Ionization chamber, electrometer, linear accelerator, field size, and energy dependence of the polarity effect in electron dosimetry

1999 ◽  
Vol 26 (2) ◽  
pp. 214-219 ◽  
Author(s):  
Chester R. Ramsey ◽  
Kelly M. Spencer ◽  
Adrian L. Oliver
Keyword(s):  
Energy Dependence ◽  
Linear Accelerator ◽  
Ionization Chamber ◽  
Field Size ◽  
Polarity Effect ◽  
Electron Dosimetry

Evaluation of Peripheral Dose for Varian Trilogy Linear Accelerator

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.

scholarly journals Assessment the Photo-neutron Contamination of IMRT and 3D-Conformal Techniques Using Thermo-luminescent Dosimeter (TLD)

2019 ◽  
pp. 1-10
Author(s):  
Ebtesam M. Mohamedy ◽  
Hassan Fathy ◽  
Wafaa M. Khalil ◽  
Nadia L. Helal ◽  
Ehab M. Attalla
Keyword(s):  
Prostate Cancer ◽  
Neutron Monitor ◽  
Linear Accelerator ◽  
Ionization Chamber ◽  
High Energy ◽  
Neutron Production ◽  
Field Size ◽  
Planning System ◽  
Energy Beam ◽  
Treatment Plans

The aim of the study is to evaluate the dependence of photo-neutron production on field size, depth in phantom and distance from isocenter and also to calculate the equivalent neutron doses for PTV and OARs of IMRT and 3DCRT techniques using TLD (600/700).The Linac Siemens Oncor installed at Nasser Institute, Cairo, Egypt. TLDs, Neutron Monitor, Ionization chamber were provided by NIS, the duration of the study was from November 2017 to July 2018. 5 prostate cancer cases were selected treated with high energy beam (15MV) Linear accelerator using 3DCRT and IMRT treatment plans. The OARs were bladder, rectum and femur. Once the plans were completed, there were copied from the planning system onto the RW3 slab phantom in which pairs of TLD chips (600/700) were placed at the exact site of PTV and OARs. The results showed that: The measured photo-neutron decreases from 0.2 mSv/Gy to 0.09 mSv/Gy as increases field sizes from 2x2 cm2 to 20x20 cm2. The measured photo-neutron was maximum at dmax =0.15 mSv/Gy and decreases gradually as increases the depth in phantom reaches to 0.07 mSv/Gy at 10cm depth in phantom. The measured photo-neutron decreases from 1.5 mSv/Gy to 0.02 mSv/Gy when measured at isocenter and at 100cm along the patient couch. Using 3DCRT for PTV and OARs were ranging from 0.027 to 0.39 mSv per photon Gy and for IMRT were 0.135 to 2.34 mSv per photon Gy. In conclusion the photo-neutron production is decreases as increases field size and distance from isocenter along patient couch while increases with depth in phantom up to dmax and decreases gradually as increases depth in phantom. IMRT requires longer beam-on time than 3DCRT leading to worse OARs sparing and increase the production of photo-neutrons than 3DCRT.

scholarly journals Experimental analysis of correction factors for reference dosimetry in a magnetic field

2017 ◽  
Vol 3 (2) ◽  
pp. 803-805
Author(s):  
Nicole Brand ◽  
Stefan Pojtinger ◽  
Savas Tsitsekidis ◽  
Daniela Thorwarth ◽  
Oliver S. Dohm
Keyword(s):  
Magnetic Field ◽  
Linear Accelerator ◽  
Ionization Chamber ◽  
Field Size ◽  
Measured Signal ◽  
Correction Factors ◽  
Ionization Chambers ◽  
Field Orientation ◽  
The Magnetic Field ◽  
Phantom Material

AbstractToday, hybrid systems of linear accelerator and MRI scanner are clinically available. Therefore it is important to investigate the feasibility of reference dosimetry with ionization chambers in the presence of a magnetic field and determine correction factors. In this work, correction factors under various conditions that influence the chamber response were experimentally investigated, using a conventional 6 MV linear accelerator together with a stand-alone magnet. We found that the correction factor for a PTW31010 ionization chamber ranges from 0.9873 to 1.009 depending on the magnetic field strength, magnetic field orientation and magnetic field size. The phantom material also does have an influence on the measured signal. Therefore, reference dosimetry with ionization chambers in the presence of a magnetic field is feasible, but requires dedicated correction factors, which depend on the experimental setup.

