Effective Dose Conversion Coefficients Research Articles

Machine Learning for Predicting Neutron Effective Dose

The calculation of effective doses is crucial in many medical and radiation fields in order to ensure safety and compliance with regulatory limits. Traditionally, Monte Carlo codes using detailed human body computational phantoms have been used for such calculations. Monte Carlo dose calculations can be time-consuming and require expertise in different processes when building the computational phantom and dose calculations. This study employs various machine learning (ML) algorithms to predict the organ doses and effective dose conversion coefficients (DCCs) from different anthropomorphic phantoms. A comprehensive data set comprising neutron energy bins, organ labels, masses, and densities is compiled from Monte Carlo studies, and it is used to train and evaluate the supervised ML models. This study includes a broad range of phantoms, including those from the International Commission on Radiation Protection (ICRP-110, ICRP-116 phantom), the Visible-Human Project (VIP-man phantom), and the Medical Internal Radiation Dose Committee (MIRD-Phantom), with row data prepared using numerical data and organ categorical labeled data. Extreme gradient boosting (XGB), gradient boosting (GB), and the random forest-based Extra Trees regressor are employed to assess the performance of the ML models against published ICRP neutron DCC values using the mean square error, mean absolute error, and R2 metrics. The results demonstrate that the ML predictions significantly vary in lower energy ranges and vary less in higher neutron energy ranges while showing good agreement with ICRP values at mid-range energies. Moreover, the categorical data models align closely with the reference doses, suggesting the potential of ML in predicting effective doses for custom phantoms based on regional populations, such as the Saudi voxel-based model. This study paves the way for efficient dose prediction using ML, particularly in scenarios requiring rapid results without extensive computational resources or expertise. The findings also indicate potential improvements in data representation and the inclusion of larger data sets to refine model accuracy and prevent overfitting. Thus, ML methods can serve as valuable techniques for the continued development of personalized dosimetry.

Rapid assessment of dose for large-scale individual: a feasibility study

In certain situations, it is crucial to quickly estimate the dose for radiation workers across different weight percentiles. This study sets out to create weight percentiles above 50 by adding proper adipose and muscle layers around the revised ORNL hermaphrodite phantom torso. Neutron fluence-to-organ absorbed and effective dose conversion coefficients were calculated to different weight percentiles. Simulations were performed in the energy range 10−9 to 20 MeV, under Six different source irradiation geometries: anterior–posterior (AP), posterior–anterior (PA), right-lateral (RLAT), left-lateral (LLAT), Rotation (ROT), and Isotropic (ISO) by MCNPX code. The maximum relative differences observed between the 50th and other percentiles ranged from 11% to 28%. Comparative analysis of the fluence-to-absorbed and effective dose conversion coefficients between the 95th percentile and VIPMAN indicated that approximately 58% and 57% of the data had a relative difference below 15%, respectively overall neutron energies and irradiation geometries. Our finding demonstrate that this straightforward method is reliable, especially when the whole body is irradiated in the energies above 1 MeV.

Evaluation of effective dose for gamma-rays of terrestrial gamma-ray flashes in aviation: spectral- and atmosphere-effects

