Dosimetry Characteristics Research Articles

ESR measurement of carbonated hydroxyapatite for dosemeter.

We have examined a dosimetry characteristic of carbonate hydroxyapatite (CO3HAp), which is a dental bone graft material. The purpose of this work is to investigate the reproducibility and stability of radiation-induced radicals on CO3HAp samples and assess the feasibility of using these materials as dosemeters. CO3HAp samples were exposed to gamma rays with dose range from 10 to 10000Gy. The electron spin resonance (ESR) spectra for irradiated samples were measured. Variation of peak-to-peak amplitude of the ESR signal intensity as a function of absorbed dose for CO3HAp was compared with that for alanine dosemeters, suggesting that the CO3HAp sample has a good linear dose response in the range from 10to 10000Gy as well as does the alanine dosemeters.

Characterization of a Modified Clinical Linear Accelerator for Ultra-High Dose Rate Beam Delivery

Irradiations at Ultra-High Dose Rate (UHDR) regimes, exceeding 40 Gy/s in single fractions lasting less than 200 ms, have shown an equivalent antitumor effect compared to conventional radiotherapy with reduced harm to normal tissues. This work details the hardware and software modifications implemented to deliver 10 MeV UHDR electron beams with a linear accelerator Elekta SL 18 MV and the beam characteristics obtained. GafChromic EBT XD films and an Advanced Markus chamber were used for dosimetry characterization, while a silicon sensor assessed the machine’s beam pulses stability and repeatability. The dose per pulse, average dose rate and instantaneous dose rate in the pulse were evaluated for four experimental settings, varying the source-to-surface distance and the beam collimation, i.e., with and without the use of a cylindrical applicator. The results showed a dose per pulse from 0.6 Gy to a few tens of Gy and an average dose rate up to 300 Gy/s. The obtained results demonstrate the possibility to perform in vitro radiobiology experiments and test new technologies for beam monitoring and dosimetry at the upgraded LINAC, thus contributing to the electron UHDR research field.

Development and characterization of Staphylococcus aureus-hydrogel-based radiation dosimeter

In the search of innovative methods within radiation dosimetry to provide solutions to the high demanding modern ionizing radiation applications, this work proposes an original approach to combine microorganisms and gel dosimetry characteristics by adapting biotechnology and molecular biology procedures. The design of bacterial culture media and the evaluation of viability as systems for radiation dosimetry are reported. In preliminary assessments, a highly promising dose-response has been observed for samples stored at 4 °C, displaying a linear trend within the investigated dose range. This underscores a promising performance, indicating the potential utility of the system as a radiation dosimeter.

Preclinical photon minibeam radiotherapy using a custom collimator: Dosimetry characterization and preliminary in-vivo results on a glioma model

PurposeThe purpose of this study is to investigate the dosimetric characteristics of a collimator for minibeam radiotherapy (MBRT) with film dosimetry and Monte Carlo (MC) simulations. The outcome of MBRT with respect to conventional RT using a glioma preclinical model was also evaluated. MethodsA multi-slit collimator was designed to be used with commercial small animal irradiator. The collimator was built by aligning 0.6 mm wide and 5 mm thick parallel lead leaves at 0.4 mm intervals. Dosimetry characteristics were evaluated by Gafchromic (CG) films and TOPAS Monte Carlo (MC) code.An in vivo experiment was performed using a glioma preclinical model by injecting two million GL261cells subcutaneously and treating with 25 Gy, single fraction, with MBRT and conventional RT. Survival curves and acute radiation damage were measured to compare both treatments. ResultsA satisfactory agreement between experimental results and MC simulations were obtained, the measured FWHM and distance between the peaks were respectively 0.431 and 1.098 mm.In vivo results show that MBRT can provide local tumor control for three weeks after RT treatment and a similar survival fraction of open beam radiotherapy. No severe acute effects were seen for the MBRT group. ConclusionsWe developed a minibeam collimator and presented its dosimetric features. Satisfactory agreement between MC and GC films was found with differences consistent with uncertainties due to fabrication and set-up errors. The survival curves of MBRT and open field RT are similar while atoxicity is dramatically lower with MBRT, preliminarily confirming the expected effect.

