Search

A thin and plane wall ionisation chamber having 900 cc volume was designed and fabricated to study the calibration coefficient dependency on ionisation chamber wall thickness for directional dose equivalent rate (Ḣ'(d)) at various low and medium energy X-ray beam qualities. Optimised wall thickness was established through measurements to achieve a near flat energy response using the developed ionisation chamber. The measurement shows that in the energy range 12-213 keV, the average calibration coefficient for directional dose equivalent rate lies within ±10% for wall thickness 1.2 mg/cm2 and 480 mg/cm2 (4 mm poly methyl methacrylate) for skin and eye lens dose monitoring, respectively. The study could be useful for the estimation of skin and eye lens doses for the paramedical staff and patient during the interventional radiology and interventional cardiology procedures by monitoring the directional dose equivalent rate., (© The Author(s) 2018. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

After a planned or unplanned radiation exposure, determination of absorbed dose has great clinical importance, informing treatment and triage decisions in the exposed individuals. Biodosimetry approaches allow for determination of dose in the absence of physical measurement apparatus. The current state-of-the-art biodosimetry method is based on the frequency of induced dicentric chromosomes in peripheral blood T cells, which is proportional to the absorbed radiation dose. Since dose-response curves used for obtaining absorbed dose for humans are based on data sourced from in vitro studies, a concerning discrepancy may be present in the reported dose. Specifically, T-cell survival after in vitro irradiation is much higher than that measured in humans in vivo and, in addition, is not dose dependent over some dose ranges. We hypothesized that these differences may lead to inappropriately inflated dicentric frequencies after in vitro irradiation when compared with in vivo irradiation of the same samples. This may lead to underestimation of the in vivo dose. To test this hypothesis, we employed the humanized mouse model, which allowed direct comparison of cell depletion and dicentric frequencies in human T cells irradiated in vivo and in vitro . The results showed similar dicentric chromosome induction frequencies measured in vivo and in vitro when assessed 24 h postirradiation despite the differences in cell survival. These results appear to validate the use of in vitro data for the estimation of the absorbed dose in human radiation biodosimetry.

Ac-based PSMA-targeted therapy has emerged as promising agent for the treatment of metastatic castration-resistant prostate cancer. Posttherapy image is used for tracer localization and dosimetry. Prior 2 photopeaks of 440 and 218 KeV were reported for posttherapy imaging. Our study of gamma ray spectrum, phantom, and clinical images show that imaging with 3 major photopeaks of 78, 218, and 440 KeV gives better quality images, high count statistics, and higher number of lesion delineations. It is therefore suggested that posttherapy imaging may be carried out using 3 major abundant photopeaks.

Traditionally, dose estimations have been performed predominantly using anthropomorphic phantoms in an upright posture. However, an exclusively upright posture could reduce accuracy when estimating organ absorbed and effective doses for exposures in realistic postures. In this work, effective dose coefficients were computed using International Commission on Radiological Protection Publication 103 recommendations for monoenergetic photon plane sources (0.05-20 MeV) directed upward from below the feet (caudal) and downward from above the head (cranial) for articulated adult male and female stylized phantoms. The Monte Carlo radiation transport code and the Phantom With Moving Arms and Legs were used to calculate organ absorbed dose and effective dose coefficients for upright and two bent (45° and 90°) phantom postures. The resulting coefficients for the bent phantoms were compared to those for the upright phantoms to determine whether the upright phantoms provide a comparable and conservative estimate when conducting dose estimations/reconstructions. For the caudal source, most organs received higher doses when in a bent posture. For the cranial source, the breast, brain, and eyes received lower doses in the bent compared to the upright posture, while all other organs received higher doses. The effective doses for the articulated phantoms were higher than for the upright posture for both irradiation geometries, which could have implications when using the traditional model to estimate or reconstruct radiation doses during actual exposures.

Recently, the International Commission on Radiological Protection (ICRP) developed new mesh-type reference computational phantoms (MRCPs) that provide high deformability compared with the current voxel-type reference computational phantoms of ICRP Publication 110. Taking advantage of this deformability, in the present study, the MRCPs were deformed to five non-standing postures (i.e. walking, sitting, bending, kneeling, and squatting) by developing and using a systematic posture-change method based on the as-rigid-as-possible (ARAP) shape-deformation algorithm and motion-capture technology. The non-standing MRCPs were then implemented in the Geant4 Monte Carlo code to calculate a comprehensive dataset of dose coefficients (DCs) for photon external exposures. These include the dose coefficients for 29 individual organs/tissues and the dose coefficients for effective doses from 0.01 MeV to 10 GeV in the antero-posterior (AP), postero-anterior (PA), left-lateral (LLAT), right-lateral (RLAT), rotational (ROT), and isotropic (ISO) geometries. To investigate the dosimetric impact of posture, the DCs of the non-standing MRCPs were compared with those of the original MRCPs (in the standing posture). The results showed that organ/tissue doses are significantly influenced by posture, with arm position mostly influencing dose to organs/tissues in the torso region and leg position influencing dose in the pelvic region. For most cases, the gonads showed notably large differences, ranging from a few tens of percentage points to several orders of magnitude, depending on posture and irradiation geometry. The effective doses showed much smaller differences than the organ/tissue doses, but they were nonetheless significant: for example, the kneeling MRCPs in the AP geometry showed lower values at energies  <10 MeV by up to 30% and greater values at higher energies by up to 40%. The presented results indicate that not only different irradiation geometries, but also different postures might be necessary in DC calculations for reliable dose estimates for radiological protection purposes.

Purpose: Modern radiotherapy practices typically report the absorbed dose (D) within the 5% relative isodose volume (i.e., the therapeutic dose region) to an accuracy of 3%-5%. Gamma-index analysis, the most commonly used method to evaluate dosimetric accuracy, has low sensitivity to discrepancies that occur outside of this region. The objective of this study was to develop an evaluation method with high sensitivity across dose distributions spanning three orders of magnitude., Methods: We generalized the gamma index to include an additional criterion, the absolute absorbed dose difference, specifically for the low-dose region (i.e., D ≤ 5%). We also proposed a method to objectively select the appropriate magnitudes for relative-dose-difference, absolute-dose-difference, and distance-to-agreement criteria. We demonstrated the generalized gamma-index method by first finding the appropriate generalized gamma-index agreement criteria at an interval of specified passing rates. Next, we used the generalized gamma index to evaluate one-, two-, and three-dimensional absorbed dose distributions in a water-box phantom and voxelized patient geometry., Results: Generalized gamma-index passing rates for one-, two-, and three-dimensional dose distributions were 55.4%, 44.5%, and 8.9%, respectively. Traditional gamma-index passing rates were 100%, 97.8%, and 96.4%, respectively. These results reveal that the generalized method has adequate sensitivity in all regions (i.e., therapeutic and low dose). Additionally, the algorithmic determination of triplets of agreement criteria revealed that they are strong functions of the specified passing rate., Conclusions: The major finding of this work is that the proposed method provides an objective evaluation of the agreement of dose distributions spanning three orders of magnitude. In particular, this generalized method correctly characterized dosimetric agreement in the low-dose region, which was not possible by traditional methods. The proposed algorithmic selection of agreement criteria decreased subjectivity and requirements of user judgment and skill. This method could find utility in a variety of applications including dose-algorithm development and translation., (© 2019 American Association of Physicists in Medicine.)

