ICRP Report Research Articles

MRI-only based material mass density and relative stopping power estimation via deep learning for proton therapy: a preliminary study

Magnetic Resonance Imaging (MRI) is increasingly being used in treatment planning due to its superior soft tissue contrast, which is useful for tumor and soft tissue delineation compared to computed tomography (CT). However, MRI cannot directly provide mass density or relative stopping power (RSP) maps, which are required for calculating proton radiotherapy doses. Therefore, the integration of artificial intelligence (AI) into MRI-based treatment planning to estimate mass density and RSP directly from MRI has generated significant interest. A deep learning (DL) based framework was developed to establish a voxel-wise correlation between MR images and mass density as well as RSP. To facilitate the study, five tissue substitute phantoms were created, representing different tissues such as skin, muscle, adipose tissue, 45% hydroxyapatite (HA), and spongiosa bone. The composition of these phantoms was based on information from ICRP reports. Additionally, two animal tissue phantoms, simulating pig brain and liver, were prepared for DL training purposes. The phantom study involved the development of two DL models. The first model utilized clinical T1 and T2 MRI scans as input, while the second model incorporated zero echo time (ZTE) MRI scans. In the patient application study, two more DL models were trained: one using T1 and T2 MRI scans as input, and another model incorporating synthetic dual-energy computed tomography (sDECT) images to provide accurate bone tissue information. The DECT empirical model was used as a reference to evaluate the proposed models in both phantom and patient application studies. The DECT empirical model was selected as the reference for evaluating the proposed models in both phantom and patient application studies. In the phantom study, the DL model based on T1, and T2 MRI scans demonstrated higher accuracy in estimating mass density and RSP for skin, muscle, adipose tissue, brain, and liver. The mean absolute percentage errors (MAPE) were 0.42%, 0.14%, 0.19%, 0.78%, and 0.26% for mass density, and 0.30%, 0.11%, 0.16%, 0.61%, and 0.23% for RSP, respectively. The DL model incorporating ZTE MRI further improved the accuracy of mass density and RSP estimation for 45% HA and spongiosa bone, with MAPE values of 0.23% and 0.09% for mass density, and 0.19% and 0.07% for RSP, respectively. These results demonstrate the feasibility of using an MRI-only approach combined with DL methods for mass density and RSP estimation in proton therapy treatment planning. By employing this approach, it is possible to obtain the necessary information for proton radiotherapy directly from MRI scans, eliminating the need for additional imaging modalities.

Natural radioactivity and radiological hazard analysis of construction stones from various quarries in Machakos County-Kenya.

The radioactivity levels of rocks sampled from the quarries of Kyasioni, Mavoloni and Kathaana located in the lower Eastern County of Machakos in Kenya were determined. Forty-two samples were collected using stratified random sampling and analysed using NaI(TI) detector with a specially designed lead shield. The parametric values of activity concentration, absorbed dose, annual dose rate and hazard indices were estimated using activity-dose relations suggested in UNSCEAR and ICRP reports. The mean activity concentration for the entire work for 238U (226Ra), 232Th and 40K were 68.33±3.11, 101.10±1.83 and 1084.02±30.28Bq/kg, respectively. Kyasioni quarry presented the highest activity concentration of 74.75±3.15, 118.48±1.91 and 1120.35±30.07Bq/kg for 226Ra, 232Th and 40K, respectively. The average annual effective dose was estimated as 0.58±0.01, 0.47±0.01 and 0.52±0.01mSv/y for Kyasioni, Kathaana and Mavoloni quarries, respectively. Other radiological parameters estimated from the corresponding activities were within the recommended limits hence guaranteeing safety to the users.

