Depth Dose Research Articles

A Monte Carlo model of an agility head for a 6 MV Elekta photon beam

IntroductionWith the advance in radiotherapy delivery, the need for a method allowing for a precise dose calculation increased. Monte Carlo modelling of radiotherapy dosages has become an important methodology for the evaluation of dose and beam performance, especially given recent advances in radiotherapy. In this study, an Elekta equipped with an Agility multileaf collimator will be modelled and validated in order to be used in further studies. MethodologyA 6 MV photon beam for the Elekta Synergy linear accelerator with an Agility head was simulated, adjusted, and confirmed using the BEAMnrc/EGSnrc algorithm. Tuning involved comparing percentage depth dose with measured data using different incident electron energies, as analyzed using the gamma index. The best energy so calculated was then used with different full half width maximums (FWHMs) and different angular divergences in order to tune the lateral profiles. Output factors for different field sizes were validated with measurements. Then, the validated model was checked for different depths. ResultsFor PDD comparison, the best electron energy was found to be 6.6 MeV, where the gamma analysis is 100%. A 0.15 cm circle FWHM was found to have the best FWHM. with an angular diverge of 0.03°. The output factors match measured values, proving that the model can achieve a suitably high accuracy. ConclusionThe validated model can be used in advanced radiotherapy dose calculation such as in VMAT, IMRT, and Stereotactic radiotherapy. The model needs to be validated in future studies for smaller field sizes, surface dose, and out-of-field dosimetry.

Influence of magnetic field on a novel scintillation dosimeter in a 1.5 T MR-linac.

For commissioning and quality assurance for adaptive workflows on the MR-linac, a dosimeter which can measure time-resolved dose during MR image acquisition is desired. The Blue Physics model 10 scintillation dosimeter is potentially an ideal detector for such measurements. However, some detectors can be influenced by the magnetic field of the MR-linac. To assess the calibration methods and magnetic field dependency of the Blue Physics scintillator in the 1.5 T MR-linac. Several calibration methods were assessed for robustness. Detector characteristics and the influence of the calibration methods were assessed based on dose reproducibility, dose linearity, dose rate dependency, relative output factor (ROF), percentage depth dose profile, axial rotation and the radial detector orientation with respect to the magnetic field. The potential application of time-resolved dynamic dose measurements during MRI acquisition was assessed. A variation of calibration factors was observed for different calibration methods. Dose reproducibility, dose linearity and dose rate stability were all found to be within tolerance and were not significantly affected by different calibration methods. Measurements with the detector showed good correspondence with reference chambers. The ROF and radial orientation dependence measurements were influenced by the calibration method used. Axial detector dependence was assessed and relative readout differences of up to 2.5% were observed. A maximum readout difference of 10.8% was obtained when rotating the detector with respect to the magnetic field. Importantly, measurements with and without MR image acquisition were consistent for both static and dynamic situations. The Blue Physics scintillation detector is suitable for relative dosimetry in the 1.5 T MR-linac when measurements are within or close to calibration conditions.

The effect of geometrical parameters of skin brachytherapy patch source on depth dose distribution using Monte Carlo simulation

Brachytherapy of superficial skin tumors using beta-emitting sources is a method that has been investigated by some researchers in both simulation and experimental studies with promising results. In the current study, the effect of geometrical parameters of some relevant radionuclides including Y-90, Re-188, P-32, and Ho-166 on the depth dose distribution in skin tissue has been investigated through Monte Carlo simulation.MCNPX Monte Carlo code was employed to model the above-mentioned patch sources in cylindrical format and then the effect of patch geometrical parameters including the source-to-skin distance (SSD), patch thickness, and patch diameter on depth dose distribution was assessed through modeling and calculation of the dose inside a cubic phantom mimicking the skin tissue.The obtained results demonstrated that increasing the SSD, patch thickness, and patch diameter (with the same activity) will reduce the depth dose distribution. Changing the SSD has a more significant effect on the dose gradient within the depth than other geometrical parameters. It was also observed that the effect of patch diameter on the skin-delivered dose gets less sensible as the patch size goes beyond the range of beta radiation inside tissue.Finally, it can be concluded that the patch source geometrical parameters can affect the depth dose distribution inside the skin tissue. This fact may be of concern regarding the delivery of a high radiation dose in a single treatment session. Therefore, variations of patch source geometrical parameters should be considered during the skin dose calculation plan.

