scholarly journals Evaluation of using radiographic films in measurements of penumbra width for radiotherapy applications and stereotactic radiosurgery

2018 ◽  
Vol 14 (1) ◽  
pp. 5204-5212
Author(s):  
Ehab A Hegazy
Keyword(s):  
Stereotactic Radiosurgery ◽  
Ionization Chamber ◽  
Field Size ◽  
Physical Parameters ◽  
Ionization Chambers ◽  
X Ray ◽  
Radiation Fields ◽  
Economic Method ◽  
Width Measurements ◽  
Penumbra Region

The accuracy of treatment field size in is a success key in cancer radiotherapy. As Increase in dose may lead to overdose side effects, and decrease in dose lead to subtherapeutic effect which increased incidence of tumor recurrence or incomplete recovery of patient. Many physical parameters should be measured very accurately in order to predict the dose distribution as physical penumbra of radiation fields. Ionization chamber is considered as slandered tools for measuring penumbra. Mega voltage x-ray energy penumbra is measured using ionization chamber due to its high accuracy in measuring absolute dose. This technique can produce the gold standard for penumbra measurements; however, it is a very time consuming and demanding process. Aim of this work is to evaluate the using radiographic films in penumbra width measurements for radiotherapy applications and stereotactic radiosurgery by comparing results obtained by standard ionization chambers to radiographic films as new tool for penumbral width measurements. Comparison between penumbra region measured by ionization chamber and o-xmat v Kodak radiographic films were carried out under the same physical and dosimeteric conditions. Penumbra width differences were found to be less than 1 mm for 6 mev, 15 mev photon beam and 6 mv, 15 mv electron beam used in radiotherapy. Measured differences were considered very small and has no effect on penumbra width measurements however o-xmat v Kodak films provide fast .easy and economic method for penumbra measurement used in radiotherapy dosimetery. 

Partial volume characteristics of ionization chambers in kilovoltage x-ray exposure measurements

2011 ◽  
Vol 11 (3) ◽  
pp. 184-188
Author(s):  
Syed F. Akber ◽  
Than S. Kehwar
Keyword(s):  
Ionization Chamber ◽  
Incident Radiation ◽  
Ionization Chambers ◽  
X Ray ◽  
Partial Volume ◽  
Spatial Response ◽  
Beam Output ◽  
Volume Characteristics ◽  
Made In ◽  
Lead Sheet

AbstractThe partial volume (spatial) response of four ionization chambers (Keithley) in kilovoltage X-ray beams, generated by the Philips Super 80CP X-ray unit, was assessed. The volume of the ionization chambers were of 10 cm3, 15 cm3, 150 cm3, and 600 cm3 used with Keithley electrometer Model 35040. The beam output was measured using a monitor chamber (Radcal 6.0 cm3) placed close to the collimator. The source to chamber distance was kept constant at 1 m. For the measurement of the response of ionization chambers of 15 cm3, 150 cm3, and 600 cm3, a slit of 2.0 mm width was made in a lead sheet of 3.2 mm thick and size of 30 × 30 cm2 and was placed on the ionization chamber. The measurements were made for 81 kVp, 400 mA, and 0.25 s and the slit was moved at an increment of 2.0 mm over the entire length of the chamber. For the measurements of the ionization chamber of 10 cm3 (CT chamber), the beams of 120 kVp, 200 mA and 0.2 s were generated, and a slit of 5 mm width was made in a similar lead sheet that was moved at an increment of 5.0 mm. From the result it appears that the sensitive volumes of the ionization chambers affect the response of the ionization chamber to incident radiation.

Ionization chambers for monitoring the position and tilt of X-ray beams

2000 ◽  
Vol 33 (3) ◽  
pp. 986-987
Author(s):  
U. W. Arndt ◽  
M. P. Kyte
Keyword(s):  
Ionization Chamber ◽  
Ionization Chambers ◽  
X Ray

An air-filled ionization chamber with a three-way split anode can be used to measure the tilt and the translation of a collimated X-ray beam with respect to the chamber axis.

Measurements of spatial variations in response of ionization chambers

2012 ◽  
Vol 20 (1) ◽  
pp. 160-165 ◽  
Author(s):  
William E. B. Miller ◽  
Alan L. Kastengren
Keyword(s):  
Space Charge ◽  
Spatial Variation ◽  
Bias Voltage ◽  
Ionization Chamber ◽  
Significant Variation ◽  
Ambient Air ◽  
Spatial Variations ◽  
Ionization Chambers ◽  
Charge Effects ◽  
X Ray

Measurements of the spatial variations in the response of three ionization chamber (IC) designs were tested as a function of chamber bias voltage, incident X-ray flux and fill gas. Two components of spatial variation are seen. When the ionization chambers are near saturation, spatial variations exist that are tied to the chamber geometry. While the response of some chambers is relatively flat, others show significant variation across the IC. These variations appear to be inherent in the response of each IC at saturation. When the chamber is far from saturation, large spatial variations in response are present when N2is used as a fill gas, but not when ambient air is used as a fill gas. These appear to be tied to space charge effects.

scholarly journals Comparison of entrance surface air kerma measurement with MTS-N (LiF: Mg, Ti) chips with a kilovoltage X-ray source

2021 ◽  
Vol 22 (1) ◽  
pp. 20-34
Author(s):  
Akintayo Daniel Omojola ◽  
Samuel Olaolu Adeneye ◽  
Michael Onoriode Akpochafor ◽  
Isiaka Olusola Akala ◽  
Azuka Anthonio Agboje
Keyword(s):  
Ionization Chamber ◽  
Radiation Detectors ◽  
Field Size ◽  
Peak Voltage ◽  
X Ray ◽  
Air Kerma ◽  
Image Distance ◽  
The Mean ◽  
Dose Accuracy ◽  
Entrance Surface Air Kerma

