Measured Dose Distributions Research Articles

Error detection using a multi-channel hybrid network with a low-resolution detector in patient-specific quality assurance.

This study aimed to develop a hybrid multi-channel network to detect multileaf collimator (MLC) positional errors using dose difference (DD) maps and gamma maps generated from low-resolution detectors in patient-specific quality assurance (QA) for Intensity Modulated Radiation Therapy (IMRT). A total of 68 plans with 358 beams of IMRT were included in this study. The MLC leaf positions of all control points in the original IMRT plans were modified to simulate four types of errors: shift error, opening error, closing error, and random error. These modified plans were imported into the treatment planning system (TPS) to calculate the predicted dose, while the PTW seven29 phantom was utilized to obtain the measured dose distributions. Based on the measured and predicted dose, DD maps and gamma maps, both with and without errors, were generated, resulting in a dataset with 3222 samples. The network's performance was evaluated using various metrics, including accuracy, sensitivity, specificity, precision, F1-score, ROC curves, and normalized confusion matrix. Besides, other baseline methods, such as single-channel hybrid network, ResNet-18, and Swin-Transformer, were also evaluated as a comparison. The experimental results showed that the multi-channel hybrid network outperformed other methods, demonstrating higher average precision, accuracy, sensitivity, specificity, and F1-scores, with values of 0.87, 0.89, 0.85, 0.97, and 0.85, respectively. The multi-channel hybrid network also achieved higher AUC values in the random errors (0.964) and the error-free (0.946) categories. Although the average accuracy of the multi-channel hybrid network was only marginally better than that of ResNet-18 and Swin Transformer, it significantly outperformed them regarding precision in the error-free category. The proposed multi-channel hybrid network exhibits a high level of accuracy in identifying MLC errors using low-resolution detectors. The method offers an effective and reliable solution for promoting quality and safety of IMRT QA.

Flexible Cotton Fabric-Based Ionizing Radiation Dosimeter for 2D Dose Distribution Measurements over a Wide Dose Range at High Dose Rates.

This work presents an ecological, flexible 2D radiochromic dosimeter for measuring ionizing radiation in the kilogray dose range. Cotton woven fabric made of cellulose was volume-modified with nitrotetrazolium blue chloride as a radiation-sensitive compound. Its features include a color change during exposure from yellowish to purple-brown and flexibility that allows it to adapt to various shapes. It was found that (i) the dose response is up to ~80 kGy, (ii) it is independent of the dose rate for 1.1-73.1 kGy/min, (iii) it can be measured in 2D using a flatbed scanner, (iv) the acquired images can be filtered using a mean filter, which improves its dose resolution, (v) the dose resolution is -0.07 to -0.4 kGy for ~0.6 to ~75.7 kGy for filtered images, and (vi) two linear dose subranges can be distinguished: ~0.6 to ~7.6 kGy and ~9.9 to ~62.0 kGy. The dosimeter combined with flatbed scanner reading and data processing using dedicated software packages constitutes a comprehensive system for measuring dose distributions for objects with complex shapes.

Correlation of thickness changes and daily dose detection of delivery analysis (DA) software in helical tomotherapy

Abstract Purpose: To assess the correlation between the dose distribution provided by the delivery analysis (DA) software and the measured dose distribution using an ArcCHECK (AC) phantom in the presence of thickness variation. Materials and Methods: Two sets of targets were established within the phantom. Target A was placed on the detector areas, whereas Target B was positioned at the centre of the phantom. Bolus was applied to the surface of the phantom at different thicknesses ranging from 0 to 2 cm to verify the dose distribution in both TomoHelical (HT) and TomoDirect (TD) techniques. The gamma passing rate (GPRs) were evaluated against predefined thresholds of 3%/3 mm and 3%/2 mm. Correlation study evaluated the level of agreement between DA and AC values. Results: Both AC and DA exhibited a decline in GPRs as the bolus thickness decreased. Significant correlations were observed between AC and DA for both HT and TD techniques, with a p value of less than 0.001. Conclusion: The results indicate that DA software has the capability to detect anatomical changes during tomotherapy treatments. This is substantiated by the statistical association found between DA and the standard AC phantom system for dose distributions in both HT and TD methods.

