Equivalent Dose Distributions Research Articles

Bayesian analysis of De distributions in optical dating: Towards a robust method for dealing with outliers

In optical dating, especially single-grain dating, various patterns of distributions in equivalent dose (D e ) are usually observed and analysed using different statistical models. None of these methods, however, is designed to deal with outliers that do not form part of the population of grains associated with the event of interest (the ‘target population’), despite outliers being commonly present in single-grain D e distributions. In this paper, we present a Bayesian method for detecting D e outliers and making allowance for them when estimating the D e value of the target population. We test this so-called Bayesian outlier model (BOM) using data sets obtained for individual grains of quartz from sediments deposited in a variety of settings, and in simulations. We find that the BOM is suitable for single-grain D e distributions containing outliers that, for a variety of reasons, do not form part of the target population. For example, D e outliers may be associated with grains that have undesirable luminescence properties (e.g., thermal instability, high rates of anomalous fading) or with contaminant grains incorporated into a sample when collected in the field or prepared in the laboratory. Grains that have much larger or smaller D e values than the target population, due to factors such as insufficient bleaching, beta-dose heterogeneity or post-depositional disturbance, may also be identified as outliers using the BOM, enabling these values to be weighted appropriately for final D e and age determination. • A Bayesian outlier model (BOM) for luminescence dating of sediments. • Outliers are identified in single-grain equivalent dose (D e ) distributions. • Outliers are weighted appropriately for final D e and age determination. • Three special cases (BOM central, minimum and maximum) for different contexts. • Tested on well-bleached, partially bleached and post-depositionally mixed samples.

Stopping power and CSDA range calculations of electrons and positrons over the 20 eV–1 GeV energy range in some water equivalent polymer gel dosimeters

In this study, the stopping power, CSDA range and radiation yield calculations of electrons and positrons over the 20 eV–1 GeV energy range in some water equivalent polymer gel dosimeters were performed. For collision stopping power calculations of electrons and positrons the effective charge concept proposed by Sugiyama were considered. Here, both the effective charge of incident electrons and positrons (z*) and the effective charge (Z*) and the effective mean excitation energy (I*) of the target material were calculated. For the density effect correction the Fano model was selected. For the radiative stopping power analytical model based on the ratio between the collision and the radiative stopping power discribed by Attix was considered. For CSDA range and radition yield the continuous slowing down approximation (CSDA) was considered and the calculations were performed using numerical integral methods. Because of their water equivalent and 3D dose distribution properties, MAGIC and MAGAS polymer gels were selected as a target materials. The calculations were performed by programming all the equations discribed in this study as a computational code. The results of the stopping power, range and radiation yield were compared with those of ESTAR program and PENELOPE Monte Carlo modelling. Some deviations in low and high energy region between the calculated and reference data were observed. However, the similarity between calculated and reference data is remarkable. For the collision stopping power and CSDA range a good agreement between the calculated and reference data was observed for energies >1 keV. Whereas, for the radiative stopping power a good agreement was observed for energies >100 keV.

In silico study on radiobiological efficacy of Ac-225 and Lu-177 for PSMA-guided radiotherapy.

The good efficacy of radioligand therapy (RLT) targeting prostate specific-membrane antigen (PSMA) for the treatment of metastatic castration-resistant prostate cancer (mCRPC) has been recently demonstrated in several clinical studies. However, the treatment effect of 177Lu-PSMA-ligands is still suboptimal for a significant fraction of patients. In contrast to external beam radiotherapy, the radiation dose distribution itself is strongly influenced by the heterogeneous tumour microenvironment. Although microdosimetry is critical for RLT treatment outcome, it is difficult to clinically or experimentally establish the quantitative relation. We propose an in silico approach to quantitatively investigate the microdosimetry and its influence on treatment outcome for PSMA-directed RLT of two different radioisotopes 177Lu and 225 Ac. The ultimate goal is optimize the combined 177 Lu and 225 Ac-PSMA therapy and maximize the anti-tumour effect, while minimizing irradiation of off-target tissues.Clinical relevance- With the proposed hybrid model we show that 177Lu-PSMA-ligands treatment assures a more homogeneously distributed dose and a lower dependency of the treatment outcome on the domain vascularisation. On the other hand, the 225Ac-PSMA-ligands treatment shows a much stronger efficacy in killing tumor cells with an equivalent mean dose distribution even in an hypoxic environment.

