Equivalent Dose Estimates Research Articles

Poster — Wed Eve—07: Software for the Estimation of Organ Equivalent and Effective Doses from Diagnostic Radiology Procedures

Diagnostic radiological imaging such as conventional radiography, fluoroscopy and computed tomography (CT) examinations will continue to provide tremendous benefits in modern healthcare. The benefit derived by the patient should far outweigh the risk associated with a properly conducted imaging examination. Nonetheless, it is very important to be able to quantify the risk associated with any radiological examination of patients, and effective dose has been considered a useful indicator of patient exposure. Quantification of the risks associated with radiological imaging is very important as such information will be helpful to physicians and their patients to compare risks from various imaging examinations and to make informed decisions whenever there is a need for any radiological imaging. The determination of equivalent and effective doses in diagnostic radiology is of interest as a basis for risk estimates from medical exposures. In this paper we describe a simple computer program OrgDose, which calculates the doses to 27 organs in the body and then calculates the organ equivalent and effective doses and the risk from various procedures in the radiology department including conventional radiography, fluoroscopy and computed tomography examinations. The program will be a useful tool for the medical and paramedical personnel who are involved with assessing organ and effective doses and risks from diagnostic radiology procedures.

Software for the estimation of organ equivalent and effective doses from diagnosticradiology procedures

Diagnostic radiological imaging such as conventional radiography, fluoroscopy andcomputed tomography (CT) examinations will continue to provide tremendous benefits inmodern healthcare. The benefit derived by the patient should far outweigh the riskassociated with a properly conducted imaging examination. Nonetheless, it is veryimportant to be able to quantify the risk associated with any radiological examinationof patients, and effective dose has been considered a useful indicator of patientexposure. Quantification of the risks associated with radiological imaging is veryimportant as such information will be helpful to physicians and their patients forcomparing risks from various imaging examinations and for making informeddecisions whenever there is a need for any radiological imaging. The determinationof equivalent and effective doses in diagnostic radiology is of interest as a basisfor estimates of risk from medical exposures. In this paper we describe a simplecomputer program OrgDose, which calculates the doses to 27 organs in the bodyand then calculates the organ equivalent and effective doses and the risk fromvarious procedures in the radiology department including conventional radiography,fluoroscopy and computed tomography examinations. The program will be auseful tool for the medical and paramedical personnel who are involved withassessing organ and effective doses and risks from diagnostic radiology procedures.

Applicability of OSL pre-dose phenomenon of quartz in the estimation of equivalent dose

The feasibility of utilizing the pre-dosed OSL signal in the estimation of the equivalent dose has been investigated. The results based on (i) the behavior of growth curve, (ii) dose recovery tests and (iii) non-bleachability of reservoir centres, R-centres, suggests that (i) the pre-dosed OSL does not seem to work satisfactorily in dose estimation unlike the pre-dosed 110 °C TL emission and (ii) it may not be applicable in case of bleached specimen.

OSL chronology of Lynch's Crater, the longest terrestrial record in NE-Australia

Lynch's Crater on the Atherton Tablelands in NE-Australia formed about 230,000 years ago during an explosive eruption, creating a maar more than 80 m deep. Since the eruption, the maar has been filled with lake sediments that are topped by peat material. A 64 m long core was recovered and an OSL dating project was undertaken to extend the chronology beyond 16 m depth, which according to 14C age control represents ∼60 ka. The predominantly organic lake sediments contained abundant fine quartz of aeolian origin, and the Single Aliquot Regenerative Method (SAR) provided satisfactory equivalent dose (D E) estimates. However, the determination of the dose rate proved both critical and difficult. Extremely low radionuclide contents led to cosmic radiation being the dominant dose rate contribution for most samples. The OSL chronology presented in this paper thus relies on modelling the changing cover by sediments and lake water over the burial time.