Development of a model for evaluating the luminescence intensity of phosphors based on the PHITS track-structure simulation

Radiation-induced phosphors are frequently used as radiation detectors to measure dose distributions of swift ions. However, the luminescence intensity per dose of the phosphor at the Bragg peak regions decreases because of the quenching effects. To precisely measure the dose distribution for various radiation types using phosphor detectors, understanding the mechanism of quenching effects, induced by the electrons at the atomic scale, is crucial. In this study, we developed a new microdosimetric model for evaluating the luminescence intensity of phosphors based on the track-structure (TS) modes applicable to arbitrary materials implemented in the Particle and Heavy Ion Transport code System (PHITS). Herein, the two dominant factors for determining the luminescence intensity, such as (1) the energy required to generate an electron-hole pair and (2) their transfer efficiency to the luminescence center, are estimated from the TS mode in PHITS by calculating the number of stopped electrons and their spatial distributions. Using the developed model, we calculated the energy required to generate an electron-hole pair in various phosphors, which revealed a complex dependency on the bandgap energy, the composition, and the density of the material. Furthermore, we simulated the quenching effects of the BaFBr detector by calculating its transfer efficiencies for swift-ion irradiation and compared the simulation results with the corresponding experimental data. The comparison suggested that the density of luminescence centers is an essential parameter of the phosphors to reproduce the experimental quenching effects. The developed model is based on the first-principles calculation without any empirical correction; therefore, it is expected to contribute widely to developing phosphor detectors.

Heterogeneous physical phantom for I-125 dose measurements and dose-to-medium determination

In this paper we present a further step in the implementation of a physical phantom designed to generate sets of "true" independent reference data as requested by TG-186, intending to address and mitigate the scarcity of experimental studies on brachytherapy (BT) validation in heterogeneous media. To achieve this, we incorporated well-known heterogeneous materials into the phantom in order to perform measurements of 125I dose distribution. The work aims to experimentally validate Monte Carlo (MC) calculations based on MBDCA and determine the conversion factors from LiF response to absorbed dose in different media, using cavity theory. The physical phantom was adjusted to incorporate tissue equivalent materials, such as: adipose tissue, bone, breast and lung with varying thickness. MC calculations were performed using MCNP6.2 code to calculate the absorbed dose in the LiF and the dose conversion factors (DCF). The proposed heterogeneous phantom associated with the experimental procedure carried out in this work yielded accurate dose data that enabled the conversion of the LiF responses into absorbed dose to medium. The results showed a maximum uncertainty of 6.92 % (k = 1), which may be considered excellent for dosimetry with low-energy BT sources. The presented heterogeneous phantom achieves the required precision in dose evaluations due to its easy reproducibility in the experimental setup. The obtained results support the dose conversion methodology for all evaluated media. The experimental validation of the DCF in different media holds great significance for clinical procedures, as it can be applied to other tissues, including water, which remains a widely utilized reference medium in clinical practice.

High-resolution three-dimensional dosimetry in clinically relevant volumes utilizing optically stimulated luminescence.

The continued development of new radiotherapy techniques requires dosimetry systems that satisfy increasingly rigorous requirements, such as high sensitivity, wide dose range, and high spatial resolution. An emerging requirement is the ability to read out doses in three dimensions (3D) with high precision and spatial resolution. A few dosimetry systems with 3D capabilities are available, but their application in a clinical workflow is limited for various reasons, primarily originating from their chemical nature. The search for a 3D dosimetry system with potential for clinical implementation is thusongoing. To demonstrate the capabilities of a novel optically-stimulated-luminescence (OSL)-based 3D dosimetry system capable of measuring radiation doses in clinically relevantvolumes. A laser-based readout system was used to measure dose distributions delivered by both photons and protons, utilizing the OSL from a mm YSO:Ce crystal. A homogeneous treatment plan consisting of two opposing photon fields was used to establish an inhomogeneity correction map of the crystal response and demonstrated the accuracy and precision of the system. The crystal was additionally irradiated with a photon treatment plan consisting of three overlapping mm fields delivered from different angles, and a proton treatment plan consisting of four pencil beams with energies 90 MeV ( ), 115 MeV, and 140 MeV. The system abilities were quantified by comparing the 3D-resolved measurements to Monte Carlosimulations. The dose map reproducibility of the system was found to be within 2% including both statistical and systematic errors. The measurements yielded integrated doses from a volume of mm with voxel volumes of just mm . An excellent agreement between the 3D-resolved measurements and the simulations was found for both photon- andproton-irradiation. The capabilities of the devised system for measuring clinically relevant fields of photons and proton pencil beams within a clinically relevant volume were demonstrated. The system poses as a promising candidate for clinical applications, and enables future research in the field of OSL-based tissue-equivalent 3Ddosimetry.