ASSESSMENT OF RADIATION DOSE OF MOBILE COMPUTED TOMOGRAPHY IN INTENSIVE CARE UNITS.

Intra-hospital transport is associated with fatal risks for the occupants of an intensive care unit (ICU). Thus, mobile CT is used in ICUs. In this study, two-dimensional equivalent dose distribution data were expanded using the inverse square law of distance to identify the potential exposure of radiologic technologists and public and the maximum number of possible daily CT procedures. The exposure dose at 1.5m from the isocentre of the mobile CT was 2.260μSv. Based on the dose limitation (5mSv/yr for controlled area and 1mSv/yr for uncontrolled area) as per National Council on Radiation Protection and Measurement report, the number of possible scans per day was 9 for radiologic technologists and 2 for public. When using the radiation shielding partition with a lead equivalent of 0.3 mmPb, the exposure dose reduced as 0.399μSv. Therefore, mobile CT can be used in ICUs when appropriate shielding is provided.

The Transport History of Alluvial Fan Sediment Inferred From Multiple Geochronometers

AbstractWe present a multi‐chronometer approach to refine the age of an alluvial fan and to infer sediment transport and deposition history in the Anza Borrego Desert region of Southern California. We measure in situ produced cosmogenic carbon‐14 (14C) from boulders on the fan surface and infrared stimulated luminescence (IRSL) ages from single feldspar grains within the alluvium. Our new IRSL age [5.3 ± 0.5 ka (±1σ)] is in excellent agreement with existing uranium‐series [U‐series; 5.3 ± 0.2 (±2σ)] ages of pedogenic carbonates. The IRSL and U‐series ages show that in situ 14C measurements [6.6 ± 1.1 ka (±1σ)] from boulders contain inherited nuclides from prior exposure in the upstream catchment, much like measurements of the longer‐lived nuclide, beryllium‐10 (10Be). However, in situ 14C ages are closer to the preferred ages inferred from IRSL and U‐series and with less scatter than comparative 10Be ages. Our data demonstrate that a multi‐geochronometer approach will produce ages of alluvial fan surfaces with the greatest degree of confidence. We then apply the paired 14C and 10Be concentrations to infer the prior exposure and storage duration of the sampled boulders of 3.1 ± 3.2 and 4.6 ± 2.3 Kyr, respectively. A mixture model analysis of the single grain IRSL ages suggests bimodal storage durations prior to remobilization with peaks at ca. 2 and 10 Kyr. We demonstrate that cosmogenic nuclide inheritance and single grain IRSL equivalent dose distributions can provide additional information regarding sediment transport history prior to deposition on the alluvial fan.

Improvement of analysis results from the GAGG scintillator Compton camera operated on an unmanned helicopter by selecting stable flight conditions

ABSTRACT A Compton camera system for use on an unmanned helicopter was previously developed to characterize the distribution of radioactive materials in highly contaminated areas. For this study, a Compton camera system was equipped with a small camera, laser distance meter, an attitude angle sensor, temperature sensors, and real-time monitoring software for better measurement of flight parameters and more precise detection of hot spot locations. To confirm whether the detection results were improved by the modifications, ground-level ambient dose equivalent rate distributions were derived from hovering and programmed flights over a field in Okuma, Fukushima Prefecture (Japan) and compared against readings from survey meters taken at the ground level. For one hovering flight, the correlation between the datasets was improved by selecting a period of stable flight position and attitude and restricting the deviation of the attitude angles. Between 6.0% and 7.6% improvement in the position resolution was achieved using the data from stable flight periods, even when only 1-minute data windows were used. The precision of hot spot detections and ambient dose equivalent rate distributions obtained from the Compton camera were thus improved by the aforementioned modifications to the system.

