Beam Quality Index Research Articles

Determination of Tissue Phantom Ratios of High Energy Photon Beams Using Monte Carlo Code

Monte Carlo codes are veritable tools in radiotherapy to understand the transport mechanism, dose distributions, and energy depositions of ionizing radiations traversing in different media. In some beam calibration protocols, a tissue-phantom-ratio at depths 20 cm and 10 cm (TPR20,10) in a phantom is used to determine the beam-quality conversion factor for different ion chambers. Thus, this study aims to evaluate the efficiency of Monte Carlo code in the determination of beam quality of high radiation energy beams similar to what is expected in clinical settings. Electron Gamma Shower National Research Council in Canada (EGSnrc) Monte Carlo Code was used to design complex ion chamber geometries according to the manufacturer’s specifications. Phase space files were used as x-ray beam radiation sources. Two set-ups (SAD and SSD) methods were used for the determination of TPR20,10 to conform to the accepted clinical procedures. Beam collimation was 10 cm by 10 cm field size with an ionization chamber placed at 20 cm and 10 cm in the water phantom to obtain doses at two points respectively. The TPR20,10 of each energy was obtained using the appropriate equations. The obtained results showed no significant difference between the measured and available TPR 20,10 data (p = 0.995). Ion chamber configurations and specifications were also found not to have a significant effect (p = 0.33) on the TPR 20,10 obtained values. The results obtained in this study are in agreement with the recommended standard values. The findings of this study show that the Monte Carlo codes can be used as a tool in determining x-ray beam quality indices of designed clinical linear accelerator (Linac) machines.

Comparison of organ dose from chest radiography with varying beam quality and constant exposure index.

The optimum X-ray tube voltage for chest radiographic examinations remains unclear; hence, the tube voltage varies between medical facilities. An exposure index (EI) was proposed to standardize the parameters for radiographic examinations. However, even if identical EI values are used to examine the same person, organ doses may vary due to differences in tube voltages. In this study, the variation in organ doses between different beam qualities under identical EI values for chest radiographic examinations was investigated using Monte Carlo simulations. A focused anti-scatter grid as well as standard and larger physique-type medical internal radiation dose (MIRD) phantoms were studied under tube voltages of 90, 100, 110, and 120 kVp. The organ doses in the MIRD phantom increased as the X-ray tube voltage decreased, even with identical EI values. The absorbed doses in the lungs of standard and large-sized MIRD phantoms at 90 kVp were 23% and 35% higher than those at 120 kVp, respectively. The doses to organs other than the lung at 90 kVp were also higher than those at 120 kVp. From the perspective of reducing radiation doses, a tube voltage of 120 kVp is considered better for chest examinations compared with a tube voltage of 90 kVp under identical EI values.

Comparison of derived correction factors for effects of ion recombination and photon beam quality index following TG-51 and TRS-398 dosimetry protocols

In this study, ion recombination correction factor (kS) and beam quality conversion factor (kQ,Q0) values were extracted following the recommendations of the TRS-398 and TG-51 dosimetry protocols for widely used cylindrical ionization chambers for high energy photon beam dosimetry to quantify the agreement between the instructions for these two protocols for absolute dosimetry inside water. Four different types of cylindrical ionization chambers comprising Farmer (TM30013), Semiflex 0.125 cm3 (TM31010), Semiflex 0.3 cm3 (TM31013), and PinPoint (TM31016) were considered, and kS and kQ,Q0 values were determined at photon energies of 6 MV and 15 MV. The maximum difference between the measured kS values according to the instructions in the TRS-398 and TG-51 protocols was 0.03%. The kS data measured with both protocols agreed well with those measured by using the Jaffe-plot approach, where the maximum difference was about 0.33%. The observed differences between the kQ,Q0 factors measured by using the TRS-398 and TG-51 dosimetry protocols at photon energies of 6 MV and 15 MV were 0.37% and 0.55%, respectively. The kQ,Q0 values measured using the TG-51 dosimetry protocols were slightly closer to those measured by a reference ionization chamber dosimeter. We conclude that the maximum differences were about 0.4% and 0.6% in the absorbed dose measurements according to the TRS-398 and TG-51 instructions at photon energies of 6 MV and 15 MV, respectively. The type of ionization chamber employed also affected the differences, where the maximum and minimum dose differences were found using the Farmer and PinPoint chambers, respectively.