Signal regeneration in ESR dating of tephra with quartz

Electron spin resonance (ESR) dating has been applied previously to quartz derived from tephra deposits using the additive dose method. In this study we compare results obtained using both additive dose and regeneration dose methods on a Japanese tephra sample. A further intercomparison is carried out using two different signals corresponding to Al and Ti–Li centres, and two different grain sizes (0.25–0.5 mm and 0.5–1 mm). Possible sensitivity changes due to heating required for zeroing the signals was checked by the regenerative – additive dose technique. The estimates of equivalent dose ( D E) obtained using the regeneration method were generally consistent with those obtained using additive dose; however, as expected the uncertainties were much smaller for the regeneration D E estimates. A significant difference was observed between the equivalent dose ( D E) derived using the Al or Ti–Li centres, and using different grain sizes.

A revised burial dose estimation procedure for optical dating of youngand modern-age sediments

The presence of genuinely zero-age or near-zero-age grains in modern-age and very young samples poses a problem for many existing burial dose estimation procedures used in optical (optically stimulated luminescence, OSL) dating. This difficulty currently necessitates consideration of relatively simplistic and statistically inferior age models. In this study, we investigate the potential for using modified versions of the statistical age models of Galbraith et al. [Galbraith, R.F., Roberts, R.G., Laslett, G.M., Yoshida, H., Olley, J.M., 1999. Optical dating of single and multiple grains of quartz from Jinmium rock shelter, northern Australia: Part I, experimental design and statistical models. Archaeometry 41, 339–364.] to provide reliable equivalent dose (D e) estimates for young and modern-age samples that display negative, zero or near-zero D e estimates. For this purpose, we have revised the original versions of the central and minimum age models, which are based on log-transformed D e values, so that they can be applied to un-logged D e estimates and their associated absolute standard errors. The suitability of these ‘un-logged’ age models is tested using a series of known-age fluvial samples deposited within two arroyo systems from the American Southwest. The un-logged age models provide accurate burial doses and final OSL ages for roughly three-quarters of the total number of samples considered in this study. Sensitivity tests reveal that the un-logged versions of the central and minimum age models are capable of producing accurate burial dose estimates for modern-age and very young (<350 yr) fluvial samples that contain (i) more than 20% of well-bleached grains in their D e distributions, or (ii) smaller sub-populations of well-bleached grains for which the D e values are known with high precision. Our results indicate that the original (log-transformed) versions of the central and minimum age models are still preferable for most routine dating applications, since these age models are better suited to the statistical properties of typical single-grain and multi-grain single-aliquot D e datasets. However, the unique error properties of modern-age samples, combined with the problems of calculating natural logarithms of negative or zero-Gy D e values, mean that the un-logged versions of the central and minimum age models currently offer the most suitable means of deriving accurate burial dose estimates for very young and modern-age samples.

The potential of optically stimulated luminescence for dating periglacial slope deposits — A case study from the Taunus area, Germany

Periglacial deposits overlying bedrock are widespread in the German low mountain ranges. The age of these deposits is still a matter of debate and therefore, three sections in the Taunus area were investigated with luminescence dating techniques. In general, the heterogeneity of the sediment, which is characterized by a mixture of grain sizes from clay to cobbles, is the main problem for dating as dose-rate determination is complicated. This is demonstrated based on comparisons of high resolution γ-ray spectrometry, neutron activation analysis, β-counting and in-situ measurements of the γ-dose-rate. Insufficient bleaching due to the transport mode, and consequently age overestimation, was expected to be a major problem for luminescence dating of periglacial slope deposits. In order to get a detailed insight into equivalent dose variations due to partial bleaching, single aliquot regenerative dose (SAR) protocols have been applied to the polymineralic fine-grain fraction, sand-sized K-feldspar and quartz extracts. Our results do not confirm partial bleaching as a problem, except for the basal layer. The luminescence properties vary substantially depending on the site, the layer and the mineral fraction that is measured for equivalent dose determination. However, hardly any systematic tendencies can be observed. Micromorphology analysis indicates post-depositional mixing which complicates the equivalent dose estimation even further. Due to the lack of accuracy, the relevance of the presented data for palaeolandscape reconstruction is limited. Based on these observations, suggestions are made to improve future attempts of dating periglacial cover beds with optically stimulated luminescence (OSL).

