Dose Distributions In Phantom Research Articles

Technical note: Phantom-based evaluation of CBCT dose calculation accuracy for use in adaptive radiotherapy.

High-quality 3D-anatomy of the day is needed for treatment plan adaptation in radiotherapy. For online x-ray-based CBCT workflows, one approach is to create a synthetic CT or to utilize a fan-beam CT with corresponding registrations. The former potentially introduces uncertainties in the dose calculation if deformable image registration is used. The latter can introduce burden and complexity to the process, the facility, and thepatient. Using the CBCT of the day, acquired on the treatment device, for direct dose calculation and plan adaptation can overcome these limitations. This study aims to assess the accuracy of the calculated dose on the CBCT scans acquired on a Halcyon linear accelerator equipped withHyperSight. HyperSight's new CBCT reconstruction algorithm includes improvements in scatter correction, HU calibration of the imager, and beam shape adaptation. Furthermore, HyperSight introduced a new x-ray detector. To show the effect of the implemented improvements, gamma comparisons of 2%/2mm, 2%/1mm, and 1%/1mm were made between the dose distribution in phantoms calculated on the CBCT reconstructions and the simulation CT scans, considering this the standard of care. The resulting gamma passing rates were compared to those obtained with the Halcyon 3.0 reconstruction and hardware without HyperSight's technologies. Various anatomical phantoms for dosimetric evaluations on brain, head and neck, lung, breast, and prostate cases have been used in thisstudy. The overall results demonstrated that HyperSight outperformed the Halcyon 3.0 version. Based on the gamma analysis, the calculated dose using HyperSight was closer to the CT scan-based doses than the calculated dose using iCBCT Halcyon 3.0 for most cases. Over all plans and gamma criteria, Halcyon 3.0 achieved an average passing rate of 92.9%, whereas HyperSight achieved 98.1%. Using HyperSight CBCT images for direct dose calculation, for example, in (online) plan adaptation, seems feasible for the investigatedcases.

Dosimetric validation of SmART-RAD Monte Carlo modelling for x-ray cabinet radiobiology irradiators

Objective. Accuracy and reproducibility in the measurement of radiation dose and associated reporting are critically important for the validity of basic and preclinical radiobiological studies performed with kilovolt x-ray radiation cabinets. This is essential to enable results of radiobiological studies to be repeated, as well as enable valid comparisons between laboratories. In addition, the commonly used single point dose value hides the 3D dose heterogeneity across the irradiated sample. This is particularly true for preclinical rodent models, and is generally difficult to measure directly. Radiation transport simulations integrated in an easy to use application could help researchers improve quality of dosimetry and reporting. Approach. This paper describes the use and dosimetric validation of a newly-developed Monte Carlo (MC) tool, SmART-RAD, to simulate the x-ray field in a range of standard commercial x-ray cabinet irradiators used for preclinical irradiations. Comparisons are made between simulated and experimentally determined dose distributions for a range of configurations to assess the potential use of this tool in determining dose distributions through samples, based on more readily available air-kerma calibration point measurements. Main results. Simulations gave very good dosimetric agreement with measured depth dose distributions in phantoms containing both water and bone equivalent materials. Good spatial and dosimetric agreement between simulated and measured dose distributions was obtained when using beam-shaping shielding. Significance. The MC simulations provided by SmART-RAD provide a useful tool to go from a limited number of dosimetry measurements to detailed 3D dose distributions through a non-homogeneous irradiated sample. This is particularly important when trying to determine the dose distribution in more complex geometries. The use of such a tool can improve reproducibility and dosimetry reporting in preclinical radiobiological research.

