scholarly journals The effect of SSD, Field size, Energy and Detector type for Relative Output Factor measurement in small photon beams as compared with Monte Carlo simulation

2019 ◽  
Vol 25 (2) ◽  
pp. 101-110
Author(s):  
Itumeleng Setilo ◽  
Oluwaseyi Michael Oderinde ◽  
Freek Cp du Plessis
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Field Size ◽  
Photon Beams ◽  
Output Measurement ◽  
Voxel Size ◽  
Output Factor ◽  
Ion Chamber ◽  
Small Fields ◽  
Mc Simulation

Abstract Introduction: Small fields photon dosimetry is associated with many problems. Using the right detector for measurement plays a fundamental role. This study investigated the measurement of relative output for small photon fields with different detectors. It was investigated for three-photon beam energies at SSDs of 90, 95, 100 and 110 cm. As a benchmark, the Monte Carlo simulation was done to calculate the relative output of these small photon beams for the dose in water. Materials and Methods: 6, 10 and 15 MV beams were delivered from a Synergy LINAC equipped with an Agility 160 multileaf collimator (MLC). A CC01 ion chamber, EFD-3G diode, PTW60019 microdiamond, EBT2 radiochromic film, and EDR2 radiographic film were used to measure the relative output of the linac. Measurements were taken in water for the CC01 ion chamber, EFD-3G diode, and the PTW60019. Films were measured in water equivalent RW3 phantom slabs. Measurements were made for 1 × 1, 2 × 2, 3 × 3, 4 × 4, 5 × 5 and a reference field of 10 × 10 cm2. Field sizes were defined at 100cm SSD. Relative output factors were also compared with Monte Carlo (MC) simulation of the LINAC and a water phantom model. The influence of voxel size was also investigated for relative output measurement. Results and Discussion: The relative output factor (ROF) increased with energy for all fields large enough to have lateral electronic equilibrium (LEE). This relation broke down as the field sizes decreased due to the onset of lateral electronic disequilibrium (LED). The high-density detector, PTW60019 gave the highest ROF for the different energies, with the less dense CC01 giving the lowest ROFs. Conclusion: These are results compared to MC simulation, higher density detectors give higher ROF values. Relative to water, the ROF measured with the air-chamber remained virtually unchanged. The ROFs, as measured in this study showed little variation due to increased SSDs. The effect of voxel size for the Monte Carlo calculations in water does not lead to significant ROF variation over the small fields studied.

Evaluation of dosimetric parameters of small fields of 6 MV flattening filter free photon beam measured using various detectors against Monte Carlo simulation

2020 ◽  
pp. 1-8
Author(s):  
Gopinath Mamballikalam ◽  
S Senthilkumar ◽  
P. M. Jayadevan ◽  
R. C. Jaon bos ◽  
P. M. Ahamed Basith ◽  
...  
Keyword(s):  
Volume Averaging ◽  
Field Size ◽  
Detector Response ◽  
Surface Dose ◽  
Output Factor ◽  
Depth Dose ◽  
Flattening Filter Free ◽  
Small Fields ◽  
Flattening Filter ◽  
Mc Simulation

Abstract Purpose: This study aims to evaluate dosimetric parameters like percentage depth dose, dosimetric field size, depth of maximum dose surface dose, penumbra and output factors measured using IBA CC01 pinpoint chamber, IBA stereotactic field diode (SFD), PTW microDiamond against Monte Carlo (MC) simulation for 6 MV flattening filter-free small fields. Materials and Methods: The linear accelerator used in the study was a Varian TrueBeam® STx. All field sizes were defined by jaws. The required shift to effective point of measurement was given for CC01, SFD and microdiamond for depth dose measurements. The output factor of a given field size was taken as the ratio of meter readings normalised to 10 × 10 cm2 reference field size without applying any correction to account for changes in detector response. MC simulation was performed using PRIMO (PENELOPE-based program). The phase space files for MC simulation were adopted from the MyVarian Website. Results and Discussion: Variations were seen between the detectors and MC, especially for fields smaller than 2 × 2 cm2 where the lateral charge particle equilibrium was not satisfied. Diamond detector was seen as most suitable for all measurements above 1 × 1 cm2. SFD was seen very close to MC results except for under-response in output factor measurements. CC01 was observed to be suitable for field sizes above 2 × 2 cm2. Volume averaging effect for penumbra measurements in CC01 was observed. No detector was found suitable for surface dose measurement as surface ionisation was different from surface dose due to the effect of perturbation of fluence. Some discrepancies in measurements and MC values were observed which may suggest effects of source occlusion, shift in focal point or mismatch between real accelerator geometry and simulation geometry. Conclusion: For output factor measurement, TRS483 suggested correction factor needs to be applied to account for the difference in detector response. CC01 can be used for field sizes above 2 × 2 cm2 and microdiamond detector is suitable for above 1 × 1 cm2. Below these field sizes, perturbation corrections and volume averaging corrections need to be applied.

scholarly journals Electron contamination for 6 MV photon beams from an Elekta linac: Monte Carlo simulation