A revised compartmental model for biokinetics and dosimetry of 2-[18F]FDG

BackgroundThe aim was to review available biokinetic data, collect own experimental data, and propose an updated compartmental model for 2-[18F]FDG in the frame of the revision of the ICRP report on dose coefficients for radiopharmaceuticals used in diagnostic nuclear medicine.MethodsThe compartmental model was developed based on published biokinetic data for 2-[18F]FDG. Additional data on urinary excretion in 23 patients (11 males, 12 females) undergoing whole-body PET/CT examinations were obtained within this study. The unknown biokinetic model parameters were derived using the software SAAM II and verified with a modified version of IDAC-Iodide. Dose coefficients for reference adults were calculated with the programme IDAC-Dose 2.1. A dynamic bladder model was employed for urinary bladder dosimetry.ResultsThe proposed model consists of following compartments: blood, heart wall, brain, liver, lungs, pancreas, spleen, kidneys, urinary bladder content and a generic pool compartment “Other”. The latter was introduced to account for 2-[18F]FDG in body organ and tissues besides the explicitly modelled ones. The model predictions showed a good agreement with experimental data. Urinary bladder wall received the highest absorbed dose coefficient of 7.5E−02 mGy/MBq under the assumption of initial urine volume of 100 ml, first voiding at 45 min p.i. and 3.75 h voiding intervals thereafter. The effective dose coefficient calculated according to the current dosimetry framework of ICRP amounted to 1.7E−02 mSv/MBq, compared to 1.9E−02 mSv/MBq in ICRP Publication 128.ConclusionA compartmental model for 2-[18F]FDG was proposed and will be used to replace the descriptive biokinetic model of ICRP Publication 128. The revised model and the provided dose coefficients are expected to improve reference dosimetry for patients administered with 2-[18F]FDG.

Microdosimetry-based quality factors for ISO reference photon and beta sources: TOPAS Monte Carlo study

In radiological protection, personnel dosimeters are calibrated in terms of operational quantities such as H p (10) and H p (0.07) against ISO reference photon and beta sources, respectively. H p (10) and H p (0.07) are defined at 1 cm and 0.07 μm depths in the ICRU-4 element tissue phantom. In present study, mean quality factor Q̅ is calculated at these depths using the TOPAS-based microdosimetric distributions at 1 μm site size and FLUKA-based Linear Energy Transfer (LET) dependent Q̅. The sources simulated are ISO reference narrow series X-rays, 137Cs and 147Pm, 85Kr, 90Sr/90Y and 106Ru/106Rh beta sources. Using the calculated microdosimetric distributions, Q̅ is calculated based on ICRP60 and ICRU40 recommendations, Keller-Hahn (KH) approximation, Microdosimetric Kinetic Model (MKM), Clonogenic Survival and Theory of Dual Radiation Action (TDRA). The study includes FLUKA-based Q̅ values calculated using Q(L) vs L relationship as per ICRP Report 60. The MKM, Clonogenic Survival-based RBE, ICRU40, TDRA and KH-based Q values of all the investigated sources are about unity. Depending on the source, microdosimetry-based Q̅ values using ICRP60 recommendations show significant difference from that calculated using other models. Q̅ values of 137Cs are unity, independent of the models.

Cardiotoxicity in breast cancer patients: the role of gated myocardial perfusion SPECT

Abstract Funding Acknowledgements Type of funding sources: None. Background Patients undergoing chemotherapy (CHT) for breast cancer (BC) need a monitoring of cardiac function due to the possible onset of cardiotoxicity. Cardiotoxicity may occur with heart failure but is often asymptomatic and is detectable only by assessing an increase in cardiac volumes (left ventricular end-diastolic (LV-EDV) and end-systolic (LV-ESV) volumes) and/or by a reduction of the left ventricular ejection fraction (LV-EF). The primary purpose of this study was to evaluate the role of gated SPECT myocardial perfusion imaging in this setting. Dosimetric evaluation was also assessed. Methods Seventeen BC patients (mean age 55.93 ± 11.04 years)with invasive ductal carcinoma HER2 + treated with surgery and with an anthracycline-based adjuvant CHT, were enrolled. The trend of cardiac function was assessed by evaluation of LV-EF, LV-EDV and LV-ESV using gSPECT in baseline conditions and at 12, 15 and 52 weeks during treatment and then at 6, 12, 24 and 48 months during follow-up. Each patient was studied 15-20 min after injection of 555 MBq of 99mTc-Tetrofosmin with gSPECT (16 frames/cardiac cycle) using an Infinia Hawkeye IV gamma-camera. Dosimetry was assed according to ICRP reports. Results Two out of the 17 patients enrolled left the protocol: one because of a second tumor and the other due to the appearance of cardiotoxicity. 15 patients completed the study: mean LVEF at baseline was 70.67 ± 5.68. The greatest modification occurred after 15th week of treatment, when mean LV-EF showed a significant decrease to 65.67 ± 8.27, while mean LV-EDV and mean LV-ESV increased from 73.60 ± 16.72 up to 84.73 ± 21.11 and from 21.93 ± 7.17 up to 30.27 ± 14.16, respectively. All parameters progressively returned similar to baseline values at the final examination (after 48th month): mean LV-EF 70.20 ± 5.65, LV-EDV 73.40 ± 16.15 and ESV 22.07 ± 7.50. In one case cardiotoxicity occurred at 15th week: LV-EF decreased from 69 to 47%, LV-EDV increased from 92 up to 142 ml and LV-ESV from 28 up to 75 ml. According to our image protocols, effective dose for gSPECT was 3.83 mSv (ICRP 106). The use of gSPET instead of MUGA (6.47 mSv–ICRP 80) allowed a dose effective saving of 2.64 mSv/each control with a total saving of 21.12 mSv/patient. Conclusions Although the small sample size, gSPECT was demonstrated to be an applicable tool for monitoring cardiac function because it correctly identified BC patient with cardiotoxicity. gSPECT also allowed a significant radiation dose saving compared to MUGA: this is particularly relevant in cardiotoxicity studies that require repeated and close evaluations.

