Calculation Of Equivalent Dose Research Articles

Calculated organ equivalent doses for individuals in a sitting posture above a contaminated ground and a PET imaging room.

In this paper, phantoms representing sitting postures were developed and implemented in the MCNPX code to perform dose calculations. For the ground contamination case, isotropic planar source of (137)Cs was used. The male sitting phantom received an effective dose rate of 37.73 nSv h(-1) for a contamination of 30 kBq m(-2). The gonadal equivalent dose of the male sitting phantom was 40 % larger than that from the standing phantom. For the positron emission tomography clinic, a point photon source with the energy of 511 keV was used. The gonadal equivalent dose of the male sitting phantom was 117 % larger than that for the standing phantom. For an 8-h day, the effective dose of the sitting phantom was 2.54 μSv for 550 MBq F-18. This study concludes that phantoms with realistic postures could and should be considered in organ equivalent dose calculations in certain environmental and medical dosimetry studies where accurate data are desired.

The neutron dose equivalent evaluation and shielding at the maze entrance of a Varian Clinac 23EX treatment room

To evaluate the neutron and photon dose equivalent rate (H(n,D) and H(G)) at the outer maze entrance and the adjacent treatment console area after the installation of a Varian Clinac 23EX accelerator with a higher beam energy than its predecessor. The evaluation was based on measurements and comparison with several empirical calculations. The effectiveness of borated polyethylene (BPE) boards, as a maze wall lining material, on neutron dose and photon dose reduction is also reported. A single energy Varian 6 MV photon linear accelerator (linac) was replaced with a Varian Clinac 23EX accelerator capable of producing 18 MV photons in a vault originally designed for the former accelerator. In order to evaluate and redesign the shielding of the vault, the neutron dose equivalent H(n,D) was measured using an Andersson-Braun neutron Rem meter and the photon dose equivalent HG was measured using a Geiger Müller and an ion chamber gamma-ray survey meter at the outer maze entrance. The measurement data were compared to semiempirical calculations such as the Kersey method, the modified Kersey method, and a newly proposed method by Falcão et al. Additional measurements were taken after BPE boards were installed on the maze walls as a neutron absorption lining material. With the gantry head tilted close to the inner maze entrance and with the jaws closed, both neutron dose equivalent and photon dose equivalent reached their maximum. Compared to the measurement results, the Kersey method overestimates the neutron dose equivalent H(n,D) by about two to four times (calculation/measurement ratio approximately 2.4-3.8). Falcão's method largely overestimates the H(n,D) (calculation/measurement ratio approximately 3.9-5.5). The modified Kersey method has a calculation to measurement ratio about 0.6-0.9. The photon dose equivalent calculation including McGinley's capture gamma dose equivalent equation estimates about 77%-98% of the measurement. After applying BPE boards as a lining material on the inner corner of the maze wall, the H(n,D) and the H(G) at maze entrance were decreased by 41% and 59%, respectively. This work indicates that the Kersey method overestimates the neutron dose equivalent H(n,D) for a Varian Clinac 23EX accelerator. The Falcão method overestimates the H(n,D) partially due to the discrepancy in the International Commission on Radiological Protection (ICRP) conversion factors caused by the uncertainties of the estimated average neutron energy. The modified Kersey method gives the closest estimation of a Varian Clinac 23EX accelerator operated at 18 MV photon mode in a maze with a similar design as in the authors' study. However, it should be used with caution because of its tendency to underestimate the H(n,D). A borated polyethylene lining can provide a cost effective method to reduce neutron and photon dose equivalent at the maze door for an existing linac vault, following the installation of a higher energy linac.

Activités de l’uranium et du radium dans des échantillons d’eau naturelle au Sahara marocain

Measure of uranium and radium activities in some natural watersamples from Moroccan SaharaThe preliminary results of 238U, 234U, 226Ra, 228Ra and 228Th activities and of 234U/238U,228Ra/226Ra, 228Th/228Ra and 226Ra/238U activity ratios obtained for 8 wells, 5 drillings, 2 springs and 3 tap water samples collected in Laayoune and Es-Smara regions in the Moroccan Sahara are given in this work. The analyzed natural water samples have been collected from sources situated in a desert region rich in phosphates. Except for the one water drilling sample no used by population, the calculation of equivalent doses to the maximal activities for each isotope show that all measured activities are inferior to the maximum contaminant levels recommended by the International Commission of Radioprotection and they don't present any risk for population health. The obtained results are comparable to those already found in other regions in Morocco or in the world.

