Determination of air‐kerma strength for the <sup>192</sup>Ir GammaMed  iX pulsed‐dose‐rate brachytherapy source

Riley, A; Pike, T; Micka, J; Fulkerson, Regina K.; DeWerd, Larry A.

doi:10.1118/1.4812420

Cited by 3 publications

(4 citation statements)

References 13 publications

(22 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Any differences in source geometries between the source type used at the calibration laboratory and the source being measured by the user (Riley et al 2013, Shipley et al 2015 could potentially require the application of a source geometry correction factor to the well chamber calibration coefficient.…”

Section: Discussionmentioning

confidence: 99%

A multicentre audit of HDR/PDR brachytherapy absolute dosimetry in association with the INTERLACE trial (NCT015662405)

et al. 2017

View full text Add to dashboard Cite

A UK multicentre audit to evaluate HDR and PDR brachytherapy has been performed using alanine absolute dosimetry. This is the first national UK audit performing an absolute dose measurement at a clinically relevant distance (20 mm) from the source. It was performed in both INTERLACE (a phase III multicentre trial in cervical cancer) and non-INTERLACE brachytherapy centres treating gynaecological tumours. Forty-seven UK centres (including the National Physical Laboratory) were visited. A simulated line source was generated within each centre's treatment planning system and dwell times calculated to deliver 10 Gy at 20 mm from the midpoint of the central dwell (representative of Point A of the Manchester system). The line source was delivered in a water-equivalent plastic phantom (Barts Solid Water) encased in blocks of PMMA (polymethyl methacrylate) and charge measured with an ion chamber at 3 positions (120° apart, 20 mm from the source). Absorbed dose was then measured with alanine at the same positions and averaged to reduce source positional uncertainties. Charge was also measured at 50 mm from the source (representative of Point B of the Manchester system). Source types included 46 HDR and PDR Ir sources, (7 Flexisource, 24 mHDR-v2, 12 GammaMed HDR Plus, 2 GammaMed PDR Plus, 1 VS2000) and 1 HDRCo source, (Co0.A86). Alanine measurements when compared to the centres' calculated dose showed a mean difference (±SD) of +1.1% (±1.4%) at 20 mm. Differences were also observed between source types and dose calculation algorithm. Ion chamber measurements demonstrated significant discrepancies between the three holes mainly due to positional variation of the source within the catheter (0.4%-4.9% maximum difference between two holes). This comprehensive audit of absolute dose to water from a simulated line source showed all centres could deliver the prescribed dose to within 5% maximum difference between measurement and calculation.

show abstract

Section: Discussionmentioning

confidence: 99%

A multicentre audit of HDR/PDR brachytherapy absolute dosimetry in association with the INTERLACE trial (NCT015662405)

et al. 2017

View full text Add to dashboard Cite

show abstract

“…Radiochromic film measurements were acquired to obtain the dose distribution in phantom from the Bebig

^{192} Ir

source in order to quantitatively investigate the impact of the source geometry on well chamber measurements and Monte Carlo simulations. Experimental methods were adapted from the surface dose characterization study of an 192 Ir PDR brachytherapy source by Riley et al Autoradiographs on Ashland Gafchromic EBT3 film (lot number 11051301) were created by exposing the film to 2Gy at a depth of 1cm from the source in a

Virtual {Water}^{normalTM}

(Med‐Cal, Verona, WI) phantom. The active source and wire were placed in a custom‐fabricated Virtual Water insert.…”

Section: Methodsmentioning

confidence: 99%

Air‐kerma strength determination of an HDR ¹⁹²Ir source including a geometric sensitivity study of the seven‐distance method

et al. 2017

View full text Add to dashboard Cite

The differences between the SK measurements determined from the seven-distance technique and the accredited UWADCL measurement results were within the k = 2 uncertainty reported for an accredited calibration. Excellent agreement was found between the measured SK and RAKR methods used at the UWMRRC and PTB, respectively. Additionally, the sensitivity study has shown that the seven-distance algorithm accurately determines the SK of a source while having a variable chamber offset among nominal positions; the uncertainty budget for the seven-distance method does not need to be expanded at this time. It has been determined that the current standard used by the UWADCL for well chamber calibrations is valid for the Bebig model Ir2.A85-2 192Ir brachytherapy source.

show abstract

“…NIST does not maintain an air‐kerma strength measurement standard for HDR

^{192}

Ir brachytherapy sources, but the AAPM recognizes interim standards that are maintained by the Accredited Dosimetry Calibration Laboratories (ADCLs) 13,14 . These interim standards utilize an interpolated air‐kerma calibration coefficient for an ionization chamber calibrated at

^{137}

Cs and M250 x‐ray beam qualities and has been used for numerous calibrations of HDR sources 13–17 . The ADCLs are responsible for disseminating the national standards from NIST to the clinic.…”