Research on Individualized Phantom Based on 3D Printing for Radiotherapy Dose Verification

Dose verification is carried out on the individualized three-dimensional phantom based on 3D printing technology, which simulates the anatomical structure of human body, contour shape, tumor anatomical structure and other dangerous organs to the greatest extent, and produces a reasonable and effective dose validation phantom. According to the need to obtain effective patient data, import Mimics software to reconstruct the parts of the body and its surrounding tissues and organs that need to be measured, and make them into three-dimensional shell components. The 3D printing is used to assemble and fill the equivalent tissue, and then the body phantom is made. The phantom was scanned by CT and the data was transmitted to TPS system. The previously completed treatment plan was transplanted to the phantom. The phantom was placed according to the patient's location information, irradiated and measured data. The three-dimensional shell assembly is completely reconstructed according to the patient's data, and the contour difference is not significant. The shell is filled with tissue radiation equivalent material whose CT value is the same as the average CT value of the shell volume. The CT image data show that the radiation equivalence of the phantom is similar to the actual tissue of the patient, and the equivalent dose distribution conforms to the conventional treatment range. It can provide a reliable means of dose verification for the accurate design of intensity modulated radiation therapy.

Using deep learning to model the biological dose prediction on bulky lung cancer patients of partial stereotactic ablation radiotherapy

To develop a biological dose prediction model considering tissue bio-reactions in addition to patient anatomy for achieving a more comprehensive evaluation of tumor control and promoting the automatic planning of bulky lung cancer. A database containing images and partial stereotactic ablation boost radiotherapy (P-SABR) plans of 94 bulky lung cancer patients was studied. Patient-specific parameters of gross tumor boost volume (GTVb), planning gross target volume (PGTV), and identified organs at risk (OARs) were extracted via Numpy and simple ITK. The original dose and structure maps for P-SABR patients were resampled to have a voxel resolution of 3.9×3.9×3mm3 . Biological equivalent dose (BED) distributions were reprogrammed based on physical dose volumes. A developed deep learning architecture, Nestnet, was adopted as the training framework. We utilized two approaches for data organization to correlate the structures and BED: (a) BED programming before training model (B-Nestnet); (b) BED programming after the training process (D-B Nestnet). The early-stop mechanism was adopted on the validation set to avoid overfitting. The evaluation criteria of predictive accuracy contain the minimum BED of GTVb and PGTV, the maximum and the mean BED of all targets, BED-volume metrics. For comparison, we also used the original Unet for BED prediction. The absolute differences were statistically analyzed with the paired-samples t test. The statistical outcomes demonstrate that D-B Nestnet model predicts biological dose distributions accurately. The average absolute biases of [max, mean] BED for GTVb, PGTV are [2.1%, 3.3%] and [2.1%, 4.7%], respectively. Averaging across most of OARs, the D-B Nestnet model is capable of predicting the errors of the max and mean BED within 6.3% and 6.1%, respectively. While the compared models performed worse with averaged max and mean BED prediction errors surpassing 10% on some specific OARs. The study developed a D-B Nestnet model capable of predicting BED distribution accurately for bulky lung cancer patients in P-SABR. The predicted BED map enables a quick intuitive evaluation of tumor ablation, modification of the ablation range to improve BED of tumor targets, and quality assessment. It represents a major step forward toward automated P-SABR planning on bulky lung cancer in real clinical practice.

Modelling heterogeneously bleached single-grain equivalent dose distributions: Implications for the reliability of burial dose determination

Abstract In optical dating, incomplete and heterogeneous resetting (“bleaching”) of the luminescence signal measured from mineral grains since the last episode of transport and deposition is commonly observed for sedimentary samples. As a result, different grains could have different equivalent dose (De) values at the time of deposition. For such samples, statistical treatment of the De distribution is required to estimate the burial dose. This study aims to assess the reliability of burial dose determination for heterogeneously bleached samples using the minimum age model (MAM). We modeled heterogeneous bleaching processes under various bleaching scenarios and simulated the resulting single-grain De distributions using a Monte Carlo method. Various factors that could potentially affect the reliability of burial dose estimates are investigated, including the distribution of residual dose, proportion of fully bleached grains, baseline dose, sample size, and unaccounted between-grain standard deviation. The simulation results reveal that the performance of the model depends primarily on the residual dose distribution. The proportion of fully bleached grains has the most influence on the reliability of MAM burial dose estimates.