Terrestrial Gamma-ray Flashes (TGFs) are intense and fast gamma-ray emissions, energy up to 100 MeV, generated within the Earth's atmosphere at altitudes below 20 km. Satellite observations indicate the TGFs are not a rare phenomenon, being produced on average at one per thunderstorm, yielding a global production rate of ≈35 TGFs/min within a latitude band of ±38°. Furthermore, the TGFs may coincide with the flight altitudes for several commercial aircraft routes, typically within the 10−14 km range, and thus cause passengers/crews unexpected exposure to large fluxes of high-energy ionizing radiation, namely for distances of the order of km.Herein, we introduce a novel approach based on a simple analytic/numeric methodology to estimate the TGFs gamma-ray emissions effective doses based on the differential fluence of photons at aircraft altitude and tabulated effective dose conversion coefficients versus the photon energy. For the first time, we examine the effective dose dependence on TGF's gamma-ray energy spectrum models found in literature and the atmosphere mass thickness crossed by the gamma-rays. Additionally, since the real irradiation geometry of the whole body in aircraft might be a combination of the several idealized geometries used in radiation protection, we considered beyond the typical anteroposterior (AP), the posteroanterior (PA), and the rotational (ROT) geometries as representative irradiation geometries in exposure to TGF gamma-ray's emissions.We calculated the effective dose versus the distance between the TGF site and the aircraft altitude (12.5 km) within the 0.1−5.0 km range and atmosphere mass thickness within the 3.3−213 g cm−2 range. Additionally, we calculated the average effective dose per fluence versus the atmosphere mass thickness crossed by the gamma-rays. At a distance of 1 km (34 g cm−2) and for the typical exponential cut-off power-law model (α = 1, EC = 7.3 MeV), the effective dose was within the 0.18−0.19 mSv range, being the respective average effective dose per fluence within the 10.8−11.6 pSv cm2 range. Moreover, for the variant of the exponential cut-off power-law model (α = 1, EC = 7.3 MeV, Emin = 1 MeV), the effective dose was within the 0.42−0.46 mSv range, being the respective average effective dose per fluence at 34 g cm−2 within the 12.7−13.6 pSv cm2 range.Generally, the data obtained agree with the scarce data found in the literature for similar conditions, evidencing the effect of the parameterization of the TGFs gamma-rays energy models, which may result in a 2- to 10-fold effective dose escalation. For the typical exponential cut-off power-law model (α = 1, EC = 7.3 MeV), the data obtained for an aircraft that passes through the vicinity of one TGF, with a distance of 1 km, points to an increase of the aircraft crew and passengers' doses of few tenths mSv over the cosmic radiation dose of few tens μSv along a typical flight of 6 h duration, representing ≈20% and ≈1% of the ICRP-2007 annual reference levels for passengers (1 mSv) and aircraft crew (20 mSv), respectively. More, with a distance of 0.5 km, the effective dose value is comparable with the annual dose for the aircraft crew due to the cosmic radiation for a typical yearly flight time of 500 h, representing ≈130% and ≈7% of the ICRP-2007 annual reference levels for passengers and aircraft crew, respectively.

Novel method for calculating the effective dose using size-specific dose estimates conversion factors in abdomen-pelvis computed tomography.

We propose a novel method for calculating the effective dose that closely reflects the individual attenuation, utilizing two conversion coefficients. A total of 180 adult patients who underwent abdomen-pelvis computed tomography were categorized into six groups based on sex and body type. The effective dose was calculated by multiplying the dose-length product with the effective dose conversion coefficient and the size-specific dose estimate conversion factor. The effective dose calculated using a simulation-based dose calculator (WAZA-ARI) was employed as the reference value. The following values, obtained through both methods, were compared within each category: distribution of the effective dose, median effective dose, and relative difference in median effective dose across additional body mass index (BMI) categories. For male patients, no significant disparity was observed in the median effective doses calculated using the two methods. The relative differences in median effective doses across additional BMI categories ranged from -5 to 6%. Conversely, among female patients, the median effective dose calculated using our method slightly undercut that calculated using WAZA-ARI, with relative differences ranging from -16 to -9%. Additionally, relative differences in median effective dose across additional BMI categories ranged from -18 to -7%. The median effective dose differed slightly depending on the calculation method because of the different reference phantoms applied in dose calculations. Our proposed method is sensitive to individual size and helps compute a size-specific effective dose.