FLASH radiotherapy using high-energy X-rays: Current status of PARTER platform in FLASH research

PurposeRecent studies indicated that ultrahigh dose rate (FLASH) radiation can reduce damage to normal tissue while maintaining anti-tumour activity compared to conventional dose rate (CONV) radiation. This paper provides a comprehensive description of the current status of the Platform for Advanced Radiotherapy Research (PARTER), which serves as the first experimental FLASH platform utilizing megavoltage X-rays and has facilitated numerous experiments. Methods and MaterialsPARTER was established in 2019 based on a superconducting linac to support experimental FLASH studies using megavoltage X-rays. Continuous upgrades have been made to the accelerator, collimators, flattening filters, monitors, other auxiliary devices, and irradiation process in order to achieve optimal results. Passive and active dosimeters are employed for measuring dose distribution and to ensure traceability of radiation doses. ResultsThe dose monitors and dosimeters demonstrate reliable performance with acceptable stability. At PARTER, the maximum mean dose rate is approximately 400 Gy/s at a surface-source distance of 20 cm (over 1000 Gy/s at smaller distances), with an instantaneous dose rate of approximately 8E5 Gy/s. Both passive and active dosimeters exhibit good linearity and agreement during FLASH X-ray irradiation. The monitors show good linearity to dose rate, with short-term fluctuations within 1.5 % for the diamond monitor. The discrepancy between measured absorbed dose and dose protocol is typically less than 4 %. The X-ray energy spectra on PARTER are comparable to those for megavoltage CONV linacs operating in flattening filter-free mode. The maximum field size of the FLASH beam is 4.5 cm × 4.5 cm. The FLASH dose profile demonstrates satisfactory flatness (1.04) and similar penumbra compared to clinical CONV linac, while the percentage depth dose curve of FLASH X-rays is steeper than that of the clinical megavoltage CONV X-ray. ConclusionsPARTER represents a pioneering platform for conducting megavolts FLASH X-ray irradiation in biological experiments. It effectively fulfills the requirements of preclinical research on megavoltage X-ray FLASH and undergoes continuous upgrades to meet increasingly demanding performance criteria.

Experience of Introducing Intraoperative Electron Accelerator Mobetron into Clinical Practice

Purpose: Тo share the experience of introducing the Mobetron intraoperative electron accelerator into
 clinical practice, including describing the methods of acceptance testing and measuring dose distributions, as well as possible clinical applications.
 Material and methods: Acceptance tests and commissioning were carried out on the intraoperative accelerator Mobetron (IntraOp, USA), dosimetry IBA (Belgium).
 Results: Experience of commissioning the Mobetron intraoperative electron accelerator and some of
 the most relevant clinical applications are described. 
 Conclusion: Commissioning the Mobetron is a lengthy and specific procedure. The most important aspect of the successful preparation and operation of the device in the clinic is the common interest and
 cooperation of specialists in various fields - radiotherapists, surgeons, medical physicists.

Implementation of a Patient Specific QA Protocol for a Novel Dedicated Stereotactic Radiosurgery Linear Accelerator

To describe the patient specific QA (Quality Assurance) protocol implemented for plan integrity verification, in stereotactic radiosurgery (SRS) and radiotherapy (SRT) treatments performed on a novel dedicated frameless image guided radiosurgery system using conical collimator, and a combination of yoked gimbals to cover near2pi solid angle. Startup and commissioning results obtained for planned vs measured dose distributions with several detectors are presented. The patient specific QA protocol includes: A) Review of the approved plan based on AAPM TG 275 report recommendations B) 1D verification using small volume ionization chambers inside an anthropomorphic head phantom C) 2D dose verification of a coronal and sagittal dose plan performed with high resolution 2D Array and respective phantom apparatus D) In-house independent MU (Monitor Unit) calculation using the same formalism of the vendor TPS (Treatment Planning Systems) RayTracing dose-calculation algorithm E) Monte Carlo based secondary dose check & plan QA. A retrospective analysis of the results of the first 15 patients treated is presented, focusing on plan complexity vs QA results. The 1D results obtained for the 15 SRS plans were within ±5% for all reported cases, with a mean percent difference of -1,25%, confirming an overall good agreement and, as expected, a partial volume effect in plans with smaller collimators. For the 2D dose verifications, with a 10% dose threshold, gamma passing rates of 97,5% (coronal) and 96,78 (sagittal) with 3% 1mm criteria, 95,1% (coronal) and 94,3% (sagittal) for 2% 1 mm criteria and 90,7% (coronal) and 90,0% (sagittal) for 1% 1mm criteria were obtained. Moreover, the results showed a correlation between lesion volume or number of collimators used with gamma passing rates. All MU verification results were within ±0,3% and provides an efficient risk mitigation approach for this new delivery technique. The verification results of the first 15 treated SRS plans confirmed point dose and planar measurements in agreement with TPS calculations, with superior results for planes with smaller lesions and fewer collimators. This also represents an integral validation of the image-based alignment system and fine treatment couch movements, as treatments are intrinsically multi-isocentric.

