Ion-recombination correction factor for spherical ion chambers irradiated by continuous photon beams

1996 ◽  
Vol 41 (6) ◽  
pp. 1025-1035 ◽  
Author(s):  
A Piermattei ◽  
L Azario ◽  
G Arcovito ◽  
M P Toni
Keyword(s):  
Correction Factor ◽  
Photon Beams ◽  
Ion Recombination ◽  
Ion Chambers

scholarly journals Dosimetric Performance of Newly Developed Farmer-Type Ionization Chamber in Radiotherapy Practice

2016 ◽  
Vol 15 (6) ◽  
pp. NP113-NP120
Author(s):  
Sathiyan Saminathan ◽  
Henry Finlay Godson ◽  
Retna Ponmalar ◽  
Ravikumar Manickam ◽  
James Mazarello ◽  
...  
Keyword(s):  
Correction Factor ◽  
Ionization Chamber ◽  
Cost Effective ◽  
High Energy ◽  
Dose Measurement ◽  
Photon Beams ◽  
Active Volume ◽  
Ion Chamber ◽  
Ion Recombination ◽  
Polarity Correction

Dose measurement with ionization chamber is essential to deliver accurate dose to the tumor in radiotherapy. The cylindrical Farmer-type ionization chamber is recommended by various dosimetry protocols for dose measurement of radiotherapy beams. The air-equivalent graphite wall Farmer-type ionization chamber (FAR 65 GB) of active volume 0.65 cm3 with aluminum as the central electrode material was fabricated. Various dosimetric parameters were studied for the newly developed ionization chamber in cobalt-60, 6 and 18 MV photon beams. The preirradiation and postirradiation leakage of the chamber was within 0.08%. The long-term stability and the stem effect of the chamber were within 0.07% and 0.3%, respectively. The sensitivity of the ionization chamber was found to be 22.15 nC/Gy. The chamber shows linear response with dose for cobalt-60, 6 and 18 MV photon beams. The ion recombination correction factor increases with increase in bias voltage. For all energies and field sizes, the polarity correction factor is almost closer to unity. The ion recombination and polarity correction measurements show that the polarizing potential and polarity recommended during the calibration of ionization chamber should be used for routine measurement to avoid the uncertainty. The chamber response is independent of dose rate and energy. The chamber is cost-effective and shows precise and reproducible response. The study carried out confirms that the newly fabricated ion chamber can be used in the measurement of absolute dose for high-energy photon beams.

Effective point of measurement of thimble ion chambers in megavoltage photon beams

2009 ◽  
Vol 37 (1) ◽  
pp. 96-107 ◽  
Author(s):  
Frédéric Tessier ◽  
Iwan Kawrakow
Keyword(s):  
Photon Beams ◽  
Ion Chambers

Comparison of parameterization methods of the collimator scatter correction factor for open rectangular fields of 6–25 MV photon beams

2000 ◽  
Vol 54 (3) ◽  
pp. 285
Author(s):  
H.Niek Jager ◽  
Stan Heukelom ◽  
Herman J van Kleffens ◽  
Rob van der Laarse ◽  
Hans J.J.M van Gasteren ◽  
...  
Keyword(s):  
Correction Factor ◽  
Scatter Correction ◽  
Photon Beams ◽  
Collimator Scatter

Comparison of parametrization methods of the collimator scatter correction factor for open rectangular fields of 6–25 MV photon beams

1997 ◽  
Vol 45 (3) ◽  
pp. 235-243 ◽  
Author(s):  
H.Niek Jager ◽  
Stan Heukelom ◽  
Herman J van Kleffens ◽  
Hans van Gasteren ◽  
Rob van der Laarse ◽  
...  
Keyword(s):  
Correction Factor ◽  
Scatter Correction ◽  
Photon Beams ◽  
Collimator Scatter

scholarly journals Estimation of Dosimetric Parameters based on KNR and KNCSF Correction Factors for Small Field Radiation Therapy at 6 and 18 MV Linac Energies using Monte Carlo Simulation Methods

2019 ◽  
Vol 9 (1Feb) ◽  
Author(s):  
S A Rahimi ◽  
B Hashemi ◽  
S R Mahdavi
Keyword(s):  
Monte Carlo ◽  
Correction Factor ◽  
Reference Conditions ◽  
Field Size ◽  
Monte Carlo Code ◽  
Small Field ◽  
Correction Factors ◽  
Photon Beams ◽  
Small Field Dosimetry ◽  
Circular Field

Background: Estimating dosimetric parameters for small fields under non-reference conditions leads to significant errors if done based on conventional protocols used for large fields in reference conditions. Hence, further correction factors have been introduced to take into account the influence of spectral quality changes when various detectors are used in non-reference conditions at different depths and field sizes.Objective: Determining correction factors (KNR and KNCSF) recommended recently for small field dosimetry formalism by American Association of Physicists in Medicine (AAPM) for different detectors at 6 and 18 MV photon beams.Methods: EGSnrc Monte Carlo code was used to calculate the doses measured with different detectors located in a slab phantom and the recommended KNR and KNCSF correction factors for various circular small field sizes ranging from 5-30 mm diameters. KNR and KNCSF correction factors were determined for different active detectors (a pinpoint chamber, EDP-20 and EDP-10 diodes) in a homogeneous phantom irradiated to 6 and 18 MV photon beams of a Varian linac (2100C/D).Results: KNR correction factor estimated for the highest small circular field size of 30 mm diameter for the pinpoint chamber, EDP-20 and EDP-10 diodes were 0.993, 1.020 and 1.054; and 0.992, 1.054 and 1.005 for the 6 and 18 MV beams, respectively. The KNCSF correction factor estimated for the lowest circular field size of 5 mm for the pinpoint chamber, EDP-20 and EDP-10 diodes were 0.994, 1.023, and 1.040; and 1.000, 1.014, and 1.022 for the 6 and 18 MV photon beams, respectively.Conclusion: Comparing the results obtained for the detectors used in this study reveals that the unshielded diodes (EDP-20 and EDP-10) can confidently be recommended for small field dosimetry as their correction factors (KNR and KNCSF) was close to 1.0 for all small field sizes investigated and are mainly independent from the electron beam spot size.

Sign in / Sign up

Export Citation Format

Share Document