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Percent depth-dose distribution discrepancies from very small volume ion chambers
Vikren Sarkar1, Brian Wang, Hui Zhao
1University of Utah. vikren.sarkar@gmail.com.
Journal of Applied Clinical Medical Physics
|June 24, 2015
Summary
Very small ion chambers may cause errors up to 5% in linear accelerator commissioning depth dose scans due to signal interference. Comparing scans with larger chambers is recommended to validate data accuracy.
Area of Science:
- Medical Physics
- Radiation Oncology
- Dosimetry
Background:
- Medical physicists utilize ion chambers for linear accelerator commissioning.
- Very small ion chambers offer potential for detailed beam characterization in steep dose gradients.
Purpose of the Study:
- To investigate the accuracy of very small ion chambers in measuring percentage depth doses (PDDs).
- To identify potential sources of error when using small ion chambers during scanning procedures.
Main Methods:
- Eight ion chambers (0.007 cc to 0.6 cc) and four scanning systems were used.
- PDDs were scanned at +300V and -300V biases.
- Scans were compared with static measurements using an external electrometer.
Main Results:
- A reproducible overresponse with depth (up to 5% at 25 cm) was observed with very small ion chambers under specific scanning conditions.
- This overresponse was not present in static measurements.
- Signal interference from scanning systems was identified as the likely cause.
Conclusions:
- The use of very small ion chambers with certain scanning systems may introduce systematic errors in PDD measurements.
- Careful validation by comparing with larger chambers is crucial when using small ion chambers in steep dose gradients.
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