A study on the treatment of brain tumors with BNCT using several moderators with different thicknesses

Boron neutron capture therapy (BNCT) is an effective binary radiation therapy that depends on nuclear capture reactions. In recent years, BNCT can be performed without a reactor owing to the development of accelerator-based neutron sources. A new BNCT irradiation facility is proposed, which is based on a 15 mA 2.5 MeV proton accelerator with a 100 μm thickness natural lithium target as a neutron converter. A great quantity of studies has shown that neutron beams with different spectra have unique therapeutic effects on tumors. An appropriate neutron beam for BNCT is obtained by Beam Shaping Assembly (BSA) and the moderator plays a main role in determining the BSA outlet beam spectrum. To figure out the dose distribution in phantom with various kinds of neutron spectrum modes during BNCT, a series of cases are calculated by MCNPX code. The results give a database for treatment of brain tumors with BNCT by using different moderators.

Prediction of patient-specific quality assurance for volumetric modulated arc therapy using radiomics-based machine learning with dose distribution.

We sought to develop machine learning models to predict the results of patient-specific quality assurance (QA) for volumetric modulated arc therapy (VMAT), which were represented by several dose-evaluation metrics-including the gamma passing rates (GPRs)-and criteria based on the radiomic features of 3D dose distribution in a phantom. A total of 4,250 radiomic features of 3D dose distribution in a cylindrical dummy phantom for 140 arcs from 106 clinical VMAT plans were extracted. We obtained the following dose-evaluation metrics: GPRs with global and local normalization, the dose difference (DD) in 1% and 2% passing rates (DD1% and DD2%) for 10% and 50% dose threshold, and the distance-to-agreement in 1-mm and 2-mm passing rates (DTA1 mm and DTA2 mm) for 0.5%/mm and 1.0%.mm dose gradient threshold determined by measurement using a diode array in patient-specific QA. The machine learning regression models for predicting the values of the dose-evaluation metrics using the radiomic features were developed based on the elastic net (EN) and extra trees (ET) models. The feature selection and tuning of hyperparameters were performed with nested cross-validation in which four-fold cross-validation is used within the inner loop, and the performance of each model was evaluated in terms of the root mean square error (RMSE), the mean absolute error (MAE), and Spearman's rank correlation coefficient. The RMSE and MAE for the developed machine learning models ranged from<1% to nearly<10% depending on the dose-evaluation metric, the criteria, and dose and dose gradient thresholds used for both machine learning models. It was advantageous to focus on high dose region for predicating global GPR, DDs, and DTAs. For certain metrics and criteria, it was possible to create models applicable for patients' heterogeneity by training only with dose distributions in phantom. The developed machine learning models showed high performance for predicting dose-evaluation metrics especially for high dose region depending on the metric and criteria. Our results demonstrate that the radiomic features of dose distribution can be considered good indicators of the plan complexity and useful in predicting measured dose evaluation metrics.

Radiotherapy delivery error detection with electronic portal imaging device (EPID)-based in vivo dosimetry.

Radiotherapy delivery error detection with electronic portal imaging device (EPID)-based in vivo dosimetry.

A method to reduce the error due to the angular dependencies of Cerenkov-light in water for optical imaging of X-rays from high-energy medical linear accelerators (LINAC)

Determining the absorbed dose distributions in phantoms for X-ray beams of high-energy medical linear accelerators (LINAC) is an important task in the quality control of a system. Although optical imaging of water during irradiation of X-ray beams from a LINAC is a promising method, depth dose profiles show underestimation in the deeper parts of the water, mainly due to the angular dependency of Cerenkov-light produced in water. To solve this problem, the authors change camera angles from 0 degree to 10 degrees and obtain optical images with a high-sensitivity cooled charge coupled device (CCD) camera during X-ray beam irradiation. Furthermore, the authors calculate the Cerenkov-light distributions with different camera angles using Monte Carlo simulation and the obtained depth profiles. Then, these depth profiles are evaluated and compared with those of a planning system. In both measured and simulated distributions, the light intensity increases as the angle increases. The measured depth profile of 10 degrees was nearly identical to the planning system. The percentage differences of depth profile between the measured optical image at the angle of 10 degrees and the planning system was -1.7 % at 100 mm depth, and the average difference was 0.8 %. We conclude that optical imaging with that angle is a promising method for reducing the error due to the angular dependency of Cerenkov-light.