DELAYED RADIATION-INDUCED MYELOPATHY AFTER SPINAL RADIOSURGERY

Spinal cord injury is arguably the most feared complication in radiotherapy and has historically limited the aggressiveness of spinal tumor treatment. We report a case series of 6 patients treated with radiosurgery who developed delayed myelopathy. Between 1996 and 2005, 1075 patients with benign or malignant spinal tumors were treated by CyberKnife (Accuray, Inc., Sunnyvale, CA) robotic radiosurgery at Stanford University Medical Center and the University of Pittsburgh Medical Center. Patients were followed prospectively with clinical and radiographic assessments at 1- to 6-month intervals. A retrospective review identified patients who developed delayed radiation-induced myelopathy. Six patients (5 women, 1 man) with a mean age of 48 years (range, 25-61 years) developed delayed myelopathy at a mean of 6.3 months (range, 2-9 months) after spinal radiosurgery. Three tumors were metastatic; 3 were benign. The metastases were in the upper to midthoracic spine, whereas the benign tumors were partially in the cervical region. Three cases involved previous radiation therapy. Dose volume histograms were generated for target and critical structures. Clinical and dosimetric factors were analyzed for factors predictive of spinal cord injury. Specific dosimetric factors contributing to this complication could not be identified, but one-half of the patients with myelopathy received spinal cord biological equivalent doses exceeding 8 Gy. Delayed myelopathy after radiosurgery is uncommon with the dose schedules used in this case series. Radiation injury to the spinal cord occurred over a spectrum of dose parameters that prevented identification of specific dosimetric factors contributing to this complication. Primarily, biological equivalent dose estimates were not usable for defining spinal cord tolerance to hypofractionated dose schedules. We recommend limiting the volume of spinal cord treated above an 8-Gy equivalent dose, because half of the complications occurred beyond this level.

MO-E-AUD B-02: Antiproton Therapy: Monte Carlo Simulations of Normal Tissue Equivalent Dose From Annihilation Neutrons

Purpose: Recent in vitro experiments at CERN have demonstrated a superior biological effectiveness for antiprotons relative to protons. A continued concern is the normal tissuedose resulting from annihilation neutrons. Using Monte Carlo simulations of a CT‐based anthropomorphic human phantom, we quantify the physical dose from annihilation byproducts and present the first organ specific calculations of normal tissue equivalent dose from neutrons in antiproton therapy. Method and Materials:MCNPX and FLUKA were utilized to model antiproton irradiation of the segmented whole‐body phantom of a 38 year old male representing the ICRP reference man. The fluence was tallied as a function of energy and organ type for a 75 MeV antiproton pencil beam with a Bragg peak located in the frontal lobe of the phantom's brain. Physical dose was calculated for each organ as a function of energy using fluence to kerma conversion coefficients (ICRU‐63). Finally, using energy dependent radiation weighting factors (ICRP‐60), the equivalent dose from neutrons was estimated for each organ.Results: The results indicate a neutron fluence on the order of 10−5 cm−2 per incident antiproton for the bladder and colon, and a neutron fluence on the order of 10−4 cm−2 per incident antiproton for the thyroid and esophagus. As anticipated, the physical and equivalent doses are dependent on the irradiation geometry and the proximity of the organs to the Bragg peak; of the organs tallied, bone and thyroid received the highest physical and equivalent dose for the given irradiation protocol. The estimates of organ physical and equivalent dose and their uncertainties are discussed. Conclusion: We have developed an anthropomorphic Monte Carlo model for antiproton therapy. The model provides a method for more sophisticated biological modeling of treatment response such as cost basis analysis of TCP and NTCP relative to other treatment modalities.