Purpose: The complexity of the modern Stereotactic Body Radiation Therapy (SBRT) techniques requires comprehensive quality assurance programs, to ensure the right treatment to the patient. Dosimetry of small radiation fields is a challenge especially for radiotherapy centres starting to work on this issue. The matter to be discussed here concerns the need of detailed measurement procedures and cross checks to be paired to the usual recommendations on detectors and correction factors., Materials and Methods: The presented work involved 24 Italian radiotherapy centres, with the specific purpose to minimize systematic errors in output factor measurements over different radiotherapy centres. Using the unshielded silicon diode IBA Razor, reference curves for the relative signal ratio (RSR) as a function of beam size were created for each Linac family., Results: With this study we have demonstrated consistency of small field dosimetry on all the centres involved, moreover all radiotherapy centres using Razor are allowed to compare measurements amongst each other and centres with values deviating more than 5% from the reference curve are advised to repeat their measurements. With this procedure, some critical issues were detected from two centres in RSR measurements, that, if implemented into the own treatment planning system, would induce an unwanted overdosage larger than 5%., Conclusions: The proposed approach could allow one to envision high-skilled therapy centres providing support to those featuring minor experience and could represent an important strategy for the clinical implementation of emerging technologies at high quality levels. The methodology adopted exploits crowd knowledge methods which could be applied in others areas of radiation dosimetry., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Background and Purpose: Absolute dosimetry in 3D with polymer gels (PG) is generally complicated and usually requires a second independent measurement with conventional detectors. This is why, PG are often used only for relative dosimetry. To overcome this drawback, we combine PG with a 1D thermoluminescence (TL) detector within the same measurement. The TL detector information is then used as additional information for calibration of the gel., Materials and Methods: The PAGAT dosimetry gel was used in combination with TLD600 (LiF:Mg,Ti). TL detectors were attached on the surface of the PG container placed inside a cylindrical phantom. To test the usability of this setup, two irradiation geometries were carried out: (a) homogeneous target coverage and (b) small-field irradiation. PG was evaluated with magnetic resonance imaging (MRI) and the TL detectors with a Harshaw 5500 hot gas reader., Results: PG dosimetry alone showed deviations of up to 4% as compared to calculations. Including additionally the dose information of the TL detectors for PG calibration, this deviation was decreased to less than 1% for both irradiation geometries. This is also reflected by the very high [Formula: see text]-passing rates of  >  96% (3%/3 mm) and  >93% (2%/2 mm), respectively., Conclusion: This study presents a novel method combining 3D PG and TL dose measurements for the purpose of absolute 3D dose measurements that can also be applied in complex anthropomorphic phantoms using only a single measurement. The method was validated for two different irradiation geometries including a homogeneous large field as well as a small field irradiation with sharp dose gradients.

National Council on Radiation Protection and Measurements Commentary 27 examines recent epidemiologic data primarily from low-dose or low dose-rate studies of low linear-energy-transfer radiation and cancer to assess whether they support the linear no-threshold model as used in radiation protection. The commentary provides a critical review of low-dose or low dose-rate studies, most published within the last 10 y, that are applicable to current occupational, environmental, and medical radiation exposures. The strengths and weaknesses of the epidemiologic methods, dosimetry assessments, and statistical modeling of 29 epidemiologic studies of total solid cancer, leukemia, breast cancer, and thyroid cancer, as well as heritable effects and a few nonmalignant conditions, were evaluated. An appraisal of the degree to which the low-dose or low dose-rate studies supported a linear no-threshold model for radiation protection or on the contrary, demonstrated sufficient evidence that the linear no-threshold model is inappropriate for the purposes of radiation protection was also included. The review found that many, though not all, studies of solid cancer supported the continued use of the linear no-threshold model in radiation protection. Evaluations of the principal studies of leukemia and low-dose or low dose-rate radiation exposure also lent support for the linear no-threshold model as used in protection. Ischemic heart disease, a major type of cardiovascular disease, was examined briefly, but the results of recent studies were considered too weak or inconsistent to allow firm conclusions regarding support of the linear no-threshold model. It is acknowledged that the possible risks from very low doses of low linear-energy-transfer radiation are small and uncertain and that it may never be possible to prove or disprove the validity of the linear no-threshold assumption by epidemiologic means. Nonetheless, the preponderance of recent epidemiologic data on solid cancer is supportive of the continued use of the linear no-threshold model for the purposes of radiation protection. This conclusion is in accord with judgments by other national and international scientific committees, based on somewhat older data. Currently, no alternative dose-response relationship appears more pragmatic or prudent for radiation protection purposes than the linear no-threshold model.

Purpose: Phantoms for horizontal beam geometry can avoid issues in vertical-beam geometry, such as change in chamber depth due to evaporation, and defining the origin at the water surface. However, their thin entrance windows would deform when these phantoms are filled, which can change the chamber depth, as pointed out by The International Atomic Energy Agency (IAEA) TRS-398. Currently, few reports (Arib et al., J Appl Clin Med Phys. 2006; 7:55-64, and Kinoshita et al., Rep Pract Oncol Radiother. 2018; 23:199-206) are available with practical data on window deformation. Therefore, we investigated the influence of entrance window deformation on chamber depths in water phantoms and the measurements in various beam modalities., Methods: To examine widely used phantoms and phantoms with different characteristics, three phantom types were investigated (the number of phantoms investigated appears in parentheses): PTW-type 41023 (2), Qualita-QWP-04 (2), and IBA-WP34 (2). Prior to the investigation, these phantoms were stored for acclimatization in a room for approximately 10 h under the following two conditions: (a) room temperature: 21 ± 2°C; (b) room temperature: 27 ± 2°C. Using a dial indicator, the centers of the windows were monitored every 30 min for 12 h immediately after the phantoms were filled, in a treatment room at the room temperature of 21 ± 2°C., Results: Immediately after the phantoms were filled, the window deformation ranged from -0.07 (inward-deformation) to 0.3 mm (outward deformation) among the six phantoms, in comparison with empty phantom windows. For 12 h after the phantoms were filled, the change in the deformation was up to 0.23 mm, but typically less than 0.15 mm., Conclusions: Reference dosimetry in photon, electron, and proton beams would not be influenced significantly by these window behaviors, whereas the window deformation has a slight impact on those heavy ion beams., (© 2018 American Association of Physicists in Medicine.)

Effective dose (E) is a risk-adjusted dosimetric quantity developed by the International Commission on Radiological Protection. It is a key metric for practical management of the risk of stochastic health effects in a comprehensive radiation protection program. The International Commission on Radiological Protection and others have emphasized repeatedly that E is not intended to represent an actual radiation dose and should not be used as a risk-related metric for a specific person or population. The cancer risk uncertainties in the low-dose range and the underlying approximations, simplifications, and sex- and age-averaging used in generating E make it unsuitable for this purpose. However, in practice, medical imaging professionals and authors of peer-reviewed medical publications frequently and incorrectly use E as a surrogate for whole-body dose in order to calculate cancer risk estimates for specific patients or patient populations. This frequent misuse has popularized E for uses for which it was neither designed nor intended. Alternatives to E have been proposed that attempt to account for known age and sex differences in radiation sensitivity. E has also been proposed as a general indicator for communicating radiation risk to patients, if its limitations are kept in mind. Forthcoming guidance from the International Commission on Radiological Protection will likely clarify if, when, and how some form of E may be used as a rough indicator of the risk of a stochastic effect, possibly with some modifications for the substantial variations in risk known to exist with respect to age, sex, and population group.

Purpose: The determination of absorbed dose to water from external beam radiotherapy using radiation detectors is currently rooted in calibration protocols that do not account for modulations encountered in patient-specific deliveries. Detector response in composite clinical fields has not been extensively studied due to the time and effort required to determine these corrections on a case-by-case basis. To help bridge this gap in knowledge, corrections for the Exradin A1SL scanning chamber were determined in a large number of composite clinical fields using Monte Carlo methods. The chamber-specific perturbations that contribute the most to the overall correction factor were also determined., Methods: A total of 131 patient deliveries comprised of 834 beams from a Varian C-arm linear accelerator were converted to EGSnrc Monte Carlo inputs. A validated BEAMnrc 21EX linear accelerator model was used as a particle source throughout the EGSnrc simulations. Composite field dose distributions were compared against a commercial treatment planning system for validation. The simulation geometry consisted of a cylindrically symmetric water-equivalent phantom with the Exradin A1SL scanning chamber embedded inside. Various chamber perturbation factors were investigated in the egs&#95;chamber user code of EGSnrc and were compared to reference field conditions to determine the plan-specific correction factor., Results: The simulation results indicated that the Exradin A1SL scanning chamber is suitable to use as an absolute dosimeter within a high-dose and low-gradient target region in most nonstandard composite fields; however, there are still individual cases that require larger delivery-specific corrections. The volume averaging and replacement perturbations showed the largest impact on the overall plan-specific correction factor for the Exradin A1SL scanning chamber, and both volumetric modulated arc therapy (VMAT) and step-and-shoot beams demonstrated similar correction factor magnitudes among the data investigated. Total correction magnitudes greater than 2% were required by 9.1% of step-and-shoot beams and 14.5% of VMAT beams. When examining full composite plan deliveries as opposed to individual beams, 0.0% of composite step-and-shoot plans and 2.6% of composite VMAT plans required correction magnitudes greater than 2%., Conclusions: The A1SL scanning chamber was found to be suitable to use for absolute dosimetry in high-dose and low-gradient dose regions of composite IMRT plans but even if a composite dose distribution is large compared to the detector used, a correction-free absorbed dose-to-water measurement is not guaranteed., (© 2018 American Association of Physicists in Medicine.)