Analyzing Statistical Age Models to Determine the Equivalent Dose and Burial Age Using a Markov Chain Monte Carlo Method

In optically stimulated luminescence (OSL) dating, statistical age models for equivalent dose (D<sub>e</sub>) distributions are routinely estimated using the maximum likelihood estimation (MLE) method. In this study, a Markov chain Monte Carlo (MCMC) method was used to analyze statistical age models, including the central age model (CAM), the minimum age model (MAM), the maximum age model (MXAM), <i>etc.</i> This method was first used to obtain sampling distributions on parameters of interest in an age model using D<sub>e</sub> distributions from individual sedimentary samples and subsequently extended to simultaneously extract age estimates from multiple samples with stratigraphic constraints. The MCMC method allows for the use of Bayesian inference to refine chronological sequences from multiple samples, including both fully and partially bleached OSL dates. This study designed easily implemented open-source numeric programs to perform MCMC sampling. Measured and simulated D<sub>e</sub> distributions are used to validate the reliability of dose (age) estimates obtained by this method. Findings from this study demonstrate that estimates obtained by the MCMC method can be used to informatively compare results obtained by the MLE method. The application of statistical age models to multiple OSL dates with stratigraphic orders using the MCMC method may significantly improve both the precision and accuracy of burial ages.

The Characteristic of Profile and Depth Dose of Neutron Clinac iX 15 MV

Several previous studies described that radiation neutrons are produced by 10 MV X-ray beams operated linac. This study was performed to exercise the characteristic of profile and neutron depth dose for 15 MV X-ray beams and also to evaluate the contribution of neutron dose to the patient. The experiment used Linac iX with 15 MV X-ray beam, TLD-100, TLD-600, and phantom. The phantom was designed to evaluate the dose profile at cross-plane and diagonal axis. TLDs were calibrated separately by gamma and neutron sources. Gamma calibration was carried out using 137Cs source whereas neutron calibration was done using 252Cf source at BATAN Facility. Neutron dose equivalents were calculated on cross-plane and diagonal axis in 10 cm × 10 cm fields at 15 positions from the central axis, on the phantom surface and depths of 2 cm, 3 cm, and 15 cm. The percentage maximum neutron dose equivalent distributions were obtained around of 3 cm depth for cross-plane and diagonal axis. Furthermore, the dose profile of neutron at different depths and off-axis position are not symmetrical. Neutron dose in out-of-field had no significant response compared to the in-field. The relative neutron dose in out-of-field is 27% and 24% normalized to the maximum neutron dose at each depth on cross-plane and diagonal axis respectively.

Reconstruction of residents\u2019 thyroid equivalent doses from internal radionuclides after the Fukushima Daiichi nuclear power station accident

There is concern among residents that their children might suffer from thyroid cancer in the near future after the Fukushima Daiichi nuclear power station (FDNPS) accident. However, the demographic and geographical distribution of thyroid equivalent doses was not thoroughly evaluated, and direct thyroid measurements were conducted only for 1,200 children, whose individual thyroid doses were assessed on the basis of those measurements accounting for the dynamics of radioiodine intake. We conducted hierarchical clustering analyses of 100 or 300 randomly sampled behavioural questionnaire sheets of children from each of seven municipalities in the evacuation area to reconstruct evacuation scenarios associated with high or low exposures to plumes. In total 896 behaviour records in the Fukushima Health Management Survey were analysed to estimate thyroid equivalent doses via inhalation, using a spatiotemporal radionuclides concentration database constructed by atmospheric dispersion simulations. After a decontamination factor for sheltering and a modifying factor for the dose coefficient—to reflect lower iodine uptake rate in Japanese—were applied, estimated thyroid equivalent doses were close to those estimated from direct thyroid measurement. The median and 95th percentile of thyroid equivalent doses of 1-year-old children ranged from 0.6 to 16 mSv and from 7.5 to 30 mSv, respectively. These results are useful for future epidemiological studies of thyroid cancer in Fukushima.

