Helpful Hints for Measurements in myQA Accept
Small Field Measurements
For big fields, it is recommended to use the continuous mode to save time. This is a considerable advantage of the measurement system consisted of Blue Phantom family and myQA Accept software.
However, for fields smaller than 5 cm × 5 cm, it is recommended to switch to the Step by Step mode due to the following challenge:
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The reference detector may disturb the field measurement (possible shadow).
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Use of chambers with small volume for better point resolution.
To avoid the possible shadow of the reference detector, measure with a Stealth chamber as reference or without a reference chamber. To eliminate the LINAC pulses without reference detector, increase the time per measurement point to a value between 0.5 and 1 second.
The above measures also overcome the second challenge, i.e., using chambers with a small volume. Since the chamber sensitivity is proportional to the volume, the electrometer has to amplify the signal, and the same time also noise, greatly.
Large Field Measurements
For large field measurements, e.g., 400 mm × 400 mm at more than 20 cm water depth, it is necessary to create diagonal queues or half-profiles, due to the physical limits of the phantom.
For exact phantom setup, please refer to the corresponding phantom user manual.
Diagonals with Collimator at 45º
One common method is to rotate the Collimator by 45º degrees and define a diagonal measurement. Therefore, enter under the diagonal scan definition in the Extended settings a Collimator Angle of 45º degrees and choose to scan with maximum possible field size.