Selection of integration time intervals for quartz OSL decay curves

In quartz optically stimulated luminescence (OSL) dating protocols, an initial integral of the OSL decay curve is used in the calculation of equivalent dose, once a background integral has been subtracted. Because the OSL signal commonly contains a number of exponentially decaying components, the exact choice of time intervals used for the initial-signal and background integrals determines the composition of the net signal. Here we investigate which combination of time intervals will produce the net signal most dominated by the fast OSL component, while keeping an acceptable level of precision. Using a three-component model of OSL decay, we show that for a specified level of precision, the net signal most dominated by the fast component can be obtained when the background integral immediately follows the initial signal and is approximately 2.5 times its length. With this ‘early-background’ approach, the contribution of slow components to the net signal is virtually zero. We apply our methods to four samples from relatively young deposits. Compared to the widely used ‘late-background’ approach, in which the background integral is taken from the last few seconds of OSL, we find less thermal transfer, less recuperation and a higher proportion of aliquots yielding an equivalent dose in agreement with expectations. We find the use of an early background to be a simple and effective way of improving the accuracy of OSL dating, and suggest is should be used in standard protocols.

Radiation-Induced Cancers From Modern Radiotherapy Techniques: Intensity-Modulated Radiotherapy Versus Proton Therapy

To assess and compare secondary cancer risk resulting from intensity-modulated radiotherapy (IMRT) and proton therapy in patients with prostate and head-and-neck cancer. Intensity-modulated radiotherapy and proton therapy in the scattering mode were planned for 5 prostate cancer patients and 5 head-and-neck cancer patients. The secondary doses during irradiation were measured using ion chamber and CR-39 detectors for IMRT and proton therapy, respectively. Organ-specific radiation-induced cancer risk was estimated by applying organ equivalent dose to dose distributions. The average secondary doses of proton therapy for prostate cancer patients, measured 20-60 cm from the isocenter, ranged from 0.4 mSv/Gy to 0.1 mSv/Gy. The average secondary doses of IMRT for prostate patients, however, ranged between 3 mSv/Gy and 1 mSv/Gy, approximately one order of magnitude higher than for proton therapy. Although the average secondary doses of IMRT were higher than those of proton therapy for head-and-neck cancers, these differences were not significant. Organ equivalent dose calculations showed that, for prostate cancer patients, the risk of secondary cancers in out-of-field organs, such as the stomach, lungs, and thyroid, was at least 5 times higher for IMRT than for proton therapy, whereas the difference was lower for head-and-neck cancer patients. Comparisons of organ-specific organ equivalent dose showed that the estimated secondary cancer risk using scattering mode in proton therapy is either significantly lower than the cases in IMRT treatment or, at least, does not exceed the risk induced by conventional IMRT treatment.