MRI guided radiotherapy devices are currently in clinical use. Detector responses are affected by the magnetic field and need to be characterized in terms of absorbed dose to water, D w , against primary standards under these conditions. The aim of this study was to commission a water calorimeter, accepted as the Dutch national standard for D w in MV photons and to validate its claimed standard uncertainty of 0.37% in the 7 MV photon beam of a pre-clinical MRI-linac in a 1.5 T magnetic field. To evaluate the primary standard on a fundamental basis, realisation of D w at 1.5 T was evaluated parameter by parameter. A thermodynamic description was given to demonstrate potential temperature effects due to the magneto-caloric effect (MCE). Methods were developed for measurement of depth, variation in detector distance and beam output in the bore of the MRI-linac. This resulted in D w measurements with a magnetic field of 1.5 T and, after ramp-down, without magnetic field. It was shown that the measurement of ΔT w and calorimeter corrections are either independent of or can be determined in a magnetic field. The chemical heat defect, h, was considered zero within its stated uncertainty, as for 0 T. Evaluation of the MCE and measurements done during magnet ramp-down, indicated no changes in the specific heat capacity of water. However, variations of the applied monitor system increased the uncertainty on beam output normalization. This study confirmed that the uncertainty for measurement of D w with a water calorimeter in a 1.5 T magnetic field is estimated to be the same as under conventional reference conditions. The VSL water calorimeter can be applied as a primary standard for D w in magnetic fields and is currently the only primary standard operable in a magnetic field that provides direct access to the international traceability framework.

Purpose: Refinement of radiomic results and methodologies is required to ensure progression of the field. In this work, we establish a set of safeguards designed to improve and support current radiomic methodologies through detailed analysis of a radiomic signature., Methods: A radiomic model (MW2018) was fitted and externally validated using features extracted from previously reported lung and head and neck (H&N) cancer datasets using gross-tumour-volume contours, as well as from images with randomly permuted voxel index values; i.e. images without meaningful texture. To determine MW2018's added benefit, the prognostic accuracy of tumour volume alone was calculated as a baseline., Results: MW2018 had an external validation concordance index (c-index) of 0.64. However, a similar performance was achieved using features extracted from images with randomized signal intensities (c-index = 0.64 and 0.60 for H&N and lung, respectively). Tumour volume had a c-index = 0.64 and correlated strongly with three of the four model features. It was determined that the signature was a surrogate for tumour volume and that intensity and texture values were not pertinent for prognostication., Conclusion: Our experiments reveal vulnerabilities in radiomic signature development processes and suggest safeguards that can be used to refine methodologies, and ensure productive radiomic development using objective and independent features., (Copyright © 2018 The Author(s). Published by Elsevier B.V. All rights reserved.)

Aim: The aim of this study is to commission and validate the portal dosimetry (PD) system using an indirect method for flattening filter free (FFF) photon beam of the upgraded c-series linear accelerator., Background: Varian Medical System clinacs with amorphous-silicon portal imager panel (aSi-1000) do not have PD for FFF beams. Recently, our c-series linear accelerator was upgraded to deliver 6MV FFF (6MVFFF) photon beam with the highest dose rate of 1400 monitor unit (MU)/min. The study, therefore, focuses on the commissioning and validation of PD for the 6MVFFF beam., Materials and Methods: An indirect method was implemented to predict the portal dose for FFF beam in Eclipse as the treatment planning system does not have direct prediction algorithm for FFF beam (version. 11). Dosimetrical characteristics of aSi-electronic portal imaging device (EPID) were evaluated for 6MVFFF beam and validation of PD for 6MVFFF beam was performed for open fields along with pretreatment quality assurance of intensity-modulated radiation therapy (IMRT), volumetric-modulated arc therapy (VMAT), and stereotactic radiosurgery (SRS) techniques for 30 patients planned with 6MVFFF beam., Results: ASi-EPID saturates between 100 and 130 cm source to detector distance (SDD) for 6MVFFF beam and resolved at more than 140 cm SDD. The squared correlation coefficient (R 2 ) for MU linearity was found to be 1 (R 2 = 1), and instantaneous dose response linearity at different SDD's was found to be 0.999 (R 2 = 0.999) for the 6MVFFF beam. Maximum gamma area index (GAI) for 3% dose difference and 3 mm distance-to-agreement criteria for IMRT, VMAT, and SRS/stereotactic radiotherapy plans was 97.9% ± 0.3%, 96.3% ± 0.5%, and 98.2% ± 0.2%, respectively., Conclusion: The results reveal that this novel method can be used to commission portal dosimetry for 6MVFFF beam as it is a convenient, faster, and accurate method., Competing Interests: None

Objectives: To statistically determine an 'optimum number of CT scanners' for obtaining 'diagnostic reference levels' (DRLs) in CT examinations as close as possible to 'ideal DRLs' when all available CT scanners are considered., Methods: First, six 'ideal DRLs' (CTDI Vol and DLP) were determined for head, chest and abdomen/pelvis examinations by using patient-dose survey data of 100 CT scanners of different models in Tehran. Then, a 'random sampling method' was applied to different percent fractions of patient dose data of 100 CT scanners. The percent differences (PD) of the DRLs obtained from 'ideal DRLs' and their coefficients of variation (CVs) were calculated. The 'optimum number of CT scanners' determined met those of 'ideal DRL' criteria; i.e. precision (CV ≤ 10%) and accuracy (PD ≤ 10%)., Results: 'Optimum number of CT scanners' for determining DRLs as close as possible to 'ideal DRLs', fulfilling the stated criteria, is 43 instead of using 100., Conclusion: 'Optimum number of CT scanners' for obtaining DRLs as close as possible to 'ideal DRLs' was determined. This optimum number can be effectively applied in patient-dose survey situations with limited resources in a time- and cost-effective manner., Key Points: • Ideal DRLs were determined by a CT patient-dose survey applied to available scanners. • 'Optimum number of CT scanners' statistically determined for DRLs is 43%. • Optimum number can be used for DRLs as if 'ideal DRLs' were determined by all scanners.