The use of dose quantities in radiological protection: ICRP publication 147 Ann ICRP 50(1) 2021

The International Commission on Radiological Protection has recently published a report (ICRP Publication 147; Ann. ICRP 50, 2021) on the use of dose quantities in radiological protection, under the same authorship as this Memorandum. Here, we present a brief summary of the main elements of the report. ICRP Publication 147 consolidates and clarifies the explanations provided in the 2007 ICRP Recommendations (Publication 103) but reaches conclusions that go beyond those presented in Publication 103. Further guidance is provided on the scientific basis for the control of radiation risks using dose quantities in occupational, public and medical applications. It is emphasised that best estimates of risk to individuals will use organ/tissue absorbed doses, appropriate relative biological effectiveness factors and dose–risk models for specific health effects. However, bearing in mind uncertainties including those associated with risk projection to low doses or low dose rates, it is concluded that in the context of radiological protection, effective dose may be considered as an approximate indicator of possible risk of stochastic health effects following low-level exposure to ionising radiation. In this respect, it should also be recognised that lifetime cancer risks vary with age at exposure, sex and population group. The ICRP report also concludes that equivalent dose is not needed as a protection quantity. Dose limits for the avoidance of tissue reactions for the skin, hands and feet, and lens of the eye will be more appropriately set in terms of absorbed dose rather than equivalent dose.

Paediatric Diagnostic Reference levels in low Resource Settings: A Guide for developing Country Practitioners with excerpts from ICRP 135

Background: The practical implementation of Diagnostic Reference Level in pediatric imaging is a complex task due to their unique individuality in terms of high sensitivity to radiation, varying body sizes and presenting pathology. Hence, good knowledge of medical technology, skill to perform patient dosimetry and to analyze mage quality is required.
 Purpose: To provide a guide on the methodological requirements for the establishment of Paediatric Diagnostic Reference Levels (PiDRLs) based on the revised and updated guidelines from the current ICRP publication 135 on Diagnostic Reference Levels (DRLs).
 Materials and method: An extensive review of the ICRP report Publication 135 on Diagnostic Reference levels in medical imaging with a focus on paediatric imaging and other related studies were undertaken. 
 Results: The ICRP report 135 updates and refines the recommendations of 2001. It highlights that the application of DRLs in paediatrics alone is not sufficient for the optimization of protection. Image quality must be evaluated. Quantities used for DRLs should be appropriate to the imaging modality being evaluated, assess the amount of ionizing radiation applied to perform a medical imaging task, and be measured directly. For interventional procedures, the complexity of the procedure may be considered in setting DRLs. DRLs shall not be used for individual patients or as trigger (alert or alarm) levels for individual patients. Appropriate weight bands (generally with 5 or 10 kg intervals) are recommended for establishing paediatric DRLs and should be promoted.
 Conclusion: The amount of radiation used for examinations of children can vary tremendously due to the great variation in patient size and weight from neonates to adult-sized adolescents. This variation in patient radiation dose is appropriate. However, variation in patient doses due to inappropriate technique or failure to child-size the imaging protocol is not appropriate. This forms the basis of the new ICRP guideline and should form the basis of developing PiDRLs.