MDMA: On the translation from rodent to human dosing

The recent paper in this journal by Goni-Allo et al. (2008) was a welcome addition to the literature on the effects of MDMA in rodents because it examined functional changes and related them to the systemic exposure (e.g., plasma concentrations) of the drug. Such pharmacodynamic– pharmacokinetic (or quantitative pharmacology) studies are vital if we are to attempt to relate preclinical findings to the possible acute and long-term consequences of human ingestion of MDMA. The debate on whether preclinical findings on the serotonergic neurotoxicity induced by MDMA in the rodent brain can be extrapolated to human recreational usage has engaged scientists’ minds for around 20 years. Concerns have been raised as to whether the administered dose of MDMA typically used to cause neurotoxicity in rats allows any translational projections to be made as to the doses required to produce similar damage in the brains of humans following recreational use of the drug. These concerns are discussed in this short article. In order to extrapolate doses used in animal studies to those in man it has been suggested by some (McCann and Ricaurte 2001) that the technique of interspecies scaling (Mordenti and Chappell 1989) should be used. Based on similar exposure (AUC, Css) to MDMA in rats and humans, this proposes that using the equation Dhuman1⁄4Danimal Whuman=Wanimal ð Þ (where D is dose in milligram and W is weight in kilogram) allows calculation of equivalent doses in animals and humans. Accordingly, the dose of 20 mg/kg in rats becomes equivalent to a human dose of 280 mg (4 mg/kg) or somewhat over three ecstasy tablets. Other investigators (Sessa and Nutt 2008) have intimated that a dose of (for example) 20 mg/kg given by intraperitoneal injection to rats can be directly extrapolated and therefore proposed that a similar oral dose is required by human users to achieve a similar effect. So, a 20 mg/kg dose in rats is deemed “equivalent” to a 1,400 mg dose (20 mg/kg× 70 kg body weight) which is around 20 ecstasy tablets. Of course, neither of these approaches has been shown to be valid for MDMA. Furthermore, the common practice of relating the pharmacological response directly to the administered dose is basically flawed. In examining the pharmacodynamics of a specific compound, factors like bioavailability, active metabolites, plasma protein binding differences, and pattern of systemic exposure can all play a major role in determining the onset, intensity, and duration of final effect. Since the exposure patterns of MDMA and active metabolite(s) can vary markedly between species, they confound any simple interpretation on a drug effect at any specific dose in one species producing a quantitatively similar effect in another, since it is impossible for all of the administered substance (at any stated dose) to be responsible for the observed pharmacological effect. For intelligent interpretation of any data collected, it is important at the very least to have a measurement of “exposure” of parent and potentially active metabolites and by that we mean the AUC or average concentration within a dosing interval or the peak plasma concentration that occurs following drug administration. Ideally, this means the unbound plasma concentration. This still fails to take into account the half-life of the drug, plasma protein binding (which can even change with plasma drug concentration in the same species), and the pharmacological action of active Psychopharmacology (2009) 204:375–378 DOI 10.1007/s00213-008-1453-8

SU-GG-T-380: Design and Shielding Considerations for the World's First Compact Synchrocyclotron Proton Therapy Unit

Purpose: Our institution will soon take delivery of the Monarch 250 Compact Proton Therapy Unit (Still River Systems). We performed facility shielding calculations that accounted for the produced neutron flux. Method and Materials: Workload assumptions (80Gy/day) yielded the number of protons produced per day. The vendor did not provide extraction efficiency, neutron yields from the treatment field shaping system, or neutron yield estimates from the synchrocyclotron. To provide a conservative neutron yield we assumed; the largest scatteredfield size and complete portal blocking, conservatively low cyclotron production efficiency (25%), and a high quality factor (20) for neutron dose equivalent calculations. Neutrons were assumed to be produced at the isocenter location, by stopping the SOBP protons in a Cu target. The room design includes a sub‐floor to allow rotation of the accelerator below the sub‐floor level. Classical analytical methods were used to calculate required barrier thicknesses based on neutron yields, accounting for angular dependences, and based on concrete (standard or high density (HD)), earth, and steel. Maze calculations used analytical approaches, heavily influenced by the number of bounce paths, and maze area. Conservative use and occupancy factors were used. Results: The shielding calculations resulted in barrier thicknesses similar to existing proton facilities; from 4ft to 6.25ft of HD concrete. Some design features included; reducing the maze ceiling height to reduce the source area of scatteredneutrons, adding an additional leg at the door entrance to allow for an unshielded door, and adding steel to surround unavoidable barrier voids. To reduce cost, the barriers that did not shield occupy‐able space, used standard concrete. Conclusion: The neutron yield from the Monarch 250 is unknown, so conservative values were used in the shielding calculations. Vault design strategies were developed to reduce overall construction cost. We allow for contingencies if we underestimated any barrier thickness.