Radiological and Dosimetric Evaluation of Biomaterial Composite Phantoms with High Energy Photons and Electrons.

The current study was undertaken to investigate the radiological and dosimetric parameters of natural product-based composite (SPI/NaOH/IA-PAE/ Rhizophora spp .) phantoms. The radiological properties of the phantoms were measured at different gamma energies from Compton scatter of photons through angles of 0, 30, 45, 60, 75, and 90 degrees. Ionization chamber (IC) and Gafchromic EBT3 film dosimeters were employed to evaluate the dosimetric characteristics for photons (6-10 MV) and electrons (6-15 MeV). Radiological property results of the composite phantoms were consistent with good quality compared to those of solid water phantoms and theoretical values of water. Photon beam quality index of the SPI15 phantom with p-values of 0.071 and 0.073 exhibited insignificant changes. In addition, good agreement was found between PDD curves measured with IC and Gafchromic EBT3 film for both photons and electrons. The computed therapeutic and half-value depth ranges matched within the limits and are similar to those of water and solid water phantoms. Therefore, the radiological and dosimetric parameters of the studied composite phantom permit its use in the selection of convenient tissue- and water-equivalent phantom material for medical applications.

3D printed 2D range modulators preserve radiation quality on a microdosimetric scale in proton and carbon ion beams

IntroductionParticle therapy using pencil beam scanning (PBS) faces large uncertain- ties related to ranges and target motion. One possibility to improve existing mitigation strategies is a 2D range modulator (2DRM). A 2DRM offers faster irradiation times by reducing the number of layers and spots needed to create a spread-out Bragg peak. We have investigated the impact of 2DRM on microdosimetric spectra measured in proton and carbon ion beams. Materials and MethodsTwo 2DRMs were designed and 3D printed, one for.124.7 MeV protons and one for 238.6 MeV/u carbon ions. Their dosimetric validation was performed using Roos and PinPoint ionization chamber and EBT3 films. Monte Carlo simulations were done using GATE. A silicon-based solid-state microdosimeter was used to collect pulse-height spectra along three depths for two irradiation modalities, PBS and a single central beam. ResultsFor both particle types, the original pin design had to be optimized via GATE simulations. The difference between the R80 of the simulated and measured depth dose curve was 0.1 mm. The microdosimetric spectra collected with the two irradiation modalities overlap well. Their mean lineal energy values differ over all positions by 5.2 % for the proton 2DRM and 2.1 % for the carbon ion 2DRM. ConclusionRadiation quality in terms of lineal energy was independent of the irradiation method. This supports the current approach in reference dosimetry, where the residual range is chosen as a beam quality index to select stopping power ratios.

Geometrical source modeling of 6MV flattening-filter-free (FFF) beam from TrueBeam linear accelerator and its commissioning validation using Monte Carlo simulation approach for radiotherapy

PurposeTo study geometrical source modeling of 6 MV flattening-filter-free (FFF) beam from TrueBeam linear accelerator and its commissioning validation using Monte Carlo simulation approach. Methods & materialSource modeling of 6MVFFF beam from TrueBeam linear accelerator has been accomplished by using PRIMO as the Monte-Carlo (MC) simulation software based on PENELOPE code. Initially, source modeling of 6MVFFF beam was validated against experimentally measured Percentage-depth-dose (PDD) and profile for 10 × 10cm2 field. Followed by commissioning validation of 6MVFFF beam has been carried out by simulating PDDs, profiles and output factors for range of field sizes. Besides, verification of absolute dose, beam quality index, performance analysis of dose distribution in heterogeneous phantom and simulation of radiation treatment plan for validation of Treatment planning system (TPS) was performed. Simulated results compared against measured; dose distributions were analyzed using gamma analysis with acceptance criteria of 2% Dose-difference (DD) and 2 mm Distance-to-agreement (DTA). ResultsGamma analysis for all the simulated and measured PDDs and profiles shows minimum passing rate of 100% and 98.04% respectively. Simulated values of absolute point dose, beam quality index and output factors shows good agreements with measurements. Gamma analysis of depth dose distribution in heterogeneous phantom obtained using MC simulation and calculated with Analytical anisotropic algorithm (AAA) agreed within 95.89%. However, heterogeneous medium of very high and low-density region shows larger dose discrepancy between MC and AAA due to the poor modeling of AAA compared to MC. The percentage of 99.81% of gamma passing and comparison of predicted Dose-volume-histogram (DVH) shows good resemblance between PRIMO simulated and AAA calculated plan. ConclusionStudy concludes that PRIMO is an independent MC simulation tools for verification and commissioning validation of external beam radiotherapy in treatment of cancer. The MC validation of external beam therapy modules grants higher confidence in accuracy of radiation dose delivery.

