Investigation Of The Culprits Responsible For The Significant Variation Of The Calibrated Dose-rate Among Gamma-knife InstitutionsKeywords: physics, Dose, dosimetry, technique, gamma knifeInteractive Manuscript
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What is the background behind your study?
RPC performed TLD-measurements on 16 GK-institutions for audits of the TG-51 non-compliant beams. The average RPC/INST ratio is 0.962 with SD of ±0.022. In 06/09, MDACC acquired GK-Perfexion. RPC-TLD was used as an independent check of dose-rate calibration. The TLD-result indicated the 16-mm-collimator dose-rate was 1% higher than that of TG-21 ion-chamber measurement in a plastic sphere-phantom (PSP), but it agreed with that of TG-51ion-chamber measurement in an Elekta solid-water phantom (ESWP).
What is the purpose of your study?
The purpose of this study is to investigate what are the culprits responsible for this significant difference between the doses were measured with RPC-TLD and calculated based on the institution dose-rate calibration.
Describe your patient group.
Describe what you did.
This study was carried out at CAM, Washington University. First, TG-21 calibration was performed using the Capintec PR-05P ion-chamber (C-PR-05P) placed in x-y plane within the WU PSP, then with MDACC PSP. The same measurements were repeated using the PTW TN3010 ion-chamber (PTW-TN3010). Secondly, TG-51 calibrations were also carried with ESWP with a PTW-TN3010 and the WU SRS water-phantom (WUWP) with an Extradin-A16 ion-chamber (E-A16).
Describe your main findings.
The difference of the TG-21 calibration measured in WU and MDACC PSP is within 0.5% (The comparison results are all normalized to the calibration based on TG-21 using PTW-TN3010 in MDACC PSP.). The result is suggested that the variation of the composition of PSP is very small. It is to our surprise the dose-rate was calibrated based TG-21 with C-PR-05P in a PSP is 2.4% higher that was calibrated with PTW-TN3010 in a PSP. The ratio of the calibrated dose-rate based on TG-51 over that on TG-21 is 1.009. The dose-rate based on TG-51 using WUWP with the E-A16 is 1% higher than that of the dose rate determined by the PTW-TN3010 in the ESWP.
Describe the main limitation of this study.
This is a retrospective study.
Describe your main conclusion.
We could safely rule out the uncertainties of the PSP is the culprit for the significant dose-rate variation.
Describe the importance of your findings and how they can be used by others.
The difference of about 2.5% is due to the type and the sensitive volume of the ion-chambers used for the calibration and the other 1% is due to the differences between the TG-21 in polystyrene and TG-51 in water dose calculations.
RPC performed TLD-measurements on 16 GK-institutions for audits of the TG-51 non-compliant beams. The average RPC/INST ratio is 0.962 with SD of ±0.022. In 06/09, MDACC acquired GK-Perfexion. RPC-TLD was used as an independent check of dose-rate calibration. The TLD-result indicated the 16-mm-collimator dose-rate was 1% higher than that of TG-21 ion-chamber measurement in a plastic sphere-phantom (PSP), but it agreed with that of TG-51ion-chamber measurement in an Elekta solid-water phantom (ESWP).
The purpose of this study is to investigate what are the culprits responsible for this significant difference between the doses were measured with RPC-TLD and calculated based on the institution dose-rate calibration.
This study was carried out at CAM, Washington University. First, TG-21 calibration was performed using the Capintec PR-05P ion-chamber (C-PR-05P) placed in x-y plane within the WU PSP, then with MDACC PSP. The same measurements were repeated using the PTW TN3010 ion-chamber (PTW-TN3010). Secondly, TG-51 calibrations were also carried with ESWP with a PTW-TN3010 and the WU SRS water-phantom (WUWP) with an Extradin-A16 ion-chamber (E-A16).
The difference of the TG-21 calibration measured in WU and MDACC PSP is within 0.5% (The comparison results are all normalized to the calibration based on TG-21 using PTW-TN3010 in MDACC PSP.). The result is suggested that the variation of the composition of PSP is very small. It is to our surprise the dose-rate was calibrated based TG-21 with C-PR-05P in a PSP is 2.4% higher that was calibrated with PTW-TN3010 in a PSP. The ratio of the calibrated dose-rate based on TG-51 over that on TG-21 is 1.009. The dose-rate based on TG-51 using WUWP with the E-A16 is 1% higher than that of the dose rate determined by the PTW-TN3010 in the ESWP.
This is a retrospective study.
We could safely rule out the uncertainties of the PSP is the culprit for the significant dose-rate variation.
The difference of about 2.5% is due to the type and the sensitive volume of the ion-chambers used for the calibration and the other 1% is due to the differences between the TG-21 in polystyrene and TG-51 in water dose calculations.
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