Analytical shielding calculations for a proton therapy facility

The University of Pennsylvania is building a proton therapy facility in collaboration with Walter Reed Army Medical Center. The proposed facility has four gantry rooms, a fixed beam room and a research room, and will use a cyclotron as the source of protons. In this study, neutron shielding considerations for the proposed proton therapy facility were investigated using analytical techniques and Monte Carlo simulated neutron spectra. Neutron spectra calculations were done using the GEANT4 (v6.2) simulation code for various materials: water, carbon, iron, nickel and tantalum to estimate the neutron production at proton beam energies of 100, 175 and 250 MeV. Dose equivalent calculations were performed using analytical methods at various critical points within the facility, by folding the GEANT4 produced neutron spectra with dose equivalent rate data from the National Council on Radiation Protection and Measurements (NCRP) Report #144.

The measurement of photoneutron dose in the vicinity of clinical linear accelerators

In Brazil, the replacement of rather old cobalt and cesium teletherapy machines with high-energy (E > 10 MV) medical linear accelerators (linacs) started in the year 2000, as part of an effort by the Ministry of Health to update radiotherapy installations. Since then, the contamination of undesirable neutrons in the therapeutic beam generated by these high-energy photons has become an issue of concern when considering patient and occupational doses. The walls of the treatment room are shielded to attenuate the primary and secondary X-ray fluence, and this shielding is generally considered adequate also to attenuate neutrons. However, these neutrons are scattered through the treatment room maze and might result in a radiological problem at the door entrance, an area of high occupancy by the workers of a radiotherapy facility. This paper presents and discusses the results of ambient dose equivalent measurements of neutron using bubble detectors. The measurements were made at different points inside the treatment rooms, including the isocentre and the maze. Several radiation oncology centres, which are users of Varian Clinac or Siemens machines, have agreed to allow measurements to be taken at their facilities. The measured values were compared with the results obtained through the semi-empirical Kersey method of neutron dose equivalent calculation at maze entrances, with reported values provided by the manufacturers as well as values published in the literature. It was found that the measured values were below the dose limits adopted by the Brazilian Regulatory Agency (CNEN), requiring no additional shielding in any of the points measured.

Skeletal dosimetry for external exposure to photons based on µCT images of spongiosa from different bone sites

Micro computed tomography (µCT) images of human spongiosa have recently been used for skeletal dosimetry with respect to external exposure to photon radiation. In this previous investigation, the calculation of equivalent dose to the red bone marrow (RBM) and to the bone surface cells (BSC) was based on five different clusters of micro matrices derived from µCT images of vertebrae, and the BSC equivalent dose for 10 µm thickness of the BSC layer was determined using an extrapolation method. The purpose of this study is to extend the earlier investigation by using µCT images from eight different bone sites and by introducing an algorithm for the direct calculation of the BSC equivalent dose with sub-micro voxel resolution. The results show that for given trabecular bone volume fractions (TBVFs) the whole-body RBM equivalent dose does not depend on bone site-specific properties or imaging parameters. However, this study demonstrates that apart from the TBVF and the BSC layer thickness, the BSC equivalent dose additionally depends on a so-called trabecular bone structure (TBS) effect, i.e. that the contribution of photo-electrons released in trabecular bone to the BSC equivalent dose also depends on the bone site-specific structure of the trabeculae. For a given bone site, the TBS effect is also a function of the thickness of the BSC layer, and it could be shown that this effect would disappear almost completely, should the BSC layer thickness be raised from 10 to 50 µm, according to new radiobiological findings.

SU-FF-T-190: Dosimetry Verification for Pencil Beam, Clarkson and Equivalent Square Dose Calculation Algorithms