Analysis of Uncertainties in Clinical High-Energy Photon Beam Calibrations Using Absorbed Dose Standards

We compared the results of absorbed dose measurements made using the TRS-398, TG-51, and DIN protocols and their associated uncertainties to reduce discrepancies in measurement results made using the three protocols. This experiment was carried out on two Varian Medical linear accelerators with 4, 6, 10, and 20 MV photon energies using FC65-G and CC15 (cylindrical) and NACP-02-type (plane-parallel) ion chambers in water phantoms. The radiation beam quality index (Q) was determined from the measurement of percentage depth dose. It was used to determine the photon beam quality factor required with the ionization chamber calibration factor to convert the ion chamber reading into the absorbed dose to water. For the same beam quality, the TRS-398/TG-51 varied from 0.01% to 1.8%, whereas the ratio for TRS-398/DIN 6800-2 varied from 0.1% to 0.88%. The chamber-to-chamber variation was 0.09% in TRS-398/TG-51, 0.03% in TRS-398/DIN, and 0.02% in TG-51/DIN 6800-2. The expanded uncertainties (k = 1) were 1.24 and 1.25 when using TRS-398 and DIN 6800-2, respectively. Using the aforementioned three protocols, the results showed little chamber-to-chamber variation and uncertainty in absorbed dose measurements. The estimated uncertainties when using cylindrical ion chambers were slightly lower than those measured using plane-parallel chambers. The results are important in facilitating comparisons of absorbed dose measurements when using the three protocols.

Experimental validation of a linac head Geant4 model under a grid computing environment

Background and purpose . This work aims to present the strategy to simulate a clinical linear accelerator based on the geometry provided by the manufacturer and summarize the corresponding experimental validation. Simulations were performed with the Geant4 Monte Carlo code under a grid computing environment. The objective of this contribution is reproducing therapeutic dose distributions in a water phantom with an accuracy less than 2%. Materials and methods. A Geant4 Monte Carlo model of an Elekta Synergy linear accelerator has been established, the simulations were launched in a large grid computing platform. Dose distributions are calculated for a 6 MV photon beam with treatment fields ranging from 5 × 5 cm2 to 20 × 20 cm2 at a source—surface distance of 100 cm. Results. A high degree of agreement is achieved between the simulation results and the measured data, with dose differences of about 1.03% and 1.96% for the percentage depth dose curves and lateral dose profiles, respectively. This agreement is evaluated by the gamma index comparisons. Over 98% of the points for all simulations meet the restrictive acceptability criteria of 2%/2 mm. Conclusion. We have demonstrated the possibility to establish an accurate linac head Monte Carlo model for dose distribution simulations and quality assurance. Percentage depth dose curves and beam quality indices are in perfect agreement with the measured data with an accuracy of better than 2%.

Comparing the dosimeter-specific corrections for influence quantities of some parallel-plate ionization chambers in conventional electron beam dosimetry

The performance characteristics of some widely employed parallel-plate ionization chambers in dosimetry of conventional high energy electron beams were evaluated and compared in the present study following the recommendations of the IAEA TRS-398 reference dosimetry protocol.Three different types of PTW-made parallel-plate ionization chambers including Roos (TM34001), Markus (TM23343), and Advanced Markus (TM34045) were employed, and correction factors for polarity (kpol), recombination (ks), and quality conversion factor (kQ,Q0) were determined at different nominal electron energies of 4, 6, 9, 12, 16, and 20 MeV produced by a Varian Trilogy clinical Linac. All measurements were performed inside a MP3-M automatic water phantom in the reference condition of 100 cm SSD (source to surface distance), reference measurement depth (zref), and 10 × 10 cm2 field size at the phantom surface.The maximum and minimum range of kpol deviations from unity were respectively found for Markus and Roos ionization chambers. The maximum ks values also belonged to the Markus ionization chamber, while the minimum ks values were observed for the Advanced Markus chamber. The measured ks values through recommendations of the TRS-398 dosimetry protocol were in good accordance with those obtained by Jaffe-plot analysis for all considered ionization chambers. The type of employed ionization chamber can minimally affect the measured electron beam quality index (R50), while it can have a more considerable impact on kQ,Q0 value, especially in the case of the Markus chamber.From the results, it can be concluded that the Roos and Advanced Markus ionization chambers have a superior performance in the case of electron beam dosimetry, although all considered ionization chambers fulfilled the criteria requested by relevant reference dosimetry protocols.