Absorbed doses of the taxi drivers in the vicinity of the patients that were injected for SPECT imaging: a Monte Carlo study

Nuclear medicine is a branch of medical science that uses radionuclides for diagnosing and treatment of diseases. In this paper, the dose of the different organs and annual effective dose of a taxi driver were calculated in a vicinity of a patient that was injected for the brain, kidney, and liver SPECT by using Monte Carlo method. Two MIRD phantoms were simulated as a driver and patient, including the simple body of a taxi in MCNPX2.4 code. The radioactivity distributions were obtained from ICRP reports and sources were defined according to them. The patients that have undergone the brain, kidney and liver SPECT with the injection of different activities of the 99mTC radioisotope were included in this study. The injected activities were 740 MBq, 185 MBq, and 333 MBq for the brain, kidney, and liver SPECT respectively. Annual effective doses were calculated for one 99mTC injected patient per working day with an assumption of 30 min ride duration. The maximum annual effective doses of the taxi driver were 2.31, 0.54, and 1.21 $$\upmu \mathrm{S}\mathrm{v}$$ in the vicinity of the patients that were injected for brain, kidney, and liver SPECT respectively. The maximum annual effective dose of the taxi driver is larger than the ICRP recommended data up to 2.3 times. We recommend that to reduce dose, the patient should sit in “position 2”, farthest back seat with respect to the driver, and the driver’s seat could have some shielding place around it.

Paediatric Diagnostic Reference levels in low Resource Settings: A Guide for Developing Country Practitioners with excerpts from ICRP

Background: The practical implementation of Diagnostic Reference Level in paediatric imaging is a complex task due to their unique individuality in terms of high sensitivity to radiation, varying body sizes and presenting pathology. Hence, good knowledge of medical technology, skill to perform patient dosimetry and to analyze mage quality is required. Purpose: To provide a guide on the methodological requirements for the establishment of Paediatric Diagnostic Reference Levels (PiDRLs) based on the revised and updated guidelines from the current ICRP publication 135 on Diagnostic Reference Levels (DRLs). Materials and method: An extensive review of the ICRP report Publication 135 on Diagnostic Reference levels in medical imaging with a focus on paediatric imaging and other related studies were undertaken. Results: The ICRP report 135 updates and refines the recommendations of 2001. It highlights that the application of DRLs in paediatrics alone is not sufficient for the optimization of protection. Image quality must be evaluated. Quantities used for DRLs should be appropriate to the imaging modality being evaluated, assess the amount of ionizing radiation applied to perform a medical imaging task, and be measured directly. For interventional procedures, the complexity of the procedure may be considered in setting DRLs. DRLs shall not be used for individual patients or as trigger (alert or alarm) levels for individual patients. Appropriate weight bands (generally with 5 or 10 kg intervals) are recommended for establishing paediatric DRLs and should be promoted. Conclusion: The amount of radiation used for examinations of children can vary tremendously due to great variation in patient size and weight from neonates to adult-sized adolescents. This variation in patient radiation dose is appropriate. However, variation in patient doses due to inappropriate technique or failure to child-size the imaging protocol is not appropriate. This forms the basis of the new ICRP guideline and should form the basis of developing PiDRLs.

Comparison of manual and dose reduction modes of a MORITA R100 CBCT.

To compare effective dose differences when acquiring (1) dose reduction mode and (2) manual mode in a MORITA R100 CBCT. 24 exposure protocols with different technique factors were performed in both the dose reduction mode and the manual mode in a Veraviewepocs 3D R100 cone beam CT device. 48 TLD were placed in a RANDO head phantom at 24 different sites. Effective doses were calculated according to the formalism published in the 103rd ICRP report. Effective doses for the dose reduction mode protocols ranged from 14 to 156 µSv [mean = 57 µSv, standard deviation (SD) = 37 µSv], whereas effective doses for the manual mode protocols ranged from 22 to 267 µSv (mean = 94 µSv, SD = 65 µSv). Thus, across all protocols, the dose reduction mode leads to a drop of the effective dose by 38 % (SD = 6 %). The estimated effective doses are significantly lower if dose reduction protocols are acquired.