Clinical Experience with Commissioning a GRID Collimator for Spatially Fractionated Radiation Therapy

In this study, we report our physics commissioning experience for clinically implementing a GRID collimator based Spatially Fractionated Radiation Therapy (SFRT). For SFRT commissioning, we utilized a commercially available brass GRID collimator (DotDecimal, Sanford, FL) that is mounted on a blocking tray for positioning into the accessory mount of the Linac. The brass GRID is 7.62 cm thick and weighs 15.8 kg. The GRID has a total of 149 divergent holes arranged in a hexagonal pattern (1.43 cm in diameter and hole-centers spaced at 2.11 cm when projected at the isocenter distance). The GRID encompasses a maximum field size of 25 × 25 cm at the isocenter. A commercial 48 × 48 × 48 cm water phantom scanning system was used to collect GRID output factors (GRID field to open field ratio), depth dose and beam profile data. Output measurements were performed using a 0.13 cm3 active volume ion-chamber and beam scans were obtained with a diode detector. Data was collected for both flattening and flattening-free beams of nominal energies 6 MV and 10 MV photons. The measurement depths were at dmax (1.5 cm for 6 MV and 2.5 cm for 10 MV), 5-cm and 10-cm respectively. For each energy and depth of measurement, collimator settings were varied from 5 × 5 cm to 28 × 28 cm. From scan profiles at different depths, the valley (lowest) to peak (highest) dose ratios (VPDR) were calculated. A commercial treatment planning system (TPS) was used to test the accuracy of dose calculations with GRID. This was accomplished by importing vendor generated DICOM RT file into the TPS. A block transmission factor of 7% for 6 MV and 10.2% for 10 MV energy beams were applied. All measured data were compared with corresponding TPS calculated data. Test patient treatment plans with GRID were created in TPS and planned distributions were verified using a commercial detector array with 2.5 mm detector spacing. The VPDR, expressed as %, are presented in Table 1. Measured and TPS calculated output factors agreed within 2% for 6 MV and within 3% for 10 MV photon beams. Percent depth doses were lower in magnitude for GRID field compared to open field for all energies studied (for e.g., 6 MV depth dose at 10 cm depth for 10 cm x10cm field 62% for GRID field vs. 66% for open field). Measured and calculated GRID beam profiles agreed within 5% dose difference and 1 mm distance-to agreement. For all test cases, the planned vs. measured dose distributions passed at an average gamma passing rate of 96.5% using a 3% dose difference/ 3 mm distance to agreement and 10% threshold criteria. The Dot Decimal GRID collimator provides a simple way of achieving SFRT in the clinic, albeit heavy to use and has an irradiation field size limitation of 25 cm × 25 cm.

Deep Learning-Based Single-View Fluorescence Dose Reconstruction for 3D Dosimetry