Dosimetry for Cell Irradiation using Orthovoltage (40-300 kV) X-Ray Facilities.

The importance of dosimetry protocols and standards for radiobiological studies is self-evident. Several protocols have been proposed for dose determination using low energy X-ray facilities, but depending on the irradiation configurations, samples, materials or beam quality, it is sometimes difficult to know which protocol is the most appropriate to employ. We, therefore, propose a dosimetry protocol for cell irradiations using low energy X-ray facility. The aim of this method is to perform the dose estimation at the level of the cell monolayer to make it as close as possible to real cell irradiation conditions. The different steps of the protocol are as follows: determination of the irradiation parameters (high voltage, intensity, cell container etc.), determination of the beam quality index (high voltage-half value layer couple), dose rate measurement with ionization chamber calibrated in air kerma conditions, quantification of the attenuation and scattering of the cell culture medium with EBT3 radiochromic films, and determination of the dose rate at the cellular level. This methodology must be performed for each new cell irradiation configuration as the modification of only one parameter can strongly impact the real dose deposition at the level of the cell monolayer, particularly involving low energy X-rays.

Direct measurement of ionization chamber absorbed dose kQ factors in clinical electron beams

An electron water calorimeter is described and is used to experimentally determine beam quality dependent conversion factors, kQ, for two ionization chamber types in high-energy electron beams. The current water calorimeter was upgraded to obtain reproducible measurements in electron beams from 10 MeV to 22 MeV (corresponding beam quality index R50 ranging over 4.20–8.97 g cm−2). Measurements of radiation induced temperature rise are made using a plane-parallel glass vessel with calibrated thermistor probes in a 4 °C water phantom. Three types of plane-parallel chambers (PTW Roos, IBA PPC40 and SNC 1045) and two types of cylindrical chambers (PTW30013 and IBA FC65-G) are measured to directly derive beam quality correction factors in the same water phantom. Relative combined standard uncertainty for kQ factors of 0.56% for 10 MeV beams and above were achieved. General agreement is obtained between the relative electron energy dependencies of the kQ factors measured in this work and those derived from TRS-398 of the IAEA and recent other experimental investigations. Furthermore, the experimental kQ values obtained here will impact future updates of reference dosimetry protocols, and the current standard uncertainties in electron reference dosimetry can be reduced by the method proposed in this work.

The dependence of inhomogeneity correction factors on photon beam quality index performed with the Anisotropic Analytical Algorithm

Abstract Purpose: The purpose of the study was to investigate the dependence of tissue inhomogeneity correction factors (ICFs) on the photon beam quality index (QI). Materials and Methods: Heterogeneous phantoms, comprising semi-infinite slabs of the lung (0.10, 0.20, 0.26 and 0.30 g/cm3), adipose tissue (0.92 g/cm3) and bone (1.85 g/cm3) in water, were constructed in the Eclipse treatment planning system. Several calculation models of 6 MV and 15 MV photon beams for quality index (TPR20,10) = 0.670±k*0.01 and TPR20,10 = 0.760±k*0.01, k = -3, -2, -1, 0, 1, 2, 3 respectively were built in the Eclipse. The ICFs were calculated with the anisotropic analytical algorithm (AAA) for several beam sizes and points lying at several depths inside of and below inhomogeneities of different thicknesses. Results: The ICFs increased for lung and adipose tissues with increasing beam quality (TPR20,10), while decreased for bone. Calculations with AAA predict that the maximum difference in ICFs of 1.0% and 2.5% for adipose and bone tissues, respectively. For lung tissue, changes of ICFs of a maximum of 9.2% (6 MV) and 13.8% (15 MV). For points where charged particle equilibrium exists, a linear dependence of ICFs on TPR20,10 was observed. If CPE doesn’t exist, the dependence became more complex. For points inside of the low-density inhomogeneity, the dependence of the ICFs on energy was not linear but the changes of ICFs were smaller than 3.0%. Measurements results carried out with the CIRS phantom were consistent with the calculation results. Conclusions: A negligible dependence of the ICFs on energy was found for adipose and bone tissue. For lung tissue, in the CPE region, the dependence of ICFs on different beam quality indexes with the same nominal energy may not be neglected, however, this dependence was linear. Where there is no CPE, the dependence of the ICFs on energy was more complicated.