Internal dosimetry with the Monte Carlo code GATE: validation using the ICRP/ICRU female reference computational model

The purpose of this work was to validate GATE-based clinical scale absorbed dose calculations in nuclear medicine dosimetry.GATE (version 6.2) and MCNPX (version 2.7.a) were used to derive dosimetric parameters (absorbed fractions, specific absorbed fractions and S-values) for the reference female computational model proposed by the International Commission on Radiological Protection in ICRP report 110.Monoenergetic photons and electrons (from 50 keV to 2 MeV) and four isotopes currently used in nuclear medicine (fluorine-18, lutetium-177, iodine-131 and yttrium-90) were investigated.Absorbed fractions, specific absorbed fractions and S-values were generated with GATE and MCNPX for 12 regions of interest in the ICRP 110 female computational model, thereby leading to 144 source/target pair configurations. Relative differences between GATE and MCNPX obtained in specific configurations (self-irradiation or cross-irradiation) are presented. Relative differences in absorbed fractions, specific absorbed fractions or S-values are below 10%, and in most cases less than 5%. Dosimetric results generated with GATE for the 12 volumes of interest are available as supplemental data.GATE can be safely used for radiopharmaceutical dosimetry at the clinical scale. This makes GATE a viable option for Monte Carlo modelling of both imaging and absorbed dose in nuclear medicine.

P30. Experience feedback of a radiation protection incident in radiotherapy: Irradiation of a pregnant patient

Introduction A woman, treated by radiotherapy in the Centre Francois Baclesse in Caen for a head and neck cancer was proving pregnant (3rd month of pregnancy during the treatment).The pregnancy was revealed after the completion of the treatment (30 fractions – 2 Gy / fraction).In order to know the dose received by the fetus, measurements have been achieved with identical conditions as for the treatment. Materials and methods Irradiation technique:VMAT on a Clinac iX (Varian) linac.2 arcs of 307 UM and 278 UM with 6 MV photons.Phantom:Compact polystyrene to simulate the body and head and neck cylindrical phantom to simulate the irradiated volume.The ionization chamber was positioned at 45 cm of the field edge.This distance was measured by the medical doctor on the patient.The measurements were achieved with the same parameters recorded on the ”record and verify” software (Mosaiq – Elekta).The measurement cumulated 5 repetitions to improve the accuracy. Results For 1 fraction:0.83 mGy For the whole treatment (30 fractions):24.9 mGy Discussion 1/The dose far from the irradiation field has 3 components [1] -Photons scattered by the irradiated volume of the patient (internal) -Photons scattered by the irradiated materials (couch) and the walls of the treatment vault -Leakage radiation from the linac 2/The 1st component of the dose (scattered photons inside the patient) is very low because of the large distance between the field edge and the measuring point.In the ICRP report #84 (Pregnancy and medical radiation) [2] off axis values of dose are given for cobalt 60:approximately 0.25% at 45 cm but for linacs this off axis dose is lower 2–5 times (depending on beam energy).Our measurements (0.04%) are so, in good agreement with the ICRP #84 data.In the literature, several authors reported equivalent fetal doses for head and neck irradiations [3] [4] [7] .For irradiated volumes closer to the uterus (Hodgkin desease), the doses are obviously much greater [5] [6] . Conclusion The value of the effective dose measured ( ≈ 25 mSv) is superior to the upper legal limit for the fetus (1 mSv). In consequence, this case was declared as an incident to the French Nuclear Safety Authority (ASN) but it is assumed not to be critical for the children: – Malformations have a threshold of 100–200 mGy or higher and are typically associated with central nervous system problems [1] – A fetal dose of 100 mGy has a small individual risk of radiation-induced cancer. There is over a 99% chance that the exposed fetus will NOT develop childhood cancer or leukaemia [2]

Computed tomography of the chest: I. Basic principles

### Key points The conventional chest radiograph superimposes a three-dimensional image onto a two-dimensional surface, so limiting its clinical usefulness. Since its introduction in 1971, X-ray computed tomography (CT) has rapidly evolved into an essential diagnostic imaging tool that forms a cross-sectional image, avoiding the super-imposition of structures that occurs in conventional chest imaging, with a >10-fold increase in attenuation sensitivity. Although CT imaging is reported by radiologists, it is important for both anaesthetists and intensivists to be able to interpret the scans, as reporting facilities may not be immediately available. Furthermore, the radiologist may not fully report all facets of a detailed scan and further information may be acquired by a physician with the ability to interpret CT scans. This is the first in a series of two articles written for anaesthetists and intensivists covering both thoracic anatomy and pathology as it relates to CT. A CT scanner makes many measurements, from different rotational angles, of X-ray attenuation ( weakening in force or intensity ) through the cross-sectional plane of the thorax. It then uses these data to reconstruct a digital representation of the cross-section with …