The Potential Role of Intensity-Modulated Proton Therapy in Hepatic Carcinoma in Mitigating the Risk of Dose De-Escalation

Purpose:To investigate the role of intensity-modulated proton therapy (IMPT) for hepatocellular carcinoma (HCC) patients to be treated with stereotactic body radiation therapy (SBRT) in a risk-adapted dose prescription regimen.Methods:A cohort of 30 patients was retrospectively selected as “at-risk” of dose de-escalation due to the proximity of the target volumes to dose-limiting healthy structures. IMPT plans were compared to volumetric modulated arc therapy (VMAT) RapidArc (RA) plans. The maximum dose prescription foreseen was 75 Gy in 3 fractions. The dosimetric analysis was performed on several quantitative metrics on the target volumes and organs at risk to identify the relative improvement of IMPT over VMAT and to determine if IMPT could mitigate the need of dose reduction and quantify the consequent potential patient accrual rate for protons.Results:IMPT and VMAT plans resulted in equivalent target dose distributions: both could ensure the required coverage for CTV and PTV. Systematic and significant improvements were observed with IMPT for all organs at risk and metrics. An average gain of 9.0 ± 11.6, 8.5 ± 7.7, 5.9 ± 7.1, 4.2 ± 6.4, 8.9 ± 7.1, 6.7 ± 7.5 Gy was found in the near-to-maximum doses for the ribs, chest wall, heart, duodenum, stomach and bowel bag respectively. Twenty patients violated one or more binding constraints with RA, while only 2 with IMPT. For all these patients, some dose de-intensification would have been required to respect the constraints. For photons, the maximum allowed dose ranged from 15.0 to 20.63 Gy per fraction while for the 2 proton cases it would have been 18.75 or 20.63 Gy.Conclusion:The results of this in-silico planning study suggests that IMPT might result in advantages compared to photon-based VMAT for HCC patients to be treated with ablative SBRT. In particular, the dosimetric characteristics of protons may avoid the need for dose de-escalation in a risk-adapted prescription regimen for those patients with lesions located in proximity of dose-limiting healthy structures. Depending on the selection thresholds, the number of patients eligible for treatment at the full dose can be significantly increased with protons.

Simple and Rapid Creation of Customized 3D Printed Bolus Utilizing iPhone X True Depth Camera

Three-dimensional (3D) printing has effectively produced patient-specific bolus materials during radiation treatment for superficial tumors along irregular skin surfaces. Traditional bolus materials in comparison, are often difficult to manipulate for proper fit, and can be difficult to reproduce. Current 3D printed boluses are made from either pre-existing computed tomography (CT) scans or complex surface scanning methods. Here, we introduce an inexpensive, convenient approach to generating 3D printed bolus from surface scanning technology available in common smartphones. 3D printed bolus was designed using surface scans from iphone X true depth cameras and a low cost 3D printer. The percentage density infill was adjusted to achieve tissue equivalence. To evaluate the clinical feasibility, fit against skin surface and radiation dose distribution was compared to traditional bolus. We fabricated customized 3D printed bolus for different areas of the face utilizing an iphone X camera and an inexpensive commercially available 3D printer. When printed at 100% density this bolus material approximated soft tissue/water and provided an equivalent dose distribution to that found with standard bolus materials on direct comparison. The bolus material was inexpensive and produces an ideal fit with the scanned anatomy. We present a simplified method of highly customized bolus production that requires minimal experience with computer modeling programs and can be accomplished with an iphone true depth camera.

Luminescence dating of sediments from central Atacama Desert, northern Chile

Abstract This study examines the feasibility of applying luminescence dating methods to quartz and potassium feldspar (K-feldspar) grains from Quaternary continental deposits of the Mejillones Peninsula and Coastal Cordillera in Central Atacama, northern Chile. Sediment burial ages were calculated using single-aliquot regenerative-dose (SAR) protocols applied to the optically stimulated luminescence (OSL) signal of quartz as well as infrared stimulated luminescence (IRSL) and post-infrared infrared stimulated luminescence (post-IR IRSL) signals of K-feldspar. Considering that the target sedimentary deposits comprise the Late Pleistocene age range, K-feldspar grains were dated using fading-corrected IRSL signals measured at 50 °C (IR50) and post-IR IRSL measured at 225 °C (pIRIR225) to minimize the potential effect of residual doses on calculated ages. The results of the analytical procedures indicate that quartz grains extracted from the studied sediments present a very weak or even no fast OSL component. The combination of a low OSL sensitivity, signal instability and equivalent dose distributions with high overdispersion (>40% for most samples) hinder reliable age estimation using quartz aliquots. Bleaching test results show that the IR50 signal from K-feldspar aliquots is well reset after 20–24 h of light exposure, while the pIRIR225 signal may present residual doses corresponding to between 10 and 15% of the natural signal. IR50 fading rates are ∼6–7%/decade for most studied samples, with exception of one sample which yielded a g-value of 18.77 ± 2.06%/decade. Fading rates for the pIRIR225 signal yielded variable results among sampling sites, with g-values ranging between 0.70 ± 0.24 and 6.77 ± 1.05%/decade. The dating results point out that quartz OSL ages are largely underestimated in relation to K-feldspar fading-corrected IR50 and pIRIR225 ages. Fading-corrected pIRIR225 K-feldspar ages indicate that the alluvial sedimentation in the downthrown block of an active normal fault in Mejillones Peninsula occurred between 163.4 ± 18.4 ka and 87.4 ± 6.6 ka. K-feldspar ages also allow to constrain the age of fault scarp degradation and fault reactivation in two main branches of the Atacama Fault System. In the Naguayan Fault, pIRIR225 ages indicate that faulting occurred after 21.4 ± 3.2 ka while in the Salar del Carmen Fault, faulting is recorded after 14.7 ± 1.0 ka.

