An Experimental Study of Intrabeam IORT Dosimetry Accuracy
H Zhang*, I Das, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL
Presentations
MO-IePD-TRACK 6-2 (Monday, 7/26/2021) 3:00 PM - 3:30 PM [Eastern Time (GMT-4)]
Purpose: The INTRABEAM (IB) System has been reported to have a large dosimetric difference between the vendor provided and user measured data. This study is aimed to verify the dosimetric accuracy by performing ionization chamber measurements of absorbed dose in a water phantom and comparing with the annual calibration data for past 10 years.
Methods: Ionization chamber measurements were performed with a PTW 34013 parallel-plate chamber at source to detector distances of 2 to 30 mm with and without a spherical applicator. The experimental output dose rates were derived by using the formula recommended by the manufacturer. The source calibration data, taken from the annual certificate files provided by manufacturer from 2011 to 2020, were reviewed and compared with the experimental results.
Results: It is found that the source data format was changed in 2017, from one dataset to two distinct datasets: one is Calibration V4.0, and other is TARGIT. The dose rate fluctuation from 2011 to 2016 at the same distance was within ±12%, from 2017 to 2020 was within 5%. However, the dose rates of 2017 certificate file increased up to 210% and 58% respectively for Calibration V4.0 and Target datasets comparing to the previous years. Experimental data with and without a spherical applicator taken in 2017 and after were found to still agree with 2011 certificate data within ±5% uncertainty, but a difference up to 200% was seen comparing with the Zeiss 2017 source data.
Conclusion: Comparing with our experimental data, the source output was found to remain almost the same from 2011 to 2020, therefore TARGIT trial dosimetry is still accurate. The large dosimetric difference is attributed to the lack of updated Zeiss QA water phantom conversion factor. We provided a new conversion factor to account for the change of calibration standard in Zeiss dosimetry laboratory.
ePosters
Keywords
Not Applicable / None Entered.
Taxonomy
TH- Brachytherapy: Intraoperative planning and image guidance
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