provide competitive TL yield to that of TLD-100 chips, being some 100 times that of the Ge-doped fibres. Pt-coated flat fibres have then been used to increase photoelectron production and hence local dose deposition, obtaining significant increase in dose sensitivity over that of undoped flat fibres. Using 250kVp X-ray beams, the TL yield reveals a progressive linear increase in dose for Pt thicknesses from 20nm up to 80nm. The dose enhancement factor (DEF) of (0.0150±0.0003)nm Pt is comparable to that obtained using gold, agreeing at the 1% level with the value expected on the basis of photoelectron generation. Finally, X-ray photoelectron spectroscopy (XPS) has been employed to characterize the surface oxidation state of the fibre medium. The charge state of Si2p was found to lie on 103.86eV of binding energy and the atomic percentage obtained from the XPS analysis is 22.41%. © 2014 Elsevier Ltd.

Pilot dose intercomparisons of 3D and 4D advanced lung radiotherapy

s / Physica Medica 30 (2014) e16ee44 e26 Contemporary therapeutic radiation oncology treatments require the de- livery of highly localized doses of radiation to well defined target regions inside the patient. The efficacy of the radiation treatment, however, re- quires knowledge of the absorbed dose in the organ of interest to better than ±5% as there is a higher risk of local recurrence or complications with incorrect exposure. Furthermore, since it is inevitable that healthy organs and tissue will also be exposed during treatment, overexposure increases the risk of secondary cancers. International regulations [1, 2] have been introduced to adapt to the fast introduction of new radiotherapy technologies and demand an improve- ment of in vivo dosimetry. Ideally, a real-time in vivo dosimeter would measure absorbed doses during radiotherapy. Optical stimulated luminescent (OSL) dosimeters, using the high sensi- tive material Al2O3:C, have been successfully used for measuring whole body doses that result from exposure to high energetic photon and beta radiation. OSL dosimeters have also been introduced in medical dosim- etry of low and high LET beams [3, 4]. Al2O3:C detectors can also be used as real time dosemeters, because the emitted stimulated light can be guided via light fibers to a remotely placed photomultiplier tube. Furthermore, during exposure to ionizing radiation Al2O3:C emits radi- oluminescent light (RL), of which the intensity is proportional to the dose rate [5]. In this study, we investigated the dosimetric response of an optical fibre coupled Al203:C RL/OSL dosemeter prototype. In our prototype, a PMMA fibre is coupled to an Al2O3:C detector composed of microparticles of Al2O3:C with diameters ranging from 5 mm to 35 mm dissolved in a photo- curable polymer. The RL/OSL dosimeter prototype is a portable and robust instrument that has been developed for the routine assessment of patient exposure to ionizing radiation during radiotherapy treatments. The design principles of hardware and software are described elsewhere [6]. In this study, we present the results obtained using radioluminescence (RL) from Al2O3:C irradiated with a 6 MV linear accelerator (Compact, Elekta, Crawly) and preliminary results obtained using optically stimulated luminescence (OSL). The dose rate dependence was assessed by varying the photon flux (MU/ min) of the linac, effectively changing the pulse rate and keeping the dose per pulse fixed. It was found that the RL measured dose response demonstrated low dose-rate dependency, to within 1%. The dose response was found to be linear in a dose range from 0.1 up to a dose of 6 Gy, with reproducibility below 0.5%. The dosimeter is benchmarked by evaluating the ability to measure depth- dose distributions and lateral dose profiles accurately. RL derived dose profiles have been compared with dose profiles measured with a standard ion chamber (PTW). Depth-dose distributions in water were acquired for a 6 MV photon beam using a 10 10 cm2 field, set at 350 MU/min, corre- sponding with 3.5 Gy/min at 10 cm depth. All data have been normalized to the depth-dose maximum. The RL measured dose agreed with the ionization chamber measured dose to within 1% (1 SD) for depths from 0.5 to 20 cm. Lateral dose profile was set at 350 MU/min (3.5 Gy/min at depth 10 cm), using a 10x10 cm2 field size. Differences between measured RL and ion chamber are within 1.5% for de direct beam and 5% in the penumbra region. These results show that the RL/OSL detector system makes it suitable for measurements of depth and lateral dose distributions in clinical photon beams. Furthermore, basic characteristics of OSL in irradiated fibers with Al2O3:C for dosimetry in therapeutic 6 MV photon beam were investigated.