Dating the setting of a late prehistoric statue-menhir at Cruz de Cepos, NE Portugal

The emergence of ‘standing stone’ monuments within the European Late Prehistoric landscape is considered to be associated with a pivotal human cultural transition from hunting and gathering to agriculture and permanent settlement, being the earliest monuments currently dated by radiocarbon to the 5th millennium BCE. However, many standing stones were first erected, subsequently collapsed, and then re-erected during the following three millennia. The excavation of the site of an apparently in situ statue-menhir at Cruz de Cepos in NE Portugal provided the rare opportunity in Iberian prehistory to apply radiocarbon and luminescence techniques to establish the date of construction. On the basis of the iconography, the standing stone was assigned to a sculptural tradition of north-western and western Iberia, loosely dated to the Early/Middle Bronze Age (ca. 2000/1900–1250 BCE). The optically stimulated luminescence (OSL) and dosimetry characteristics of quartz extracted from sediment samples taken from locations associated with the socket pit and surrounding backfilling deposits were examined, producing OSL single grain ages at eight locations. Comparison of the OSL and calibrated radiocarbon ages shows very good agreement, with the mid-3rd millennium BCE dates confirming original erection during the Copper Age and not a much later transformation of the monument. These encouraging results indicate that OSL has the potential to provide reliable dating of depositional processes related to the construction process and is suitable for wider application to megalithic monuments of this type.

2109: Ultrahypofractionation in breast cancer: Retrospective study of dosimetry features

2109: Ultrahypofractionation in breast cancer: Retrospective study of dosimetry features

Synthesis and thermoluminescence behavior of novel Sm3+ doped YCa4O(BO3)3 under beta irradiation

This study investigates the luminescent properties and dosimetric potential of YCa4O(BO3)3:0.5%Sm3+ phosphor synthesized via the combustion method. Dose-response investigations unveil a noteworthy linear increment in thermoluminescence (TL) intensity, emphasizing a remarkable linearity spanning a broad dose range from 0.1 to 300 Gy. Unusual heating rate effects are explored, revealing a shift in TL glow curve peak temperature (i.e 200 °C) towards higher temperatures with increasing heating rate. Speculative models, including Kinetic Trapping Effect, Thermal Quenching Compensation, and Defect Activation Energy Changes, are proposed. The study employs the Tmax-Tstop method to identify characterize glow curve peaks, and the Initial Rise method for the low-temperature segment analysis, revealing seven distinct trap levels at various depths within the bandgap. Glow curve deconvolution using the Complex Glow Curve Deconvolution (CGCD) method delineates a multi-peak structure, offering valuable insights into luminescent mechanisms. The model exhibits a Figure of Merit (FOM) of 1.71%, within an acceptable range, affirming its reliability. However, interpretation of the activation energy and frequency factor values suggests intricate site processes, necessitating a nuanced analysis to understand the material's luminescent characteristics. The YCa4O(BO3)3:0.5%Sm3+ phosphor demonstrates promising characteristics for precise dosimetry, with linear dose response, absence of saturation effects, and intriguing heating rate behavior.

Commissioning and clinical evaluation of a novel high-resolution quality assurance digital detector array for SRS and SBRT.

We aimed to perform the commissioning and clinical evaluation of myQA SRS detector array for patient-specific quality assurance (PSQA) of stereotactic radiosurgery (SRS)/ stereotactic body radiotherapy (SBRT) plans. To perform the commissioning of myQA SRS, its dose linearity, dose-rate dependence, angular dependence, and field-size dependence were investigated. Ten SBRT plans were selected for clinical evaluation: 1) Common clinical deviations based on the original SBRT plan (Plan0), including multileaf collimator (MLC) positioning deviation and treatment positioning deviation were introduced. 2) Compared the performance of the myQA SRS and a high-resolution EPID dosimetry system in PSQA measurement for the SBRT plans. Evaluation parameters include gamma passing rate (GPR) and distance-to-agreement (DTA) pass rate (DPR). The dose linearity, angle dependence, and field-size dependence of myQA SRS system exhibit excellent performance. The myQA SRS is highly sensitive in the detection of MLC deviations. The GPR of (3%/1mm) decreases from 90.4% of the original plan to 72.7%/62.9% with an MLC outward/inward deviation of 3mm. Additionally, when the setup error deviates by 1mm in the X, Y, and Z directions with the GPR of (3%/1mm) decreasing by an average of -20.9%, -25.7%, and -24.7%, respectively, and DPR (1mm) decreasing by an average of -33.7%, -32.9%, and -29.8%. Additionally, the myQA SRS has a slightly higher GPR than EPID for PSQA, However, the difference is not statistically significant with the GPR of (3%/1mm) of (average 90.4%% vs. 90.1%, p=0.414). Dosimetry characteristics of the myQA SRS device meets the accuracy and sensitivity requirement of PSQA for SRS/SBRT treatment. The dose rate dependence should be adequately calibrated before its application and a more stringent GPR (3%/1mm) evaluation criterion is suggested when it is used for SRS/SBRT QA.