3D dose distribution measurement is crucial for precise radiotherapy. Radiation-excited fluorescence imaging has potential for the 3D dosimetry with high spatial resolution, but multiple fluorescence images from different view-angles are required for analytical reconstruction techniques. Furthermore, the imaging data are contaminated by anisotropic Cherenkov light emission and statistical noise. This project aims to establish a novel deep learning-based model to predict 3D dose distributions from a single-view 2D fluorescence image while simultaneously removing the adverse effects of Cherenkov signals and other noises. A total of 124 single-aperture static photon beams were delivered to an acrylic tank containing 1 g/L quinine hemisulfate water solution with varying aperture shapes and collimator angle. The emitted optical signals were detected by a low-cost CMOS camera for 20 seconds, and image pre-processing was performed to obtain input 2D fluorescence images with 0.3 × 0.3 mm spatial resolution. 3D back-projected dose distribution images were also calculated from the input fluorescence images. Ground-truth of 3D dose distributions and 2D field map images were obtained from a clinical treatment planning system with 1.4 × 1.4 × 1.4 mm spatial resolution. The proposed deep learning-based dose reconstruction method involved 3 steps. First, 2D fluence map images at the bottom plane of the tank were predicted from the fluorescence images by using a customized convolutional neural network (CNN). Second, the predicted fluence map images were transformed into the 2D field map images on the isocenter plane by applying perspective transformation. Finally, 2D dose distributions at a given radiological depth were calculated by using the predicted field map images, the back-projected dose distribution images, and the radiological depth value as inputs of a shallow CNN. Both CNN models were trained separately, and the 3D dose distributions were predicted by concatenating the output 2D dose distributions at various radiological depths. The proposed CNN model yielded accurate 2D field map images. Averaged Dice similarity coefficient and mean absolute error of the field maps in the test data was 92.0% ± 4.6% and 0.0132 ± 0.0113, respectively. Moreover, our deep learning-based approach was able to predict accurate 3D dose distributions from the 2D fluorescence images. Mean squared error and averaged 3D gamma passing ratio (3%/3mm) were 9.55 mGy ± 6.8 mGy and 86.3% ± 9.86%, respectively. Theproposed deep learning-based method calculated accurate 3D dose distributions from a single-view 2D fluorescence image. Since this technique require only a single CMOS camera image and fluorescent material, it can be readily used for any external radiotherapy modalities, including SRS/SBRT with small fields. This method is useful for acquiring 3D dose distribution data for precise dose verification within a few seconds.

Evaluation of Patient-Specific Quality Control (QC) for Markerless Dynamic Tumor Tracking (MDTT) Deliveries

To report on the patient-specific QC for MDTT for liver and lung tumors treated using the dome-of-liver/diaphragm as a surrogate for the target position and compare to the QC of conventional fiducial-based tracking. Vero4DRT is a linear accelerator that has a gimbal-mounted waveguide and collimation system allowing the radiation beam to perform dynamic tumor tracking based on a patient's respiratory motion. A correlation model is built between an external IR marker placed on the chest and an internal structure, which may be implanted fiducial surrogates or in the case of MDTT, an anatomic landmark. During treatment an orthogonal kV image pair is taken every second. The auto detected internal structure position versus the predicted position is recorded in treatment log files. Five IMRT tracking plans were delivered to two commercial motion phantoms with in-house additions for patient-specific tracking QC. For point dose measurements, a 0.6cc farmer chamber was placed inside the dynamic tracking phantom which contains fiducials for fiducial-based tracking delivery and an anatomic landmark for MDTT. For 2D dose distribution measurements, a radiographic film insert for the Quasar Respiratory Motion Phantom was constructed. The phantom contains both fiducials and has a liver-dome shape at one end to facilitate MDTT. Both motion platforms were interfaced with software that enabled patient-specific respiratory motion traces acquired during a 4DCT scan. Each plan was delivered three times on each phantom: 1) in static mode, 2) during fiducial-based tracking, and 3) during MDTT. Chamber measurements taken during static and tracked delivery were compared to the average chamber dose from the treatment planning software (TPS). Film distributions measured during tracked deliveries were compared to the static film distribution using gamma analysis with FILMQA PRO software. Finally, dynamic tracking treatment statistics, extracted from log files, were compared between fiducial and markerless tracking deliveries. All chamber measurements resulted in dose differences <2.5% compared with the TPS. Dose differences between fiducial-based and MDTT were 0.26% on average (range 0.03-0.62%). For film dose map analysis, gamma pass rates were >95% for all plans for all tracking methods. The average gamma pass rate for 3%/3mm was 99.4% (fiducial-based) vs 98.4% (markerless). For 2%/2mm, the average gamma pass rate was 96.4% (fiducial-based tracking) vs 95.6% (MDTT). Dynamic treatment statistics from logs files reported an average 3D absolute deviation from predicted position of 0.52mm (±0.24) for fiducial tracking and 1.19mm (±0.50) for MDTT. Both fiducial-based and MDTT plans meet passing criteria for patient-specific QC. 3D absolute deviation of detected versus predicted position are larger for MDTT compared to fiducial tracking, however no significant impact on dose delivery was measured.

