PyMCGPU-IR Monte Carlo code test for occupational dosimetry.

PyMCGPU-IR is an innovative occupational dose monitoring tool for interventional radiology procedures. It reads the radiation data from the Radiation Dose Structured Report of the procedure and combines this information with the position of the monitored worker recorded using a 3D camera system. This information is used as an input file for the fast Monte Carlo radiation transport code MCGPU-IR in order to assess the organ doses, Hp(10) and Hp(0.07), as well as the effective dose. In this study, Hp(10) measurements of the first operator during an endovascular aortic aneurysm repair procedure and a coronary angiography using a ceiling suspended shield are compared to PyMCGPU-IR calculations. Differences in the two reported examples are found to be within 15%, which is considered as being very satisfactory. The study highlights the promising advantages of PyMCGPU-IR, although there are still several improvements that need to be implemented before its final clinical use.

Practical guidelines for personal monitoring and estimation of effective dose and dose to the lens of the eye in interventional procedures.

Estimation of effective dose and dose to the lens of the eye for workers involved in interventional procedures is challenging. The interventional procedures in question involve high doses and, due to this, workers need to wear protective garments. As a result, various methodologies have been developed to assess the effective dose and dose to the lens of the eye. In the present study, measurements from four European dosimetry services, over and under protective garments, have been collected and analysed in order to provide practical guidelines based on the routine use of personal dosemeters from staff in interventional workplaces. The advantages and limitations of using one or two dosemeters are discussed.

Validation of organ dose calculations with PyMCGPU-IR in realistic interventional set-ups.

INTRODUCTION: Interventional radiology procedures are associated with high skin dose exposure. The 2013/59/EURATOM Directive establishes that the equipment used for interventional radiology must have a device or a feature informing the practitioner of relevant parameters for assessing patient dose at the end of the procedure. This work presents and validates PyMCGPU-IR, a patient dose monitoring tool for interventional cardiology and radiology procedures based on MC-GPU. MC-GPU is a freely available Monte Carlo (MC) code of photon transport in a voxelized geometry which uses the computational power of commodity Graphics Processing Unit cards (GPU) to accelerate calculations. METHODOLOGIES: PyMCGPU-IR was validated against two different experimental set-ups. The first one consisted of skin dose measurements for different beam angulations on an adult Rando Alderson anthropomorphic phantom. The second consisted of organ dose measurements in three clinical procedures using the Rando Alderson phantom. RESULTS: The results obtained for the skin dose measurements show differences below 6%. For the clinical procedures the differences are within 20% for most cases. CONCLUSIONS: PyMCGPU-IR offers both, high performance and accuracy for dose assessment when compared with skin and organ dose measurements. It also allows the calculation of dose values at specific positions and organs, the dose distribution and the location of the maximum doses per organ. In addition, PyMCGPU-IR overcomes the time limitations of CPU-based MC codes.

Need for harmonisation of extremity dose monitoring in nuclear medicine: results of a survey amongst national dose registries in Europe.

Staff handling radiopharmaceuticals in nuclear medicine (NM) may receive significant extremity doses. Over the last decade in particular there has been an increase in NM procedures and new radiopharmaceuticals have been introduced. However, literature provides limited recent data on the exposure of the extremities. In addition, proper assessment of the equivalent dose to the skin can be difficult when applied to the fingertips. In order to gain insight in the actual exposure and to find out how European countries are dealing with monitoring of the extremities, a survey was performed amongst European regulatory authorities. The questions covered general aspects of the national dose registries (NDRs), the measured extremity doses and the practice of the monitoring of workers. The survey shows that extremity dosimetry is performed for about 25%-50% of the monitored workers in NM. Also, the recorded extremity doses in the NDRs are low (mean values 5-29 mSv yr-1) compared to the dose limit. Despite the recommendations that have been published in the last 10 years, few countries provide guidance on the wearing position of extremity dosemeters and the correction factor to estimate the maximum equivalent skin dose from the measured dose. This may lead to an underestimation of the maximum skin dose. Thermoluminescence ring dosemeters are widely used, but wrist dosemeters are also very common, even though the correlation of the measurement with the maximum skin dose is worse than for ring dosemeters. Furthermore, not all countries had a central registration of the extremity dose at the time the survey was performed.