Synthesis and characterization of high-sensitivity Dy,Eu co-doped CaSO4 thermoluminescent phosphor using coprecipitation technique.

In this work, (99 - x)CaSO4 -Dy2 O3 -xEu2 O3 , (where x = 0, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5) thermoluminescence phosphors were prepared using a coprecipitation method. The thermoluminescence (TL) dosimetry (TLD) characteristics such as TL sensitivity, dose-response, minimum detectable dose, thermal fading, and the effect of sunlight on the prepared phosphors were investigated. The obtained results indicated that the most sensitive phosphor was obtained at x = 0.05. Large thermal fading of 6% after 1 h and 26% after 24 h from irradiation followed by 71% after 1 month with no additional fading was observed within a time frame exceeding 2 months throughout the remaining duration of the investigation, which also spanned over 2 months. Despite the phosphor's high fading rate, the relative sensitivity of the prepared samples was ~90% compared with TLD-100. The marked effect of day sunlight was also determined. High dose-response within the low-dose range from 0.01 to 5 Gy was observed. The obtained results suggested that the synthesized phosphor is well suited for applications involving radiation biology and radiotherapy dosimetry.

Chromium activated Ca9Al (PO4)7 nanophosphors: synthesis, morphology and dosimetry characteristics

In this article, a sol–gel route was employed to prepare nanophosphor materials including Ca9−x CrxAl (PO4)7 series (where 0.05 ≤ x ≤ 0.5 (mol%)). All subseries were irradiated to a γ- test dose of 5 Gy and the thermoluminescence (TL) response of Cr-activated (0.1 mol%) Ca9Al (PO4)7 sample has the best TL response and was chosen for investigations. The phase, particle size, surface morphology, and elemental mapping of the chosen sample Cr0.1 in comparison with other ones (Cr0.05 and Cr0.5) were scrutinized using x-ray diffraction (XRD), transmission electron microscope (TEM), SEM-EDX mapping, and XPS techniques. XRD profiles showed that all diffraction peaks assigned to the trigonal R 3 c space group and the average of particle sizes obtained by the modified Scherer method and TEM data are closely related. The presence of Cr3+ ions in the Ca9Al (PO4)7 lattice was assured by XPS spectra. Cr0.1 chosen sample was studied after irradiation to different γ-doses and displayed a prominent glow curve at 205 °C ± 3.97 °C. It showed a linear dose–response curve from 200 mGy up to 10 Gy with fading of 24% upon 24 h and almost no significant signal loss for further interval times. The average Zeff value was ∼11 at both 662 and 1250 keV energies making this sample a bone-equivalent material (11.3–11.8). Values of activation energies (eV) calculated by different methods were comparable. Results the dosimetric properties of that the Cr0.1 sample can be surely considered as an additional recommended detector as other available ones in marketing.

Investigation of the Dosimetry Characteristics of the GAFCHROMIC® EBT3 Film Response to Alpha Particle Irradiation

The purpose of this study was to investigate the dosimetric characteristics of the GAFCHROMIC® EBT3 film responding to alpha particle irradiation. Unlaminated GAFCHROMIC® EBT3 film pieces, were irradiated with a 30.055 kBq 241Am alpha source, at eight different dose levels, between 0 and 509 Gy. The irradiations were performed inside an enclosed box. Epson Expression 10000 XL scanner in transmission mode was used to digitize irradiated films 24 hours post-irradiations as 16-bit RGB images in tagged image file format (TIFF). Optical density (OD) values were obtained by following the OD theorem. Raw and normalized pixel values (PVnorm) from the red, green, and blue colour channels were sampled from a 3 × 3 mm2 region of interest. Calibration curves were created for both data sets (OD and PVnorm) and were fit accordingly. Monte Carlo simulations with the Geant4 toolkit were performed to establish a dose rate at the point within the sensitive layer of the film. An alpha dosimetry protocol for EBT3 films was obtained from the Monte Carlo calculated dose rate and dose calibration curves for alpha radiation were created. It is necessary to extend this study for different film types and compare to photon dosimetry calibration curves.