Deep learning-based fluorescence image correction for high spatial resolution precise dosimetry

Objective. While radiation-excited fluorescence imaging has great potential to measure absolute 2D dose distributions with high spatial resolution, the fluorescence images are contaminated by noise or artifacts due to Cherenkov light, scattered light or background noise. This study developed a novel deep learning-based model to correct the fluorescence images for accurate dosimetric application. Approach. 181 single-aperture static photon beams were delivered to an acrylic tank containing quinine hemisulfate water solution. The emitted radiation-exited optical signals were detected by a complementary metal-oxide semiconductor camera to acquire fluorescence images with 0.3 × 0.3 mm2 pixel size. 2D labels of projected dose distributions were obtained by applying forward projection calculation of the 3D dose distributions calculated by a clinical treatment planning system. To calibrate the projected dose distributions for Cherenkov angular dependency, a novel empirical Cherenkov emission calibration method was performed. Total 400-epoch supervised learning was applied to a convolutional neural network (CNN) model to predict the projected dose distributions from fluorescence images, gantry, and collimator angles. Accuracy of the calculated projected dose distributions was evaluated with that of uncorrected or conventional methods by using a few quantitative evaluation metrics. Main results. The projected dose distributions corrected by the empirical Cherenkov emission calibration represented more accurate noise-free images than the uncalibrated distributions. The proposed CNN model provided accurate projected dose distributions. The mean absolute error of the projected dose distributions was improved from 2.02 to 0.766 mm·Gy by the CNN model correction. Moreover, the CNN correction provided higher gamma index passing rates for three different threshold criteria than the conventional methods. Significance. The deep learning-based method improves the accuracy of dose distribution measurements. This technique will also be applied to optical signal denoising or Cherenkov light discrimination in other imaging modalities. This method will provide an accurate dose verification tool with high spatial resolution.

Novel tongue-positioning device to reduce tongue motions during radiation therapy for head and neck cancer: Geometric and dosimetric evaluation.

This study aimed to assess the performance of a tongue-positioning device in interfractional tongue position reproducibility by cone-beam computed tomography (CBCT). Fifty-two patients treated with radiation therapy (RT) while using a tongue positioning device were included in the study. All patients were treated with 28 or 30 fractions using the volumetric modulated arc therapy technique. CBCT images were acquired at the 1st, 7th, 11th, 15th, 19th, 23th, and 27th fractions. Tongues on planning computed tomography (pCT) and CBCT images were contoured in the treatment planning system. Geometric differences in the tongue between pCT and CBCT were assessed by the Dice similarity coefficient (DSC) and averaged Hausdorff distance (AHD). Two-dimensional in vivo measurements using radiochromic films were performed in 13 patients once a week during sessions. The planned dose distributions were compared with the measured dose distributions using gamma analysis with criteria of 3%/3 mm. In all patients, the mean DSC at the 1st fraction (pCT versus 1st CBCT) was 0.80 while the mean DSC at the 27th fraction (pCT versus 27th CBCT) was 0.77 with statistical significance (p-value = 0.015). There was no statistically significant difference in DSC between the 1st fraction and any other fraction, except for the 27th fraction. There was statistically significant difference in AHD between the 1st fraction and the 19th, 23th, and 27th fractions (p-value < 0.05). In vivo measurements showed an average gamma passing rate of 90.54%. There was no significant difference between measurements at the 1st week and those at other weeks. The tongue geometry during RT was compared between pCT and CBCT. In conclusion, the novel tongue-positioning device was found to minimize interfractional variations in position and shape of the tongue.