SU-GG-T-360: Monte Carlo-Based Pre-Installation Proton Therapy Shielding Verification for a Single-Room Proton Therapy Facility

Purpose: To validate analytic shielding and maze calculations prior to construction of a doorless in-room accelerator proton therapy facility. Method and Materials: The MCNPX Monte Carlo program (version 2.6c) was used to model the treatment facility. LA 150 cross-sections were used for all materials available. Maze walls, floors, and shielding walls, including all passage ways were included in the room geometry. Treatment losses were modeled with an Fe target placed at isocenter. The cyclotron was geometrically modeled with anticipated proton loss points. The cyclotron was modeled both with and without localized compound shielding. Simulations were performed for gantry angles of 0°, 90°, and 180° for the target source and 0°, 90°, and 135° for the cyclotron source. The 135° beam was simulated since it places the accelerator in a direct line-of-sight of an personnel access area in the lower level shielding wall. Neutron dose equivalent and photon dose values were tallied using mesh tallies throughout the treatment room, maze, and outside of the shielding enclosure and compared with design values. Neutron dose equivalent estimates used the ICRP-74 neutron flux-to-dose rate conversion factors. Results: MCNPX simulations confirmed the analytical shielding estimates and indicated areas of under and over-shielding in the facility plans. Beyond the shielding walls, photon dose equivalent values were less than 10% of the neutron values. Neutrons streaming from the accelerator through a lower maze shielding void contribute to the personnel dose to in the treatment control area. Use of 1″ of simple compound shielding reduces this contribution by a factor of 2.25. Conclusion: MCNPX is a valuable tool for pre-installation verification of shielding design and indicate that doorless proton therapy vaults are feasible.

Simulation of the cosmic-ray induced dose-rate within a Martian soil profile

Determination of luminescence ages of Martian sediments requires procedures for accurate estimation of equivalent dose and dose-rate below the Martian surface. We have developed a new Monte Carlo code utilizing Geant4 simulation toolkit to calculate the GCR dose-rate within a Martian soil profile. Our results suggest that total GCR induced dose-rate at the Martian surface is ∼ 43 mGy a - 1 for average solar activity (modulation parameter = 600 MeV ), and is much higher than the environmental dose-rate of ∼ 0.7 mGy a - 1 . Furthermore, we discuss the dependence of the total GCR dose-rate on solar activity, and implications for luminescence dating of Martian sediments.

LET dependence of thermoluminescent efficiency and peak height ratio of CaF 2:Tm

First-order thermoluminescence (TL) kinetics computerized glow curve deconvolution (CGCD) and manual analysis of the composite peak structures have been applied to study the behaviour of glow peaks 3 and 5 in CaF 2:Tm (TLD-300, Harshaw-Thermo Fisher Scientific) single crystals after heavy charged particle (HCP) irradiation with respect to Co 60 gamma rays for a linear energy transfer (LET) interval from 2.3 to 339.4 keV μ m - 1 . The ratio of peak 5 to peak 3 heights can be used to evaluate effective LET and correct measured doses for TL efficiency. The applicability of this idea to dose equivalent estimation in exotic radiation fields of complex composition is discussed critically.

Biological dosimetry in the ENEIDE Mission on the International Space Station

Space radiation represents one of the major health hazards to crews of interplanetary missions. As the duration of space flight increases, according to International Space Station (ISS) and Mars mission programs, the risk associated with exposure to ionizing radiation also increases. Although physical dosimetry is routinely performed in manned space missions, it is generally accepted that direct measurement of biological endpoints (biological dosimetry) is necessary for a precise assessment of radiation risk in extraterrestrial activities. Chromosomal aberrations (CAs) in peripheral blood lymphocytes (PBLs) are particularly suitable to this purpose, as they can provide estimates of both equivalent radiation dose and risk. In this study, cytogenetic analysis was performed on PBL chromosomes of an Italian astronaut involved in two different 10-day missions on the ISS (Marco Polo, April 2002, and ENEIDE, May 2005). Blood samples were collected before and after flights. CAs were evaluated in either mitotic spreads or in prematurely condensed chromosomes (PCC) by Fluorescence in Situ Hybridization (FISH). In addition, blood samples were exposed to graded doses of X-rays in vitro before and after the flight and cytogenetic damage evaluated to investigate whether the space environment alters the sensitivity of human cells to ionizing radiation. The yield of baseline chromosomal aberrations was not modified following Marco Polo and ENEIDE mission. This is consistent with the low dose absorbed in these short-term space missions. Preliminary results from Marco Polo mission suggested a significant increase in intrinsic radiosensitivity of lymphocytes after landing compared to pre-flight and follow-up (6 months after landing) samples. However, this effect was not observed during the ENEIDE mission. The results suggest that intra-indi-vidual variations in radiosensitivity are significant, but they cannot be related to the space flight.