Review of extremity dosimetry in nuclear medicine.

The exposure of the fingers is one of the major radiation protection concerns in nuclear medicine (NM). The purpose of this paper is to provide an overview of the exposure, dosimetry and protection of the extremities in NM. A wide range of reported finger doses were found in the literature. Historically, the highest finger doses are found at the fingertip in the preparation and dispensing of18F for diagnostic procedures and90Y for therapeutic procedures. Doses can be significantly reduced by following recommendations on source shielding, increasing distance and training. Additionally, important trends contributing to a lower dose to the fingers are the use of automated procedures (especially for positron emission tomography (PET)) and the use of prefilled syringes. On the other hand, the workload of PET procedures has substantially increased during the last ten years. In many cases, the accuracy of dose assessment is limited by the location of the dosimeter at the base of the finger and the maximum dose at the fingertip is underestimated (typical dose ratios between 1.4 and 7). It should also be noted that not all dosimeters are sensitive to low-energy beta particles and there is a risk for underestimation of the finger dose when the detector or its filter is too thick. While substantial information has been published on the most common procedures (using99mTc,18F and90Y), less information is available for more recent applications, such as the use of68Ga for PET imaging. Also, there is a need for continuous awareness with respect to contamination of the fingers, as this factor can contribute substantially to the finger dose.

Validation of the MC-GPU Monte Carlo code against the PENELOPE/penEasy code system and benchmarking against experimental conditions for typical radiation qualities and setups in interventional radiology and cardiology.

INTRODUCTION: Interventional procedures are associated with potentially high radiation doses to the skin. The 2013/59/EURATOM Directive establishes that the equipment used for interventional radiology must have a device or a feature informing the practitioner of relevant parameters for assessing patient dose at the end of the procedure. Monte Carlo codes of radiation transport are considered to be one of the most reliable tools available to assess doses. However, they are usually too time consuming for use in clinical practice. This work presents the validation of the fast Monte Carlo code MC-GPU for application in interventional radiology. METHODOLOGIES: MC-GPU calculations were compared against the well-validated Monte Carlo simulation code PENELOPE/penEasy by simulating the organ dose distribution in a voxelized anthropomorphic phantom. In a second phase, the code was compared against thermoluminescent measurements performed on slab phantoms, both in a calibration laboratory and at a hospital. RESULTS: The results obtained from the two simulation codes show very good agreement, differences in the output were within 1%, whereas the calculation time on the MC-GPU was 2500 times shorter. Comparison with measurements is of the order of 10%, within the associated uncertainty. CONCLUSIONS: It has been verified that MC-GPU provides good estimates of the dose when compared to PENELOPE program. It is also shown that it presents very good performance when assessing organ doses in very short times, less than one minute, in real clinical set-ups. Future steps would be to simulate complex procedures with several projections.

The 2019-2023 Strategic Plan of the Spanish Society of Radiological Protection (SEPR).

The Spanish Society for Radiological Protection (SEPR) is a scientific and technical organization that aims to bring together all radioprotection professionals from all the sectors of activity where ionizing and non-ionizing radiation is produced. The development of the SEPR's Strategic Plan every 5 years is the cornerstone of all the different activities that the Society carries out. This document establishes the SEPR goals and objectives for that period, as well as the activities planned to achieve them. It is a living and open document that draws on past experiences while looking to the future. The Strategic Plan 2019-2023, approved on June 2019, is the Third Strategic Plan of the SEPR. In its preparation, account has been taken of the experience obtained in the application of the two previous Strategic Plans, as well as of the new demands of the general public and of professionals in the area of radiological protection that have become apparent during the previous period. This paper describes the development of the current Strategic Plan, as well as the Plan itself, and briefly analyzes its implementation in the Conclusion.

Radiation-induced lens opacities: Epidemiological, clinical and experimental evidence, methodological issues, research gaps and strategy.