Objective: Radiation detectors are key components that ensure the accuracy and performances of dosimetry equipment. The study is aimed to compare the mean entrance surface air kerma (ESAK) between a DCT-10mm ionization chamber (IC) and MTS-N (LiF: Mg, Ti) chips when both detectors are exposed to ≤ 5mGy with a 10 by 10 field size, with an X-ray source and to determine the accuracy of the Thermoluminescent (TL) chips. Also, the dose will be compared to similar studies. Materials and Methods: A functional, Digital Radiography (DR) X-ray System was used. A DCT-10mm ionization chamber (IC) and an XR Multidetector was positioned at a Source to Image Distance (SID) of 100cm on polystyrene, about 20cm thick. An X-ray spectrum generated at a Practical Peak Voltage (PPV) of 60-107kV with Half Value Layer (HVL) of 2.4-4.3mmAl and filtration > 3mmAl was used. The same setup was used for the MTS-N chips. Results: The mean doses for 1-5 mGy with the MTS-N chips were 1.07±0.07, 1.60±0.13, 2.23±0.11, 2.58±0.07 and 3.45±0.10 mGy respectively, with accuracies of 7, 20, 26, 36 and 31%. Dose accuracy at 1and 2mGy was within 25% respectively. Dose accuracies at 3, 4 and 5mGy was within >25%. The correction factor for 1-5mGy was 0.94, 1.25, 1.35, 1.55 and 1.45 respectively. Conclusion: Validation of the MTS-N chips with the reference ionization chamber to this study was within 36%. The Radiation and Nuclear Safety Authority (STUK) recommends that ESAK be within 25% for entrance surface dose. ESAK accuracy mostly increased with dose as observed in this study.

An Ionization Chamber Study of Electron and Ion Decay in Irradiated Ammonia

1973 ◽  
Vol 51 (24) ◽  
pp. 4159-4166 ◽  
Author(s):  
D. R. McCracken ◽  
D. A. Armstrong
Keyword(s):  
High Voltage ◽  
Ionization Chamber ◽  
Cell Walls ◽  
Negative Ions ◽  
Free Diffusion ◽  
Ionization Chambers ◽  
X Ray ◽  
Chamber Study ◽  
Positive Ion

Ionization chambers with plane parallel and coaxial electrodes have been used to study the ion and electron concentrations in ammonia subjected to 120 kvp X-ray pulses of 17 and 30 ms duration. Differences in the numbers of positive and negative ions collected on the application of pulses of high voltage imply that free diffusion of electrons to the cell walls occurs in the early part of the X-ray pulse until it is inhibited by the positive ion space charge. Thereafter, positive and negative ions decay at equal rates.The rate constant for the neutralization reaction[Formula: see text]at 1200 Torr of ammonia and 297°K was calculated to be 4.2 ± 1.0 × 10−5 cm3 ion−1 s−1. However, unless extensive precautions are taken to remove electron-attaching impurities reactions between NH4+•nNH3 ions and impurity negative ions are dominant. The results are discussed and compared to other work on electron–ion neutralization reactions.

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 dose and cancer risk to newborn from chest X-ray in South-South Nigeria: a call for protocol optimization

2021 ◽  
Vol 52 (1) ◽  
Author(s):  
Akintayo Daniel Omojola ◽  
Michael Onoriode Akpochafor ◽  
Samuel Olaolu Adeneye ◽  
Isiaka Olusola Akala ◽  
Azuka Anthonio Agboje
Keyword(s):  
Cancer Risk ◽  
Age Groups ◽  
Field Size ◽  
Radiological Protection ◽  
International Studies ◽  
X Ray ◽  
Thermoluminescent Dosimeters ◽  
Chest X Ray ◽  
Neonatal Patient ◽  
The Mean

Abstract Background The use of X-ray as a diagnostic tool for complication and anomaly in the neonatal patient has been helpful, but the effect of radiation on newborn stands to increase their cancer risk. This study aims to determine the mean, 50th percentile (quartile 2 (Q2)), and 75th percentile (quartile 3 (Q3)) entrance surface dose (ESD) from anteroposterior (AP) chest X-ray and to compare our findings with other relevant studies. The study used calibrated thermoluminescent dosimeters (TLDs), which was positioned on the central axis of the patient. The encapsulated TLD chips were held to the patients’ body using paper tape. The mean kilovoltage peak (kVp) and milliampere seconds (mAs) used was 56.63(52–60) and 5.7 (5–6.3). The mean background TLD counts were subtracted from the exposed TLD counts and a calibration factor was applied to determine ESD. Results The mean ESDs of the newborn between 1 and 7, 8 and 14, 15 and 21, and 22 and 28 days were 1.09 ± 0.43, 1.15 ± 0.50, 1.19 ± 0.45, and 1.32 ± 0.47 mGy respectively. A one-way ANOVA test shows that there were no differences in the mean doses for the 4 age groups (P = 0.597). The 50th percentile for the 4 age groups was 1.07, 1.26, 1.09, and 1.29 mGy respectively, and 75th percentile were 1.41, 1.55, 1.55, and 1.69 mGy respectively. The mean effective dose (ED) in this study was 0.74 mSv, and the estimated cancer risk was 20.7 × 10−6. Conclusion ESD was primarily affected by the film-focus distance (FFD) and the patient field size. The ESD at 75th percentile and ED in this study was higher compared to other national and international studies. The estimated cancer risk to a newborn was below the International Commission on Radiological Protection (ICRP) limit for fatal childhood cancer (2.8 × 10−2Sv−1).

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