One possible dose measurement method for CBCT is to use a point dose detector and move it through the CBCT field with a motor and measure the dose profile and the full CTDI. It can be made either in a phantom or free in air. A 15 cm CTDI phantom may be shorter than the full beam so maybe free in air is preferable. For free in air measurements the true thickness of the beam can also be verified at the same time. With the right calculations the CTDI and CTDI100 can be collected, and there are programs that do this automatically after a measurement. Can compensate for CBCT that do not do a full 360 degree rotation etc..
It was not possible to add attachments here but an article that verifies this method can be found here:
A method to characterize the radiation output from a cone beam O-arm using a device for dose and dose profile scanning measurement
http://www.lunduniversity.lu.se/lup/publication/4027057
This solution can already be bought for commercial use:
http://www.rti.se/accessories/detail/ct-dose-profiler
http://www.rti.se/accessories/detail/rti-mover
For questions about the products or if you need more information on measurements, for example on Aquilion ONE, you can contact: info@rti.se
A rotation symmetrical point dose detector can also be used to measure the peak dose in isocenter during a rotation in CBCT, if that is a possible way to go for standard measurements.
For more information about point dose measurement in CT you can see the IEC standard 60601-2-44: Edition 3.0 amendment 1.
Dental CBCT (and Panoramic) seems to have its own standard (for example IEC 60601-2-63) and they talk more about dose measurements at the detector during one rotation and DAP measurements (if I understand it right).