Variation of linear accelerator wedge factors with field size and wedge position

BackgroundOne of the most significant Intensity Modulated Radiation Therapy treatment benefits is a high target to normal tissue dose ratio. To improve this advantage, an additional accessory such as a compensator is used to delivering doses. Compensator-based IMRT treatment is usually operated with an energy higher than 10 MV. Photoneutrons, which have high linear energy transfer and radiobiological effectiveness, are produced by colliding high-energy photon beams with linear accelerator structures, then they deliver the unwanted doses to patients and staff. Therefore, the neutron energy spectra should be determined in order to calculate and reduce the photoneutron risk.Objective: We have conducted a comprehensive and precise study on the influence of brass compensator thickness and field size on neutron contamination spectrum in an Elekta SL 75/25 medical linear accelerator with and without the flattening filter by Monte Carlo method.Materials and Methods: MCNPX MC Code version 2.6.0 was utilized to simulate the detailed geometry of Elekta SL 75/25 head components based on Linac’s manual. This code includes an important feature to simulate the photo-neutron interactions. Photoneutrons spectrum was calculated after the Linac output benchmarking based on tuning the primary electron beam.Results and Conclusion: Based on the Friedman and Wilcoxon nonparametric tests results (P<0.05), photoneutron fluence directly depends on the field size and compensator thickness. Moreover, the unflattened beam provides lower photoneutron fluence than the flattened beam. Photoneutrons fluence is not negligible in compensator-based IMRT treatment. However, in order to optimize treatment plans, this additional and unwanted dose must be accounted for patients.

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Factor 10 Expedience of Monthly Linac Quality Assurance via an Ion Chamber Array and Automation Scripts

Technology in Cancer Research & Treatment ◽

10.1177/1533033819876897 ◽

2019 ◽

Vol 18 ◽

pp. 153303381987689

Author(s):

Lawrie B. Skinner ◽

Yong Yang ◽

Annie Hsu ◽

Lei Xing ◽

Amy S. Yu ◽

...

Keyword(s):

Quality Assurance ◽

Standard Deviation ◽

Linear Accelerator ◽

Data File ◽

Field Size ◽

Linear Accelerators ◽

Ion Chamber ◽

Medical Linear Accelerators ◽

Jaw Position ◽

Dosimetric Leaf Gap

Purpose: While critical for safe and accurate radiotherapy, monthly quality assurance of medical linear accelerators is time-consuming and takes physics resources away from other valuable tasks. The previous methods at our institution required 5 hours to perform the mechanical and dosimetric monthly linear accelerator quality assurance tests. An improved workflow was developed to perform these tests with higher accuracy, with fewer error pathways, in significantly less time. Methods: A commercial ion chamber array (IC profiler, Sun Nuclear, Melbourne, Florida) is combined with automation scripts to consolidate monthly linear accelerator QA. The array was used to measure output, flatness, symmetry, jaw positions, gated dose constancy, energy constancy, collimator walkout, crosshair centering, and dosimetric leaf gap constancy. Treatment plans were combined with automation scripts that interface with Sun Nuclear’s graphical user interface. This workflow was implemented on a standard Varian clinac, with no special adaptations, and can be easily applied to other C-arm linear accelerators. Results: These methods enable, in 30 minutes, measurement and analysis of 20 of the 26 dosimetric and mechanical monthly tests recommended by TG-142. This method also reduces uncertainties in the measured beam profile constancy, beam energy constancy, field size, and jaw position tests, compared to our previous methods. One drawback is the increased uncertainty associated with output constancy. Output differences between IC profiler and farmer chamber in plastic water measurements over a 6-month period, across 4 machines, were found to have a 0.3% standard deviation for photons and a 0.5% standard deviation for electrons, which is sufficient for verifying output accuracy according to TG-142 guidelines. To minimize error pathways, automation scripts which apply the required settings, as well as check the exported data file integrity were employed. Conclusions: The equipment, procedure, and scripts used here reduce the time burden of routine quality assurance tests and in most instances improve precision over our previous methods.