Application of the Ion Chamber Array in Magnetic Resonance Accelerator QA

The magnetic resonance accelerator (MR-Linac) is gradually widely used due to high-quality soft tissue contrast and real-time tracking. However, the special dosimetry characteristics and wide field sizes of MR-Linac increase the QA difficulty with conventional measurement method. The purpose of this study was to confirm an ion chamber array could be used for measuring the beam quality, the profiles, as well as the positioning accuracy of all MLC leaves efficiently, by comparing results with the conventional method. To propose a new QA approach for solving the common problem in data acquisition caused by the wide fields of MR-Linac. The research was based on a MR-Linac fixed with 1.5T MR and 7MeV energy photon beam. The conventional QA method adopted the MR water tank with a gantry angle of 0°and an SSD of 133.5 cm, both microdiamond and ionization chamber detector were used to acquire the dose profiles (PDD, inline, crossline and diagonal). Field sizes 1 × 1 cm2, 2 × 2 cm2, 3 × 3 cm2, 5 × 5 cm2, 10 × 10 cm2, 15 × 15 cm2, 22 × 22 cm2, 40 × 22 cm2,57 × 22 cm2 were measured with depth 13mm, 50mm, 100mm for vertical beam. As for the wide fields (larger than 15 × 15 cm2), two profiles of x axis (one from left to right, the other from right to left) needed to be gathered and then stitched into one final profile. A boot phantom with an ionization chamber detector was used for measuring beam quality. We defined the profiles measured by conventional method as the baseline. An ion chamber array was adopted to acquire TPR, PDD, profiles and MLC positioning, comparing to the conventional method. The center of ion chamber array was placed to the isocenter of MR-Linac, the array could move to the right and left offset positions through engaging the pin into correct hole of QA platform, such 'once positioning and twice movements' operation could finish within 3 minutes. The central detector of the ion chamber array was used for measuring beam quality. TPRs for different depths were acquired by stacking solid water on the ion chamber array. As for the profiles, we could get the final profile by 'once positioning and twice movements' efficiently. As for the positioning accuracy of MLC leaves, firstly the central leaf pair was put on y = 0 to measure 'open profile' under the open field. Then we moved the MLC leaves to different positions to get the n profile (n for different leaf positions). The ratio of n profile to open profile could show the positioning accuracy of MLC. We adopted 2D gamma (1mm / 2%) to compare the profiles between the ion chamber array and the conventional method, the results were within 98%. The beam quality consistency of ion chamber array comparing to the wedge tank was within 1% according to daily measurement. The ion chamber array could reflect the MLC positioning differences, the sensitivity was 0.5 mm. The ion chamber array showed a convenient QA method both for the dosimetry and for the MLC positioning accuracy which did reduce the overall measurement time, it was recommended for daily and monthly QA for MR-Linac.

Noninvasive Radiation Markers Based on Lung Cancer CT Images and Dosimetry Features to Predict the Immune Response to Radiotherapy in Tumor Microenvironment

For lung cancer patients with complex conditions, doctors need to determine treatment plan in combination with changes of immune response during radiotherapy. It was urgent to find a strategy to predict immune response to intervene the treatment at an early stage. The radiotherapy process and tumor microenvironment status of 105 lung cancer patients were tracked and recorded in our hospital from 2019 to 2022, public database TCGA-LUAD/LUSC queue of TCIA image data was downloaded as external verification set. Data was analyzed according to the following methods: First, the 3D slicer software was used to process the CT imageomics data, and the doseomics information was calculated by DVHmetrics package from R software. Then Python was brought in to develop a non-invasive radiation scoring system through machine learning methods (T-test, LASSO, random forest and Xgboost). Finally, combined with the clinical information related to the patient's immune response, a nomogram was made to study the correlation between the score markers and the ratio of CD4 cells/CD8 cells in the tumor microenvironment, the prognosis of lung cancer, as well as the incidence of radiation pneumonia. The radiation markers score formula was obtained with CT imageomics and DVH dosimics features, which achieved an AUC of 0.67-0.75 in predicting CD4/CD8 condition in tumor microenvironment after radiotherapy. It was worth noticing that in predicting the prognosis of lung cancer, it was difficult to distinguish between the radiation score and the patient's survival status (P>0.05). However, we found that the radiation pneumonitis of lung cancer patients in the low score group (42.6%) was significantly higher than that in the high score group (13.4%). Radiation markers score was a non-invasive method to evaluate the immune response of patients with lung cancer, which can be used to predict the incidence of radiation pneumonitis.