The development and testing of a novel spherical radiotherapy phantom system for the commissioning and patient-specific quality assurance of mono-isocentric multiple mets SRS plans.

To develop a single radiotherapy phantom system capable of performing both patient-specific quality assurance (QA) measurements and commissioning measurements for mono-isocentric LinAc-based stereotactic radiosurgery ("mLSRS") treatment plans. Design A 20-cm diameter spherical phantom was designed which contained within it a film cartridge. The surface of the sphere was machined to display a set of angular markings at both the equator and the meridian representing a spherical coordinate system. A stand was designed which allows for free rotation about any vector passing through the center of the sphere. A program was created using Python 3 to: (a) Compute the measurement setup necessary to intersect exactly one film plane with three user specified dicom points contained within the QA plan; (b) Extract the intersection dose plane from the three dimensional DICOM dose file and; (c) Generate a synthetic computed tomography (CT) in the exact measurement geometry which is subsequently used for phantom positioning during the QA measurement. To assess the functionality of the phantom system dynamic conformal arc mLSRS plans that were generated by a clinically commissioned multiple metastasis treatment planning system (BrainLab Elements version 2.0) using patient-specific data. A total of seven patient plans were created that contained a total of 31 targets {<Volume>=(0.382±0.534)cc: Range [0.051, 2.05]cc, <Off-Axis Distance>=(30±16)mm: Range[0, 55]mm} 27 of which were directly measured with film and analyzed. Each planned isocenter was mapped to the phantom's center and the dose was recomputed. From the phantom dose distribution dicom points of interest were selected in sets of three and input into the provided software. The software computed the plane that intersects with the entered three points and instructed the user on the setup geometry to place the film in the intersecting plane. The software then generated a synthetic CT scan with embedded fiducial markers rotated into the setup orientation. This CT was then used as the setup reference image in ExacTrac image guidance system (tolerance 0.7mm & 0.5deg). All plans were delivered on a Varian Truebeam linear accelerator with HDMLC, Exactrac and a 6 degree of freedom couch. After delivery of each test plan a 10×10 reference field was delivered to a known dose approximately equal to the maximum dose contained within the plan for film calibration. The test film was scanned simultaneously with the 10×10 reference film and a film that received zero dose using an Epson 10000XL flatbed scanner after waiting 24hours. The test film was scaled according to the reference film and analyzed via the gamma analysis (3%, 1mm, 10%) implemented in Ashland Film QA Pro software. The spherical phantom system was able to perform validation measurements on a variety of patient-specific plan geometries. The average gamma pass-rate γ(3%, 1mm,10%) for all measurements was 96.7% (σ=3.6%). A novel spherical radiotherapy phantom system has been designed and tested on clinically relevant test plans.

Impact of image reconstruction method on dose distributions derived from 90Y PET images: phantom and liver radioembolization patient studies

PET images acquired after liver 90Y radioembolization therapies are typically very noisy, which significantly challenges both visualization and quantification of activity distributions. To improve their noise characteristics, regularized iterative reconstruction algorithms such as block sequential regularized expectation maximization (Q.Clear for GE Healthcare, USA) have been proposed. In this study, we aimed to investigate the effects which different reconstruction algorithms may have on patient images, with reconstruction parameters initially narrowed down using phantom studies. Moreover, we evaluated the impact of these reconstruction methods on voxel-based dose distribution in phantom and patient studies (lesions and healthy livers). The International Electrotechnical Commission (IEC)/NEMA phantom, containing six spheres, was filled with 90Y and imaged using a GE Discovery 690 PET/CT scanner with time-of-flight enabled. The images were reconstructed using Q.Clear (with β parameter ranging from 0 to 8000) and ordered subsets expectation maximization. The image quality and quantification accuracy were evaluated by computing the hot () and cold () contrast recovery coefficients, background variability (BV) and activity bias. Next, dose distributions and dose volume histograms were generated using MIM® software’s SurePlan LiverY90 toolbox. Subsequently, parameters optimized in these phantom studies were applied to five patient datasets. Dose parameters, such as D max, D mean, D 70, and V 100Gy , were estimated, and their variability for different reconstruction methods was investigated. Based on phantom studies, the β parameter values optimized for image quality and quantification accuracy were 2500 and 300, respectively. When all investigated reconstructions were applied to patient studies, D mean, D50, D 70, and V 100Gy showed coefficients of variation below 8%; whereas the variability of D max was up to 30% for both phantom and patient images. Although β = 300−1000 would provide accurate activity quantification for a region of interest, when considering activity/dose voxelized distribution, higher β value (e.g. 4000–5000) would provide the greatest accuracy for dose distributions. In this 90Y radioembolization PET/CT study, the β parameter in regularized iterative (Q.Clear) reconstruction was investigated for image quality, accurate quantification and dose distributions based on phantom experiments and then applied to patient studies. Our results indicate that more accurate dose distribution can be achieved from smoother PET images, reconstructed with larger β values than those yielding the best activity quantifications but noisy images. Most importantly, these results suggest that quantitative measures, which are commonly used in clinics, such as SUVmax or SUVpeak( equivalent of D max), should not be employed for 90Y PET images, since their values would highly depend on the image reconstruction.