In 2011, the International Commission on Radiological Protection (ICRP) recommended reducing the occupational equivalent dose limit for the lens of the eye from 150 mSv/year to 20 mSv/year, averaged over five years, with no single year exceeding 50 mSv. With this recommendation, several important assumptions were made, such as lack of dose rate effect, classification of cataracts as a tissue reaction with a dose threshold at 0.5 Gy, and progression of minor opacities into vision-impairing cataracts. However, although new dose thresholds and occupational dose limits have been set for radiation-induced cataract, ICRP clearly states that the recommendations are chiefly based on epidemiological evidence because there are a very small number of studies that provide explicit biological and mechanistic evidence at doses under 2 Gy. Since the release of the 2011 ICRP statement, the Multidisciplinary European Low Dose Initiative (MELODI) supported in April 2019 a scientific workshop that aimed to review epidemiological, clinical and biological evidence for radiation-induced cataracts. The purpose of this article is to present and discuss recent related epidemiological and clinical studies, ophthalmic examination techniques, biological and mechanistic knowledge, and to identify research gaps, towards the implementation of a research strategy for future studies on radiation-induced lens opacities. The authors recommend particularly to study the effect of ionizing radiation on the lens in the context of the wider, systemic effects, including in the retina, brain and other organs, and as such cataract is recommended to be studied as part of larger scale programs focused on multiple radiation health effects.

Report of IRPA task group on issues and actions taken in response to the change in eye lens dose limit.

In 2018, the International Radiation Protection Association (IRPA) established its third task group (TG) on the implementation of the eye lens dose limit. To contribute to sharing experience and raising awareness within the radiation protection community about protection of workers in exposure of the lens of the eye, the TG conducted a questionnaire survey and analysed the responses. This paper provides an overview of the results of the questionnaire.

A European survey on the regulatory status for the estimation of the effective dose and the equivalent dose to the lens of the eye when radiation protection garments are used.

Following the proposal of the ICRP for the reduction of the dose limit for the lens of the eye, which has been adopted by the International Atomic Energy Agency and the European Council, concerns have been raised about the implementation of proper dose monitoring methods as defined in national regulations, and about the harmonisation between European countries. The European Radiation Dosimetry Group organised a survey at the end of 2017, through a web questionnaire, regarding national dose monitoring regulations. The questions were related to: double dosimetry, algorithms for the estimation of the effective dose, methodology for the determination of the equivalent dose to the lens of the eye and structure of the national dose registry. The results showed that more than 50% of the countries that responded to the survey have legal requirements about the number and the position of dosemeters used for estimation of the effective dose when radiation protection garments are used. However, in only five out of 26 countries are there nationally approved algorithms for the estimation of the effective dose. In 14 out of 26 countries there is a legal requirement to estimate the dose to the lens of the eye. All of the responding countries use some kind of national database for storing individual monitoring data but in only 12 out of 26 countries are the estimated effective dose values stored. The personal dose equivalent at depth 3 mm is stored in the registry of only seven out of 26 countries. From the survey, performed just before the implementation of the European Basic Safety Standards Directive, it is concluded that national occupational exposure frameworks require intensive and immediate work under the coordination of the competent authorities to bring them into line with the latest basic safety standards and achieve harmonisation between European countries.

Effect of the radiation protective apron on the response of active and passive personal dosemeters used in interventional radiology and cardiology.

In fluoroscopy guided interventional procedures, workers use protective garments and often two personal dosemeters, the readings of which are used for the estimation of the effective dose; whereas the dosemeter above the protection can be used for the estimation of the equivalent dose of the lens of the eye. When a protective apron is worn the scattered field that reaches the dosemeter is different from the case where no protection is used; this study analyses the changes in the response of seven passive and eight active personal dosemeters (APDs) when they are placed above a lead or lead equivalent garment for S-Cs and x-ray diagnostic qualities. Monte Carlo simulations are used to support the experimental results. It is found that for passive dosemeters, the influence on the dosemeter's response to the lead or lead equivalent was within the range 15%-38% for the x-ray qualities. This effect is smaller, of the order of 10%, when lead-free garments are used, and much smaller, within 1%-10%, for most of the APDs used in the study. From these results it is concluded that when comparing passive and active dosemeter measurements worn above the protection, a difference of 20%-40% is expected. The effect is small when deriving the effective dose from double dosimetry algorithms, but it can be of major importance when eye lens monitoring is based on the use of the dosemeter worn above the protection.