The radiation oncology workforce: A focus on medical dosimetry

The 2012 Radiation Oncology Workforce survey was conducted to assess the current state of the entire workforce, predict its future needs and concerns, and evaluate quality improvement and safety within the field. This article describes the dosimetrist segment results. The American Society for Radiation Oncology (ASTRO) Workforce Subcommittee, in conjunction with other specialty societies, conducted an online survey targeting all segments of the radiation oncology treatment team. The data from the dosimetrist respondents are presented in this article. Of the 2573 dosimetrists who were surveyed, 890 responded, which resulted in a 35% segment response rate. Most respondents were women (67%), whereas only a third were men (33%). More than half of the medical dosimetrists were older than 45 years (69.2%), whereas the 45 to 54 years age group represented the highest percentage of respondents (37%). Most medical dosimetrists stated that their workload was appropriate (52%), with respondents working a reported average of 41.7 ± 4 hours per week. Overall, 86% of medical dosimetrists indicated that they were satisfied with their career, and 69% were satisfied in their current position. Overall, 61% of respondents felt that there was an oversupply of medical dosimetrists in the field, 14% reported that supply and demand was balanced, and the remaining 25% felt that there was an undersupply. The medical dosimetrists׳ greatest concerns included documentation/paperwork (78%), uninsured patients (80%), and insufficient reimbursement rates (87%). This survey provided an insight into the dosimetrist perspective of the radiation oncology workforce. Though an overwhelming majority has conveyed satisfaction concerning their career, the study allowed a spotlight to be placed on the profession׳s current concerns, such as insufficient reimbursement rates and possible oversupply of dosimetrists within the field.

Medical dosimetry with a RL/OSL prototype: 6 MV photon beams

Medical dosimetry with a RL/OSL prototype: 6 MV photon beams

Applications of triple GEM detectors beyond particle and nuclear physics

Micro-Pattern Gaseous Detectors (MPGD) have opened the way for the construction of detectors whose performance surpasses that of the previous generations in terms of spatial resolution, high-rate capability and increased radiation hardness. Led by the Micro-Mesh Gaseous Structure (Micromegas) and the Gas Electron Multiplier (GEM), some MPGDs are mature technologies used in a variety of experiments at high energy physics. What we report in this article is the experience explored in the last years with a compact GEM detector system in several applications as medical imaging, dosimetry and beam diagnostics for high energy beams and for nuclear reactors. For sake of shortness, only performance on soft X-ray and neutron detection will be described in detail. Also a description of the new promising highly pixelated GEM detector will be presented.

History of articles in medical radiation dosimetry and protection--looking back the transition from analog radiography to digital radiography

History of articles in medical radiation dosimetry and protection--looking back the transition from analog radiography to digital radiography

Characterisation of OSL and OSLN droplets for dosimetry

In spite of considerable progress in neutron dosimetry, there is no dosemeter that is capable of measuring neutron doses independently of the neutron spectrum with good accuracy. Carbon-doped aluminium oxide (Al2O3:C) is a sensitive material for ionising radiation (beta-ray, X ray and electron) and has been used for applications in personal and medical dosimetry as an optically stimulated luminescence (OSL) dosemeter. Al2O3:C has a low sensitivity to neutron radiation; this prevents its application to neutron fields, representing a disadvantage of Al2O3:C-OSL when compared with LiF, which is used as a thermoluminescent detector. Recently an improvement for neutron dosimetry (Passmore and Kirr. Neutron response characterisation of an OSL neutron dosemeter. Radiat. Prot. Dosim. 2011; 144: 155-60) uses Al2O3:C coated with (6)Li2CO3 (OSLN),which gives the high-sensitive response as known for Al2O3:C with the advantage of being also sensitive to thermal neutrons. In this article, the authors compare small-size detectors (droplets) of Al2O3:C (OSL) and of Al2O3:C+(6)Li2CO3 (OSLN) and discuss the advantages and drawbacks of both materials, regarding size vs. response.