Assessment of Radiation Exposure and Attributed Risk During Chest, Abdominal and Pelvic Computed Tomography Procedures

Adult patients' exposure and ascribed cancer risk were calculated using CT-Expo dosimetry software. A total of eight CT scanners and 395 examination patients were used in the study. The predicted effective dose values for chest CT, abdominal CT, and pelvic CT were 8.0mSv, 10.9mSv, and 5.6mSv, respectively. The estimated dose–length product to effective dose (ICRP 103) conversion coefficients for chest CT, abdominal CT, and pelvic CT were 0.020mSv•mGy-1, 0.016mSv•mGy-1, and 0.013mSv•mGy-1, respectively. In chest CT, organ doses were 16.6mSv (lung), 14.9mSv (esophagus), and 10.8mSv (breast); in abdominal CT: 15.5mSv (stomach) and 13.7mSv (liver); and in pelvic CT: 17.9mSv (bladder) and 11.3mSv (colon). The estimated cancer incident cases per million were 168 for lung cancer (chest CT) and 103 for stomach cancer (abdominal CT). The study allows comparing the risk of CT examinations to those of other radiological procedures.

Numerical studies on the important fission products for estimating the source term during a severe accident

In this paper, we select important fission products for the estimation of the source term during a severe accident of a PWR. The selection is based on the numerical results obtained from depletion calculations for the typical PWR fuel via the in-house code named DEGETION (Depletion, Generation, and Transmutation of Isotopes on Nuclear Application), release fractions of the fission products derived from NUREG-1465, and effective dose conversion coefficients from ICRP 119. Then, for the selected fission products, we obtain the adjoint solutions of the Bateman equations for radioactive decay in order to determine the importance of precursors producing the aforementioned fission products via radioactive decay, which would provide insights into the assumption used in MACCS 2 for a level 3 PSA analysis in which up to six precursors are considered in the calculations of radioactive decays for the fission product after release from the reactor.

Virtual estimation of effective dose in neutron fields

The PODIUM project aims to provide real-time assessments of occupationally exposed workers by tracking their motion and combining this with a simulation of the radiation field. The present work describes the approach that would be taken in mixed neutron-gamma fields, and details the methods for generating and applying an effective dose rate map; the required fluence to effective dose conversion coefficients at intercardinal angles are also presented. A proof-of-concept of the approach is demonstrated using a simple simulated workplace field within a calibration laboratory, with corroborative comparisons made against survey instrument measurements generally confirming good agreement. Simulated tracking of an individual within the facility was performed, recording a 1.25 μSv total effective dose and accounting for dose rates as low as 0.5 nSv h−1, which is much lower than anything that could be accurately measured by physical neutron dosemeters in such a field.

Technical Note: Patient-weight dependence of the effective dose conversion coefficients for diagnostic x-ray imaging procedures.

The aim of this study was to provide a method and reference data for the evaluation of the weight dependence of the conversion coefficients from air collision kerma integrated over beam area to the effective dose for patients undergoing diagnostic x-ray examinations. A simple physics-based analytical model was developed in order to calculate the weight dependence of the effective dose conversion coefficients based on existing values of the conversion coefficients between patient effective dose and air collision kerma integrated over beam area calculated by the Monte Carlo method on the base of computational MIRD-5-type stylized models. The analytical expressions that make possible taking into account a patient's weight when assessing the effective dose were presented. The following categories of diagnostic x-ray examinations are considered: CT; plain radiography; cardiac angiography; fluoroscopy. The results indicate that the weight dependence of the effective dose conversion coefficients for different categories of diagnostic x-ray examinations has the same form. Correction factor for evaluation of the new value of the effective dose conversion coefficient for a patient with weight Wpa. when we know its value for a standard patient with weight Wst. depends on the ratios of their weights (Wst. /Wpat. ) and fractions of the incident energy which is imparted to a patient. The paper presents an approach and necessary data for the estimation of the weight dependence of the effective dose conversion coefficients for patients undergoing different diagnostic x-ray examinations.