Development and validation of an analytical model allowing accurate predictions of gamma and electron beam dose distributions in a water medical phantom.

The aim of this work was to study photon and electron dose distributions in a phantom filled with water using the Monte Carlo Geant4 tool for electron energies ranging from 1 to 21MeV and for photon energies ranging from 1.25MeV to 25MeV, corresponding to conventional radiotherapy Linac energies. The results of the Geant4 calculations were validated based on the relevant experimental data previously published. The results obtained were fitted and analytical models of dose distributions were developed for gamma radiation and electrons. For each of these models, one-dimensional (including dose depth profiles as a function of the depth inside the phantom) and two-dimensional (including the dose distribution as a function of depth and lateral position inside the phantom) dose distributions have been considered. Results are presented for photons and electrons of various energies. The coefficient of determination [Formula: see text] illustrates an excellent match between the developed analytical model and the Geant4 results. It is demonstrated that the analytical models developed in the present study can be applied in various fields such as those used for calibration applications and radiation therapy. It is concluded that the analytical models developed allow for quick, easy and reliable clinical dose estimates and offer promising alternatives to the standard tools and methods used in radiotherapy for treatment planning.

Surface and near-surface dose measurements at beam entry and exit in a 1.5 T MR-Linac using optically stimulated luminescence dosimeters

The objective of this study is to measure surface and near-surface dose at entry and exit surfaces in a 1.5 T MR-Linac (Elekta AB, Stockholm, Sweden) using optically stimulated luminescence dosimeters (OSLDs). OSLDs were expected to be useful for measuring surface dose in a strong magnetic field because they can be taped to undersides to measure exit dose, and their dose response have been shown to be reasonably insensitive to variations in beam angle, beam energy, and magnetic fields.The surface and near-surface dose at the entry and exit of a 20 cm thick solid water phantom was measured with OSLDs for 5 × 5, 10 × 10, and 22 × 22 cm2 field sizes. The solid water phantom was elevated off the couch top to produce an air gap of 3.7 cm so as to observe the electron return effect (ERE) near the beam exit surface. Measurement depths ranged from surface to 15 mm deep from entry and exit surfaces. The phantom dose distribution was also computed in the Monaco (Elekta AB, Stockholm, Sweden) Monte Carlo treatment planning system (TPS).For the 5 × 5, 10 × 10, and 22 × 22 cm2 field sizes the surface dose at depth 0 mm was extrapolated from OSLD measurements to be 10.9%, 12.0%, and 13.5%. The surface entry dose was found to be far less field size-dependent compared to a conventional linac, likely due to a lack of electronic contamination due to the strong magnetic field perpendicular to the beam. The ERE effect was observed in the measurements near the exit surface of the phantom, and was in close agreement with the TPS calculation.