Preliminary results of a small X-ray irradiator for equivalent dose estimation

In most established method for luminescence dating, the ratio of 90Sr/90Y radionuclides has been employed to provide reference laboratory doses to sample. Recently a small X-ray irradiator (Varian VF-50J) was introduced as an alternative to the traditionally used radioactive sources. Test results are presented whether the use of the small X-ray irradiator is possible in the dating technique. Aspects of the assessment of the X-ray irradiator include consideration of the measured optically stimulated luminescence signal and the relationship between X-ray tube currents and dose rates, as well as the dependence of equivalent dose for various dose rates. The test performances are assessed in relation to use with heated quartz.

Optimization of the ‘double SAR’ procedure for polymineral fine grains

The “double SAR” protocol has been used to measure the equivalent dose of polymineral grains from fine-grained samples. However, the optical ages obtained with this protocol using the different luminescence signals from a sample are not always consistent. Quartz optical ages are believed to be more reliable than feldspar ages. The post-IR OSL signals from polymineral fine grains are believed to be dominated by the signal from quartz. The ages obtained with the “double SAR” protocol using the post-IR OSL signals from polymineral fine grains are therefore considered to be more reliable than those obtained using the IRSL signals. Thus, the feldspar contribution to the post-IR OSL signals should be reduced as much as possible. In this paper, the effects of IR-stimulation temperature and duration before OSL measurement on the post-IR OSL signals from quartz extracts and polymineral grains, and their equivalent dose values were tested. The results show that the IR stimulation causes the quartz post-IR OSL signals to be reduced even at room temperature if the IR stimulation lasts long enough, but does not affect quartz equivalent dose estimation using post-IR OSL signals. In the ‘double SAR’ procedure, the IR-stimulation time should be determined by an IR-bleaching D e plateau test, and the bleaching should preferably be performed at room temperature.

Getting ready for the manned mission to Mars: the astronauts’ risk from space radiation

Space programmes are shifting towards planetary exploration and, in particular, towards missions by human beings to the Moon and to Mars. Radiation is considered to be one of the major hazards for personnel in space and has emerged as the most critical issue to be resolved for long-term missions both orbital and interplanetary. The two cosmic sources of radiation that could impact a mission outside the Earth's magnetic field are solar particle events (SPE) and galactic cosmic rays (GCR). Exposure to the types of ionizing radiation encountered during space travel may cause a number of health-related problems, but the primary concern is related to the increased risk of cancer induction in astronauts. Predictions of cancer risk and acceptable radiation exposure in space are extrapolated from minimal data and are subject to many uncertainties. The paper describes present-day estimates of equivalent doses from GCR and solar cosmic radiation behind various shields and radiation risks for astronauts on a mission to Mars.

Investigating the amount of zeroing in modern sediments of River Danube, Austria

Sediments attributed to flooding events of River Danube concerning the bleaching of the optical stimulated luminescence (OSL) signal were investigated. It is demonstrated that the OSL signal in both quartz and feldspar is not completely but differentially bleached in the sediment grains. Partial bleaching of the samples is clearly indicated by the scatter of equivalent dose determined for several individual single aliquots. It is also shown that residual ages in feldspars are significantly higher than those calculated for quartz. It is furthermore demonstrated that analysing measurement-time dependent equivalent dose estimates is not a suitable method to identify partial bleaching in the investigated sediment grains. However, the transport and deposition process of the investigated samples was probably disturbed by an artificial input of sediment, and this case study may thus not be representative of undisturbed high flood events in the past.