Evaluation of fetal, medical and occupational exposure in ERCP procedures using Monte Carlo simulation and virtual anthropomorphic phantoms

In this study, computational modeling was applied to evaluate medical and occupational exposure, to ionizing radiation, during the Endoscopic Retrograde Cholangiopancreatography (ERCP) procedure of a pregnant woman in the second gestational trimester. The fetal dose evaluation and the construction of a photon fluence map inside the procedure room were also performed. The medical staff and patient were represented by virtual anthropomorphic phantoms. These phantoms were incorporated to the radiation transport code MCNPX (version 2.7.0). The photon beam was projected on the right lateral lower section of the liver of the patient, producing a FOV of 15×15 cm2. The spectral influence was evaluated using tube voltages of 70 kVp and 80 kVp with a total filtration of 5 mmAl. The influence of the suspended shield, lead curtain and fetal shield were evaluated on the Conversion Coefficients for Equivalent Dose (CC[HT]) and Effective Dose (CC[E]) for the medical staff and patient. The removal of the lead curtain and suspended shield was considered the most critical configuration to the medical staff. In this situation, an increase up to 633% in the CC[HT]eye lens and 900% in CC[E], for the medical staff, was reached. The CC[E]Patient ranged between 0.13 mSv/Gy.cm2 (70 kVp with all protective devices) and 0.15 mSv/Gy.cm2 (80 kVp without fetal shield) and the values obtained are in agreement with the literature. The CC[HT]fetus oscillated between 2.2E-1 mSv/Gy.cm2 (70 kV with fetal shield) and 2.7E-1 mSv/Gy.cm2 (80 kV without fetal shield). The outcomes of this work are useful in the prior monitoring of the radiation doses and risks, and a reduction on these may be reached for the medical team and patient, which is a complicated arrangement in ERCP procedures.

CONSTRUCTION AND APPLICATION OF BREP PHANTOM FOR CHINESE WOMEN OF CHILDBEARING AGE IN RADIATION PROTECTION.

The purpose of this study is to construct boundary representation (BREP) phantom for Chinese women of childbearing age, to estimate the external radiation dose and to analyze radiation protection scheme. The BREP phantom for Chinese women of childbearing age was constructed by image segmentation, 3D reconstruction, non-uniform rational B-spline surface construction and voxelization. The photon-irradiated organ absorbed dose-conversion coefficients (DCCK) of the three female specific organs and the photon effective dose-conversion coefficient (ECCK) were calculated by Monte-Carlo method. The results showed that age, body fat-tissue thickness, direction and area of irradiation, organ location and volume all affected the dose of women specific organs when receiving medical exposure. In the case of ensuring the quality of the diagnosis, radiation protection for female specific organs can be achieved by organ dose modulation techniques and reducing exposure area or volume.

Review of airkerma-area product, effective dose and dose conversion coefficients for non-cardiac interventional fluoroscopy procedures.

To provide current data on average air kerma-area product (PKA ) and effective dose (E) for noncardiac interventional fluoroscopy procedures and suggested values of dose coefficients (DCE ) for conversion of PKA to estimates of effective dose. A PubMed literature search covering the time period from 2006 to August 2019 was performed to obtain recent data on PKA , E and DCE for interventional fluoroscopy procedures. There is very wide variation in the reported values of PKA , E, and DCE in the literature. A number of factors are involved in this variability and the resultant uncertainty in average values of these dose quantities. The values of PKA , average E and suggested DCE presented here can be of use for comparison of the radiation detriment from different procedures and may be useful for categorizing detriment within an order of magnitude or so. They do not represent actual or expected radiation dose or detriment from any specific procedure or for a specific patient and should be not be used as such.

Effective Dose Assessment for Patients Undergoing Contemporary Fluoroscopically Guided Interventional Procedures.