Determination of consensus kQ values for megavoltage photon beams for the update of IAEA TRS-398

The IAEA is currently coordinating a multi-year project to update the TRS-398 Code of Practice for the dosimetry of external beam radiotherapy based on standards of absorbed dose to water. One major aspect of the project is the determination of new beam quality correction factors, kQ, for megavoltage photon beams consistent with developments in radiotherapy dosimetry and technology since the publication of TRS-398 in 2000. Specifically, all values must be based on, or consistent with, the key data of ICRU Report 90.Data sets obtained from Monte Carlo (MC) calculations by advanced users and measurements at primary standards laboratories have been compiled for 23 cylindrical ionization chamber types, consisting of 725 MC-calculated and 179 experimental data points. These have been used to derive consensus kQ values as a function of the beam quality index TPR20,10 with a combined standard uncertainty of 0.6%. Mean values of MC-derived chamber-specific factors for cylindrical and plane-parallel chamber types in 60Co beams have also been obtained with an estimated uncertainty of 0.4%.

Dosimetry quality control based on percent depth dose rate variation for checking beam quality in radiotherapy.

Recently, the quality management inside a radiotherapy department has been crucial to treat cancer efficiently. Thus, many international bodies recommend multiple methods to check in periodically the dosimetry quality beyond the depth of 10 cm as the beam quality index. However, they evade checking out the beam dosimetry quality on both the build-up dose and the electronic equilibrium regions. The objective of this study is to cover the overall variation of the percent depth dose (PDD) by including all sub-regions in the procedure evaluation of the beam quality. In this work, we have studied and examined the dosimetry quality by considering the whole PDD variation. The PDD rate is therefore introduced to determine accurately the quality as an overall notion in external beam radiotherapy according to the field size and photon beam energy. We have presented the reasons and methods to introduce particles contamination, such as electrons and low photon energy in this new approach. The latter enables us to figure the dosimetry quality by extending the International Atomic Energy Agency (IAEA) procedure at any field size less than 25 × 25 cm2 under the current conditions without being limited to 10 × 10 cm2 on the exponential decay region.

Validation of PRIMO Monte Carlo Model of Clinac®iX 6MV Photon Beam.

Purpose:This study aims to model 6MV photon of Clinac®iX linear accelerator using PRIMO Monte Carlo (MC) code and to assess PRIMO as an independent MC-based dose verification and quality assurance tool.Materials and Methods:The modeling of Clinac®iX linear accelerator has been carried out by using PRIMO simulation software (Version 0.3.1.1681). The simulated beam parameters were compared against the measured beam data of the Clinac®iX machine. The PRIMO simulation model of Clinac®iX was also validated against Eclipse® Acuros XB dose calculations in the case of both homogenous and inhomogeneous mediums. The gamma analysis method with the acceptance criteria of 2%, 2 mm was used for the comparison of dose distributions.Results:Gamma analysis shows a minimum pass percentage of 99% for depth dose curves and 95.4% for beam profiles. The beam quality index and output factors and absolute point dose show good agreement with measurements. The validation of PRIMO dose calculations, in both homogeneous and inhomogeneous medium, against Acuros® XB shows a minimum gamma analysis pass rate of 99%.Conclusions:This study shows that the research software PRIMO can be used as a treatment planning system-independent quality assurance and dose verification tool in daily clinical practice. Further validation will be performed with different energies, complex multileaf collimators fields, and with dynamic treatment fields.