2020 ◽  
Vol 2 (2) ◽  
pp. 97-101
Author(s):  
Choirul Anam ◽  
Djarwani S Soejoko ◽  
Freddy Haryanto ◽  
Sitti Yani ◽  
Geoff Dougherty
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Intensity Distribution ◽  
External Beam Radiotherapy ◽  
Absorbed Dose ◽  
Field Size ◽  
Photon Beams ◽  
Initial Electron ◽  
Depth Dose ◽  
Air Column

In external beam radiotherapy, the photons from a linear accelerator (linac) machine undergo multiple interactions, not only in the patient but also in the linac head and the air column between the linac head and the patient. Electrons are released from these interactions and contaminate the beams. The current study evaluates electron contamination for 6 MV photon beams from an Elekta linac using Monte Carlo simulation. The linac head was simulated by the BEAMnrc code and the absorbed dose in a phantom was calculated using the DOSXYZnrc code. The parameters of the initial electron beams on the target, such as mean energy and radial intensity distribution, were determined by matching the calculated dose distributions with the measured dose (at 10 x 10 cm2 field size and 90 cm source-skin distance). The central axis depth-dose curves of electron contamination were calculated for various field sizes from 5 x 5 cm2 to 40 x 40 cm2. We investigated the components that generated the electron contamination for a field size of 10 x 10 cm2. The optimal initial electron beam energy was 6.3 MeV with a full-width half maximum (FWHM) of the radial intensity distribution of 1.0 mm. These parameters were found to be in good agreement with the measured data. Electron contamination increased as the field size increased. At a depth of 1.0 mm and field sizes of 5 x 5, 10 x 10, 20 x 20, 30 x 30, and 40 x 40 cm2, the doses from electron contamination were 3.71, 5.19, 14.39, 18.97 and 20.89 %, respectively. Electron contamination decreased with increased depth. At a depth of 15 mm, the electron contamination was about 1 %. It was mainly generated in the air column between the linac head and the phantom (3.65 %), the mirror (0.99 %), and the flattening filter (0.59 %) (for the depth of 1.0 mm and the field size of 10 x 10 cm2).

Characterisation of small photon field outputs in a heterogeneous medium using X-ray voxel Monte Carlo dose calculation algorithm

2017 ◽  
Vol 17 (1) ◽  
pp. 114-123
Author(s):  
Karthikeyan Nithiyanantham ◽  
Ganesh K. Mani ◽  
Sambasivaselli Raju ◽  
Senniandavar Velliangiri ◽  
Maniyan Paramasivam ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Soft Tissue ◽  
Dose Calculation ◽  
Field Size ◽  
Planning System ◽  
Photon Beams ◽  
Calculation Algorithm ◽  
Output Factor ◽  
Voxel Monte Carlo ◽  
Monte Carlo Dose Calculation

AbstractAimTo characterise small photon beams using the Monte Carlo dose calculation algorithm for small field ranges in a heterogeneous medium.Materials and methodAn in-house phantom constructed with three different mediums, foam, polymethyl methacrylate and delrin resembling the densities of lung, soft tissue and bone respectively, was used in this study. Photon beam energies of 6 and 15 MV and field sizes of 8×8, 16×16, 24×24, 32×32 and 40×40 mm using X-ray voxel Monte Carlo (XVMC) algorithm using different detectors were validated. The relative output factor was measured in three different mediums having six different tissue interfaces; at the depth of 0, 1, 2 and 3 cm. The planar dose verification was undertaken using gafchromic films and considered dose at the lung and bone medium interfaces. For all the measurements, 104×104 mm was taken as the reference field size. The relative output factor for all other field sizes was taken and compared with planning system calculated values.ResultsFrom field size 16×16 mm and above, the relative output factors were analysed in bone and soft tissue medium having lung as first medium. The maximum deviations were observed as 1·8 and 1·3% for 6 MV and 2·5 and 1·1% for 15 MV photon beams for bone and soft tissue, respectively. For lung as measurement medium, the maximum deviation of 14·8 and 19·2% were observed and having bone as first medium with 8×8 mm for 6 and 15 MV photon beams, respectively. The fluence verification of dose spectrum for the lung–bone interface scenarios with smaller field sizes were found within 2% of deviation with treatment planning system (TPS).ConclusionThe accuracy of dose calculations for small field sizes in XVMC-based treatment planning algorithm was studied in different inhomogeneous mediums. It was found that the results correlated with measurement data for field size 16×16 mm and above. Noticeable deviation was observed for the smallest field size of 8×8 mm with interfaces of significant change in density. The observed results demands further analysis of work with smaller field sizes.

scholarly journals Method for calculation the absolute dose in the Monte Carlo simulation

2019 ◽  
Vol 2 (5) ◽  
pp. 90-96
Author(s):  
Oanh Thi Luong ◽  
Luong Thanh Dang ◽  
Tai Thanh Duong
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
General Hospital ◽  
Dose Distribution ◽  
Linear Accelerator ◽  
Photon Beams ◽  
Ion Chamber ◽  
Measured Dose ◽  
The Absolute ◽  
Good Agreement