The EURALOC Project

SummaryFor radiation protection purposes, it has generally been assumed that there is a threshold of dose below which no non‐cancer effects arise. Early dose threshold estimates for detectable lens opacities were defined at 0.5–2 Gy after acute or 5–6 Gy after protracted exposures. Due to the heterogeneity of ophthalmological data and too short observation periods, the thresholds were reconsidered in the ICRP report 118 (2012) and reduced to 0.5 Gy. An overview will be given of epidemiological studies that prompted the change in ICRP recommendations. These studies reported excess risks of lens opacities, but could not provide statistical significant evidence of a dose threshold. The results from all these studies are difficult to compare or combine. Moreover, another point of concern is the dosimetry which was often poor. These issues limit the possibility of a quantitative synthesis of evidence for a dose‐response analysis in the low dose region to confirm this new dose threshold and urged the need of a harmonised European initiative. The EURALOC project, initiated in December 2014, aims at quantifying this dose‐response relationship between ionising radiation and cataract among a cohort of European interventional cardiologists.

SU‐E‐I‐86: Ultra‐Low Dose Computed Tomography Attenuation Correction for Pediatric PET CT Using Adaptive Statistical Iterative Reconstruction (ASiR™)

Purpose:To develop ultra‐low dose computed tomography (CT) attenuation correction (CTAC) acquisition protocols for pediatric positron emission tomography CT (PET CT).Methods:A GE Discovery 690 PET CT hybrid scanner was used to investigate the change to quantitative PET and CT measurements when operated at ultra‐low doses (10–35 mAs). CT quantitation: noise, low‐contrast resolution, and CT numbers for eleven tissue substitutes were analyzed in‐phantom. CT quantitation was analyzed to a reduction of 90% CTDIvol (0.39/3.64; mGy) radiation dose from baseline. To minimize noise infiltration, 100% adaptive statistical iterative reconstruction (ASiR) was used for CT reconstruction. PET images were reconstructed with the lower‐dose CTAC iterations and analyzed for: maximum body weight standardized uptake value (SUVbw) of various diameter targets (range 8–37 mm), background uniformity, and spatial resolution. Radiation organ dose, as derived from patient exam size specific dose estimate (SSDE), was converted to effective dose using the standard ICRP report 103 method. Effective dose and CTAC noise magnitude were compared for 140 patient examinations (76 post‐ASiR implementation) to determine relative patient population dose reduction and noise control.Results:CT numbers were constant to within 10% from the non‐dose reduced CTAC image down to 90% dose reduction. No change in SUVbw, background percent uniformity, or spatial resolution for PET images reconstructed with CTAC protocols reconstructed with ASiR and down to 90% dose reduction. Patient population effective dose analysis demonstrated relative CTAC dose reductions between 62%–86% (3.2/8.3−0.9/6.2; mSv). Noise magnitude in dose‐reduced patient images increased but was not statistically different from pre dose‐reduced patient images. Conclusion: Using ASiR allowed for aggressive reduction in CTAC dose with no change in PET reconstructed images while maintaining sufficient image quality for co‐localization of hybrid CT anatomy and PET radioisotope uptake.

Dose Estimation for a Study of Nuclear Workers in France, the United Kingdom and the United States of America: Methods for the International Nuclear Workers Study (INWORKS).