Mathematical parameterization of dosimetry quality index checking of the photon beam based on IAEA TRS-398 protocol

The quality is essential for radiation use in medicine and the beam quality index is the basic parameter to periodically check the normal functioning of Linac head in radiotherapy treatment. It is recommended by IAEA protocols TRS-398 based on absorbed dose in water. The PDD method is used as a basis of the parameterization of the photon beam quality for predicting its variation with beam energy and field size. The objective of this work is to establish a mathematical law for predicting and checking the beam dosimetry quality index according to field size and beam energy based on IAEA TRS-398 protocol.For an easier and more reliable procedure determination of the beam quality based on TRS 398, two empirical laws were therefore established with an accuracy better than 2%. They can serve the basic floor to medical physicist to verify and to control the dosimetry output quality at arbitrary field size. Our findings aim to facilitate the dosimetry quality control that set in use according to current conditions for checking out the radiotherapy efficiency and the safety inside the treatment room.

First measurements with a plastic scintillation dosimeter at the Australian MRI-LINAC

MRI-LINACs combine MRI and LINAC technologies with the potential for image guided radiation therapy with optimal soft-tissue contrast. In this work, we present the advantages and limitations of plastic scintillation dosimeters (PSDs) for relative dosimetry with MRI-LINACs. PSDs possess many desirable qualities, including magnetic field insensitivity and irradiation angle independence, which are expected to make them suitable for dosimetry with MRI-LINACs. An in-house PSD was used to measure field size output factors as well as a percent depth dose distribution and the beam quality index TPR20/10 at a cm2 field size. Measurements were repeated with a Scanditronix/Wellhofer FC65-G ionisation chamber and PTW 60019 microDiamond detector for comparison. Relative differences were calculated between the three detectors, where the mean difference in dose was 1.2% between the PSD and ionisation chamber, 1.9% between the PSD and microDiamond detector and 1.3% between the microDiamond detector and the ionisation chamber. The closeness between the three mean differences in doses suggests that PSDs are feasible for relative dosimetry with MRI-LINACs.

Effect of ICRU report 90 recommendations on Monte Carlo calculated kQ for ionization chambers listed in the Addendum to AAPM’s TG‐51 protocol

The ICRU has published new recommendations for ionizing radiation dosimetry. In this work, the effect of recommendations on the water-to-air and graphite-to-air restricted mass electronic stopping power ratios (sw, air and sg, air ) and the individual perturbation correction factors Pi was calculated. The effect on the beam quality conversion factors kQ for reference dosimetry of high-energy photon beams was estimated for all ionization chambers listed in the Addendum to AAPM's TG-51 protocol. The sw, air , sg, air , individual Pi, and kQ were calculated using EGSnrc Monte Carlo code system and key data of both ICRU report 37 and ICRU report 90. First, the Pi and kQ were calculated using precise models of eight ionization chambers: NE2571 (Nuclear Enterprise), 30013, 31010, 31021 (PTW), Exradin A12, A12S, A1SL (Standard imaging), and FC-65P (IBA). In this simulation, the radiation sources were one 60 Co beam and ten photon beams with nominal energy between 4MV and 25MV. Then, the change in kQ for ionization chambers listed in the Addendum to AAPM's TG-51 protocol was calculated by changing the specification of the simple-model of ionization chamber. The simple-models were made with only cylindrical component modules. In this simulation, the radiation sources of 60 Co beam and 24MV photon beam were used. The significant changes (p<0.05) were observed for sw, air , sg, air , the wall correction factor Pwall , and the waterproofing sleeve correction factor Psleeve . The decrease in sw, air varied from -0.57% for a 60 Co beam to -0.36% for the highest beam quality. The decrease in sg, air varied from -0.72% to -1.12% in the same range. The changes in Pwall and Psleeve were up to 0.41% and 0.14% and those maximum changes were observed for the 60 Co beam. All changes in the central electrode correction factor Pcel , the stem correction factor Pstem , and the replacement correction factor Prepl were from -0.02% to 0.12%. Those changes were statistically insignificant (p=0.07 or more) and were independent of photon energy. The change in kQ was mainly characterized by the change in sw, air , Pwall , and Psleeve . The relationship between the change in kQ and the beam quality index was linear approximately. The changes in kQ of the simple-models were agreed with those of the precise-models within 0.08%. The effects of ICRU-90 recommendations on kQ for the ionization chambers listed in the Addendum to AAPM's TG-51 protocol were from -0.15% to 0.30%. To remove the known systematic effect on the clinical reference dosimetry, the kQ based on ICRU-37 should be updated to the kQ based on ICRU-90.