scholarly journals Estimation of Out-of-Field Dose Variation using Markus Ionization Chamber Detector

2020 ◽  
Vol 2 (1) ◽  
pp. 8-15
Author(s):  
Ahmed M. Abdelaal ◽  
Ehab M. Attalla ◽  
Wael M. Elshemey
Keyword(s):  
Ionization Chamber ◽  
Field Size ◽  
The Poor ◽  
Collimator Angle ◽  
Different Depths ◽  
Almost All ◽  
Dose Variation

Objective: The aim of This work to provide evaluation  for the out-of-field dose with different plan parameters as field size and depth using Markus ionization chamber detector in the measurement that are frequently used in electron and superficial dosimetery, in radiotherapy. Methods: This is carried out through the application of these detector in estimation of the out-of-field dose with important dosimetric parameters such as field size (from 5×5 to 30×30 cm2) and depth (from 1.5 to 30 cm) at energy 6 MV and collimator angle 0° at SSD 100 cm. Results: Results show that, the Markus detector reported an increase in out-of-field dose with field size, depth in almost all measurements. For 6 MV and 0° collimator  angle, the out-of-field dose at field size of 5×5 cm2 (depth of 1.5 cm) is 1.1%  and at field size of  30×30 cm2 (depth of 1.5 cm) is 4.4% . The out-of-field dose for a depth of 1.5 cm (field size of 10×10 cm2) is 2.3% and for a depth of 30 cm (field size of 10×10 cm) is 5.5%. the measured out-of-field dose by Markus detector overestimated in the calculated at different field sizes (2.7% instead of 2.3% at field size of 10×10 cm2 and 5.2% instead of 4.4% at field size of 30×30 cm2) and different depths (2.7% instead of 1.1% at depth of 1.5 cm and 4.1% instead of 3.4% at depth of 30 cm). Analysis: The result reported an increase in mean out-of-field dose with field size, depth, energy and SSD. Markus ionization chamber detector show overestimation of the measured out-of-field dose in the calculated values at all field sizes and depths, this may be attributed to the poor detection of out-of-field dose by TPS.

Khảo sát một số đặc tính bức xạ của buồng ion hóa CC13 và diode bán dẫn razor đối với các chùm photon kích thước nhỏ trên máy gia tốc tuyến tính xạ trị Clinac IX

2020 ◽  
Author(s):  
Tu Vu Ngoc
Keyword(s):  
Radiation Field ◽  
Dose Response ◽  
Dose Distribution ◽  
Ionization Chamber ◽  
Field Size ◽  
Photon Beams ◽  
Silicon Diode ◽  
Depth Dose ◽  
The Difference

Purpose: Compare percent depth dose (PDD) and off-center ratio (OCR) measured by the CC13 ionization chamber and the RAZOR silicon diode in small photon beams. Method and Materials: Some dosimetric characteristics, such as PDD, OCR, penumbra and radiation field size, were considered in this study for 2x2, 3x3, and 4x4 cm2 field sizes. We used the CC13 ionization chamber and the RAZOR silicon diode to measure dose distribution with depth along the axis and off-center of the beam. From the results obtained, the team investigated the differences in radiation parameters measured by the two types of probes above. Results: There are significant differences in the radiation parameters investigated for the CC13 ionization chamber and the RAZOR silicon diode, especially the width of penumbra. For PDD curves, the difference is less than 5% from dmax to 30 cm, however the difference becomes greater in the build-up region, which reaches to 33% at the water phatom surface. The width of penumbra measured by CC13 is always larger than that of RAZOR, the ratio of the penumbra width between two detectors is 1.8 and 1.3 for energies of 6 MV and 15 MV, respectively. Conclusion: The RAZOR silicon diode has better dose response than the CC13 ionization chamber for measuring the PDD and the OCR in small photon beams.

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