Report of IRPA task group on the impact of the eye lens dose limits.

In 2012 IRPA established a task group (TG) to identify key issues in the implementation of the revised eye lens dose limit. The TG reported its conclusions in 2013. In January 2015, IRPA asked the TG to review progress with the implementation of the recommendations from the early report and to collate current practitioner experience. This report presents the results of a survey on the view of the IRPA professionals on the new limit to the lens of the eye and on the wider issue of tissue reactions. Recommendations derived from the survey are presented. This report was approved by IRPA Executive Council on 31 January 2017.

Field correction factors for a PTW-31016 Pinpoint ionization chamber for both flattened and unflattened beams. Study of the main sources of uncertainties.

PURPOSE: The primary aim of this study was to determine correction factors, kQclin,Qmsrfclin,fmsr for a PTW-31016 ionization chamber on field sizes from 0.5 cm × 0.5 cm to 2 cm × 2 cm for both flattened (FF) and flattened filter-free (FFF) beams produced in a TrueBeam clinical accelerator. The secondary objective was the determination of field output factors, ΩQclin,Qmsrfclin,fmsr over this range of field sizes using both Monte Carlo (MC) simulation and measurements. METHODS: kQclin,Qmsrfclin,fmsr for the PTW-31016 chamber were calculated by MC simulation for field sizes of 0.5 cm × 0.5 cm, 1 cm × 1 cm, and 2 cm × 2 cm. MC simulations were performed with the PENELOPE code system for the 10 MV FFF Particle Space File from a TrueBeam linear accelerator (LINAC) provided by the manufacturer (Varian Medical Systems, Inc. Palo Alto, CA, USA). Simulations were repeated taking into account chamber manufacturing tolerances and accelerator jaw positioning in order to assess the uncertainty of the calculated correction factors. Output ratios were measured on square fields ranging from 0.5 cm × 0.5 cm to 10 cm × 10 cm for 6 MV and 10 MV FF and FFF beams produced by a TrueBeam using a PTW-31016 ionization chamber; a Sun Nuclear Edge detector (SunNuclear Corp., Melbourne, FL, USA) and TLD-700R (Harshaw, Thermo Scientific, Waltham, MA, USA). The validity of the proposed correction factors was verified using the calculated correction factors for the determination of ΩQclin,Qmsrfclin,fmsr using a PTW-31016 at the four TrueBeam energies and comparing the results with both TLD-700R measurements and MC simulations. Finally, the proposed correction factors were used to assess the correction factors of the SunNuclear Edge detector. RESULTS: The present work provides a set of MC calculated correction factors for a PTW-31016 chamber used on a TrueBeam FF and FFF mode. For the 0.5 cm × 0.5 cm square field size, kQclin,Qmsrfclin,fmsr is equal to 1.17 with a combined uncertainty of 2% (k = 1). A detailed analysis of the most influential parameters is presented in this work. PTW-31016 corrected measurements were used for the determination of ΩQclin,Qmsrfclin,fmsr for 6 MV and 10 MV FF and FFF and the results were in agreement with values obtained using a TLD-700R detector (differences < 3% for a 0.5 cm square field) for the four energies studied. Uncertainty in field collimation was found to be the main source of influence of ΩQclin,Qmsrfclin,fmsr and caused differences of up to 15% between calculations and measurements for the 0.5 cm × 0.5 cm field. This was also confirmed by repeating the same measurements at two different institutions. CONCLUSIONS: This study confirms the need to introduce correction factors when using a PTW-31016 chamber and the hypothesis of their low energy dependence. MC simulation has been shown to be a useful methodology to determine detector correction factors for small fields and to analyze the main sources of uncertainty. However, due to the influence of the LINAC jaw setup for field sizes below or equal to 1 cm, MC methods are not recommended in this range for field output factor calculations.

Evaluation of an automated FDG dose infuser to PET-CT patients.