Purpose: The QA team of the Japan carbon-ion radiation oncology study group (J-CROS) was organized in 2015 to enhance confidence in the accuracy of clinical dosimetry and ensure that the facility QA procedures are adequate. The team conducted onsite dosimetry audits in all the carbon-ion radiation therapy centers in Japan., Materials and Methods: A special phantom was fabricated for the onsite dosimetry audit. Target volumes such as the GTV, CTV, and PTV were contoured to the obtained CT images, and two plans with different isocenter depths were created. The dose at the isocenter was measured by an ionization chamber, in the onsite audit and compared with the calculated dose., Results: For all the centers, the average of the percentage ratio between the measured and calculated doses (measured/calculated) was 0.5% (-2.7% to +2.6%) and the standard deviation, 1.7%. In all the centers, the beams were within the set tolerance level of 3%., Conclusions: The audit demonstrated that the dose at a single point in the water phantom was within tolerance, but it is a big step to say that all doses are correct. In addition, this external dosimetry audit encouraged centers to improve the quality of their dosimetry systems., (© 2018 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)

Objective: This study aims to benchmark a Monte Carlo (MC) model of the 18 MV photon beam produced by the Siemens Oncor® linac using the BEAMnrc and DOSXYZnrc codes., Methods: By matching the percentage depth doses and beam profiles calculated by MC simulations with measurements, the initial electron beam parameters including electron energy, full width at half maximum (spatial FWHM), and mean angular spread were derived for the 10×10 cm2 and 20×20 cm2 field sizes. The MC model of the 18 MV photon beam was then validated against the measurements for different field sizes (5×5, 30×30 and 40×40 cm2) by gamma index analysis., Results: The optimum values for electron energy, spatial FWHM and mean angular spread were 14.2 MeV, 0.08 cm and 0.8 degree, respectively. The MC simulations yielded the comparable measurement results of these optimum parameters. The gamma passing rates (with acceptance criteria of 1% /1 mm) for percentage depth doses were found to be 100% for all field sizes. For cross-line profiles, the gamma passing rates were 100%, 97%, 95%, 96% and 95% for 5×5, 10×10, 20×20, 30×30 and 40×40 cm2 field sizes, respectively., Conclusions: By validation of the MC model of Siemens Oncor® linac using various field sizes, it was found that both dose profiles of small and large field sizes were very sensitive to the changes in spatial FWHM and mean angular spread of the primary electron beam from the bending magnet. Hence, it is recommended that both small and large field sizes of the 18 MV photon beams should be considered in the Monte Carlo linac modeling.

After years of establishment of computed radiography (CR) and digital radiography (DR), manufacturers have introduced exposure indicator/index (EI) as a feedback mechanism for patient dose. However, EI consistency is uncertain for CR. Most manufacturers recommended EI values in a range of numbers for all examination, instead of giving the exact range for a specific body part, raising a concern of inappropriate exposure given to the patient in clinical practice. The aims of this study were to investigate the EI consistency in DR systems produced in constant exposure parameters and clinical condition, and to determine the interaction between the anatomical part and EI. A phantom study of skull, chest, abdomen and hand was carried out and four systems were used for comparison-Fuji CR, Carestream CR, Siemens DR and Carestream DR. For each projection, the phantom positioning and exposure parameters were set according to the standard clinical practice. All exposure parameters and clinical conditions were kept constant. Twenty (20) exposures were taken for each projection and the EI was recorded. Findings showed that EI is not consistent in DR systems despite constant exposure parameters and clinical condition except in Siemens DR, through skull examination. Statistical analysis showed a significant interaction between anatomical parts and EI values (P < 0.05). EI alone was proven to be less reliable to provide technologist a correct feedback on exposure level. The interaction between anatomical parts and EI values intensifies the need for an anatomical-specific EI values set by all manufacturers for accurate feedback on the exposure parameters used and the detector entrance dose.

Objectives: A nationwide survey was performed assessing current practice of dose data analysis in computed tomography (CT)., Material and Methods: All radiological departments in Switzerland were asked to participate in the on-line survey composed of 19 questions (16 multiple choice, 3 free text). It consisted of four sections: (1) general information on the department, (2) dose data analysis, (3) use of a dose management software (DMS) and (4) radiation protection activities., Results: In total, 152 out of 241 Swiss radiological departments filled in the whole questionnaire (return rate, 63%). Seventy-nine per cent of the departments (n = 120/152) analyse dose data on a regular basis with considerable heterogeneity in the frequency (1-2 times per year, 45%, n = 54/120; every month, 35%, n = 42/120) and method of analysis. Manual analysis is carried out by 58% (n = 70/120) compared with 42% (n = 50/120) of departments using a DMS. Purchase of a DMS is planned by 43% (n = 30/70) of the departments with manual analysis. Real-time analysis of dose data is performed by 42% (n = 21/50) of the departments with a DMS; however, residents can access the DMS in clinical routine only in 20% (n = 10/50) of the departments. An interdisciplinary dose team, which among other things communicates dose data internally (63%, n = 76/120) and externally, is already implemented in 57% (n = 68/120) departments., Conclusion: Swiss radiological departments are committed to radiation safety. However, there is high heterogeneity among them regarding the frequency and method of dose data analysis as well as the use of DMS and radiation protection activities., Key Points: • Swiss radiological departments are committed to and interest in radiation safety as proven by a 63% return rate of the survey. • Seventy-nine per cent of departments analyse dose data on a regular basis with differences in the frequency and method of analysis: 42% use a dose management software, while 58% currently perform manual dose data analysis. Of the latter, 43% plan to buy a dose management software. • Currently, only 25% of the departments add radiation exposure data to the final CT report.

The results of the comparison between SSDL-ININ and SSDL-CPHR (pilot laboratory) demonstrates the competence of the SSDL-ININ for the performance of the KR in 192Ir. The RININ/CHPR ratio for the calibration coefficients is 0.989 ± 0.005. The comparison uses three SI-HDR 1000-Plus as transfer chambers, series: A02423, A941755 and A973052. CPHR used a secondary standard PTW 3304 chamber, s/n 154, calibrated at PTB and ININ employed a secondary standard SI-90008 s/n A963391, calibrated at NPL. To determine KR, the SSDL-CPHR used the IAEA TEC-DOC-1274 and the SSDL-ININ used the IPEM (UK) code of practice. The latter uses a correction factor by source's geometry, ksg. The results show that both codes are equivalent; however, for the use of well chambers in the highlands or in locations with reduced atmospheric pressure, it is needed to apply an additional factor k'P, or, to design a well chamber with air-equivalent walls for the application of the conventional kPT.

The Australasian College of Physical Scientists and Engineers in Medicine (ACPSEM) Radiation Oncology Specialty Group (ROSG) formed a series of working groups to develop recommendations for guidance of radiation oncology medical physics practice within the Australasian setting. These recommendations provide a standard for safe work practices and quality control. It is the responsibility of the medical physicist to ensure that locally available equipment and procedures are sufficiently sensitive to establish compliance. The recommendations are endorsed by the ROSG, have been subject to independent expert reviews and have also been approved by the ACPSEM Council. For the Australian audience, these recommendations should be read in conjunction with the Tripartite Radiation Oncology Practice Standards and should be read in conjunction with relevant national, state or territory legislation which take precedence over the ACPSEM publication Radiation Oncology Reform Implementation Committee (RORIC) Quality Working Group, RANZCR, 2011a; Kron et al. Clin Oncol 27(6):325-329, 2015; Radiation Oncology Reform Implementation Committee (RORIC) Quality Working Group, RANZCR, 2018a, b).

International dosimetry protocols are based on determinations of absorbed dose to water. Ideally, the phantom material should be water equivalent; that is, it should have the same absorption and scatter properties as water. This study presents theoretical, experimental and Monte Carlo modeling of water-equivalence of Fricke and polymer (NIPAM, PAGAT and itaconic acid ITABIS) gel dosimeters. Mass and electronic densities along with effective atomic number were calculated by means of theoretical approaches. Samples were scanned by standard computed tomography. Photon mass attenuation coefficients and electron stopping powers were examined. Theoretical, Monte Carlo and experimental results confirmed good water-equivalence for all gel dosimeters. Overall variations with respect to water in the low energy radiology range (up to 130 kVp) were found to be less than 3% in average., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