Simple and Rapid Creation of Customized 3-dimensional Printed Bolus Using iPhone X True Depth Camera

PurposeThree-dimensional printing has produced customized bolus during radiation therapy for superficial tumors along irregular skin surfaces. In comparison, traditional bolus materials are often difficult to manipulate for a proper fit. Current 3-dimensional printed boluses are made from either preexisting computed tomography scans or complex surface scanning methods. Herein, we introduce an inexpensive, convenient approach to generate a 3-dimensional printed bolus from surface scanning technology available in common smartphones. Methods and materialsA three-dimensional printed bolus was designed using surface scans from iPhone X true depth cameras and a low-cost 3-dimensional printer. The percentage density infill was adjusted to achieve tissue equivalence. To evaluate the clinical feasibility, fit against the skin surface and radiation dose distribution were compared with those of the traditional bolus. ResultsWe fabricated a customized 3-dimensional printed bolus for different areas of the face using an iPhone X camera and inexpensive commercially available 3-dimensional printer. When printed at 100% density, the bolus material approximated soft tissue/water and provided an equivalent dose distribution to that found with standard bolus materials on direct comparison. The bolus material is inexpensive and produces an ideal fit with the scanned anatomy. ConclusionsWe present a simplified method of highly customized bolus production that requires minimal experience with computer modeling programs and can be accomplished with an iPhone true depth camera.

RADIATION SHIELDING STUDY FOR THE VERTICAL TEST SYSTEM FOR SUPERCONDUCTING RF CAVITIES.

A vertical test system (VTS) for superconducting radio frequency cavities had been designed and constructed at Peking University. During the test, field emission electrons in the cavity will be accelerated and some of them will hit the flange of cavity with high-energy. These high-energy electrons will have a significant impact on the radiation safety of the system and environment. In this paper, the Particle-in-Cell solver in CST software was used to analyze the behavior of electrons emitted from different field emission positions and found the worst field emission site which deposited the most energy on the cavity wall. The impact information of the electrons emitted from the worst field emission site was utilized to character the source term. Prompt dose equivalent rate distribution and residual radioactivity was predicted by using the Monte Carlo simulation program FLUKA. Further vertical test results are consistent with the simulation results.

Beam shaping assembly study for BNCT facility based on a 2.5\xa0MeV proton accelerator on Li target

A new study for a boron neutron capture therapy irradiation facility, based on a 2.5 MeV proton accelerator on a thick Li target as neutron converter, is presented here. The beam shaping assembly (BSA) modeling has been performed with the use of the MCNP5 Monte Carlo code. The fast (i.e., > 10 keV) neutron component yielded by the 7Li(p,n)7Be reaction is slowed down through TiF3 neutron spectrum shifter, while to obtain a high-quality epithermal neutron beam at the beam port exit additional layers for thermal neutrons removal and shielding of gamma rays were used. Moreover, 60Ni and Ti6Al14V were selected to filter out and further remove the residual fast neutron component, while cadmium was chosen as thermal neutrons absorber, and bismuth was selected for gamma rays shielding. The therapeutic effectiveness of the proposed BSA was evaluated by performing a set of dose-equivalent distribution calculations in a standard Snyder head phantom. The simulation results show that the proposed BSA modeling meets all the recommended by IAEA criteria and provides one possible technical choice for an accelerator-based BNCT irradiation facility in a hospital environment.