OBJECTIVE. The purpose of this study was to establish procedure-specific air kerma-area product (KAP) and effective dose for a large number of fluoroscopically guided interventional (FGI) procedures. MATERIALS AND METHODS. This retrospective study collected dose data for consecutive adult cases from 12 examination rooms between May 2016 and October 2018. A total of 24,911 cases (50.9% men) were categorized by procedure. Effective dose was calculated using KAP and procedure-specific KAP to effective dose conversion coefficients, mostly from National Council on Radiation Protection and Measurements (NCRP) Report 160. Data analysis was conducted with statistical software to determine mean value and five percentiles (10th, 25th, 50th, 75th, 95th). RESULTS. KAP and effective dose were presented for 101 procedures; a national benchmark is not available from NCRP Reports 168 and 172 for the KAP value of 89 procedures and for the effective dose of all 101 procedures. Twelve procedures that comprised at least 50% of patient cases had median KAP values less than 3.26 Gy · cm2 and a median effective dose of less than 0.70 mSv. However, some infrequent procedures might be associated with a higher dose. The 95th percentile of KAP was greater than or equal to 500 Gy · cm2 for 16 procedures and 985 Gy · cm2 for portography; for effective dose it was greater than or equal to 100 mSv for 21 procedures and 256 mSv for portography. CONCLUSION. The values for KAP and effective dose provided in this article can aid in design and review of clinical research protocols and dose management programs and in assessing compliance with the Joint Commission's standards for organizations providing fluoroscopy services in the absence of national benchmarks for more than 89 procedures.

Effective dose conversion coefficient for gamma ray exposure from an overhead plume

The external radiation exposure from an overhead plume containing gamma emitting radionuclides can contribute substantial dose to the ground receptor during normal operations as well as accidental release conditions of nuclear facilities. In order to estimate the effective dose conversion coefficients (DCCs) directly, a finite plume Monte Carlo model along with the reference phantom at the ground receptor location needs to be implemented. In the present study, a comprehensive simulation of radiation transport from the Gaussian plume source to the ICRP reference adult voxel phantoms (receptor) is carried out using the FLUKA Monte Carlo code. The organ absorbed doses as well as the effective DCCs of the adult reference phantom are computed for different meteorological parameters and downwind distances. To illustrate the application of this model, an overhead Gaussian plume containing two different gamma emitting radionuclides, 135Xe and 41Ar are considered. From these simulations, the ratio of the effective dose rate to the kerma rate are estimated as 0.6 Sv Gy−1 and 0.65 Sv Gy−1 for the exposure from 135Xe and 41Ar, respectively. This ratio is constant irrespective of the meteorological conditions and cloud models. Further results show that the effective DCCs as a function of the downwind distance vary by an order of magnitude for an unstable weather category; however, the variations are very small in the case of a stable category. This study demonstrates an accurate method for calculating the effective dose to the ground receptor from an external plume which can be further applied for any radionuclide under any meteorological condition.

Development of a scintillation detector for real-time measurement of space proton effective dose

In this study, a scintillation detector was developed to measure the space proton effective dose for astronauts based on the proton effective dose conversion coefficients provided by International Commission on Radiological Protection Report No. 116. In the Monte Carlo N-Particle Transport Code X (version 2.6.0) simulation process, by modulating the depth and solid angle of truncated conical holes in an iron shell from lower-energy protons to higher-energy protons, the energy deposited in the scintillator by isotropic protons was nearly proportional to the corresponding effective dose, with a maximum relative deviation of 13.28% at thirteen energy points in the energy range of 10–400 MeV. Therefore, the detector can monitor proton effective dose indirectly in real time by measuring the deposited energy. We calibrated the photoelectric conversion efficiency of the detector at the cobalt source, tested the response of the detector in the energy range of 30–100 MeV in unidirectional proton field, and validated the simulation with the experimental results.

