The D and V notation are conventions that are designed to designate volumes and doses that correspond to features and goals in a treatment plan (doses and volumes).
DXX designates the minimum absorbed dose received by XX% of the total volume of a structure of interest.
Example: D90 of the prostate = 65 Gy.
This means that 90% of the prostate volume receives at least 65 Gy. This is determined from the cummulative DVH (explained in this post) and can be read off the cDVH. The D90 can be visualized in a TPS by setting the minimum display dose to 65 Gy.
Note: Instead of percent of the volume DXX could be specified in absolute volume, such as cm3.
|D50 of the breast volume is determined on the cDVH to be equal to 307 cGy.|
VXX designates the volume that receives XX Gy.
Example: V120 of the prostate
This would be the volume of the prostate that receives 120 Gy from the current plan. This value is also determined from the cDVH. Your graphical TPS will display this as a 3D volume or an isodose contour.
Note: Instead of gray the dose in VXX could be specified as percent dose (typically normalized to DRx).
|V8 (or V57%) of the breast volume is determined from the cDVH to be equal to 147.8 cm3.|
The V and D notations are simply arbitrary conventions, which are easy to confuse. Hopefully this post will serve as a reference to remind you what the notations mean.
I hope this helps and let me know if you have questions or corrections.