For adult patients with diffuse low-grade glioma (LGG) proton therapy is an emerging radiotherapy modality. The number of proton facilities is rapidly increasing. However, there is a shortage of published data concerning the clinical effectiveness compared to photon radiotherapy and potential proton-specific toxicity. This study aimed to systematically review and summarize the relevant literature on proton therapy for adult LGG patients, including dosimetric comparisons, the type and frequency of acute and long-term toxicity and the clinical effectiveness. A systematic search was performed in several medical databases and 601 articles were screened for relevance. Nine articles were deemed eligible for in-depth analysis using a standardized data collection form by two independent researchers. Proton treatment plans compared favorably to photon-plans regarding dose to uninvolved neural tissue. Fatigue (27-100%), alopecia (37-85%), local erythema (78-85%) and headache (27-75%) were among the most common acute toxicities. One study reported no significant long-term cognitive impairments. Limited data was available on long-term survival. One study reported a 5-year overall survival of 84% and 5-year progression-free survival of 40%. We conclude that published data from clinical studies using proton therapy for adults with LGG are scarce. As the technique becomes more available, controlled clinical studies are urgently warranted to determine if the potential benefits based on comparative treatment planning translate into clinical benefits., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Proper characterization of Cs sources used for dosimeter calibration and performance testing is crucial for accurate and precise knowledge of air kerma rate and delivered dose. A 269 GBq Cs source was relocated to a new facility, which had a footprint of approximately 2.8 m × 3.6 m and a 3.4 m high ceiling. A small room size, such as in the new facility, may significantly increase backscatter from the walls or room return. Due to the limited source strength, a relatively close irradiation position of 1.00 m from the source was selected to decrease required exposure times. Proximity to the small but cylindrical source has the potential to alter the 1/r relationship (inverse square law) of air kerma rate with distance associated with point sources. Practical tutorials concerning dosimetry irradiation facilities are largely absent from the archival literature. For those reasons, standard characterization experiments were repeated multiple times, great care was taken with positioning, several experiments were added to the standard ones, an ion chamber and dosimeters were used rather than film for greater accuracy and precision, and practical details of the process were recorded. The impacts of room size and finite source dimensions were quantified and mitigated by the efforts reported here. Recommendations for simple but thorough facility characterization, beam calibration, and quality control resulted.

Purpose: To assess the efficiency of combined use of ArcCheck ® detector (AC) and portal dosimetry (PDIP) for delivery quality assurance of head and neck and prostate volumetric-modulated arc therapy., Materials and Methods: Measurement processes were studied with the Gamma index method according to three analysis protocols. The detection sensitivity to technical errors of each individual or combined measurement processes was studied by inserting collimator, dose and MLC opening error into five head and neck and five prostate initial treatment plans. A total of 220 plans were created and 660 analyses were conducted by comparing measurements to error free planned dose matrix., Results: For head and neck localization, collimator errors could be detected from 2° for AC and 3° for PDIP. Dose and MLC errors could be detected from 2% and 0.5 mm for AC and PDIP. Depending on the analysis protocol, the detection sensitivity of total simulated errors ranged from 54% to 88% for AC vs 40% to 74% for PDIP and 58% to 92% for the combined process. For the prostate localization, collimator errors could be detected from 4° for AC while they could not be detected by PDIP. Dose and MLC errors could be detected from 3% and 0.5 mm for AC and PDIP. The detection sensitivity of total simulated errors ranged from 30% to 56% for AC vs 16% to 38% for PDIP and 30% to 58% for combined process., Conclusion: The combined use of the two measurement processes did not statistically improve the detectability of technical errors compared to use of single process., (© 2018 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)

Purpose: A joint IAEA/AAPM international working group has developed a Code of Practice (CoP) for the dosimetry of small static fields used in external megavoltage photon beam radiotherapy, published by the IAEA as TRS-483. This summary paper introduces and outlines the main aspects of the CoP., Methods: IAEA TRS-483 is a condensation of the wide range of different approaches that have been described in the literature for the reference dosimetry of radiotherapy machines with nominal accelerating potential up to 10 MV that cannot establish the conventional 10 cm × 10 cm reference field, and for the determination of field output factors for relative dosimetry in small static photon fields. The formalism used is based on that developed by Alfonso et al. [Med Phys. 2008;35:5179-5186] for this modality., Results: Three introductory sections describe the rationale and context of the CoP, the clinical use of small photon fields, and the physics of small-field dosimetry. In the fourth section, definitions of terms that are specific to the CoP (as compared to previous CoPs for broad-beam reference dosimetry, such as IAEA TRS-398 and AAPM TG-51) are given; this section includes a list of the symbols and equivalences between IAEA and AAPM nomenclature to facilitate the practical implementation of the CoP by end users of IAEA TRS-398 and AAPM TG-51. The fifth section summarizes the equations and procedures that are recommended in the CoP and the sixth section provides an overview of the methods used to derive the data provided in IAEA TRS-483., Conclusions: This is the first time an international Code of Practice for the dosimetry of small photon fields based on comprehensive data and correction factors has been published. This joint IAEA/AAPM CoP will ensure consistent reference dosimetry traceable to the international System of Units and enable common and internationally harmonized procedures to be followed by radiotherapy centers worldwide for the dosimetry of small static megavoltage photon fields., (© 2018 American Association of Physicists in Medicine.)

A Fano cavity test was performed for four general-purpose Monte Carlo codes, EGSnrc, PENELOPE, MCNP6 and Geant4 to evaluate the accuracy of their electron transport algorithms in magnetic fields. In the simulations, a plane-parallel ionization chamber was modelled as a circular gas disk sandwiched between two circular solid wall disks. It was assumed that an isotropic and uniform line source per unit mass along the central axis of the gas and solid emits mono-energetic electrons with energies 0.01, 0.1, 1.0 and 3.0 MeV at different magnetic field strengths 0, 0.35, 1.0, 1.5 and 3.0 T in the electron transport mode (no Bremsstrahlung). The relative difference between the calculated dose to the gas region and the initial total energy of emitted electrons per unit mass was defined as the accuracy of Monte Carlo codes. In all results, EGSnrc with the enhanced electric and magnetic field (EEMF) macros was not considerably sensitive to the step size parameters and showed accuracy less than 0.18%  ±  0.06% with a coverage factor k  =  2. The other codes could not achieve competent accuracy with their default settings of step size parameters, compared to EGSnrc with the EEMF macros. With the step size parameters carefully selected, the accuracy of PENELOPE and MCNP6 was within 1.0% and 0.4%, respectively. However, Geant4 showed accuracy within 1.7% except in 3.0 T. EGSnrc with the EEMF macros achieved the best accuracy for the Fano test at the electron energies and the magnetic field strengths investigated in this study and thus, would be recommended to simulate dose responses of ionization chambers in the presence of magnetic fields.

Cerenkov light is created in clinical applications involving high-energy radiation such as in radiation therapy. There is considerable interest in using Cerenkov light as a means to perform in vivo dosimetry during radiation therapy; however, a better understanding of the light-to-dose relationship is needed. One such method to solve this relationship is that of a deconvolution formulation, which relies on the Cerenkov scatter function (CSF). The CSF describes the creation of Cerenkov photons by a pencil beam of high-energy radiation, and the subsequent scattering that occurs before emission from the irradiated medium surface. This study investigated the dependence of the CSF on common radiation beam parameters (beam energy and incident angle) and the type of irradiated medium. An analytical equation with fitting coefficients of the CSF was obtained for common beam energies in a stratified skin model and optical phantom. Perturbation analysis was performed to investigate the dependence of the deconvolved Cerenkov images on the full-width at half-maximum and amplitude of the CSF. The irradiated material and beam angle had a large impact on the deconvolution process, whereas the beam energy had little effect., ((2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).)

In 2005, the International Commission on Radiological Protection (ICRP) decided to create a new committee, Committee 5, to take charge of the Commission's work on environmental radiological protection. Committee 5 was tasked with ensuring that the system for environmental radiological protection would be reconcilable with that for radiological protection of humans, and with the approaches used for protection of the environment from other potential hazards. The task was completed over three consecutive terms, resulting in inclusion of protection of the environment in the 2007 Recommendations; in ICRP Publications 108 and 114 where the concept of Reference Animals and Plants (RAPs) and their corresponding data were described; in ICRP Publication 124 on how to apply the system in planned, existing, and emergency exposure situations; and in publications on improved dosimetry (ICRP Publication 136) and ecologically relevant 'weighting factors' for different types of radiation (being finalised for public consultation). With the beginning of this new term, ICRP has moved to integrate its approach to protection of humans and the environment within the system of radiological protection by tasking aspects of an integrated system to each of the committees. Acknowledging that Committee 5 had fulfilled its mission, in 2016, ICRP revised the mandates for the committees effective of 1 July 2017 (the mandate for Committee 3 was also widened to include exposures incurred in veterinary practice). ICRP is moving towards the future, building on the previous successes, and will under these revised mandates approach radiological protection in a holistic manner (an integrated system) where appropriate consideration is given to the understanding of exposures and effects in the environment under different exposure situations and scenarios, and what protective actions might be warranted under such circumstances.