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Grid Monte Carlo Simulation of a Medical Linear Accelerator

European Journal of Engineering Research and Science ◽

10.24018/ejers.2018.3.12.1001 ◽

2018 ◽

Vol 3 (12) ◽

pp. 40-43 ◽

Cited By ~ 1

Author(s):

Didi Samir ◽

Mustapha Zerfaoui ◽

Abdelilah Moussa ◽

Yassine Benkhouya ◽

Mehdi El Ouartiti

Keyword(s):

Monte Carlo ◽

Linear Accelerator ◽

Field Size ◽

Dose Profile ◽

Depth Dose ◽

Grid Simulation ◽

Medical Linear Accelerator ◽

Measured Dose ◽

Better Than ◽

Good Agreement

A full grid simulation of the head of an Elekta Synergy Platform medical linear accelerator is performed using the Geant4 Monte Carlo platform. The simulation includes all components of the accelerator head and a homogeneous water phantom. Results in terms of depth doses and lateral dose profiles are presented for 6 MV photon beam with the 10x10 cm2 reference field size at 100 cm distance from the source. Overall, a good agreement with the measured dose data is achieved with a precision better than 0.93% and 2.63% for the depth dose profile and lateral dose profiles respectively.

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Evaluation of Peripheral Dose for Varian Trilogy Linear Accelerator

10.21203/rs.3.rs-272397/v1 ◽

2021 ◽

Author(s):

Bo Yang ◽

Tingtian Pang ◽

Xiansong Sun ◽

Tingting Dong ◽

Rui Li ◽

...

Keyword(s):

Linear Accelerator ◽

Ionization Chamber ◽

Beam Energy ◽

Wedge Angle ◽

Field Size ◽

Measure Data ◽

Interest Points ◽

Peripheral Dose ◽

Radiation Beam ◽

Dosimetric System

Abstract Objective To measure and evaluate the peripheral dose(PD) for Trilogy linear accelerator in different setup condition and investigate the feasibility of the diode dosimetric system to measure the peripheral dose.Methods Peripheral dose were measured using a CC13 ionization chamber and the diode dosimetric system in a set of solid water phantom. Measurements were performed for different depths, field sizes, physical and virtual wedge, radiation beam energy and up at distance of 1cm to 31cm beyond the field edges. PD is separated into PDleakage and PDscatter by measure peripheral dose with or without scattering phantom. CRIS phantom was used for this research with the diode dosimetric system at the interest points of the breast, thyroid, and lens.Results All the measure data were normalized to isocenter. The measured PD decreases exponentially as a function of distance up to 31cm from the edge. PD shows no significant relevant to depth and it increases with the increased field size. As the physics wedge angle increase, PD increases about 1%, but enhanced dynamic wedge decreased 2-3% compared with open field. As the beam energy increase, PD decreased. All PD data difference less than 1% between CC13 ionization chamber and diode. The PD of CRIS phantom for Volume Modulated ARC Therapy (VMAT) is minimum and the mean dose for breast、thyroid and lens is 6.72 mGy、2.90 mGy and 2.37 mGy respectively.Conclusion The diode dosimetric system provides an sufficient assessment in peripheral regions of 6MV X-ray beam. PD changes because of field size、depth、beam energy etc and the assessment of PD would be helpful to evaluate the dose received by the relevant critical structures near the treatment field. Furthermore it is advantaged to use external shielding for critical organs.

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Wedge angle confirmation in computer controlled wedge field

International Journal of Radiology & Radiation Therapy ◽

10.15406/ijrrt.2020.07.00270 ◽

2020 ◽

Vol 7 (3) ◽

pp. 81-86

Author(s):

Salman Farrukh

Keyword(s):

Linear Accelerator ◽

Beam Energy ◽

Wedge Angle ◽

Target Volume ◽

Field Size ◽

Published Data ◽

Linear Accelerators ◽

Water Phantom ◽

Ion Chamber ◽

Computer Controlled

Aim: The use of computer controlled wedge system is an important segment of radiotherapy and increases the uniformity of dose in the target volume. The aim of this study is to verify the virtual wedge angles from the machine setup angles in Siemens ONCOR Linear accelerator (Linac) and compare with published data of different linear accelerators as a function of beam energy and field sizes. Method and material: This experiment was carried out on Siemens ONCOR impression linear accelerator (Linac). The doses at different depth were measured by using CC13 ion chamber. During our work the source to surface distance was kept 100 cm. The square field sizes on which we worked were 10 cm2, 15cm2 and 20 cm2.The selected Virtual wedge angles for our study are 15°, 30°, 45° and 60°.This work is carried out for both photon energies 15 MV and 6 MV, tissue equivalent water phantom IBA blue water phantom inside which all the observations were taken. The LDA 99 detector for virtual wedge profile was used. The wedge angle were calculated for the Siemen’s given formula. The variation in wedge angle from machine setup angle and published data as a function of beam energy and field sizes were analyzed. Results: The variation increases with field size and wedge angle but decreases with beam energy. Conclusion: Deviations are under 3% which are acceptable before treatment planning.