In this study, we presented the method for calculation the absolute dose in the Monte Carlo simulation following the prescription of Popescu et al for the 6 MV photon energy. The BEAMnrc was used to simulate 6 MV photon beams from a Siemens Primus M5497 linear accelerator at DongNai general hospital. The DOSXYZnrc was then used to calculate the dose distribution in a homogeneous phantom (in form of CT images). The absolute dose obtained from the MC and TPS were compared with measured ones using an ion chamber (Farmer Type Chamber FC65-P, IBA). The average doses discrepancy between the simulated and measured dose was 0.53±0.37% and between the simulated and TPS was 1.00±0.51%. Results showed good agreement between simulated, measured and calculated dosed on a homogeneous phantom.

Monte Carlo study on mucosal dose in oral and naval cavity using photon beams with small field

2011 ◽  
Vol 10 (4) ◽  
pp. 261-271 ◽  
Author(s):  
James C.L. Chow ◽  
Amir M. Owrangi
Keyword(s):  
Monte Carlo ◽  
Beam Energy ◽  
Field Size ◽  
Small Field ◽  
Beam Angle ◽  
Photon Beams ◽  
Dose Ratio ◽  
Dose Enhancement ◽  
Bone Interface ◽  
Energy Beam

AbstractWe study how mucosal dose in the oral or nasal cavity depends on the irradiated small segmental photon fields varying with beam energy, beam angle and mucosa thickness. Dose ratio (mucosal dose with bone underneath to dose at the same point without bone) reflecting the dose enhancement due to the bone backscatter was determined by Monte Carlo simulation (EGSnrc-based code), validated by measurements. Phase space files based on the 6 and 18 MV photon beams with small field size of 1 × 1 cm2, produced by a Varian 21 EX linear accelerator, were generated using the BEAMnrc Monte Carlo code. Mucosa phantoms (mucosa thickness = 1, 2 and 3 mm) with and without a bone under the mucosa were irradiated by photon beams with gantry angles varying from 0 to 30°. Doses along the central beam axis in the mucosa and the dose ratio were calculated with different mucosa thicknesses. For the 6 MV photon beams, the dose at the mucosa-bone interface increased by 44.9–41.7%, when the mucosa thickness increased from 1 to 3 mm for the beam angle ranging from 0 to 30°. These values were lower than those (58.8–53.6%) for the 18 MV photon beams with the same beam angle range. For both the 6 and 18 MV photon beams, depth doses in the mucosa were found to increase with an increase of the beam angle. Moreover, the dose gradient in the mucosa was greater for the 18 MV photon beams compared to the 6 MV. For the dose ratio, it was found that the dose enhancement due to the bone backscatter increased with a decrease of mucosa thickness, and was more significant at both the air-mucosa and mucosa-bone interface. Mucosal dose with bone was investigated by Monte Carlo simulations with different experimental configurations, and was found vary with the beam energy, beam angle and mucosa thickness for a small segmental photon field. The dosimetric information in this study should be considered when searching for an optimized treatment strategy to minimize the mucosal complications in the head-and-neck intensity-modulated radiation therapy.

Investigation of field output factors using IAEA-AAPM TRS-483 code of practice recommendations and Monte Carlo simulation for 6 MV photon beams

2021 ◽  
pp. 1-6
Author(s):  
Sumalee Yabsantia ◽  
Sivalee Suriyapee ◽  
Nakorn Phaisangittisakul ◽  
Sornjarod Oonsiri ◽  
Taweap Sanghangthum ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Field Method ◽  
Correction Factors ◽  
Photon Beams ◽  
Small Field Dosimetry ◽  
Code Of Practice ◽  
Edge Detectors ◽  
Output Factors ◽  
Measured Field ◽  
Mc Simulation

Abstract Introduction: This study aims to experimentally determine field output factors using the methodologies suggested by the IAEA-AAPM TRS-483 for small field dosimetry and compare with the calculation from Monte Carlo (MC) simulation. Methods: The IBA-CC01, Sun Nuclear EDGE and IBA-SFD detectors were employed to determine the uncorrected and the corrected field output factors for 6 MV photon beams. Measurements were performed at 100 cm source to axis distance, 10 cm depth in water, and the field sizes ranged from 1 × 1 to 10 × 10 cm2. The use of field output correction factors proposed by the TRS-483 was utilised to determine field output factors. The measured field output factors were compared to that calculated using the egs_chamber user code. Results: The decrease in the percentage standard deviation of the measured three detectors was observed after applying the field output correction factors. Measured field output factors using CC01 and EDGE detectors agreed with MC values within 3% for field sizes down to 1 × 1 cm2, except the SFD detector. Conclusions: The corrected field output factors agree with the calculation from MC, except the SFD detector. CC01 and EDGE are suitable for determining field output factors, while the SFD may need more implementation of the intermediate field method.

Sign in / Sign up

Export Citation Format

Share Document