A method of absorbed dose determination using vitamin B2 water for optical imaging of X-rays from high energy medical linear accelerators

Determination of absorbed dose distributions in phantoms in X-ray beams of high energy medical linear accelerators (LINAC) is important for quality control checks of the system. Although optical imaging of water during irradiations of X-ray beams from a LINAC is a promising method, depth dose profiles showed underestimation in deeper parts of the water mainly probably because of the angular dependency of Cerenkov-light produced in water. To solve the problem, the authors added vitamin B2 to water and obtained optical images with a high-sensitivity cooled charge coupled device (CCD) camera during X-ray beams irradiations. Then, the depth and lateral distributions of these optical images were evaluated and compared with those of the dose planning system. The depth dose profiles of vitamin B2 water were similar to those calculated by the dose planning system, although there was dependency on the vitamin B2 concentrations. The lateral profiles of the optical images of vitamin B2 water were slightly smoother than those of the dose planning system at the edge of the distribution. With the measured light spectra of the vitamin B2 water, it was confirmed that the Cerenkov-light was converted to longer wavelength of light by the addition of vitamin B2. The authors conclude that vitamin B2 water has a potential to be a promising material to reduce the difference from those of dose planning system for determining the depth dose profiles.

Assessing localized dosimetric effects due to unplanned gas cavities during pelvic MR-guided radiotherapy using Monte Carlo simulations.

It has been proposed that beam modulation and opposing beam configurations can cancel effects of the Electron Return Effect (ERE) during MR-guided radiotherapy (MRgRT). However, this may not always be the case for unplanned gas cavities outside of the target in the pelvic region. We evaluate dosimetric effects, including effects in the rectal wall, due to unplanned spherical air cavities during MRgRT. Nine virtual cuboid water phantoms containing spherical air cavities (0.5-7.5cm diameter) and a reference phantom without air were created. Monte Carlo dose calculations of 7MV photons under the influence of a 1.5T transverse magnetic field were produced using Monaco 5.19.02 Treatment Planning System (TPS) (Elekta AB, Stockholm, Sweden). Cavities in the path of a single and multiple beam plans were considered. Dose distributions of phantoms with and without air cavities were compared (ΔD% ) using a spherical coordinate system originating in the center of the cavity. Effects in the rectal wall were quantified by comparing dose volume histogram (DVH) parameters for solid and gaseous filling from simulated rectal wall structures. Max(ΔD% ) of ~70% and 20% were observed around large cavities in the path of a single and multiple beam plans, respectively. Approximately 45cm3 of phantom surrounding the largest cavity in a single beam received dose changes of >10%. Dmean in the rectal wall was unchanged when comparing gaseous and solid filling in the path of a single beam; however, D1cc and Dmax increased by up to ~45% and ~63%, respectively. Unplanned gas cavities in the path of a single beam during pelvic MRgRT with a 1.5T transverse magnetic field cause dose changes which may impact toxicity in the rectal wall, depending on local dose and fractionation. Effects are reduced but not eliminated with a five-beam plan.

Rotational radiotherapy of breast cancer with polyenergetic kilovoltage X-ray beams: An experimental and Monte Carlo phantom study

PurposeWe investigated the feasibility of kilovoltage rotational radiotherapy for breast cancer (kV-EBRT) via Monte Carlo simulations and measurements on phantoms. MethodsWe derived the dose distributions for X-ray beams at 150 kV, 300 kVp and 320 kV irradiating breast cylindrical phantoms of 14 cm diameter, mimicking the pendant breast. Simulations were based on the Geant4 toolkit. The point-like X-ray source was rotated either over a full circle or on a limited arc around the phantom. We studied the influence on the surface dose of the distance between the tumor lesion to the skin, of the irradiation protocol (full scan or partial scan) and of the X-ray tube current modulation. ResultsRotational kV-EBRT permitted a periphery-to-center dose ratio from 13% to 9% in homogeneous breast phantoms. Dose distributions in phantoms with off-center simulated lesions, showed a skin-to-tumor dose ratio of 16% and 34% for lesions at 3.25 and 5.25 cm from cylinder axis, respectively. Simulation of the X-ray tube current modulation during the rotation, permits to reach a dose ratio of 20% for the lesion located at 5.25 cm from phantom axis. ConclusionsWe showed the possibility of using low-energy X-ray spectra for kV-EBRT with collimated beams, for obtaining a periphery-to-center dose ratio in the same order of conventional accelerator based megavoltage radiotherapy, when the irradiated area is localized in the center of the breast. For tumors localized near the breast border, we showed that the tube current modulation can be a good solution in order to reduce the skin-to-tumor dose ratio.

