Effects of collimator backscatter in an Elekta linac by Monte Carlo simulation

Kairn, Tanya; Crowe, Scott; Poole, Christopher; Fielding, Andrew

doi:10.1007/bf03178640

Cited by 11 publications

(4 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In Elekta linacs, however, there is a backscatter plate which prevents particles from the downstream direction entering the monitor chamber. It was shown that with the backscatter plate in place the proportion of particles backscattered into the monitor chamber is less than 0.35% and, therefore, corrections for field size dependence in monitor chamber dose are not necessary when running MC simulations of the Elekta linac. Moreover, since jaw opening is kept constant for all cone sizes, backscattering into the monitor chamber will not influence the calculation of ROF for stereotactic cones.…”

Section: Discussionmentioning

confidence: 99%

Dosimetric characterization of Elekta stereotactic cones

Borzov

Nevelsky

Bar-Deroma

et al. 2017

J Applied Clin Med Phys

View full text Add to dashboard Cite

PurposeDosimetry of small fields defined by stereotactic cones remains a challenging task. In this work, we report the results of commissioning measurements for the new Elekta stereotactic conical collimator system attached to the Elekta VersaHD linac and present the comparison between the measured and Monte Carlo (MC) calculated data for the 6 MV FFF beam. In addition, relative output factor (ROF) dependence on the stereotactic cone aperture variation was studied and penumbra comparison for small MLC‐based and cone‐based fields was performed.MethodsCones with nominal diameters of 15 mm, 12.5 mm, 10 mm, 7.5 mm, and 5 mm were employed in our study. Percentage depth dose (PDD), off‐axis ratios (OAR), and ROF were measured using a stereotactic field diode (SFD). BEAMnrc code was used for MC simulations.ResultsMC calculated and measured PDDs for all cones agreed within 1%/0.5 mm, and OAR profiles agreed within 1%/0.5 mm. ROF obtained from the measurements and MC calculations agreed within 2% for all cone sizes. Small‐field correction factors for the SFD detector Kfield,3 × 3(SFD) were derived using MC calculations as a baseline and were found to be 0.982, 0.992, 0.997, 1.015, and 1.017 for the 5, 7.5, 10, 12.5, and 15‐mm cones respectively. The difference in ROF was about 10%, 6%, 3.5%, 3%, 2.5%, and 2% for ±0.3 mm variations in 5, 7.5, 10, 12.5, and 15‐mm cone aperture respectively. In case of single static field, cone‐based collimation produced a sharper penumbra compared to the MLC‐based.ConclusionsAccurate MC simulation can be an effective tool for verification of dosimetric measurements of small fields. Due to the very high sensitivity of output factors on the cone diameter, manufacture‐related variations in cone size may lead to considerable variations in dosimetric characteristics of stereotactic cones.

show abstract

Section: Discussionmentioning

confidence: 99%

Dosimetric characterization of Elekta stereotactic cones

Borzov

Nevelsky

Bar-Deroma

et al. 2017

J Applied Clin Med Phys

View full text Add to dashboard Cite

show abstract

“…Various authors have quantified the backscatter into the monitor chamber [10,[20][21][22][23]. In this study the empirical correction suggested by Ahmed et al has been incorporated into the STTs to account for the back scatter [24].…”

Section: Back Scatter Correctionmentioning

confidence: 99%

Validation and automation of the DYNJAWS component module of the BEAMnrc Monte Carlo code

Kakakhel

Baveas

Fielding

et al. 2011

Australas Phys Eng Sci Med

Self Cite

View full text Add to dashboard Cite

The purpose of this work is to validate and automate the use of DYNJAWS; a new component module (CM) in the BEAMnrc Monte Carlo (MC) user code. The DYNJAWS CM simulates dynamic wedges and can be used in three modes; dynamic, step-and-shoot and static. The step-and-shoot and dynamic modes require an additional input file defining the positions of the jaw that constitutes the dynamic wedge, at regular intervals during its motion. A method for automating the generation of the input file is presented which will allow for the more efficient use of the DYNJAWS CM. Wedged profiles have been measured and simulated for 6 and 10 MV photons at three field sizes (5 cm × 5 cm, 10 cm × 10 cm and 20 cm × 20 cm), four wedge angles (15°, 30°, 45° and 60°), at d (max) and at 10 cm depth. Results of this study show agreement between the measured and the MC profiles to within 3% of absolute dose or 3 mm distance to agreement for all wedge angles at both energies and depths. The gamma analysis suggests that dynamic mode is more accurate than the step-and-shoot mode. The DYNJAWS CM is an important addition to the BEAMnrc code and will enable the MC verification of patient treatments involving dynamic wedges.

show abstract

“…The four beams in the treatment were simulated separately and MCDTK was used to evaluate a weighted sum of the doses, taking into account the number of monitor units per beam as well as the effect of backscatter from the secondary collimators (minimal, in this case, due to the backscatter plate) into the linear accelerator's monitor chamber [17,18]. MCDTK was then used to produce dose maps, isodose diagrams and cumulative dose volume histograms using the dose distributions from both the treatment planning system and the Monte Carlo simulations.…”

Section: B Monte Carlo Simulations and Dose Comparisonsmentioning

confidence: 99%

Experimental Evaluation of MCDTK, the Monte Carlo DICOM Tool-Kit

et al. 2013

Self Cite

View full text Add to dashboard Cite

The Monte Carlo DICOM Tool-Kit (MCDTK) is a software suite designed for treatment plan dose verification, using the BEAMnrc and DOSXYZnrc Monte Carlo codes. MCDTK converts DICOM-format treatment plan information into Monte Carlo input files and compares the results of Monte Carlo treatment simulations with conventional treatment planning dose calculations. In this study, a treatment is planned using a commercial treatment planning system, delivered to a pelvis phantom containing ten thermoluminescent dosimeters and simulated using BEAMnrc and DOSXYZnrc using inputs derived from MCDTK. The dosimetric accuracy of the Monte Carlo data is then evaluated via comparisons with the dose distribution obtained from the treatment planning system as well as the in-phantom point dose measurements. The simulated beam arrangement produced by MCDTK is found to be in geometric agreement with the planned treatment. An isodose display generated from the Monte Carlo data by MCDTK shows general agreement with the isodose display obtained from the treatment planning system, except for small regions around density heterogeneities in the phantom, where the pencil-beam dose calculation performed by the treatment planning system is likely to be less accurate. All point dose measurements agree with the Monte Carlo data obtained using MCDTK, within confidence limits, and all except one of these point dose measurements show closer agreement with the Monte Carlo data than with the doses calculated by the treatment planning system. This study provides a simple demonstration of the geometric and dosimetric accuracy of Monte Carlo simulations based on information from MCDTK.

show abstract

Effects of collimator backscatter in an Elekta linac by Monte Carlo simulation

Cited by 11 publications

References 14 publications

Dosimetric characterization of Elekta stereotactic cones

Dosimetric characterization of Elekta stereotactic cones

Validation and automation of the DYNJAWS component module of the BEAMnrc Monte Carlo code

Experimental Evaluation of MCDTK, the Monte Carlo DICOM Tool-Kit

Contact Info

Product

Resources

About