Characteristics of a plastic scintillation detector in photon beam dosimetry.

Plastic scintillating detectors (PSD) have gained popularity due to small size and are ideally suited in small-field dosimetry due to no correction needed and hence detector reading can be compared to dose. Likewise, these detectors are active and water equivalent. A new PSD from Blue Physics is characterized in photon beam. Innovation in small-field dosimetry detector has led us to examine Blue Physics PSD (BP-PSD) for use in photon beams from linear accelerator. BP-PSD was acquired and its characteristics were evaluated in photon beams from a Varian TrueBeam. Data were collected in a 3D water tank. Standard parameters; dose, dose rate, energy, angular dependence and temperature dependence were studied. Depth dose, profiles and output in a reference condition as well as small fields were measured. BP-PSD is versatile and provides data very similar to an ion chamber when Cerenkov radiation is properly accounted. This device measures data pulse by pulse which very few detectors can perform. The differences between ion chamber data and PSD are<2% in most cases. The angular dependence is a bit pronounces to 1.5% which is due to PSD housing. Depth dose and profiles are comparable within<1% to an ion chamber. For small fields this detector provides suitable field output factor compared to other detectors and Monte Carlo (MC) simulated data without any added correction factor. The characteristics of Blue Physics PSD is uniquely suitable in photon beam and more so in small fields. The data are reproducible compared to ion chamber for most parameters and ideally suitable for small-field dosimetry without any correction factor.

Technical note: Commissioning of a low-cost system for directly 3D printed flexible bolus.

To present the commissioning process of a low-cost solution for directly 3D printed flexible patient specific bolus. The 3D printing solution used in this study consisted of a resin stereolithography 3D printer and a flexible curing resin. To test the dimensional accuracy of the 3D printer, rectangular cuboids with varying dimensions were 3D printed and their measured dimensions were compared to the designed dimensions. Percent Depth Dose (PDD) profiles were measured by irradiating film embedded in a 3D printed phantom made of the flexible material. A CT of the phantom was acquired and used to replicate the irradiation setup in the treatment planning system. PDDs were calculated for both the native HU of the phantom, and with the phantom HU overridden to 300 HU to match its physical density. Dosimetric agreement was characterized by comparing calculated to measured depths of R90, R80, and R50. Upon completion of the commissioning process, a bolus was 3D printed for a clinical case study for treatment of the nose. Dimensional accuracy of the printer and material combination was found to be good, with all measured dimensions of test cuboids within 0.5mm of designed. PDD measurements demonstrated the best dosimetric agreement when the material was overridden to 300 HU, corresponding to the measured physical density of the material of 1.18g/cc. Calculated and measured depths of R90, R80, and R50 all agreed within 1mm. The bolus printed for the clinical case was free from defects, highly conformal, and led to a clinically acceptable plan. The results of the commissioning measurements performed indicate that the 3D printer and material solution are suitable for clinical use. The 3D printer and material combination can provide a low-cost solution a clinic can implement in-house to directly 3D print flexible bolus.

Numerical simulation of electron beam depth dose distribution in water phantom passed through modified plastic materials

The aim of the study is to evaluate the feasibility of using modified plastics for 3D printing of boluses for electron beam therapy. Filaments for 3D printing made from plastic materials with an admixture of copper were studied. Test samples were made from these filaments and investigated. Mathematical models of such products were created based on the obtained data. The thicknesses of the boluses made from each modified material were calculated to achieve the same electron beam depth dose distribution in the water phantom as natural plastic. Using a the developed model of a therapeutic electron beam and newly created models of test object materials, the electron beam depth dose distributions in the water phantom that passed through the materials under study were obtained in bolus geometry. The results of the work demonstrate the potential of using modified plastics for creating forming elements in electron beam therapy. The application of this plastic samples for electron beam shaping with individual configuration allows to modify the irradiation field based on the clinical tasks quickly and efficiently and to increase the effectiveness of electron beam radiotherapy procedures.

