Room: Exhibit Hall
Purpose: To develop an AAPM-approved process to review the performance of ionization chambers used for clinical radiation dosimetry and determine whether they meet an objective reference-class specification for use in absolute clinical dosimetry (i.e., TG-51)
Methods: An outcome of the publication of the AAPMâ€™s Addendum to TG-51 was the definition of a specification for a reference-class ionization chamber. The next step from such a specification is to develop a procedure whereby new types of ionization chamber can be evaluated and added to the list of recommended reference-class chambers given in the TG-51 Addendum.An adhoc working group of the WGTG51 developed a procedure for the collection, submission and review of ion chamber data and this has been trialled in collaboration with a number of manufacturers. The aim of the procedure is to simplify the review process for AAPM as much as possible by specifying what data is required and how it must be presented. At the same time, the process must be accessible to all ion chamber manufacturers, so that development of new chamber designs is not stifled.
Results: Example data was obtained from a number of manufacturers and it was found that, although the specification in the TG-51 Addendum was quite clear, there were still some ambiguities as to how the different parameters might be evaluated and weighted in an overall pass/fail score. The issue of raw data versus processed results also arose and how to address different chamber types (pp vs cyl). Overall the exercise was positive for both sides.
Conclusion: The trial has indicated that a separate body is needed to administer the final approvals procedure and AAPM is currently reviewing a submission for a formal working group under the CLA SC. Eventual extension to cover other calibration situations (e.g. small fields) is anticipated.