Re‑irradiation plus hyperthermia for recurrent pediatric sarcoma; a simulation study to investigate feasibility.

Recurrent pediatric tumors pose a challenge since treatment options may be limited, particularly after previous irradiation. Positive results have been reported for chemotherapy and hyperthermia, but the combination of re‑irradiation and hyperthermia has not been investigated thus far, although it is a proven treatment strategy in adults. The theoretical feasibility of re‑irradiation plus hyperthermia was investigated for infield recurrent pediatric sarcoma in the pelvic region and the extremities. A total of 46recurrent pediatric sarcoma cases diagnosed at the Academic Medical Center (Amsterdam, TheNetherlands) between 2002 and 2017 were evaluated. Patients not previously irradiated, outfield recurrences and locations other than the pelvis and extremities were excluded, ultimately yielding four eligible patients: Two with sarcomas in the pelvis and two in an extremity. Re‑irradiation and hyperthermia treatment plans were simulated for 23x2Gy treatment schedules and weekly hyperthermia. The radiosensitizing effect of hyperthermia was quantified using biological modelling with a temperature‑dependent change in the parameters of the linear‑quadratic model. The possible effectiveness of re‑irradiation plus hyperthermia was estimated by calculating the equivalent radiotherapy dose distribution. Treatment planning revealed that tumors located in the pelvis and the extremities can be effectively heated in children. Equivalent dose distributions indicated that hyperthermic radiosensitization can be quantified as a target‑selective additional D95% of typically 10Gy, thereby delivering a possibly curative dose of 54Gy, without substantially increasing the equivalent dose to the organs at risk. Therefore, re‑irradiation plus hyperthermia is a theoretically feasible and possibly effective treatment option for recurrent pediatric sarcoma in the pelvic region and the extremities, and its clinical feasibility is worthy of evaluation.

OSL over-dispersion: A pilot study for the characterisation of extreme events in the shallow marine realm

Identification of extreme events in the sedimentary record relies on the correct characterisation of the deposit by means of multiple parameters and different diagnostic criteria. Multiple proxies based on well-tested geological, biological, and chemical analyses have been used to distinguish tsunami layers from other marine extreme events. However, few proxies distinguish or compare the “degree of sedimentary chaos” of an event relative to background sediments and between other extreme events. In this pilot study, the potential of Optically Stimulated Luminescence (OSL), normally used as a dating method, is demonstrated and a new potential sedimentological proxy is proposed when analysing in depth the OSL signal from single grain measurements to distinguish between underwater deposits derived from marine extreme events embedded in the texturally and compositionally homogeneous shallow shelf archive of the eastern Mediterranean. Newly and previously collected sediment samples from underwater excavations and a sediment core offshore Caesarea Maritima (Israel) were used in this experiment. Each sample was associated with either tsunami, storm, or fair weather (normal) marine conditions based on multiple proxies. In this study, single grain over-dispersion (SG-OD) values and ranges are used as a potentially novel way to quantify the degree of sedimentary chaos, thus the degree of scatter of the dose distribution as a function of the efficiency of exposure to sunlight (zeroing) of the quartz grains entrained during transport and deposition. Given that turbidity of a fluid should be associated with lower light penetration, and higher energy flow with greater sediment density (as can occur in tsunamis relative to storms), these conditions should be reflected in variations in single grain over-dispersion values, hence identifying luminescence distribution patterns related to known depositional conditions. This quantification is coupled with detailed statistical analysis of the resulting single grain equivalent dose distributions, minimally used in OSL-dating. Three types of underwater deposits were categorised based on three distribution typologies, to which, preliminary, conservative single grain over-dispersion ranges were assigned: <25% for Gaussian-like sands deposited under normal marine conditions; 25–60% for storm-laid sediments depicting bimodal distributions; and >60% for tsunami-related deposits showing asymmetric distributions with strong positive skewness. This new tool provides a means to study offshore extreme marine events, without potential dismissal of other identification criteria and proxies. Based on these results, single grain over-dispersion OSL could be considered as a potential new sedimentological proxy for identification, comparison and characterisation of marine-derived extreme events in the shallow shelf (such as tsunami deposits), as it is intrinsic to the sediment grain, and the degree of sedimentary chaos of the event itself.