Users Manual Part 2

Clinical User’s Guide
IBA | 20-5|
Volume 1 - Treatment Session
|Part III
- The Pencil Beam Scanning (PBS) Suite Pencil Beam Scanning Principles
|
This combination of longitudinal and transversal dose distribution lies at the core of
the PBS delivery technique.
Repainting Modes
When a given layer is scanned by the proton beam more than once (or repainted),
the total dose to be delivered at each layer in the target is divided by the number of
scans or paintings that is to be achieved. This delivery process is repeated a number
of times, as specified in the treatment plan, and results in the delivery of the entire
prescribed dose within the layer.
As a result of this process, the weight of the spots in each layer is scaled in function
of the total dose to be delivered at that layer and the number of paintings to be
performed.
Figure 20-3. Scaling Sample: 3 Paintings
The order in which the layers are scanned or painted and hence the way in which the
prescribed dose is delivered to each of the layers in the target volume defines several
possible types of repainting techniques.
Note: Some of these repainting techniques may not be available at your center.
The repainting types are as follows:
None (no layer repainting)
In-Layers Repainting
Decrease in Energy
Back and Forward
Mixed Repainting
In addition to the repainting type principles that are described in the sections below,
Chapter 22, “PBS Multiple Repainting, contains detailed information on how the
different repainting types are identified and represented.