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Dosimetric determination of tissue maximum ratios in small fields

Journal of Radiotherapy in Practice ◽

10.1017/s1460396918000055 ◽

2018 ◽

Vol 17 (3) ◽

pp. 289-291 ◽

Cited By ~ 1

Author(s):

Qurat-ul-ain Shamsi ◽

Saeed Ahmad Buzdar ◽

Atia Atiq ◽

Maria Atiq ◽

Saima Altaf ◽

...

Keyword(s):

Treatment Planning ◽

Linear Accelerator ◽

Field Size ◽

Maximum Difference ◽

Water Phantom ◽

Planning Software ◽

Small Fields ◽

Good Agreement

AbstractAimsThis exploration is intended to measure tissue maximum ratios (TMRs) in smaller fields through CC01 detector and to compare CC01 measured TMRs with Pinnacle treatment planning software (TPS) calculated TMRs.Materials and methodsCC01 compact chamber detector was used to measure TMR in water phantom for 6 and 18 MV beam delivered from Varian linear accelerator. Pinnacle TPS was employed in this study to calculate TMR from the measured percentage depth doses data. CC01 measured TMR data was compared with the calculated TMR data at depths from 5 to 20 cm for field sizes varying from 1 to 10 cm2.ResultsFor the smallest given field size of 1 cm2, CCO1 measured 13·95% higher TMR value for 18 MV beam than that for 6 MV beam. At 20 cm depth for 1 cm2 field size, TMR due to 18 MV beam was 52·4% higher than the TMR due to 6 MV beam. For 6 MV beam, the maximum difference appeared between the measured TMR and pinnacle calculated TMR was 2·8% and for 18 MV beam, the maximum difference was 4%.ConclusionFor both 6 and 18 MV beam, there was good agreement between CC01 measured and Pinnacle calculated TMRs for the field sizes ranging from 1 to 10 cm2. This exploration can be extended to the determination of other dosimetric parameters like TARs, TPRs in small fields.

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Radiotherapy for laryngeal cancer—technical aspects and alternate fractionation

Journal of Radiation Research ◽

10.1093/jrr/rrx023 ◽

2017 ◽

Vol 58 (4) ◽

pp. 495-508 ◽

Cited By ~ 5

Author(s):

Hideya Yamazaki ◽

Gen Suzuki ◽

Satoaki Nakamura ◽

Ken Yoshida ◽

Koji Konishi ◽

...

Keyword(s):

Linear Accelerator ◽

Treatment Time ◽

Chemotherapeutic Agents ◽

Concurrent Chemotherapy ◽

Field Size ◽

Dose Fractionation ◽

Glottic Cancer ◽

Tumor Control ◽

Special Focus ◽

Overall Treatment Time

Abstract Early laryngeal, especially glottic, cancer is a good candidate for radiotherapy because obvious early symptoms (e.g. hoarseness) make earlier treatment possible and with highly successful localized control. This type of cancer is also a good model for exploring the basic principles of radiation oncology and several key findings (e.g. dose, fractionation, field size, patient fixation, and overall treatment time) have been noted. For example, unintended poor outcomes have been reported during transition from 60Cobalt to linear accelerator installation in the 1960s, with usage of higher energy photons causing poor dose distribution. In addition, shell fixation made precise dose delivery possible, but simultaneously elevated toxicity if a larger treatment field was necessary. Of particular interest to the radiation therapy community was altered fractionation gain as a way to improve local tumor control and survival rate. Unfortunately, this interest ceased with advancements in chemotherapeutic agents because alternate fractionation could not improve outcomes in chemoradiotherapy settings. At present, no form of acceleration can potentially compensate fully for the lack of concurrent chemotherapy. In addition, the substantial workload associated with this technique made it difficult to add extra fractionation routinely in busy clinical hospitals. Hypofractionation, on the other hand, uses a larger single fractionation dose (2–3 Gy), making it a reasonable and attractive option for T1–T2 early glottic cancer because it can improve local control without the additional workload. Recently, Japan Clinical Oncology Group study 0701 reprised its role in early T1–T2 glottic cancer research, demonstrating that this strategy could be an optional standard therapy. Herein, we review radiotherapy history from 60Cobalt to modern linear accelerator, with special focus on the role of alternate fractionation.

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