In the framework of the International Nuclear Workers Study conducted in France, the UK and the U.S. (INWORKS), updated and expanded methods were developed to convert recorded doses of ionizing radiation to estimates of organ doses or individual personal dose equivalent [H(p)(10)] for a total number of 308,297 workers, including 40,035 women. This approach accounts for differences in dosimeter response to predominant workplace energy and geometry of exposure and for the recently published ICRP report on dose coefficients for men and women separately. The overall mean annual individual personal dose equivalent, including zero doses, is 1.73 mSv [median = 0.42; interquartile range (IQR): 0.07, 1.59]. Associated individual organ doses were estimated. INWORKS includes workers who had potential for exposure to neutrons. Therefore, we analyzed neutron dosimetry data to identify workers potentially exposed to neutrons. We created a time-varying indicator for each worker, classifying them according to whether they had a positive recorded neutron dose and if so, whether their neutron dose ever exceeded 10% of their total external penetrating radiation dose. The number of workers flagged as being exposed to neutrons was 13% for the full cohort, with 15% of the cohort in France, 12% of the cohort in the UK and 14% in the U.S. We also used available information on in vivo and bioassay monitoring to identify workers with known depositions or suspected internal contaminations. As a result of this work, information is now available that will allow various types of sensitivity analyses.

Dose to ‘water-like’ media or dose to tissue in MV photons radiotherapy treatment planning: still a matter of debate

The difference between Monte Carlo Treatment Planning (MCTP) based on the assumption of ‘water-like’ tissues with densities obtained from CT procedures, or on tissue compositions derived from CT-determined densities, have been investigated. Stopping powers and electron fluences have been calculated for a range of media and body tissues for 6 MV photon beams, including changes in their physical data (density and stopping powers). These quantities have been used to determine absorbed doses using cavity theory. It is emphasized that tissue compositions given in ICRU or ICRP reports should not be given the standing of physical constants as they correspond to average values obtained for a limited number of human-body samples.It has been shown that mass stopping-power ratios to water are more dependent on patient-to-patient composition differences, and therefore on their mean excitation energies (I-values), than on mass density. Electron fluence in different media are also more dependent on media composition (and their I-values) than on density. However, as a consequence of the balance between fluence and stopping powers, doses calculated from their product are more constant than what the independent stopping powers and fluence variations suggest.Additionally, cancelations in dose ratios minimize the differences between the ‘water-like’ and ‘tissue’ approaches, yielding practically identical results except for bone, and to a lesser extent for adipose tissue. A priori, changing from one approach to another does not seem to be justified considering the large number of approximations and uncertainties involved throughout the treatment planning tissue segmentation and dose calculation procedures. The key issue continues to be the composition of tissues and their I-values, and as these cannot be obtained for individual patients, whatever approach is selected does not lead to significant differences from a water reference dose, the maximum of these being of the order of 5% for bone tissues. Considering, however, current developments in advanced dose calculation methods, planning in terms of dose-to-tissue should be the preferred choice, under the expectancy that progress in the field will gradually improve some of the crude approximations included in MCTP and numerical transport methods.The small differences obtained also show that a retrospective conversion from dose-to-tissue to dose-to-water, based on a widely used approach, would mostly increase the final uncertainty of the treatment planning process. It is demonstrated that, due to the difference between electron fluence distributions in water and in body tissues, the conversion requires an additional fluence correction that has so far been neglected. An improved expression for the conversion and data for the fluence correction factor are provided. These will be necessary even in a dose-to-tissue environment, for the normalization of the treatment plan to the reference dosimetry of the treatment unit, always calibrated in terms of absorbed dose to water.

Practical Strategies to Reduce Pediatric CT Radiation Dose

The objective of this article is to provide a brief review of CT scanning radiation sensitivity in children and explain CT scan parameters that affect radiation dose. We discuss key factors influencing radiation dose and study quality and how these factors can be used to optimize scan protocols with the goal of reducing pediatric CT radiation dose without compromising diagnostic quality. Finally, we provide some practical tips for reducing radiation doses to children.