Preliminary study on dosimetry characteristics of a novel cylindrical dose verification system.

To develop a novel ionization chamber array dosimetry system, study its dosimetry characteristics, and perform preliminary tests for plan dose verification. The dosimetry characteristics of this new array were tested, including short-term and long-term reproducibility, dose linearity, dose rate dependence, field size dependence, and angular dependence. The open field and MLC field plans were designed for dose testing. Randomly select 30 patient treatment plans (10 intensity-modulated radiation therapy [IMRT] plans and 20 volumetric modulated arc therapy [VMAT] plans) that have undergone dose verification using Portal Dosimetry to perform verification measurement and evaluate dose verification test results. The dosimetry characteristics of the arrays all performed well. The gamma passing rates (3%/2mm) were more than 96% for the combined open field and MLC field plans. The average gamma pass rates were (99.54±0.58)% and (96.70±3.41)% for the 10 IMRT plans and (99.32±0.89)% and (94.91±6.01)% for the 20 VMAT plans at the 3%/2mm and 2%/2mm criteria, respectively, which is similar to the Portal Dosimetry's measurement results. This novel ionization chamber array demonstrates good dosimetry characteristics and is suitable for clinical IMRT and VMAT plan verifications.

Effects of Radiofrequency Electromagnetic Field (RF-EMF) exposure on pregnancy and birth outcomes: A systematic review of experimental studies on non-human mammals

Effects of Radiofrequency Electromagnetic Field (RF-EMF) exposure on pregnancy and birth outcomes: A systematic review of experimental studies on non-human mammals

Dosimetry characteristics of Epoxy/MWCNT nanocomposite in the field of gamma-rays: Effect of thickness

Polymer-carbon nanostructures have been used as gamma-ray dosimeters. The thickness of the sensitive volume material plays an important role in the determination of the dosimetry response. In this work, the thickness effect of a real-time dosimeter based on the Epoxy/Multi-walled carbon nanotube (MWCNT) nanocomposite was investigated. The amount of electrical percolation threshold (EPT) for Epoxy/MWCNT nanocomposite was initially simulated using the finite element method. Then, the 0.1 MWCNT wt% nanocomposite was fabricated using a solution method with three thicknesses of 1, 2, and 3 mm. FESEM images demonstrated a good dispersion state of the inclusions into the Epoxy matrix. The samples were irradiated by gamma-rays of Co-60 source over the dose rates of 25–166 mGy/min. In addition, dosimetric characteristics were performed, including linearity, bias-polarity, angular dependence, energy dependence, field size, and repeatability. Results revealed that with increasing the thickness, the dosimetry response was enhanced remarkably.

Determination of small-field output factors for beam-matched linear accelerators using various detectors and comparison of detector-specific output correction factors using IAEA Technical Report Series 483 protocol.