An experience with an automated infuser device at a university hospital is presented in this paper. Occupational doses at operators' fingertips were measured using optically stimulated luminescence dosemeters for two different scenarios: (i) using a semi-automatic system to prepare the fluorodesoxiglucose (FDG) injections that were delivered to the patient manually and (ii) using an automated infusion device that prepares and delivers the FDG dose. The accuracy of the activity prepared by the automatic system was also verified. Reductions in fingertip doses of 60 % using the fully automatic system have been measured. The difference between the programmed and the delivered activity was 2 %. The use of the automatic infuser in the authors' institution has led to a substantial reduction in hand radiation doses. But contamination risks, even though reduced, still exist; therefore, radioisotope manipulation should follow strict radiation protection rules to avoid incidents. Improved accuracy in dose delivery reduces chances of dose misadministration.

Influence of dosemeter position for the assessment of eye lens dose during interventional cardiology.

The equivalent dose limit for the eye lens for occupational exposure recommended by the ICRP has been reduced to 20 mSv y(-1) averaged over defined periods of 5 y, with no single year exceeding 50 mSv. The compliance with this new requirement could not be easy in some workplace such as interventional radiology and cardiology. The aim of this study is to evaluate different possible approaches in order to have a good estimate of the eye lens dose during interventional procedures. Measurements were performed with an X-ray system Philips Allura FD-10, using a PMMA phantom to simulate the patient scattered radiation and a Rando phantom to simulate the cardiologist. Thermoluminescence (TL) whole-body and TL eye lens dosemeters together with Philips DoseAware active dosemeters were located on different positions of the Rando phantom to estimate the eye lens dose in typical cardiology procedures. The results show that, for the studied conditions, any of the analysed dosemeter positions are suitable for eye lens dose assessment. However, the centre of the thyroid collar and the left ear position provide a better estimate. Furthermore, in practice, improper use of the ceiling-suspended screen can produce partial protection of some parts of the body, and thus large differences between the measured doses and the actual exposure of the eye could arise if the dosemeter is not situated close to the eye.

Status of eye lens radiation dose monitoring in European hospitals.

A questionnaire was developed by the members of WG12 of EURADOS in order to establish an overview of the current status of eye lens radiation dose monitoring in hospitals. The questionnaire was sent to medical physicists and radiation protection officers in hospitals across Europe. Specific topics were addressed in the questionnaire such as: knowledge of the proposed eye lens dose limit; monitoring and dosimetry issues; training and radiation protection measures. The results of the survey highlighted that the new eye lens dose limit can be exceeded in interventional radiology procedures and that eye lens protection is crucial. Personnel should be properly trained in how to use protective equipment in order to keep eye lens doses as low as reasonably achievable. Finally, the results also highlighted the need to improve the design of eye dosemeters in order to ensure satisfactory use by workers.

Dose variations in tumor volumes and organs at risk during IMRT for head-and-neck cancer.

Many head-and-neck cancer (HNC) patients treated with radiotherapy suffer significant anatomical changes due to tumor shrinkage or weight loss. The purpose of this study was to assess dose changes over target volumes and organs at risk during intensity-modulated radiotherapy for HNC patients. Sixteen HNC IMRT patients, all requiring bilateral neck irradiation, were enrolled in the study. A CTplan was performed and the initial dose distribution was calculated. During the treatment, two subsequent CTs at the 15th (CT15) and 25th (CT25) fractions were acquired. The initial plan was calculated on the CT15 and CT25, and dose-volume differences related to the CTplan were assessed. For target volumes, mean values of near-maximun absorbed dose (D2%) increased at the 25th fraction, and doses covering 95% and 98% of volume decreased significantly at the 15th fraction. Contralateral and ipsilateral parotid gland mean doses increased by 6.1% (range: -5.4, 23.5%) and 4.7% (range: -9.1, 22.3%), respectively, at CT25. The D2% in the spinal cord increased by 1.8 Gy at CT15. Mean absorbed dose increases at CT15 and CT25 were observed in: the lips, 3.8% and 5.3%; the oral cavity, 3.5% and 2.5%; and lower middle neck structure, 1.9% and 1.6%. Anatomical changes during treatment of HNC patients affect dose distribution and induce a loss of dose coverage to target volumes and an overdosage to critical structures. Appropriate organs at risk have to be contoured and monitored in order to know if the initial plan remains suitable during the course of the treatment. Reported dosimetric data can help to identify patients who could benefit from adaptive radiotherapy.