Treatment verification using Varian\u2019s dynalog files in the Monte Carlo system PRIMO

BackgroundThe PRIMO system is a computer software that allows the Monte Carlo simulation of linear accelerators and the estimation of the subsequent absorbed dose distributions in phantoms and computed tomographies. The aim of this work is to validate the methods incorporated in PRIMO to evaluate the deviations introduced in the dose distributions by errors in the positioning of the leaves of the multileaf collimator recorded in the dynalog files during patient treatment.MethodsThe reconstruction of treatment plans from Varian’s dynalog files was implemented in the PRIMO system. Dose distributions were estimated for volumetric-modulated arc therapy clinical cases of prostate and head&neck using the PRIMO fast Monte Carlo engine DPM. Accuracy of the implemented reconstruction methods was evaluated by comparing dose distributions obtained from the simulations of the plans imported from the treatment planning system with those obtained from the simulations of the plans reconstructed from the expected leaves positions recorded in the dynalog files. The impact on the dose of errors in the positions of the leaves was evaluated by comparing dose distributions estimated for plans reconstructed from expected leaves positions with dose distributions estimated from actual leaves positions. Gamma pass rate (GPR), a hereby introduced quantity named percentage of agreement (PA) and the percentage of voxels with a given systematic difference (α/Δ) were the quantities used for the comparisons. Errors were introduced in leaves positions in order to study the sensitivity of these quantities.ResultsA good agreement of the dose distributions obtained from the plan imported from the TPS and from the plan reconstructed from expected leaves positions was obtained. Not a significantly better agreement was obtained for an imported plan with an increased number of control points such as to approximately match the number of records in the dynalogs. When introduced errors were predominantly in one direction, the methods employed in this work were sensitive to dynalogs with root-mean-square errors (RMS) ≥0.2 mm. Nevertheless, when errors were in both directions, only RMS >1.2 mm produced detectable deviations in the dose. The PA and the α/Δ showed more sensitive to errors in the leaves positions than the GPR.ConclusionsMethods to verify the accuracy of the radiotherapy treatment from the information recorded in the Varian’s dynalog files were implemented and verified in this work for the PRIMO system. Tolerance limits could be established based on the values of PA and α/Δ. GPR3,3 is not recommended as a solely evaluator of deviations introduced in the dose by errors captured in the dynalog files.

CT beam dosimetric characterization procedure for personalized dosimetry

Personalized dosimetry in computed tomography (CT) can be realized by a full Monte Carlo (MC) simulation of the scan procedure. Essential input data needed for the simulation are appropriate CT x-ray source models and a model of the patient’s body which is based on the CT image. The purpose of this work is to develop comprehensive procedures for the determination of CT x-ray source models and their verification by comparison of calculated and measured dose distributions in physical phantoms. Mobile equipment together with customized software was developed and used for non-invasive determination of equivalent source models of CT scanners under clinical conditions. Standard and physical anthropomorphic CT dose phantoms equipped with real-time CT dose probes at five representative positions were scanned. The accumulated dose was measured during the scan at the five positions. ImpactMC, an MC-based CT dose software program, was used to simulate the scan. The necessary inputs were obtained from the scan parameters, from the equivalent source models and from the material-segmented CT images of the phantoms. 3D dose distributions in the phantoms were simulated and the dose values calculated at the five positions inside the phantom were compared to measured dose values. Initial results were obtained by means of a General Electric Optima CT 660 and a Toshiba (Canon) Aquilion ONE. In general, the measured and calculated dose values were within relative uncertainties that had been estimated to be less than 10%. The procedures developed were found to be viable and rapid. The procedures are applicable to any scanner type under clinical conditions without making use of the service mode with stationary x-ray tube position. Results show that the procedures are well suited for determining and verifying the equivalent source models needed for personalized CT dosimetry based on post-scan MC calculations.