Section: Introductionmentioning

confidence: 99%

“…13,14 These interim standards utilize an interpolated air-kerma calibration coefficient for an ionization chamber calibrated at 137 Cs and M250 x-ray beam qualities and has been used for numerous calibrations of HDR sources. [13][14][15][16][17] The ADCLs are responsible for disseminating the national standards from NIST to the clinic. This is achieved through a well-chamber calibration with a NIST-measured source and subsequent transfer calibration of a clinic's well chamber at an ADCL.…”

mentioning

confidence: 99%

On the stability of well‐type ionization chamber source strength calibration coefficients

2020

View full text Add to dashboard Cite

To investigate the variability and stability of brachytherapy source strength calibration coefficients for air-communicating and pressurized well-type ionization chambers among high-dose rate (HDR), low-dose rate (LDR), and electronic brachytherapy (EBT) source qualities. These qualities of an ionization chamber are important features to assess given their role in maintaining traceability to a primary national standards laboratory and facilitating efficacious patient care in brachytherapy. Methods: The calibration records from the University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL) customer well-type ionization chamber database were retrospectively analyzed for calibrations performed between 1996 and 2019. A statistical analysis was performed and differentiated among calibration type to quantify the distribution of chamber calibration coefficients among several chamber models. Distributions were quantified based on their moments and by quantile analysis. For LDR calibrations, chamber response was further differentiated by seed type to study the variability in seed dependence within and across chamber models. In addition to these metrics, the calibration lineage at the UWADCL was used to assess the stability of these calibration coefficients among chamber model and source type based on the ratio of subsequent calibration coefficients. Results: The distribution of brachytherapy source strength calibration coefficients for a particular chamber model is not necessarily normally distributed and is sensitive to changes in the machining tolerances or design of the chamber model. Calibration source quality also influenced the distributions of calibration coefficients for a chamber model; the air-kerma rate calibration coefficients for EBT sources were the most variable followed by LDR and then HDR source types. The stability of a chamber's source strength calibration coefficient exhibited a similar dependence on the source quality. Air-communicating and pressurized chambers exhibited an average stability between subsequent calibrations of 0.2% and 3.0%, respectively, for HDR calibrations, but could exhibit more than double this variability characteristic of their leptokurtic distributions. For LDR calibrations, the spread and stability in a model's calibration ratio toward another seed type is extensive and notable. For some seed types and chamber models exhibit variations of <0.5% while others exceeded 2.0%. Furthermore, the magnitude of this dependence is outside the variability of the source's source strength due to manufacturing, which was determined from the manufacturer and NIST source strength intercomparison records at the UWADCL. As a result, establishing and disseminating calibration conversion factors among different source and chamber models is not advised as it would substantially increase the uncertainty in a clinical user's determination of source strength. Conclusions: The calibration of a well-type ionization chamber is unique to the chamber, source, and source holder. Attempting...

show abstract

Determination of air‐kerma strength for the ¹⁹²Ir GammaMed iX pulsed‐dose‐rate brachytherapy source

Abstract: The resulting effect of the pointlike characteristics of the PDR brachytherapy source likely account for the differences observed between well chamber and in-air measurements.

Cited by 3 publications

References 13 publications

A multicentre audit of HDR/PDR brachytherapy absolute dosimetry in association with the INTERLACE trial (NCT015662405)

A multicentre audit of HDR/PDR brachytherapy absolute dosimetry in association with the INTERLACE trial (NCT015662405)

Air‐kerma strength determination of an HDR ¹⁹²Ir source including a geometric sensitivity study of the seven‐distance method

On the stability of well‐type ionization chamber source strength calibration coefficients

Contact Info

Product

Resources

About

Determination of air‐kerma strength for the 192Ir GammaMed iX pulsed‐dose‐rate brachytherapy source

Abstract: The resulting effect of the pointlike characteristics of the PDR brachytherapy source likely account for the differences observed between well chamber and in-air measurements.

Cited by 3 publications

References 13 publications

A multicentre audit of HDR/PDR brachytherapy absolute dosimetry in association with the INTERLACE trial (NCT015662405)

A multicentre audit of HDR/PDR brachytherapy absolute dosimetry in association with the INTERLACE trial (NCT015662405)

Air‐kerma strength determination of an HDR 192Ir source including a geometric sensitivity study of the seven‐distance method

On the stability of well‐type ionization chamber source strength calibration coefficients

Contact Info

Product

Resources

About

Determination of air‐kerma strength for the ¹⁹²Ir GammaMed iX pulsed‐dose‐rate brachytherapy source

Air‐kerma strength determination of an HDR ¹⁹²Ir source including a geometric sensitivity study of the seven‐distance method