Phantoms simulating the human body play a central role in radiation dosimetry. The first computational body phantoms were based upon mathematical expressions describing idealised body organs. With the advent of more powerful computers in the 1980s, voxel phantoms have been developed. Being based on three-dimensional images of individuals, they offer a more realistic anatomy. Hence, the International Commission on Radiological Protection (ICRP) decided to construct voxel phantoms representative of the adult Reference Male and Reference Female for the update of organ dose coefficients. Further work on phantom development has focused on phantoms that combine the realism of patient-based voxel phantoms with the flexibility of mathematical phantoms, so-called 'boundary representation' (BREP) phantoms. This phantom type has been chosen for the ICRP family of paediatric reference phantoms. Due to the limited voxel resolution of the adult reference computational phantoms, smaller tissues, such as the lens of the eye, skin, and micron-thick target tissues in the respiratory and alimentary tract regions, could not be segmented properly. In this context, ICRP Committee 2 initiated a research project with the goal of producing replicas of the ICRP Publication 110 phantoms in polygon mesh format, including all source and target regions, even those with micron resolution. BREP phantoms of the fetus and the pregnant female at various stages of gestation complete the phantoms available for radiation protection computations.

Since the early 1980s, the European Radiation Dosimetry Group (EURADOS) has been maintaining a network of institutions interested in the dosimetry of ionising radiation. As of 2017, this network includes more than 70 institutions (research centres, dosimetry services, university institutes, etc.), and the EURADOS database lists more than 500 scientists who contribute to the EURADOS mission, which is to promote research and technical development in dosimetry and its implementation into practice, and to contribute to harmonisation of dosimetry in Europe and its conformance with international practices. The EURADOS working programme is organised into eight working groups dealing with environmental, computational, internal, and retrospective dosimetry; dosimetry in medical imaging; dosimetry in radiotherapy; dosimetry in high-energy radiation fields; and harmonisation of individual monitoring. Results are published as freely available EURADOS reports and in the peer-reviewed scientific literature. Moreover, EURADOS organises winter schools and training courses on various aspects relevant for radiation dosimetry, and formulates the strategic research needs in dosimetry important for Europe. This paper gives an overview on the most important EURADOS activities. More details can be found at www.eurados.org .

European Radiation Dosimetry Group (EURADOS) Working Group 7 is a network on internal dosimetry that brings together researchers from more than 60 institutions in 21 countries. The work of the group is organised into task groups that focus on different aspects, such as development and implementation of biokinetic models (e.g. for diethylenetriamine penta-acetic acid decorporation therapy), individual monitoring and the dose assessment process, Monte Carlo simulations for internal dosimetry, uncertainties in internal dosimetry, and internal microdosimetry. Several intercomparison exercises and training courses have been organised. The IDEAS guidelines, which describe - based on the International Commission on Radiological Protection's (ICRP) biokinetic models and dose coefficients - a structured approach to the assessment of internal doses from monitoring data, are maintained and updated by the group. In addition, Technical Recommendations for Monitoring Individuals for Occupational Intakes of Radionuclides have been elaborated on behalf of the European Commission, DG-ENER (TECHREC Project, 2014-2016, coordinated by EURADOS). Quality assurance of the ICRP biokinetic models by calculation of retention and excretion functions for different scenarios has been performed and feedback was provided to ICRP. An uncertainty study of the recent caesium biokinetic model quantified the overall uncertainties, and identified the sensitive parameters of the model. A report with guidance on the application of ICRP biokinetic models and dose coefficients is being drafted at present. These and other examples of the group's activities, which complement the work of ICRP, are presented.

The X-band in vivo EPR tooth dosimetry is promising as a tool for the initial triage after a large-scale radiation accident. The dielectric losses caused by water on the tooth surface (WTS) are one of the major sources of inaccuracies in this method. The effect was studied by theoretical simulation calculations and experiments with water films of various thicknesses on teeth. The results demonstrate the possibility of sufficiently accurate measurements of the radiation-induced signal of the tooth enamel provided that the thickness of the water film on the tooth is below 60 µm. The sensitivity of the cavity decreases with increasing thickness of the water layer. The interference of WTS can be diminished by normalization of the radiation-induced signal to the signal of a reference sample permanently present in the cavity., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Purpose: Conventional techniques (3D-CRT) for craniospinal irradiation (CSI) are still widely used. Modern techniques (IMRT, VMAT, TomoTherapy ® , proton pencil beam scanning [PBS]) are applied in a limited number of centers. For a 14-year-old patient, we aimed to compare dose distributions of five CSI techniques applied across Europe and generated according to the participating institute protocols, therefore representing daily practice., Material and Methods: A multicenter (n = 15) dosimetric analysis of five different techniques for CSI (3D-CRT, IMRT, VMAT, TomoTherapy ® , PBS; 3 centers per technique) was performed using the same patient data, set of delineations and dose prescription (36.0/1.8 Gy). Different treatment plans were optimized based on the same planning target volume margin. All participating institutes returned their best treatment plan applicable in clinic., Results: The modern radiotherapy techniques investigated resulted in superior conformity/homogeneity-indices (CI/HI), particularly in the spinal part of the target (CI: 3D-CRT:0.3 vs. modern:0.6; HI: 3D-CRT:0.2 vs. modern:0.1), and demonstrated a decreased dose to the thyroid, heart, esophagus and pancreas. Dose reductions of >10.0 Gy were observed with PBS compared to modern photon techniques for parotid glands, thyroid and pancreas. Following this technique, a wide range in dosimetry among centers using the same technique was observed (e.g., thyroid mean dose: VMAT: 5.6-24.6 Gy; PBS: 0.3-10.1 Gy)., Conclusions: The investigated modern radiotherapy techniques demonstrate superior dosimetric results compared to 3D-CRT. The lowest mean dose for organs at risk is obtained with proton therapy. However, for a large number of organs ranges in mean doses were wide and overlapping between techniques making it difficult to recommend one radiotherapy technique over another.

The aim of this study was to investigate the feasibility and sensitivity of using individual volume-based 3D gamma indices for composite dose-volume histogram (DVH)-based intensity-modulated radiation therapy (IMRT) quality assurance (QA). Composite IMRT QA for 15 cervical cancer patients was performed with ArcCHECK. The percentage dosimetric errors (%DEs) of DVH metrics when comparing treatment planning system and QA-reconstructed dose distribution, percentage gamma passing rates (%GPs) with different criteria for individual volumes and global gamma indices were evaluated, as well as their correlations. Receiver operating characteristic (ROC) curves were applied in order to study the sensitivities of the global and individual volume gamma indices. Most %DEs of the DVH metrics were within 3%. The γPTV and γrectum were <80% at 2%/2 mm; apart from these two individual volume indices, all other individual volume gamma indices and global indices had acceptable %GPs. For the criteria of 2%/2 mm, 3%/3 mm and 4%/4 mm, individual volume-based %GPs and global %GPs were correlated in 11, 1 and 12 out of 24 %DE metrics, and in 5, 4 and 5 out of 24 %DE metrics, respectively. Individual volume-based %GPs had a higher percentage of correlation with DVH metrics (%DEs) compared with global %GPs in composite IMRT QA. The areas under the curve (AUCs) of individual volume %GPs were higher than those of global %GPs. In conclusion, individual volume-based %GPs had a higher correlation with %DEs of metrics and a higher sensitivity presented by ROC analysis compared with global %GPs for composite IMRT QA. Thus, use of individual volume-based 3D gamma indices was found to be feasible and sensitive for composite IMRT QA.

