AAA Portal Dose Prediction
As mentioned recently, Eclipse 15 offers two options for predicting portal dose. The "classic" PDIP (Portal Dose Image Prediction) algorithm is a dedicated 2D-algorithm to predict the portal dose image. Since the introduction of PDIP (we described PDIP nearly 10 years ago), physicists have criticized that separate algorithms are used for 3D patient dose calculation and image prediction.
Varian has reacted upon this and now offers Portal Dose Prediction with AAA.
This is the first clinical VMAT verification worldwide (another "First"!), where predicted dose was calculated with AAA:
The measured image (right) is nearly indistinguishable from the dose distribution predicted with AAA (left). Passing rate for the 1%/1mm criterion is 99.1%. The evaluated area is the Complete Irradiation Area Outline (CIAO).
No separate license is needed for AAA PDP. However, the TrueBeam with FFF energies must be equipped with the 43*43 cm DMI imager.
Configuration
To configure the AAA 15.0.17 Calculation Model for Portal Dose Prediction, a new "Add On" must be created in Beam Configuration workspace by selecting "New Add On":
Add On Type is "Portal Dose Imager":
A new object is created underneath:
We fill in the SID of 1000 mm and Calibration MU = 100:
Now beam data can be calculated for the new Add On:
This gives an Absolute dose scaling factor, just as for the Open Beam:
The profiles are automatically fetched from the AAA model:
As one can see from the screenshots, this "walk-through" was for 6X1.
The last step is to approve the model:
Now the functionality can be used clinically, by specifying AAA as the Portal Dose algorithm in the clinical plan:
The next step would be to create a verification plan, as usual.
Discussion
Portal Dose Prediction with AAA is simplyfying the process of portal dosimetry. No extra measurements are necessary to configure an algorithm on the Eclipse side. As soon as more photon energies are released, PDIP will become entierly obsolete (at least for DMI users).
On the TrueBeam side there are no changes, the imager calibration remains untouched. This makes it possible to work in parallel with PDIP and AAA.
H.K.
Notes
1 Currently, only 6FFF plans can be predicted. The other photon energies can be configured in Beam Configuration, but their use for Portal Dose Prediction is blocked by the user interface of External Beam Planning. We assume that there is nothing special about 6FFF. Probably there was simply not enough time to validate the other energies before release date.