Bare spherical gel dosimeter with optical computed tomography scanning

Radiochromic polyvinyl alcohol-iodide (PVA-I) hydrogel dosimeter with crosslinking by glutaraldehyde (GTA) has been reported. Because of the transparent gel’s mechanical strength, a study to cast samples in spherical shapes was initiated. The bare sample, 47 mm in diameter was mounted on a funnel and held by suction in a custom, 96 mm diameter, cylindrical vessel for 3D optical CT scanning. A solution of the same formulation without GTA provided refractive index matching inside the vessel for optic scanning and eliminated concentration gradients. The gel sphere remained in the vessel after draining the solution for the ‘in-air’ irradiation. A 20 Gy, maximum dose to the gel sphere was delivered by a single, 6 MV, x-ray beam. Comparison of central axis depth doses for the gel reconstruction and Monte Carlo calculation revealed similar results, indicating accurate 3D dosimetry within 1 mm of the gel surface will be possible. The gel recorded slightly greater dose in build-up region and slightly lower dose in the exit hemisphere relative to the calculation.

Linear-energy-transfer-independent nanoclay radio-fluorogenic gel dosimeter under energetic ion beams of 28Si14+, 40Ar18+, 56Fe26+, 132Xe54+, and 12C6+

Recently, a radio-fluorogenic gel dosimeter that can evaluate the depth–dose distribution of high-energy carbon ion beams within a radio-therapeutic dose range was reported. This study performed a detailed characterization of this gel dosimeter using five types of ion beams (high-energy carbon, silicon, argon, iron, and xenon ion beams). In addition, this paper explains the mechanism of linear-energy-transfer (LET)-independent sensitivity by evaluating the effect of the composition conditions and contribution of water-decomposed molecules and radicals. Thus, it was observed that the dosimeter could be used to evaluate the dose distribution of various high-energy heavy ion beams in bioequivalent materials. The LET range was 25–8000 eV/nm. Additionally, it was suggested that this feature was caused by two mechanisms, i.e., an increase in the reaction by hydrogen peroxide and a decrease in the contribution of OH radicals by degassing.

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.

Evaluation of the water-equivalent characteristics of the SP34 plastic phantom for film dosimetry in a clinical linear accelerator.

In this study, some confusing points about electron film dosimetry using white polystyrene suggested by international protocols were verified using a clinical linear accelerator (LINAC). According to international protocol recommendations, ionometric measurements and film dosimetry were performed on an SP34 slab phantom at various electron energies. Scaling factor analysis using ionometric measurements yielded a depth scaling factor of 0.923 and a fluence scaling factor of 1.019 at an electron beam energy of <10 MeV (i.e., R50 < 4.0 g/cm2). It was confirmed that the water-equivalent characteristics were similar because they have values similar to white polystyrene (i.e., depth scaling factor of 0.922 and fluence scaling factor of 1.019) presented in international protocols. Furthermore, percentage depth dose (PDD) curve analysis using film dosimetry showed that when the density thickness of the SP34 slab phantom was assumed to be water-equivalent, it was found to be most similar to the PDD curve measured using an ionization chamber in water as a reference medium. Therefore, we proved that the international protocol recommendation that no correction for measured depth dose is required means that no scaling factor correction for the plastic phantom is necessary. This study confirmed two confusing points that could occur while determining beam characteristics using electron film dosimetry, and it is expected to be used as basic data for future research on clinical LINACs.

Dosimetric characterization of a new surface-conforming electron MLC prototype.

The purpose is toreduce normal tissue radiation toxicity for electron therapy through the creation of a surface-conforming electron multileaf collimator (SCEM). The SCEM combines the benefits of skin collimation, electron conformal radiotherapy, and modulated electron radiotherapy. An early concept for the SCEM was constructed. It consists of leaves that protrude towards the patient, allowing the leaves to conform closely to irregular patient surfaces. The leaves are made of acrylic to decrease bremsstrahlung, thereby decreasing the out-of-field dose. Water tank scans were performed with the SCEM in place for various field sizes for all available electron energies (6, 9, 12, and 15 MeV) with a 0.5cm air gap to the water surface at 100cm source-to-surface distance (SSD). These measurements were compared with Cerrobend cutouts with the field size-matched at 100 and 110cm SSD. Output factor measurements were taken in solid water for each energy at dmax for both the cerrobend cutouts and SCEM at 100cm SSD. Percent depth dose (PDD) curves for the SCEM shifted shallower for all energies and field sizes. The SCEM also produced a higher surface dose relative to Cerrobend cutouts, with the maximum being a 9.8% increase for the 3cm × 9cm field at 9 MeV. When compared to the Cerrobend cutouts at 110cm SSD, the SCEM showed a significant decrease in the penumbra, particularly for lower energies (i.e., 6 and 9 MeV). The SCEM also showed reduced out-of-field dose and lower bremsstrahlung production than the Cerrobend cutouts. The SCEM provides significant improvement in the penumbra and out-of-field dose by allowing collimation close to the skin surface compared to Cerrobend cutouts. However, the added scatter from the SCEM increases shallow PDD values. Future work will focus on reducing this scatter while maintaining the penumbra and out-of-field benefits the SCEM has over conventional collimation.