Objective: Recent well-publicized sentinel events have resulted in an appropriately heightened awareness of CT dose. Concern also exists regarding the potential of CT dose increasing the risk of cancer. Several professional societies, governmental and accreditation agencies, and CT vendors have responded to these concerns with campaigns, mandatory standards, and software enhancements. The objective of this article is to review such CT dose management efforts., Conclusion: Although CT dose awareness campaigns, mandatory standards, and software enhancements are well intentioned, their implementation is often suboptimal.

The first aim of this study has been to extend the systematic experimental study of the field size dependence of the output factor correction for three micro-ionization chambers (PTW 31014, PTW 31022 and IBA Razor chamber), two silicon diodes (PTW 60017 and IBA Razor Diode) and the synthetic diamond detector microDiamond (PTW 60019) in a 6 MV photon beam down to an effective field side length of 2.6mm, and to summarize the present knowledge of this factor by treating it as a function of the dosimetric field size. In order to vary the dosimetric field size over this large range, output factors measurements were performed at source-to-surface distances of 60cm and 90cm. Since the output factors obtained with the organic scintillation detector Exradin W1 (Standard Imaging, Middleton, USA) at all field sizes closely agreed with those measured by EBT3 radiochromic films (ISP Corp, Wayne, USA), the scintillation detector served as the reference detector. The measured output correction factors reflect the influences of the volume averaging and density effects upon the uncorrected output factor values. In case of the microDiamond detector these opposing influences result in output factor correction values less than 1 for moderately small field sizes and larger than 1 for very small field sizes. Our results agree with most of the published experimental as well as Monte-Carlo simulated data within detector-specific limits of uncertainty. The dosimetric field side length has been identified as a reliable determinant of the output factor correction, and typical functional curve shapes of the field-size dependent output factor correction vs. dosimetric field side length have been associated with gas-filled, silicon diode and synthetic diamond detectors. The second aim of this study has been a novel, semi-empirical approach to calculate the field-size dependent output correction factors of small photon detectors by convolving film measured true dose profile data with measured lateral response functions of the detectors. To achieve this, the set of previously published 2D lateral dose response functions was complemented by those of the novel detectors PTW PinPoint chamber 31022 (PTW Freiburg, Freiburg, Germany), Razor chamber and Razor Diode (IBA Dosimetry, Schwarzenbruck, Germany). The output correction factors calculated from the lateral dose response functions closely fit with the directly measured output correction factors, thus supporting the latter by an independent method., (Copyright © 2018. Published by Elsevier GmbH.)

Low-level neutron measurements are required for applications such as environmental monitoring, measurements of weak sources and the determination of neutron fluxes at underground laboratories. When analyzing low-level neutron measurements, it is important to be able to distinguish the signal due to neutrons from any background term that may originate within the detector. A solution to this problem has been developed for the case of measurements carried out with 3He spherical proportional counters of the type which are often used in Bonner sphere spectrometers. To determine this background, measurements were carried out in the former UDO underground laboratory of the Physikalisch-Technische Bundesanstalt located in the Asse salt mine. The analysis of the data was carried out using Bayesian parameter estimation. The result of the analysis is a very general parameterised function that can be used to describe the pulse height spectrum due to the background of the proportional counters.

Purpose: The present study aimed to define the errors in SUV and demonstrate the feasibility of SUV harmonization among contemporary PET/CT scanners using a novel National Institute of Standards and Technology (NIST)-traceable 68 Ge/ 68 Ga source as the reference standard., Methods: We used 68 Ge/ 68 Ga dose calibrator and PET sources made with same batch of 68 Ge/ 68 Ga embedded in epoxy that is traceable to the NIST standard. Bias in the amount of radioactivity and the radioactive concentrations measured by the dose calibrators and PET/CT scanners, respectively, was determined at five Japanese sites. We adjusted optimal dial setting of the dose calibrators and PET reconstruction parameters to close the actual amount of radioactivity and the radioactive concentration, respectively, of the NIST-traceable 68 Ge/ 68 Ga sources to harmonize SUV. Errors in SUV before and after harmonization were then calculated at each site., Results: The average bias in the amount of radioactivity and the radioactive concentrations measured by dose calibrator and PET scanner was -4.94% and -12.22%, respectively, before, and -0.14% and -4.81%, respectively, after harmonization. Corresponding averaged errors in SUV measured under clinical conditions were underestimated by 7.66%, but improved by -4.70% under optimal conditions., Conclusion: Our proposed method using an NIST-traceable 68 Ge/ 68 Ga source identified bias in values obtained using dose calibrators and PET scanners, and reduced SUV variability to within 5% across different models of PET scanners at five sites. Our protocol using a standard source has considerable potential for harmonizing the SUV when contemporary PET scanners are involved in multicenter studies., (Copyright © 2018 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.)

A diagnostic reference level is an advisory dose level set by a regulatory authority in a country as an efficient criterion for protection of patients from unwanted medical exposure. In computed tomography, the direct dose measurement and data collection methods are commonly applied for determination of diagnostic reference levels. Recently, a new quality-control-based dose survey method was proposed by the authors to simplify the diagnostic reference-level determination using a retrospective quality control database usually available at a regulatory authority in a country. In line with such a development, a prospective dual-purpose quality control dosimetry protocol is proposed for determination of diagnostic reference levels in a country, which can be simply applied by quality control service providers. This new proposed method was applied to five computed tomography scanners in Shiraz, Iran, and diagnostic reference levels for head, abdomen/pelvis, sinus, chest, and lumbar spine examinations were determined. The results were compared to those obtained by the data collection and quality-control-based dose survey methods, carried out in parallel in this study, and were found to agree well within approximately 6%. This is highly acceptable for quality-control-based methods according to International Atomic Energy Agency tolerance levels (±20%).

In 2016 the ICRU published a new report dealing with key data for ionizing radiation dosimetry (ICRU Report 90). New recommendations have been made for the mean excitation energies I for air, graphite and liquid water as well as for the graphite density to use when evaluating the density effect. In addition, the ICRU Report 90 discusses renormalized photoelectric cross sections, but refuses to give a recommendation on the use of renormalization factors. However, the Consultative Committee for Ionizing Radiation recommends to use renormalized photoeffect cross sections. Goal of the present work is to evaluate the impact of these new recommendations on clinical reference dosimetry for high energy photon and electron beams. The beam quality correction factor k Q was calculated by Monte Carlo simulations for compact and parallel plate ionization chambers. In case of photons seven phase space files from clinical accelerators and twelve spectra taken from literature from 4 MV to 24 MV and additionally a 60 Co source were applied. As electron source thirteen electron spectra available in literature were used in the range of 4 MeV-21 MeV. The new ICRU recommendations have a small impact on Monte Carlo calculated k Q values for the chosen ionization chambers in the range of 0.1%-0.35% only-the difference increases for higher photon energies. The impact of the ICRU Report 90 recommendations on Monte Carlo calculated stopping power ratios s w,a , perturbation factors p and beam quality correction factors k Q was investigated and confirmed a decrese of s w,a by a fraction of a percent for photon and electron beams. This study indicates that the impact of the new ICRU recommendation is within 0.35%. The determined deviations should be taken into account, when widely published Monte Carlo calculated values are examined.