33 Commissioning and dosimetric characteristics of new halcyon system

Introduction A new Halcyon linear accelerator had been installed at clinique Charcot in Sainte-Foy-Les-Lyon. It’s the first one in France. The accelerator head is mounted on a ring gantry. There is no jaws and, for each bank, two MLC (proximal and distal) of 29 and 28 leaves of 1 cm width at isocenter with an offset of 5 mm to minimize the transmission. The maximum speed of the leaves is 5 cm/s. The maximum field size is 28 × 28 cm2. Halcyon system has one unique energy of 6XFFF and a maximum dose rate of 800 UM/min. The MV imaging panel size is 43 × 43 cm2, fxed at a distance source to imager of 154 cm and its resolution is 0.22 mm at isocenter. Currently, Halcyon system has only MV imaging (MV/MV or MV CBCT). Imaging dose is calculated by TPS Eclipse (Varian) and taken into account during optimization. Beam model of Halcyon is already preinstalled and fully modelled in Eclipse. Methods All the preinstalled data in Eclipse were measured in a water tank Blue Phantom2 (IBA) using CC13 (IBA), EDGE (SunNuclear) et Farmer (PTW) detectors in accordance with Varian measurements. PDD, profiles, FOC, transmission factor and DLG measurements were compared with preinstalled beam model. Calculated dose distribution with AAA algorithm for PDD and profiles were compared with our measurements using tolerances from SFPM report n°27. End-to-end and RapidArc commissioning were performed. Imaging dose from clinical radiotherapy plans were calculated from several anatomical regions and measured in an anthropomorphic phantom CIRS with a semiflex (PTW) ionisation chamber. Results A very good superposition of preinstalled data with our measurements was observed for every data. Largest variations were observed for small field profiles 2 × 2 cm2. Mean and maximum variations for FOC measurements were −0.03% and 0.71%. Leaf transmission measured through both banks is 0.005%. Beam quality index (PDD(10) with SSD = 100 cm) is 63.5% (Varian specification 63% ± 1). Maximum depth dose for a 10x10cm2 field size at SSD = 100 cm is 1.28 cm (Varian specification 1.3 cm ± 0.2). For every field sizes 100% of the points for PDD and profiles pass the tolerances from SFPM report n°27. Gantry isocentricity measured with Drum phantom (Varian) is 0.65 mm. Absolute dose difference at isocenter for a VMAT plan measured during an End-to-End test performed in the IMRT Thorax Phantom (CIRS) is 1%. Conclusions An excellent agreement between Varian preinstalled beam model and our measures were observed and therefore no changes to the preinstalled beam model have been made.

Open beam dosimetric characteristics of True Beam medical linear accelerator with flattening filter (WFF) and flattening filter free (FFF) beam

Abstract True Beam medical linear accelerator is capable of delivering flattening filter free (FFF) and with flattening filter (WFF) photon beams. True Beam linear accelerator is equipped with five photon beam energies (6 FFF, 6 WFF, 10 FFF, 10 WFF and 15 WFF) as well as six electron beam energies (6 MeV, 9 MeV, 12 MeV, 15 MeV and 18 MeV). The maximum dose rate for the 6 WFF, 10 WFF and 15 WFF is 600 MU/min, whereas 6 FFF has a maximum dose rate of 1400 MU/min and 10 FFF with a maximum dose rate of 2400 MU/min. In this report we discussed the open beam dosimetric characteristics of True Beam medical linear accelerator with FFF and WFF beam. All the dosimetric data (i.e. depth dose, cross-line profiles, diagonal profiles, output factors, MLC transmission, etc.) for 6 MV, 6 FFF, 10 MV, 10 FFF and 15 MV were measured and compared with the published data of the True Beam. Multiple detectors were used in order to obtain a consistent dataset. The measured data has a good consistency with the reference golden beam data. The measured beam quality index for all the beams are in good agreement with the published data. The percentage depth dose at 10 cm depth of all the available photon beams was within the tolerance of the Varian acceptance specification. The dosimetric data shows consistent and comparable results with the published data of other True Beam linear accelerators. The dosimetric data provide us an appreciated perception and consistent among the published data and may be used for future references.