Assessment of Effect Technical Directional Bremsstrahlung Splitting (DBS) on Spectra and Parameters of Simulation with Monte carlo Method BEAMnrc Code (Study Monte Carlo)

Introduction: Previous studies have shown that a Monte Carlo method for the transportations photon beam in medical linear accelerator is a good way. Strip of simulation can be used to measure the dose distribution in phantoms and patients' body. EGSnrc Code is the only code written for use in the field of radiation therapy that has many subset codes that BEAMnrc code is an important one, in which transferred electrons and photons simulation takes place in the head of medical device. DBS technique (Directional Bremsstrahlung Splitting) is a technique that applies a braking radiation in collision. In this study will be discussed to evaluate the effect of this technique on simulation time and particle number of phase-space data and its effect on output spectrum photon beam (6MV) Siemens accelerator Primus model Materials and Methods: : Beginning the geometry of accelerator was stimulated according to its specifications by using the appropriate combination code BEAMnrc. Scoring plane that get phase-space data, in parts of the device such as: target, it was determined the flattening filter by using BEAMDP program to extract their average energy and output spectra in these parts. Also the other side of the research, simulation parameters and output spectra were compared by changing the amount of DBS. Results: Due to the importance of time in fast Mont Carlo, in the simulation with low history of DBS. Considering the time and quality of the spectrum, DBS can be useful. Conclusion: The results show that by changing the number of DBS from 1 to 1000, the amount of simulation time (Elapsed Time) and CPU time and number of particles into phase- space file, respectively have been 7.1, 7 and 36.9 times.

Characterization of EPID software for VMAT transit dosimetry.

Dosimetry check (DC) is a commercial software that allows reconstruction of 3D dose distributions using transit electronic portal imaging device (EPID) images. In this work, we evaluated the suitability of DC software for volumetric modulated arc therapy (VMAT) transit dosimetry. The volumetric gamma agreement index 3%/3mm between twenty VMAT dose distributions reconstructed by DC and calculated with treatment planning system (TPS) were compared to those obtained using PTW OCTAVIUS®4D to assess DC accuracy in VMAT quality assurance (QA). The sensitivity of DC in detecting VMAT delivery and set-up errors and anatomical variations has been investigated by measuring the variation of the gamma agreement index before and after the introduction of specific errors in four VMAT plans related to different anatomical sites. The influence of dose computation algorithm in presence of density inhomogeneity was also assessed. The assessment of VMAT QA shows agreements with TPS maps comparable to OCTAVIUS® 4D (OCT) in homogeneous phantom (p < 0.001). DC mean gamma agreement index was 94.2%±3.4, versus 95.6%±2.5 of OCT, lower dose threshold was set to 10%. Introduction of deliberate errors resulted in lower gamma agreement index and in 38/56 cases the gamma agreement index was over the detection threshold. The dose computation algorithm of DC is accurate in all anatomical sites except lung. However in lung cases, the aqua vivo approach used in this work reduced the algorithm dependence of DC results. DC accurately reproduced VMAT 3D dose distributions in phantom and is sensitive to detect errors caused by delivery inaccuracy and anatomical variations of patients.