Beam matching is widely used to ensure that linear accelerators used in radiotherapy have equal dosimetry characteristics. Small-field output factors (OF) were measured using different detectors infour beam-matched linear accelerators and the measured OFs were compared with existing treatment planning system (TPS) Monte Carlo algorithm calculated OFs. Three Elekta Versa HDTM and one Elekta InfinityTMlinear accelerators with photon energies of 6 MV flattening filter (FF), 10 MVFF, 6 MV flattening filter free (FFF) and 10 MVFFF were used in this study. All the Linac'swere beam-matched, Dosimetry beam data were ± 1% compare with Reference Linac. Ten different type of detectors (four ionizationchambers and six diode detectors) were used for small-field OF measurements. The OFs were measured for field sizes of 1 × 1 to 10 × 10 cm2, and normalized to 10 × 10 cm2 field size. The uncorrected and corrected OFs were calculated from these measurements. The corrected OF was compare with existing treatment planning system (TPS) Monte Carlo algorithm calculated OFs. The small-field corrected and Uncorrected OF variations among the linear accelerators was within 1% for all energies and detectors. An increase in field size led to a reduction in the difference between OFs among the detectors, which was the case for all energies. The RSD values decreased with increasing field size. The TRS 483 provided Detector-specificoutput-correction factor (OCF) reduced uncertainty in small-field measurements. It is necessary to implement the OF-correction of small fields in a TPS. Special care must be taken to incorporate the corrected small-field OF in a TPS.

Thermoluminescence and optically stimulated luminescence properties of NaMgF3:Dy,Eu synthesized by hydrothermal method and DFT calculations for the bandgap

This study indicates Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) radiation dosimetry characteristics for NaMgF3:Dy1%,Eu0.1% fluoroperovskite. Nanocrystalline NaMgF3:Dy1%,Eu0.1% material was synthesized by hydrothermal technique. The structure and optical properties were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), derivative thermogravimetry (DTG), radioluminescence (RL) and photoluminescence (PL) techniques. The bands on RL spectrum at 365, 488 and 477 nm might be attributed to Eu,2+ Eu3+ and Dy3+ ion emissions, respectively. The experimentally obtained TL glow curve was analyzed by the computerized glow curve deconvolution (CGCD) and various heating rate (VHR) methods and the order of kinetics (b), activation energy (E), and frequency factor (s) were determined for the appeared four peaks of the TL glow curve with 2°C /s heating rate. The energy bandgaps were calculated and the dependence of bandgap on composition was reported through the Density Functional Theory (DFT) computation.

Investigation of alanine dosimeter for output measurement in radiotherapy: Results from multicenter in Thailand

Background: Alanine dosimeters are generally used in high-dose industrial applications (kGy). Later, research into employing alanine as a dosimeter in radiotherapy (1-20 Gy) has increased, since alanine may be an alternative transfer dosimeter for quality control, postal audit, and intercomparison between laboratories. However, several factors such as the dosimeter’s characteristic should be investigated while utilizing alanine in radiotherapy. In addition, the optimal electron paramagnetic resonance (EPR) reader should be configured to match the absorbed dose range. Objectives: This study aims to optimize the EPR setting parameters, study the characteristics of alanine dosimeters, and estimate the uncertainty of the 6MV-FFF linear accelerator in a dose ranging from 1 to 20 Gy. The output measurements from different facilities were also investigated. Materials and methods: The alanine dosimeters were irradiated with a 6MV-FFF beam using linear accelerator, Varian TrueBeam (Varian Medical Systems, Inc, CA, USA), 100 cm SSD, with a field size of 10x10 cm2 at 1 to 30 Gy. The EPR operation parameter has been optimized for these dose ranges. The characteristics of alanine dosimeters were then investigated, along with the estimation of uncertainty in using alanine. Finally, the alanine dosimeter proficiency was validated using 9 distinct linear accelerator machines. Results: The EPR parameters were found to be optimized at 1.589 mW of MP, 7.018 G of MA, and 40.96 ms of TC. The expanded uncertainty (k=2) was reported at 2.68% in the 1-20 Gy dose range. The alanine dosimeters’ characteristics were found to have good uniformity and reproducibility, low fading, and angle-and dose-independence. Although the investigation was performed in 9 different linear accelerator machines, the difference of delivered dose output was measured and reported with difference percentages within ±1%. Conclusion: This study reports the feasibility of using alanine dosimeters in radiotherapy. The important EPR parameter setting, and alanine dosimetry characteristics were investigated, whose results suggest that alanine can be used at a dose range of 1-30 Gy. This especially benefits the SRS treatment which uses a high dose per fraction, and this dosimeter can be an alternative transfer dosimeter. Nonetheless, various factors should be explored using an appropriate phantom prior to clinical application.

PO-2341 Adjuvant Hypofractionated SIB Radiotherapy: Retrospective study of dosimetry features

PO-2341 Adjuvant Hypofractionated SIB Radiotherapy: Retrospective study of dosimetry features