Diagnostic Reference Levels for Computed Tomography Examinations in Iran: A Nationwide Radiation Dose Survey

Introduction: International Commission on Radiological Protection introduced three basic principles of radiation protection, namely justification, optimization, and dose limit. Medical exposure has no dose limits, and generally, diagnostic reference levels are used as a tool for optimization of patient protection. Material and Methods: Dosimetry was performed on 20 CT scanners located in 14 cities in 12 provinces of Iran. A calibrated pencil-shaped ionization chamber, standard head and body CT dosimetry phantoms and a radiation monitor were used to determine and calculate Computed Tomography Dose Index (CTDI) and Dose Length Product (DLP). The DLP-based estimates of effective dose were derived using effective dose conversion coefficients. Results: The nCTDIw values for head phantoms fell within the range of 22.05-168.38 and 43.77-426.69 µGy/mAs for 5 and 10mm slice thicknesses, respectively. These values for body phantom were 4.65-146.39 and 9.43-308.92 µGy/mAs for 5 and 10mm slice thicknesses, respectively. The third quartile of CTDIvol and DLP values for head CT examinations were 49.85 mGy and 1161.00 mGy-cm, respectively. The body CT examinations had the values of 8.89 mGy and 370.97 mGy-cm, respectively. The findings of this study revealed that the above-mentioned values can be considered as national diagnostic reference levels for head and body CT examinations in Iran. Conclusion: The results of the current study suggested that there is a need to re-assess DRLs for CT examinations at regular time intervals by the appropriate regulatory authority which can improve the continuous performance of CT scanners in Iran.

Effective Dose Calculation Program (EDCP) for the usage of NORM-added consumer product

The aim of this study is to develop the Effective Dose Calculation Program (EDCP) for the usage of Naturally Occurring Radioactive Material (NORM) added consumer products. The EDCP was developed based on a database of effective dose conversion coefficient and the Matrix Laboratory (MATLAB) program to incorporate a Graphic User Interface (GUI) for ease of use. To validate EDCP, the effective dose calculated with EDCP by manually determining the source region by using the GUI and that by using the reference mathematical algorithm were compared for pillow, waist supporter, eye-patch and sleeping mattress. The results show that the annual effective dose calculated with EDCP was almost identical to that calculated using the reference mathematical algorithm in most of the assessment cases. With the assumption of the gamma energy of 1 MeV and activity of 1 MBq, the annual effective doses of pillow, waist supporter, sleeping mattress, and eye-patch determined using the reference algorithm were 3.444 mSv year−1, 2.770 mSv year−1, 4.629 mSv year−1, and 3.567 mSv year−1, respectively, while those calculated using EDCP were 3.561 mSv year−1, 2.630 mSv year−1, 4.740 mSv year−1, and 3.780 mSv year−1, respectively. The differences in the annual effective doses were less than 5%, despite the different calculation methods employed. The EDCP can therefore be effectively used for radiation protection management in the context of the usage of NORM-added consumer products. Additionally, EDCP can be used by members of the public through the GUI for various studies in the field of radiation protection, thus facilitating easy access to the program.

Calculation of dose conversion coefficients for radioactive cesium in contaminated soil by depth and density

Radiation dose to personnel on the ground contaminated with radioactive cesium after nuclear power plant accident depends on cesium activity, depth profile of the activity, and soil mass density. A dosimetry method was developed to calculate radiation dose resulting from external exposure to radioactive cesium in soil with arbitrary depth profile. Dose conversion coefficients to calculate effective dose based on cesium radioactivity in soil were produced by using a radiation transport code. The dose conversion coefficient was produced for each 1 cm thickness disk source by soil depth by changing soil mass density from 0.5 to 2 g/cm3. Radiation dose due to a volumetric source can be calculated with summation of radiation doses from multiple thin disk sources. When radioactive cesium is distributed within 0–1 cm depth of soil with mass density of 1 g/cm3, effective dose conversion coefficients were 6.2 × 10−6 and 2.4 × 10−6 mSv/h per kBq/m2 for 134Cs and 137Cs nuclides, respectively. Effective doses decreased exponentially with increasing soil depth or mass density. Radiation dose on the contaminated ground can be calculated with the dose database established in this study for any shape of depth profile.