A Feasibility Study of IMRT of Lung Cancer Using Gafchromic EBT3 Film

Intensity modulated radiation therapy (IMRT) is an advanced method for delivery of three dimensional therapies, which provides optimal dose distribution with giving multiple nonuniform fluency to the patient. The complex dose distribution of IMRT should be checked to ensure that the accurate dose is delivered. Today, film dosimetry is a powerful tool for radiotherapy treatment Quality Assurance (QA) and a good method to verify dose distribution in phantoms. This study aimed to evaluate the accuracy of IMRT treatment planning system, Prowess Panther® software, with Gafchromic EBT3 films in a inhomogeneity phantom. The IMRT plan was generated by Prowess Panther® treatment planning system (TPS) version 5.2 on a inhomogeneity phantom, then it was irradiated by ONCOR linear accelerator (Linac) with 6 (MV) photon beam energy. The Gafchromic EBT3 film located between the phantom has measured the dose distribution. To compare between TPS calculated doses and film measured doses, Gamma criteria 3%/3 mm, 4%/4 mm, 5%/5 mm, 6%/6 mm and 7%/7 mm Dose Difference (DD) and Distance to Agreement (DTA), respectively were used. Gammas passing rates for PTV are obtained 67.5% for 3%/3mm, 78.8% for 4%/4mm, 86.3% for 5%/5mm, 91.2% for 6%/6mm and 94.3% for 7%/7mm and for organs at risk is 72.4% for 3%/3mm, 82.8% for 4%/4mm, 89.8% for 5%/5mm, 93.3% for 6%/6mm and 95.4% for 7%/7mm (respectively DD/DTA). By increasing the range of criteria the capability increased. The results show that the use of EBT3 film in a inhomogeneity phantoms allows us to evaluate the dose differences between the EBT3 measured dose distribution and TPS calculated dose distribution .Hence, a result Prowess Panther® TPS can be used for IMRT technique treatment.

Efficient double-scattering proton therapy with a patient-specific bolus

PurposePassive scattering proton radiotherapy utilizes beam-specific compensators to shape the dose to the distal end of the tumor target. These compensators typically require therapists to enter the treatment room to mount between beams. This study investigates a novel approach that utilizes a single patient-specific bolus to accomplish the role of multi-field compensators to improve the efficiency of the treatment delivery. MethodsRay-tracing from the proton virtual source was used to convert the beam-specific compensators (mounted on the gantry nozzle) into an equivalent bolus thickness on the patient surface. The field bolus contours were combined to create a single bolus. A 3D acrylic bolus was milled for a head phantom. The dose distribution of the compensator plan was compared to the bolus plan using 3D Gamma analysis and film measurements. Boluses for two clinical patients were also designed. ResultsThe calculated phantom dose distribution of the original proton compensator plan was shown to be equivalent to the plan with the surface bolus. Film irradiations with the proton bolus also confirmed the dosimetric equivalence of the two techniques. The dose distribution equivalency of the bolus plans for the clinical patients were demonstrated. ConclusionsWe presented a novel approach that uses a single patient-specific bolus to replace patient compensators during passive scattering proton delivery. This approach has the potential to reduce the treatment time, the compensator manufacturing costs, the risk of potential collision between the compensator and the patient/couch, and the waste of compensator material.

FoCa: a modular treatment planning system for proton radiotherapy with research and educational purposes

FoCa is an in-house modular treatment planning system, developed entirely in MATLAB, which includes forward dose calculation of proton radiotherapy plans in both active and passive modalities as well as a generic optimization suite for inverse treatment planning.The software has a dual education and research purpose. From the educational point of view, it can be an invaluable teaching tool for educating medical physicists, showing the insights of a treatment planning system from a well-known and widely accessible software platform. From the research point of view, its current and potential uses range from the fast calculation of any physical, radiobiological or clinical quantity in a patient CT geometry, to the development of new treatment modalities not yet available in commercial treatment planning systems.The physical models in FoCa were compared with the commissioning data from our institution and show an excellent agreement in depth dose distributions and longitudinal and transversal fluence profiles for both passive scattering and active scanning modalities. 3D dose distributions in phantom and patient geometries were compared with a commercial treatment planning system, yielding a gamma-index pass rate of above 94% (using FoCa’s most accurate algorithm) for all cases considered.Finally, the inverse treatment planning suite was used to produce the first prototype of intensity-modulated, passive-scattered proton therapy, using 13 passive scattering proton fields and multi-leaf modulation to produce a concave dose distribution on a cylindrical solid water phantom without any field-specific compensator.