On the need to revise the arm structure in stylized anthropomorphic phantoms in lateral photon irradiation geometry

Distributions of radiation absorbed dose within human anatomy have been estimated through Monte Carlo radiation transport techniques implemented for two different classes of computational anthropomorphic phantoms: (1) mathematical equation-based stylized phantoms and (2) tomographic image-based voxel phantoms. Voxel phantoms constructed from tomographic images of real human anatomy have been actively developed since the late 1980s to overcome the anatomical approximations necessary with stylized phantoms, which themselves have been utilized since the mid 1960s. However, revisions of stylized phantoms have also been pursued in parallel to the development of voxel phantoms since voxel phantoms (1) are initially restricted to the individual-specific anatomy of the person originally imaged, (2) must be restructured on an organ-by-organ basis to conform to reference individual anatomy and (3) cannot easily represent very fine anatomical structures and tissue layers that are thinner than the voxel dimensions of the overall phantom. Although efforts have been made to improve the anatomic realism of stylized phantoms, most of these efforts have been limited to attempts to alter internal organ structures. Aside from the internal organs, the exterior shapes, and especially the arm structures, of stylized phantoms are also far from realistic descriptions of human anatomy, and may cause dosimetry errors in the calculation of organ-absorbed doses for external irradiation scenarios. The present study was intended to highlight the need to revise the existing arm structure within stylized phantoms by comparing organ doses of stylized adult phantoms with those from three adult voxel phantoms in the lateral photon irradiation geometry. The representative stylized phantom, the adult phantom of the Oak Ridge National Laboratory (ORNL) series and two adult male voxel phantoms, KTMAN-2 and VOXTISS8, were employed for Monte Carlo dose calculation, and data from another voxel phantom, VIP-Man, were obtained from literature sources. The absorbed doses for lungs, oesophagus, liver and kidneys that could be affected by arm structures in the lateral irradiation geometry were obtained for both classes of phantoms in lateral monoenergetic photon irradiation geometries. As expected, those organs in the ORNL phantoms received apparently higher absorbed doses than those in the voxel phantoms. The overestimation is mainly attributed to the relatively poor representation of the arm structure in the ORNL phantom in which the arm bones are embedded within the regions describing the phantom's torso. The results of this study suggest that the overestimation of organ doses, due to unrealistic arm representation, should be taken into account when stylized phantoms are employed for equivalent or effective dose estimates, especially in the case of an irradiation scenario with dominating lateral exposure. For such a reason, the stylized phantom arm structure definition should be revised in order to obtain more realistic evaluations.

Luminescence dating of the last earthquake of the Sabzevar thrust fault, NE Iran

Iran is one of the world's most tectonically active regions, yet dating past earthquakes for neotectonic studies has been limited. One of the main reasons for this is that organic material suitable for radiocarbon dating of deformed sediments is rare. We investigate the use of infrared stimulated luminescence (IRSL) from coarse-grained feldspars to date colluvial deposits associated with the Sabzevar thrust fault in northeastern Iran. The single-aliquot regenerative (SAR) dose measurement procedure was used for this study. The current study investigates monitoring and correcting for sensitivity changes, recovering a known laboratory dose and equivalent dose estimation using three SAR IRSL methods. It is shown that SAR has recovered a given laboratory dose using a range of preheat temperatures but D e determination of natural samples requires its own preheat plateaus for two of these SAR methods. The SAR IRSL method provided an age of 1.7±0.3 ka for colluvium, predating the last earthquake event on the Sabzevar fault. This result suggests that this fault is likely to be responsible for an earthquake that destroyed Sabzevar city in AD 1052.

Equivalent dose in quartz from young samples using the SAR protocol and the effect of preheat temperature

Major concerns in the dating of samples younger than a few hundred years by the optically stimulated luminescence (OSL) technique are thermal transfer and partial bleaching. Thermal transfer during preheating enhances the OSL signal due to the charge transfer from thermally sensitive, but light-insensitive, traps to optical centres of quartz and results in an overestimate in equivalent dose, especially for very young samples. In this study, the single-aliquot regenerative-dose protocol is used to obtain values of equivalent dose ( D e ) from young samples taken from various environments around Istanbul. Within this framework, we aim to investigate the effect of preheat temperature on equivalent dose from 150 to 300 ∘ C , the reproducibility of D e measurements for young deposits and the contribution from thermal transfer of charge to the equivalent dose estimation. It was observed that the measured dose is influenced significantly by preheat temperature and the increase in the D e is clearly due to thermal transfer of charge from deep thermally sensitive traps to OSL trap during preheating of the samples prior to the main OSL measurements.