Symposium: European standard on medical physics services

s / Physica Medica 30 (2014) e1ee15 e13 The high penetration of cloud computing technology leads to a situation where all applications will abandon their traditional operation and move to the cloud, where they can be delivered as services. In medical physics science, as the technology continuously breaks the ethical and security barriers, sharing of medical imaging data between experts world-wide tends to become a routine task. Examples of current accomplishments of international communication via the web will be presented. ICRP COMMITTEE 3 OVERVIEW (PROTECTION IN MEDICINE) E. Va~ no , D.L. Miller , M. Rehani . ICRP Committee 3. Chairman; ICRP Committee 3. Vice-Chairman; ICRP Committee 3 Committee 3 of ICRP is concerned with protection of persons and unborn children when ionising radiation is used for medical diagnosis, therapy, or biomedical research. According to the 2011-2017 Strategic Plan, Committee 3 develops recommendations and guidance for protection of patients, staff, and the public against radiation exposure in medicine. This paper presents an overview of the work of the Committee in recent years and current work in progress. The ICRP reports dealing with radiological protection (RP) in medicine in the last 10 years cover topics on: education and training in RP; preventing accidental exposures in radiation therapy; doses to patients from radiopharmaceuticals; radiation safety aspects of brachytherapy; release of patients after therapy with unsealed radionuclides; and managing radiation dose in interventional radiology, digital radiology, computed tomography, paediatrics, cardiology and other medical specialties. Work in progress deals with RP in Ion Beam Therapy, Occupational Protection in Brachytherapy, Justification in Imaging, RP in Cone Beam CT, Doses to Patients and Staff from Radiopharmaceuticals (update), Occupational Protection in Interventional Radiology, and Diagnostic Reference Levels for Diagnostic and Interventional Imaging. The Committee is also involved in preparation of a document on effective dose (and its use medicine). SYMPOSIUM: EUROPEAN STANDARD ON MEDICAL PHYSICS SERVICES Stelios Christofides , Derek Pearson , Gerard Colenbrander , Luca Moro . Medical Physics Department, Nicosia General Hospital, Nicosia, Cyprus; Professional Adviser to the Chief Scientific Officer, NHS England. U.K.; Department of Medical Physics, Spaarnehospital, Hoofddorp, The Netherlands; Medical Physics Department, Salvatore Maugeri Foundation,

Kilo-Voltage Imaging Doses to Organs-at-Risk in CBCT-guided Breast Radiation Therapy

Recently kilo-voltage cone beam computed tomography (kVCBCT) scans have been widely used in the external beam radiation therapy of breast cancer patients to improve daily setup accuracy so that high dose of tumoricidal radiation can be delivered accurately to the partial volume, as well as to the whole breast. Although early studies investigated the kV imaging doses from kVCBCT scans to critical structures in the pelvis and head regions, the knowledge of dose depositions to the various organs-at-risk (OARs) in thoracic kVCBCT scans of the patient chest is largely missing. Therefore, the goal of this study is to systematically investigate the kV imaging doses to the OARs during CBCT-guided radiation therapy of breast cancer patients. Twenty breast cancer patients in supine orientation were retrospectively assorted into two groups by the lesion site (left vs. right breast). Critical structures such as the heart, the lungs, the normal breast and the thyroid were delineated on the Eclipse treatment planning system based on the planning CT images, which together were subsequently converted into patient CT phantoms for Monte Carlo simulations with an in-house DICOM utility tool. A benchmarked EGS4 Monte Carlo code was used to calculate the 3D dose distributions in the patients scanned by the kVCBCT with a half-fan pelvis protocol pre-defined by the manufacturer. The correlation between the imaging doses received by the OARs and the patient size as well as the lesion site was studied. Furthermore, a similar study was carried out on an adult female anthropomorphic phantom as defined in ICRP report 110 with cortical bone and red bone marrow delineated in the ribs, scapulae, clavicles, thoracic and cervical spines. The mean doses deposited to the heart, the lungs, the normal breast and the thyroid were found to be 3.1, 3.2, 3.3, and 1.5 cGy per CBCT scan, respectively. There were no significant differences observed between the dose depositions to the left and the right lungs, due primarily to the 364° arc rotation defined for the half-fan pelvis scan. A strong correlation was observed between the patient size and the imaging doses, with lower organ doses in the patients of larger sizes. The surface dose for the skin of the breast could reach 7-8 cGy per scan due to proximity to the kV source. The ICRP phantom study indicated that the kVCBCT-contributed mean doses to the cortical bones and the red bone marrows in the thoracic region were 6.1 and 4.0 cGy, respectively for each scan. Compared to the negligible doses (< 0.2% of therapeutic dose except for ipsilateral lung) from the mega-voltage photon beams in breast radiation therapy, each kVCBCT scan contributed 4-10 times more doses to the various OARs on average. Caution should be exercised to avoid multiple kVCBCT acquisitions for each fraction in CBCT-guided breast radiation therapy.