Development and benchmarking of a dose rate engine for raster-scanned FLASH helium ions.

Radiotherapy with charged particles at high dose and ultra-high dose rate (uHDR) is a promising technique to further increase the therapeutic index of patient treatments. Dose rate is a key quantity to predict the so-called FLASH effect at uHDR settings. However, recent works introduced varying calculation models to report dose rate, which is susceptible to the delivery method, scanning path (in active beam delivery) and beam intensity. This work introduces an analytical dose rate calculation engine for raster scanned charged particle beams that is able to predict dose rate from the irradiation plan and recorded beam intensity. The importance of standardized dose rate calculation methods is explored here. Dose is obtained with an analytical pencil beam algorithm, using pre-calculated databases for integrated depth dose distributions and lateral penumbra. Dose rate is then calculated by combining dose information with the respective particle fluence (i.e., time information) using three dose-rate-calculation models (mean, instantaneous, and threshold-based). Dose rate predictions for all three models are compared to uHDR helium ion beam (145.7 MeV/u, range in water of approximatively 14.6cm) measurements performed at the Heidelberg Ion Beam Therapy Center (HIT) with a diamond-detector prototype. Three scanning patterns (scanned or snake-like) and four field sizes are used to investigate the dose rate differences. Dose rate measurements were in good agreement with in-silico generated distributions using the here introduced engine. Relative differences in dose rate were below 10% for varying depths in water, from 2.3 to 14.8cm, as well as laterally in a near Bragg peak area. In the entrance channel of the helium ion beam, dose rates were predicted within 7% on average for varying irradiated field sizes and scanning patterns. Large differences in absolute dose rate values were observed for varying calculation methods. For raster-scanned irradiations, the deviation between mean and threshold-based dose rate at the investigated point was found to increase with the field size up to 63% for a 10mm × 10mm field, while no significant differences were observed for snake-like scanning paths. This work introduces the first dose rate calculation engine benchmarked to instantaneous dose rate, enabling dose rate predictions for physical and biophysical experiments. Dose rate is greatly affected by varying particle fluence, scanning path, and calculation method, highlighting the need for a consensus among the FLASH community on how to calculate and report dose rate in the future. The here introduced engine could help provide the necessary details for the analysis of the sparing effect and uHDR conditions.

An open-source software for calculating 1D gamma index in radiation therapy

PurposeThis study was developed to create computer software for performing the gamma index comparison between measurement and Monte Carlo (MC) simulation for the percentage depth dose (PDD) and beam off-center ratio profile (OCR). Materials and methodsThe gamma software was built in the matrix laboratory (MATLAB) software environment. The developed software was compared with ScanDosematch and Bistromath software’s gamma evaluation to assess its accuracy. A set of reference and evaluated dose distribution, which were obtained from measurement and MC simulation, was input to the software to calculate the 1D gamma index using different criteria (i.e. 3%/3 mm, 2%/3 mm, and 2%/2 mm). ResultsWe compared the two results of gamma index at 3%/3 mm, 2%/3 mm, and 2%/2 mm criteria, one calculated by the proposed software and one manually. The comparison showed high agreement between the proposed software and theoretical calculation. ConclusionsBased on the results, we concluded that our developed software has high accuracy, compared to theoretical calculation. This software could serve as a non-commercial and open-source tool for researchers and students.

The assessment of the clinical impact of using a single set of radiotherapy planning data for two kilovoltage therapy units.