DETERMINATION OF NEUTRON EFFECTIVE DOSES IN WHOLE BODY POINT SOURCE EXPOSURES.

The objective of this work is to obtain fluence to effective dose conversion coefficients for neutron point sources, using the GEANT4 toolkit. These calculations aim to investigate the aspects of neutron transport in the human body through Monte Carlo simulation using the International Commission on Radiological Protection (ICRP) voxel phantoms, described in its publication 110. A benchmarking of the code was made for the case of monoenergetic plane parallel neutron beam in the antero-posterior (AP) irradiation geometry and organ absorbed dose conversion coefficients were compared with those found in the ICRP publication 116. The results showed good agreement with ICRP results in the studied energy range. Conversion coefficients were presented for specific conditions with 241Am-Be and 252Cf point neutron sources 1 m away from the phantom in the AP geometry.

Calculation of the Photon Dose Conversion Coefficient Based on Boundary Representation Phantoms of Different Postures.

Based on the hybrid Chinese reference adult female phantom, the Chinese reference female boundary representation (BREP) phantoms involving sitting, walking, and squatting postures were established. The photon effective dose conversion coefficient (ECCK) and some organ absorbed dose conversion coefficients (DCCK) were calculated under six standard irradiation geometries, and the irradiation source included 20 monoenergetic photon energies ranging from 0.01 MeV to 10 MeV. The results indicate that the postures, location of the organs, and irradiation geometries have an impact on the dose conversion coefficients. With the same irradiation geometry, the DCCKs of different organs are different; when the photon energy is from 0.02 MeV to 0.1 MeV, significant differences exist in the DCCK of phantoms of various postures, and the maximum relative deviation is 80%. For the ECCKs, there are greater differences among phantoms of various postures with the same irradiation geometry when the photon energy is from 0.02 MeV to 0.05 MeV, and the maximum relative deviation is about 20%.

Dose conversion coefficients for Chinese reference adult male and female voxel phantoms from idealized neutron exposures

ABSTRACTA whole-body voxel phantom called CRAF representing the Chinese adult female was constructed in this study from color photographs. The CRAF has a height of 160 cm and a weight of 54 kg with 80 organs and tissues, including almost all organs required in the ICRP Publication 103. Masses of all organs in CRAF are consistent with the Chinese reference data within 1%. Our research group has previously developed a Chinese reference adult male phantom called CRAM, which has a height of 170 cm and a weight of 60 kg with 80 tissues and organs. A new set of fluence-to-dose conversion coefficients based on the Chinese reference adult voxel phantoms CRAM and CRAF are presented for six idealized external neutron exposures from 10−8 MeV to 20 MeV. The calculation of organ-absorbed doses and effective doses were performed with the Monte Carlo transport code MCNPX 2.4. The resulting dose conversion coefficients were compared with those published in ICRP Publication 116, which represents the reference Caucasian. It was observed that the two sets of organ-absorbed dose conversion coefficients agreed well for most organs in ROT and ISO geometry; however, considerable deviations were found in some organs in AP, PA, RLAT and LLAT exposures. Organ-absorbed dose coefficients difference showed good agreement with the difference of organ depth distribution between Chinese and ICRP phantoms. For neutrons with energies above 2 MeV, the effective dose conversion coefficients of Chinese reference adult are almost identical to those of ICRP Publication 116 in AP, PA, ROT and ISO geometries, while are generally 15% higher than those of ICRP Publication 116 from lateral geometries. When energies range from 10−8 MeV to 1 MeV, differences are within 10% in AP (–5%), PA (–8%) and ROT (4%) geometries; however, relatively large discrepancies are shown in lateral and ISO geometries, with differences of 15% for LLAT, 20% for RLAT and 12% for ISO, respectively.