Purpose: To study the accuracy of Brainlab pencil beam and Clarkson algorithms in homogeneous phantoms and heterogeneous geometries. Materials and method: In this study PMMA was used as the homogenous phantom. Different heterogeneous geometries were designed by introducing different materials between the PMMA slabs. In each situation one material is used with different thicknesses: (a) thickness of 2.7 cm and 8.1cm low‐density material and (b) thickness of 3.8 cm and 7.6 cm of high‐density material. The low‐ and high‐density material is placed beneath 6 cm of PMMA. All the phantoms were CT scanned. Six different irregularly shaped beams were designed using a Brainlab multileaf collimator. Calculations were performed for these beams in the homogenous phantom using the Brainlab pencil beam, Clarkson, Modified Clarkson and equivalent square dose calculation algorithms. The percentage depth doses based on different models were compared to measurements. A dose of 150 cGy was specified to a point beneath the inhomogeneous material for the heterogeneous cases. Modified Clarkson, pencil beam and equivalent square algorithms were used to calculate the dose and then compared to measurements. Results: All the models agreed well with measurements; the equivalent square method showed the highest average deviations of 0.55% from measured dose values. In heterogeneous geometries the equivalent square method gave very large deviations (up to 17 %). Clarkson and pencil beam algorithms disagreed with measurements by 4.8 % and 3.8 % for the low‐density material of 2.7 cm thickness, and by 8 % and 6.9 % for the low‐density material of 8.7 cm thickness, respectively. Conclusion: All Brainlab dose calculation models are reliable for homogeneous phantom but some may differ significantly from measurements in heterogeneous geometries, especially in low‐density issues.

Optically stimulated luminescence (OSL) dating investigations of rock and underlying soil from three case studies

Three rock samples and associated underlying surface (floor) soils of geoarchaeological significance from Greece, Sweden and a modern surface stone-sample from a Danish site were investigated using OSL dating. Thin slice, sub-samples, from drilled core surfaces were prepared. A single-aliquot regenerative-dose (SAR) protocol was used on whole rock slices to estimate the laboratory equivalent dose. Laboratory tests showed that the SAR protocol successfully corrected for sensitivity changes and that a known laboratory dose could be measured accurately. The luminescence signals from quartz and feldspar stimulated by blue light and from feldspar under IR stimulation were employed in equivalent dose calculations. Only IR signals showed measurable fading on a laboratory timescale. Laboratory tests showed that daylight bleaching of the rock surfaces is rapid, and that the light-exposed region extended into the solid rock. The geoarchaeological ages obtained for the rocks and soils were in satisfactory agreement with independent age estimates.

A comparison of ambient dose equivalent meters and dose calculations at constant flight conditions

Ambient dose-equivalent results from an in-flight comparison between different tissue-equivalent proportional counters and silicon diode spectrometers from seven European institutes are presented and compared with calculations using the EPCARD computer program. The measurements were performed on 40 000 and 32 000 ft in narrow target areas at latitudes N 57 ∘ and N 42 ∘ . Keeping the altitude and geographic position almost constant provided unique conditions for comparisons. The different measuring systems as well as the calculations are in remarkably good agreement, with an average standard deviation in the ambient dose equivalent between 6% and 21%. The ratio between calculated and measured ambient dose-equivalent rates varies between 0.91 and 1.09, with an average of 1.00 ± 0.08 ( 1 s ) . Nevertheless some systematic differences in the experimentally determined ambient dose equivalent and its low-LET and high-LET components are noticed and discussed. It is concluded that the standard deviation between different instruments can through optimization and harmonization of the calibration procedures be reduced by up to a factor of two.

2214: Postoperative Nomogram Predicting the 9-Year Probability of Prostate Cancer Recurrence After Permanent Prostate Brachytherapy

A preoperative nomogram for prostate cancer recurrence after permanent prostate brachytherapy (PPB) has been independently validated as accurate and discriminating. We have developed two PPB post-implant nomograms with outcomes extending the predictions to 9 years; one using the D90 dose (the minimum dose 90% of the prostate) and the second using biological equivalent dose (BED) calculations which provide a method of comparing different isotopes and combined therapies.