SBRT of lung tumours: Monte Carlo simulation with PENELOPE of dose distributions including respiratory motion and comparison with different treatment planning systems.

The purpose of this work was to simulate with the Monte Carlo (MC) code PENELOPE the dose distribution in lung tumours including breathing motion in stereotactic body radiation therapy (SBRT). Two phantoms were modelled to simulate a pentagonal cross section with chestwall (unit density), lung (density 0.3 g cm(-3)) and two spherical tumours (unit density) of diameters respectively of 2 cm and 5 cm. The phase-space files (PSF) of four different SBRT field sizes of 6 MV from a Varian accelerator were calculated and used as beam sources to obtain both dose profiles and dose-volume histograms (DVHs) in different volumes of interest. Dose distributions were simulated for five beams impinging on the phantom. The simulations were conducted both for the static case and including the influence of respiratory motion. To reproduce the effect of breathing motion different simulations were performed keeping the beam fixed and displacing the phantom geometry in chosen positions in the cranial and caudal and left-right directions. The final result was obtained by combining the different position with two motion patterns. The MC results were compared with those obtained with three commercial treatment planning systems (TPSs), two based on the pencil beam (PB) algorithm, the TMS-HELAX (Nucletron, Sweden) and Eclipse (Varian Medical System, Palo Alto, CA), and one based on the collapsed cone algorithm (CC), Pinnacle(3) (Philips). Some calculations were also carried out with the analytical anisotropic algorithm (AAA) in the Eclipse system. All calculations with the TPSs were performed without simulated breathing motion, according to clinical practice. In order to compare all the TPSs and MC an absolute dose calibration in Gy/MU was performed. The analysis shows that the dose (Gy/MU) in the central part of the gross tumour volume (GTV) is calculated for both tumour sizes with an accuracy of 2-3% with PB and CC algorithms, compared to MC. At the periphery of the GTV the TPSs overestimate the dose up to 10%, while in the lung tissue close to the GTV PB algorithms overestimate the dose and the CC underestimates it. When clinically relevant breathing motions are included in the MC simulations, the static calculations with the TPSs still give a relatively accurate estimate of the dose in the GTV. On the other hand, the dose at the periphery of the GTV is overestimated, compared to the static case.

Monte Carlo simulation of MOSFET detectors for high-energy photon beams using the PENELOPE code.

The aim of this work was the Monte Carlo (MC) simulation of the response of commercially available dosimeters based on metal oxide semiconductor field effect transistors (MOSFETs) for radiotherapeutic photon beams using the PENELOPE code. The studied Thomson&Nielsen TN-502-RD MOSFETs have a very small sensitive area of 0.04 mm(2) and a thickness of 0.5 microm which is placed on a flat kapton base and covered by a rounded layer of black epoxy resin. The influence of different metallic and Plastic water build-up caps, together with the orientation of the detector have been investigated for the specific application of MOSFET detectors for entrance in vivo dosimetry. Additionally, the energy dependence of MOSFET detectors for different high-energy photon beams (with energy >1.25 MeV) has been calculated. Calculations were carried out for simulated 6 MV and 18 MV x-ray beams generated by a Varian Clinac 1800 linear accelerator, a Co-60 photon beam from a Theratron 780 unit, and monoenergetic photon beams ranging from 2 MeV to 10 MeV. The results of the validation of the simulated photon beams show that the average difference between MC results and reference data is negligible, within 0.3%. MC simulated results of the effect of the build-up caps on the MOSFET response are in good agreement with experimental measurements, within the uncertainties. In particular, for the 18 MV photon beam the response of the detectors under a tungsten cap is 48% higher than for a 2 cm Plastic water cap and approximately 26% higher when a brass cap is used. This effect is demonstrated to be caused by positron production in the build-up caps of higher atomic number. This work also shows that the MOSFET detectors produce a higher signal when their rounded side is facing the beam (up to 6%) and that there is a significant variation (up to 50%) in the response of the MOSFET for photon energies in the studied energy range. All the results have shown that the PENELOPE code system can successfully reproduce the response of a detector with such a small active area.