Monte Carlo Dosimetry Validation for X-Ray Guided Endovascular Procedures

Endovascular treatment is continuously gaining ground in vascular surgery procedures. However, current patient radiation dose estimation does not take into account the exact patient morphology and organs' composition. Monte Carlo (MC) simulation can accurately estimate the dose by recreating the irradiation process generated during X-ray-guided interventions. This study aimed to validate the MC simulation models by comparing simulated and measured dose distributions in endovascular aortic aneurysm repair (EVAR) procedures. We conducted a clinical study in patients treated for EVAR. Patient dose measurements were taken with passive dosimeters using Optically Stimulated Luminescence technology in 4 specific anatomical points on the skin: xiphoid process, pubic symphysis, right and left iliac crest. Dose measurements were compared to the corresponding simulated doses with the Geant4 Application for Emission Tomography (GATE) and GPU Geant4-based Monte Carlo Simulations (GGEMS) MC simulations softwares. The MC simulation took as input the computed tomography scan of the patient and the parameters of the imaging system (orientation angles, tube voltage, and aluminum filtration) and gives as output the three-dimensional (3D) dose map for each patient and angulation. A good agreement with real doses was found for doses simulated by the MC GATE method (P<0.0001; r=0.97; 95% confidence interval [CI] [0.96-0.98]), as well as for doses simulated by the GGEMS method (P<0.0001; r=0.96; 95% CI [0.94-0.97]). The mean relative error for all measurements was 5±5% in the MC GATE group and 6±5% in the GGEMS group. Process execution on GGEMS (6sec) was faster than the GATE MC simulation (5hr). Considering the current imaging settings, this study shows the potential of using the GATE and GGEMS MC simulations platforms to model the 3D dose distributions during EVAR procedures.

Acute normal tissue responses in a murine model following fractionated irradiation of the head and neck with protons or X-rays

Background The purpose of this study was to investigate acute normal tissue responses in the head and neck region following proton- or X-irradiation of a murine model. Materials and methods Female C57BL/6J mice were irradiated with protons (25 or 60 MeV) or X-rays (100 kV). The radiation field covered the oral cavity and the major salivary glands. For protons, two different treatment plans were used, either with the Bragg Peak in the middle of the mouse (BP) or outside the mouse (transmission mode; TM). Delivered physical doses were 41, 45, and 65 Gy given in 6, 7, and 10 fractions for BP, TM, and X-rays, respectively. Alanine dosimetry was used to assess delivered doses. Oral mucositis and dermatitis were scored using CTC v.2.0-based tables. Saliva was collected at baseline, right after end of irradiation, and at day 35. Results The measured dose distribution for protons (TM) and X-rays was very similar. Oral mucositis appeared earlier, had a higher score and was found in a higher percentage of mice after proton irradiation compared to X-irradiation. Dermatitis, on the other hand, had a similar appearance after protons and X-rays. Compared to controls, saliva production was lower right after termination of proton- and X-irradiation. The BP group demonstrated saliva recovery compared to the TM and X-ray group at day 35. Conclusion With lower delivered doses, proton irradiation resulted in similar skin reactions and increased oral mucositis compared to X-irradiation. This indicates that the relative biological effectiveness of protons for acute tissue responses in the mouse head and neck is greater than the clinical standard of 1.1. Thus, there is a need for further investigations of the biological effect of protons in normal tissues.

Monte Carlo calculations of dose profiles with the ‘given profile” method and comparison with measurements

Measurement of complex dose distributions which typically occur in modern radiation therapy methods is demanding. One of the main difficulties arises from the volume averaging effect due to the extended size of the employed dosimeter. Although small-sized detectors such as solid state detectors are obviously best suited in such situations, ionization chambers are frequently used. The question then arises whether the volume averaging effect plays such a role that it must be taken into account. In this work a procedure is presented which can answer this question and offer correction factors if needed.The new method of this work is based on the Monte Carlo tool for dose calculations and was applied at profile measurements. It is using the ‘Given Profile’ procedure and enables a comparison between profiles in a water phantom in a chamber-free geometry (true profiles) and measured profiles. Based on this procedure a specific in-air profile was obtained which was then commonly applied as a new input source option at all measured depths.The calculated profile data simulating a measurement with the PTW Semiflex chamber well agreed with corresponding measurements at all depths. The identical source model also yielded profile data for the chamber-free geometry. The comparison between calculated chamber-free data and measured data clearly demonstrates that a volume averaging effect indeed occurs in the field edge region for this type of a mid-sized ionization chamber. The ratio of these data gives values in the order of 1.1 inside the field edges and values between 0.4 and 0.8 outside. The method presented in this work, although connected with the known effort of the Monte Carlo tool for dose calculations, is well feasible and results in meaningful data with respect to chamber-free profile data in water. It was shown, that the volume averaging effect plays a role at profile measurements with the Semiflex chamber. The ratio between calculated chamber-free data and measured data can be used as a correction factor to obtain the true profiles in water. It is suggested that the ‘Given Profile’ method could be additionally included in the existing choice of source options in codes of the EGSnrc system.