Kilovoltage therapy units are used for superficial radiotherapy treatment delivery. Peer reviewed studies for MV linear accelerators describe tolerances to dosimetrically match multiple linear accelerators enabling patient treatment on any matched machine. There is an absence of literature on using a single planning data set for multiple kilovoltage units which have limited ability for beam adjustment. This study reviewed kilovoltage dosimetry and treatment planning scenarios to evaluate the feasibility of using ACPSEM annual QA tolerances to determine whether two units (of the same make and model) were dosimetrically matched. The dosimetric characteristics, such as measured half value layer (HVL), percentage depth dose (PDD), applicator factor and output variation with stand-off distance for each kV unit were compared to assess the agreement. Independent planning data based on the measured HVL for each beam energy from each kV unit was prepared. Monitor unit (MU) calculations were performed using both sets of planning data for approximately 200 clinical scenarios and compared with an overall agreement between units of < 2%. Additionally, a dosimetry measurement comparison was completed at each site for a subset of nine scenarios. All machine characterisation measurements were within the ACPSEM Annual QA tolerances, and dosimetric testing was within 2.5%. This work demonstrates that using a single set of planning data for two kilovoltage units is feasible, resulting in a clinical impact within published uncertainty.

Particular issues to be considered in small field dosimetry for TrueBeam STx commissioning

This study aims to report the relevant issues concerning small fields in the commissioning of a TrueBeam STx for photon energies of 6MV, 10MV, 6FFF, and 10FFF. Percent depth doses, profiles, and field output factors were measured according to the beam model configuration of the treatment planning system. Multiple detectors were used based on the IAEA TRS-483 protocol as well as EBT3 radiochromic film. Analytical Anisotropic and Acuros XB algorithms, were configured and validated through basic dosimetry comparisons and end-to-end clinical tests.

Automated Image Analysis of Transmission Electron Micrographs: Nanoscale Evaluation of Radiation-Induced DNA Damage in the Context of Chromatin.

Heavy ion irradiation (IR) with high-linear energy transfer (LET) is characterized by a unique depth dose distribution and increased biological effectiveness. Following high-LET IR, localized energy deposition along the particle trajectories induces clustered DNA lesions, leading to low electron density domains (LEDDs). To investigate the spatiotemporal dynamics of DNA repair and chromatin remodeling, we established the automated image analysis of transmission electron micrographs. Human fibroblasts were irradiated with high-LET carbon ions or low-LET photons. At 0.1 h, 0.5 h, 5 h, and 24 h post-IR, nanoparticle-labeled repair factors (53BP1, pKu70, pKu80, DNA-PKcs) were visualized using transmission electron microscopy in interphase nuclei to monitor the formation and repair of DNA damage in the chromatin ultrastructure. Using AI-based software tools, advanced image analysis techniques were established to assess the DNA damage pattern following low-LET versus high-LET IR. Low-LET IR induced single DNA lesions throughout the nucleus, and most DNA double-strand breaks (DSBs) were efficiently rejoined with no visible chromatin decondensation. High-LET IR induced clustered DNA damage concentrated along the particle trajectories, resulting in circumscribed LEDDs. Automated image analysis was used to determine the exact number of differently sized nanoparticles, their distance from one another, and their precise location within the micrographs (based on size, shape, and density). Chromatin densities were determined from grayscale features, and nanoparticles were automatically assigned to euchromatin or heterochromatin. High-LET IR-induced LEDDs were delineated using automated segmentation, and the spatial distribution of nanoparticles in relation to segmented LEDDs was determined. The results of our image analysis suggest that high-LET IR induces chromatin relaxation along particle trajectories, enabling the critical repair of successive DNA damage. Following exposure to different radiation qualities, automated image analysis of nanoparticle-labeled DNA repair proteins in the chromatin ultrastructure enables precise characterization of specific DNA damage patterns.

Development of a semi empirical calculation approach for the determination of percentage depth dose in water for higher energy photon beams using a medical linear accelerator

The development of a calculation approach to determine the Percentage Depth Dose (PDD) by manual calculation for medical linear accelerator of 6 MV and 15 MV photon beam energy. The equation to determine PDD can be divided into two components i.e., the primary component and the scatter component. To calculate the primary component, the linear attenuation coefficient needs to be calculated. The measurement of charge was taken at various depths and for different field sizes using 6 MV and 15 MV photon beams. To determine the linear attenuation coefficient, a graph of ln (MR) where, MR represents corrected meter reading was plotted against depth in cm. By plotting another graph of linear attenuation coefficient against field size, to determine the effective linear attenuation coefficient. The scattered component KS was graphically plotted against depth in cm and derived an equation for scatter component. The calculated PDD for 6 MV was found to be within 1 % difference and for 15 MV percentage difference within 3 %. It was found that numerically developed PDD values table for higher energy photon beam becomes valid and it can be utilized for the manual dose calculation.