HZE ion fragmentation cross-section sensitivity and propagated errors in HZE exposure estimates

It has long been recognized that galactic cosmic rays are of such high energy that they tend to pass through available shielding materials resulting in exposure of astronauts and equipment within space vehicles and habitats. Any protection provided by shielding materials result not so much from stopping such particles but by changing their physical character in interaction with shielding material nuclei forming, hopefully, less dangerous species. Clearly, the fidelity of the nuclear cross-sections is essential to correct specification of shield design and sensitivity to cross-section error is important in guiding experimental validation of cross-section models and database. We examine the Boltzmann transport equation which is used to calculate dose equivalent during solar minimum, with units (cSv/yr), associated with various depths of shielding materials. The dose equivalent is a weighted sum of contributions from neutrons, protons, light ions, medium ions and heavy ions using the ICRP-60 LET dependent quality factors. We investigate the sensitivity of dose equivalent calculations due to errors in nuclear fragmentation cross-sections. We do this error analysis for all possible projectile-fragment combinations (14,365 such combinations) to estimate the sensitivity of the shielding calculations to errors in the nuclear fragmentation cross-sections. Numerical differentiation with respect to the cross-sections will be evaluated in a broad class of materials including polyethylene, aluminum and copper. We will identify the most important cross-sections to ensure adequate experimental study and evaluate their impact on propagated errors in shielding estimates.

Calculation of total effective dose equivalent and collective dose in the event of a LOCA in Bushehr Nuclear Power Plant

In this research, total effective dose equivalent (TEDE) and collective dose (CD) are calculated for the most adverse potential accident in Bushehr Nuclear Power Plant from the viewpoint of radionuclides release to the environment. Calculations are performed using a Gaussian diffusion model and a slightly modified version of AIREM computer code to adopt for conditions in Bushehr. The results are comparable with the final safety analysis report which used DOZAM code. Results of our calculations show no excessive dose in populated regions. Maximum TEDE is determined to be in the WSW direction. CD in the area around the nuclear power plant by a distance of 30 km (138 man Sv) is far below the accepted limits. Thyroid equivalent dose is also calculated for the WSW direction (maximum 25.6 mSv) and is below the limits at various distances from the reactor stack.

Dose measurement using the fast component of LM-OSL signals from quartz

A method is described for equivalent dose determination using the linearly modulated optically stimulated luminescence (LM-OSL) signal from quartz. After analysis of the LM-OSL curves, only the fast component from quartz is used for equivalent dose calculation. The results of applying the method to purified quartz and to grains without mineral separation are presented.

Modeling of Pneumonitis Risk using Monte Carlo Corrected Dosimetry

Purpose/Objective: Treatment planning and NTCP assessment for lung cancer has been previously based on water equivalent dose calculations. We have developed a method to recalculate archived treatment plans using Monte Carlo methods to account for tissue heterogeneity. The impact of this on modeling the risk of radiation pneumonitis (RP) was evaluated.

Response of Harshaw neutron thermoluminescence dosemeters in terms of the revised ICRP/ICRU recommendations

To monitor workers for external neutron radiation dose, the Y-12 National Security Complex utilises the thermoluminescence dosemeters (TLDs) manufactured by Harshaw. At Y-12, the majority of external dose to workers is due to low-energy photon and/or beta particles emitted from uranium and its progeny. However, some neutron dose is expected since neutrons are produced from (alpha,n) reactions in various compounds found at the plant, including UF4 and UF6. Neutron sources, such as 252Cf, are also used throughout the complex. The Harshaw neutron dosemeter consists of two gamma-sensitive elements (7Li) and two neutron-sensitive elements enriched in 6Li with various shielding/filter materials placed around each of them. In this work, the energy response of the dosemeter to neutrons has been calculated using the Monte Carlo transport code MCNP Version 4-C and, these results are compared with the measured response of the dosemeter to unmoderated and D2O-moderated 252Cf neutrons. The response of the dosemeter has also been determined in terms of the personal absorbed dose and personal dose equivalent as a function of neutron energy based on the recommendations of the ICRP Publication 60 and ICRU Report 49. The energy response of the dosemeter characteristics can be used to generate spectral conversion coefficients for routine neutron absorbed dose and dose equivalent calculations.

Refining target coverage and normal tissue avoidance with helical tomotherapy vs linac-based IMRT for oropharyngeal cancer

Refining target coverage and normal tissue avoidance with helical tomotherapy vs linac-based IMRT for oropharyngeal cancer