The neutron autoradiography technique using polycarbonate nuclear track detectors (NTD) has been extended to quantify the boron concentration in hard tissues, an application of special interest in Boron Neutron Capture Therapy (BNCT). Chemical and mechanical processing methods to prepare thin tissue sections as required by this technique have been explored. Four different decalcification methods governed by slow and fast kinetics were tested in boron-loaded bones. Due to the significant loss of the boron content, this technique was discarded. On the contrary, mechanical manipulation to obtain bone powder and tissue sections of tens of microns thick proved reproducible and suitable, ensuring a proper conservation of the boron content in the samples. A calibration curve that relates the 10 B concentration of a bone sample and the track density in a Lexan NTD is presented. Bone powder embedded in boric acid solution with known boron concentrations between 0 and 100 ppm was used as a standard material. The samples, contained in slim Lexan cases, were exposed to a neutron fluence of 10 12 cm -2 at the thermal column central facility of the RA-3 reactor (Argentina). The revealed tracks in the NTD were counted with an image processing software. The effect of track overlapping was studied and corresponding corrections were implemented in the presented calibration curve. Stochastic simulations of the track densities produced by the products of the 10 B thermal neutron capture reaction for different boron concentrations in bone were performed and compared with the experimental results. The remarkable agreement between the two curves suggested the suitability of the obtained experimental calibration curve. This neutron autoradiography technique was finally applied to determine the boron concentration in pulverized and compact bone samples coming from a sheep experimental model. The obtained results for both type of samples agreed with boron measurements carried out by ICP-OES within experimental uncertainties. The fact that the histological structure of bone sections remains preserved allows for future boron microdistribution analysis., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A generic formalism is proposed for reference dosimetry in the presence of a magnetic field. Besides the regular correction factors from the conventional reference dosimetry formalisms, two factors are used to take into account magnetic field effects: (1) a dose conversion factor to correct for the change in local dose distribution and (2) a correction of the reading of the dosimeter used for the reference dosimetry measurements. The formalism was applied to the Elekta MRI-Linac, for which the 1.5 T magnetic field is orthogonal to the 7 MV photon beam. For this setup at reference conditions it was shown that the dose decreases with increasing magnetic field strength. The reduction in local dose for a 1.5 T transverse field, compared to no field is 0.51%  ±  0.03% at the reference point of 10 cm depth. The effect of the magnetic field on the reading of the dosimeter was measured for two waterproof ionization chambers types (PTW 30013 and IBA FC65-G) before and after multiple ramp-up and ramp-downs of the magnetic field. The chambers were aligned perpendicular and parallel to the magnetic field. The corrections of the readings of the perpendicularly aligned chambers were 0.967  ±  0.002 and 0.957  ±  0.002 for respectively the PTW and IBA ionization chambers. In the parallel alignment the corrections were small; 0.997  ±  0.001 and 1.002  ±  0.003 for the PTW and IBA chamber respectively. The change in reading due to the magnetic field can be measured by individual departments. The proposed formalism can be used to determine the correction factors needed to establish the absorbed dose in a magnetic field. It requires Monte Carlo simulations of the local dose and measurements of the response of the dosimeter. The formalism was successfully implemented for the MRI-Linac and is applicable for other field strengths and geometries.

Treatment of small skin lesions using HDR brachytherapy applicators is a widely used technique. The shielded applicators currently available in clinical practice are based on a tungsten-alloy cup that collimates the source-emitted radiation into a small region, hence protecting nearby tissues. The goal of this manuscript is to evaluate the correction factors required for dose measurements with a plane-parallel ionization chamber typically used in clinical brachytherapy for the 'Valencia' and 'large field Valencia' shielded applicators. Monte Carlo simulations have been performed using the PENELOPE-2014 system to determine the absorbed dose deposited in a water phantom and in the chamber active volume with a Type A uncertainty of the order of 0.1%. The average energies of the photon spectra arriving at the surface of the water phantom differ by approximately 10%, being 384 keV for the 'Valencia' and 343 keV for the 'large field Valencia'. The ionization chamber correction factors have been obtained for both applicators using three methods, their values depending on the applicator being considered. Using a depth-independent global chamber perturbation correction factor and no shift of the effective point of measurement yields depth-dose differences of up to 1% for the 'Valencia' applicator. Calculations using a depth-dependent global perturbation factor, or a shift of the effective point of measurement combined with a constant partial perturbation factor, result in differences of about 0.1% for both applicators. The results emphasize the relevance of carrying out detailed Monte Carlo studies for each shielded brachytherapy applicator and ionization chamber.

Purpose: To study correlations between dose-volume parameters of the whole bladder and bladder trigone and late urinary toxicity in locally advanced cervical cancer patients treated with pulsed-dose-rate brachytherapy., Methods and Materials: Patients with locally advanced cervical cancer treated with chemoradiation therapy and pulsed-dose-rate brachytherapy from 2004 to 2015 were included. Cumulative dose-volume parameters of the whole bladder and bladder trigone were converted into 2-Gy/fraction equivalents (EQD2, with α/β = 3 Gy); these parameters, as well as clinical factors, were analyzed as predictors of toxicity in patients without local relapse., Results: A total of 297 patients fulfilled the inclusion criteria. The median follow-up period was 4.9 years (95% confidence interval 4.5-5.3 years). In patients without local relapse (n = 251), the Kaplan-Meier estimated grade 2 or higher urinary toxicity rates at 3 years and 5 years were 25.4% and 32.1%, respectively. Minimal dose to the most exposed 2 cm 3 of the whole bladder [Formula: see text] , bladder International Commission on Radiation Units & Measurements (ICRU) (B ICRU ) dose, and trigone dose-volume parameters correlated with grade 2 or higher toxicity. At 3 years, the cumulative incidence of grade 2 or higher complications was 22.8% (standard error, 2.9%) for bladder [Formula: see text]  < 80 Gy EQD2 versus 61.8% (standard error, 12.7%) for [Formula: see text]  ≥ 80 Gy EQD2 (P = .001). In the subgroup of patients with bladder [Formula: see text]  ≤ 80 Gy EQD2 , a trigone dose delivered to 50% of the volume (D 50% ) > 60 Gy EQD2 was significant for grade 2 or higher toxicity (P = .027). The probability of grade 3 or higher toxicities increased with bladder [Formula: see text]  > 80 Gy EQD2 (16.7% vs 1.6%; hazard ratio [HR], 5.77; P = .039), B ICRU dose > 65 Gy EQD2 (4.9% vs 1.3%; HR, 6.36; P = .018), and trigone D 50%  > 60 Gy EQD2 (3.1% vs 1.2%; HR, 6.29; P = .028). Pearson correlation coefficients showed a moderate correlation between bladder [Formula: see text] , B ICRU dose, and bladder trigone D 50% (P < .0001)., Conclusions: These data suggest that [Formula: see text]  ≤ 80 Gy EQD2 should be advised for minimizing the risk of severe urinary complications (<15%). Bladder trigone dose was also predictive of severe late urinary toxicity. These constraints need further confirmation in a multicenter prospective setting., (Copyright © 2018 Elsevier Inc. All rights reserved.)

Purpose: Reference dosimetry data can provide an independent second check of acquired values when commissioning or validating a treatment planning system (TPS). The Imaging and Radiation Oncology Core at Houston (IROC-Houston) has measured numerous linear accelerators throughout its existence. The results of those measurements are given here, comparing accelerators and the agreement of measurement versus institutional TPS calculations., Methods: Data from IROC-Houston on-site reviews from 2000 through 2014 were analyzed for all Elekta accelerators, approximately 50. For each, consistent point dose measurements were conducted for several basic parameters in a water phantom, including percentage depth dose, output factors, small-field output factors, off-axis factors, and wedge factors. The results were compared by accelerator type independently for 6, 10, 15, and 18 MV. Distributions of the measurements for each parameter are given, providing the mean and standard deviation. Each accelerator's measurements were also compared to its corresponding TPS calculation from the institution to determine the level of agreement, as well as determining which dosimetric parameters were most often in error., Results: Accelerators were grouped by head type and reference dosimetric values were compiled. No class of linac had better overall agreement with its TPS, but percentage depth dose and output factors commonly agreed well, while small-field output factors, off-axis factors, and wedge factors often disagreed substantially from their TPS calculations., Conclusion: Reference data has been collected and analyzed for numerous Elekta linacs, which provide an independent way for a physicist to double-check their own measurements to prevent gross treatment errors. In addition, treatment planning parameters more often in error have been highlighted, providing practical caution for physicists commissioning treatment planning systems for Elekta linacs., (© 2018 American Association of Physicists in Medicine.)