Measurement of the radiation dose and radiation isocenter of the TrueBeam accelerator using 3D polymer gel dosimeters from the VIPAR family with different chemical history

This work describes the measurements of the ionizing radiation dose and the determination of the radiation isocenter using a tool consisting of three-dimensional polymer gel dosimeters and a dedicated software package. Specific polymer gel dosimeters were selected. Their inherent common feature is the possibility of high-resolution three-dimensional measurement of dose distribution in radiotherapy and the presence of the N-vinylpyrrolidone monomer in the composition alongside other substances such as the cross-linking agent N,N'-methylenebisacrylamide, oxygen scavengers, stabilizers and gel matrix. The aim of this study was to analyze the influence of the chemical history of N-vinylpyrrolidone (purity and aging) on the dose response of some dosimeters. In addition, this work seeks to answer the question of how important purity and aging of N-vinylpyrrolidone are in dosimetry applications, such as routine testing of medical accelerators.

Dosimetric Investigation of Six Ru-106 Eye Plaques by EBT3 Radiochromic Films and Monte Carlo Simulation.

Ophthalmic brachytherapy using radioactive plaques is an effective technique for the treatment of uveal melanoma. Ru-106 eye plaques are considered as interesting issue due to their steep gradient dose. The pre-planning evaluation of dosimetric parameters is essential for the treatment planning system. The current study aims at providing dose distributions of six Ru-106 eye plaques (CCA, CCB, CGD, CIB, COB and COD) using radiochromic EBT3 film, Geant4 Monte Carlo toolkit and the treatment planning software (Plaque Simulator). In this experimental study, an in-house phantom was employed for depth dose measurements with EBT3 films. Also, Geant4.10.5 scoring mesh was implemented to obtain the 2D dose distribution of the plaques. The results were compared with Plaque Simulator software and the manufacturer's (BEBIG) data. The gamma index criterion (3%/3 mm) was used to evaluate dose distributions obtained by the film measurements and Geant4 simulation. A good agreement was achieved between simulation and experimental results. Gamma index passing rate was 94.2%, 89.3%, 88.2%, 82.2%, 92.2% and 90.1% for CCA, CCB, CGD, CIB, COB and COD plaques, respectively. Absolute dose rate (mGy/min) obtained by EBT3 film at the depth of 2 mm was 79.4 mGy/min, 81.0 mGy/min, 78.6 mGy/min, 62.2 mGy/min, 75.2 mGy/min and 81.2 mGy/min for CCA, CCB, CGD, CIB, COB and COD plaques, respectively. The measured dose distributions and lateral dose profiles may be utilized in the treatment planning system to cover clinical volumes such as the clinical target volume and the gross tumor volume.

Luminescence imaging of water irradiated by protons under FLASH radiation therapy conditions

Objective. FLASH radiation therapy with ultrahigh dose rates (UHDR) has the potential to reduce damage to normal tissue while maintaining anti-tumor efficacy. However, rapid and precise dose distribution measurements remain difficult for FLASH radiation therapy with proton beams. To solve this problem, we performed luminescence imaging of water following irradiation by a UHDR proton beam captured using a charge-coupled device camera. Approach. We used 60 MeV proton beams with dose rates of 0.03–837 Gy s−1 from a cyclotron. Therapeutic 139.3 MeV proton beams with dose rates of 0.45–4320 Gy s−1 delivered by a synchrotron-based proton therapy system were also tested. The luminescent light intensity induced by the UHDR beams was compared with that produced by conventional beams to compare the dose rate dependency of the light intensity and its profile. Main results. Luminescence images of water were clearly visualized under UHDR conditions, with significantly shorter exposure times than those with conventional beams. The light intensity was linearly proportional to the delivered dose, which is similar to that of conventional beams. No significant dose-rate dependency was observed for 0.03–837 Gy s−1. The light-intensity profiles of the UHDR beams agreed with those of conventional beams. The results did not differ between accelerators (synchrotron or cyclotron) and beam energies. Significance. Luminescence imaging of water is achievable with UHDR proton beams as well as with conventional beams. The proposed method should be suitable for rapid and easy quality assurance investigations for proton FLASH therapy, because it facilitates real-time, filmless measurements of dose distributions, and is useful for rapid feedback.