Impact of proton therapy on the DNA damage induction and repair in hematopoietic stem and progenitor cells

Proton therapy is of great interest to pediatric cancer patients because of its optimal depth dose distribution. In view of healthy tissue damage and the increased risk of secondary cancers, we investigated DNA damage induction and repair of radiosensitive hematopoietic stem and progenitor cells (HSPCs) exposed to therapeutic proton and photon irradiation due to their role in radiation-induced leukemia. Human CD34+ HSPCs were exposed to 6 MV X-rays, mid- and distal spread-out Bragg peak (SOBP) protons at doses ranging from 0.5 to 2 Gy. Persistent chromosomal damage was assessed with the micronucleus assay, while DNA damage induction and repair were analyzed with the γ-H2AX foci assay. No differences were found in induction and disappearance of γ-H2AX foci between 6 MV X-rays, mid- and distal SOBP protons at 1 Gy. A significantly higher number of micronuclei was found for distal SOBP protons compared to 6 MV X-rays and mid- SOBP protons at 0.5 and 1 Gy, while no significant differences in micronuclei were found at 2 Gy. In HSPCs, mid-SOBP protons are as damaging as conventional X-rays. Distal SOBP protons showed a higher number of micronuclei in HSPCs depending on the radiation dose, indicating possible changes of the in vivo biological response.

Carbon-fiber alternative to the commercial gating surrogate for the Varian Truebeam™

Background In this study we present the Tracking Accessory 3 (TA3) as an alternative to the commercial gating block (GB) surrogate for the Varian Truebeam™ gating system (TGS). The TGS requires three visible reflectors to track the surrogate, presenting an opportunity for a surrogate to be made with less material and thus smaller dosimetric footprint than the commercial four reflector model. Materials and methods Relative dose and depth dose profiles below the TA3 and the GB were measured with radiosensitive film. Accuracy and reproducibility of the detected motion amplitude for three TA3s and one GB were determined using a respiratory phantom with surrogate to determine the camera’s tracking volume. Clinical performance was evaluated prospectively in 10 breast cancer patients treated with deep inspiration breath hold monitored with TA3 and compared to previously published results. Non-parametric statistics were applied to test for significance. Results and conclusions Surface doses were increased up to 94% and 187% for the TA3 and GB, respectively, compared to no surrogate. The surface area influenced by at least 25% increase in dose was 12 cm2 and 105 cm2 for the TA3 and GB, respectively. The water equivalent thickness of the surrogates was found to be 1 mm for the TA3 and 3 mm for GB. The difference in measured amplitude were <0.2 mm for TA3 compared to the GB. The TA3s and GB were detected at all extremes of the clinically relevant tracking volume of the TGS. Clinical performance showed no significant differences. The TA3 caused less surface dose increase compared to the commercial GB. In the tested range all surrogates measured motion amplitude within 0.2 mm of reference value, which is not a clinically relevant difference. The TA3 showed no significant differences in clinical performance to similarly positioned surrogates.

Monte carlo simulation of electron beams from varian truebeam linear accelerator used in radiotherapy: estimation of initial beam parameters

In Radiotherapy (RT), electron beams are widely used to treat superficial tumours. The dose delivered to the patients was precisely estimated by Monte Carlo (MC) methods. MC codes need Initial Beam Parameter (IBP) [mean energy, energy spectrum, spot size] and structural details of the machines as input to predict the dose. This study determined the IBP of Varian TrueBeam (TB) Linear Accelerator using PRIMO and validated it using depth dose curves and profiles. The MC Code GEANT 4 (VirtuaLinac) and PENELOPE (PRIMO) were used. The energies used were 6,9,12 & 18 MeV, the applicator used was 10x10 cm2 and 25x25 cm2, and the source to surface distance value was set as 100cm. The MC model available in PRIMO for TB was validated. Initial mean energies were obtained of 6.81, 9.77, 13.15 and 19.79 MeV for 6, 9, 12 and 18 MeV nominal energies, respectively. Sigma of Gaussian distribution was estimated as 0.59, 0.62, 0.71 and 0.82, respectively. The average values of percentage dose difference between the measured and MC simulated PDD and profiles were within 5%. Found that PRIMO is a convenient and easy-to-operate software application with the potential to estimate dose distribution in water phantoms or CT Images precisely.