Isocenter to Wedge Tray Distance Attribute
| Tag | (300A,00D9) |
|---|---|
| Type | Required (1) |
| Keyword | IsocenterToWedgeTrayDistance |
| Value Multiplicity | 1 |
| Value Representation | Single (FL) |
Isocenter to downstream edge of wedge tray (mm).
See Section C.8.8.25.4 and Section C.8.8.25.10
Section C.8.8.25.4
C.8.8.25.4 Virtual Source-Axis Distances and the Use of Trays in Ion Therapy
The apparent source position in ion therapy is not constant or can be different in x or y direction. The apparent source position (as measured from field size projections) shall be called Virtual Source, the distance from the virtual source to isocenter the Virtual SAD.
Most of the cases, no trays are used for blocks, compensators and wedges. However, the concept of trays together with the mounting position is useful for specifying exactly at which point the position of these devices shall be measured. Therefore, trays shall always be present, even though they are only virtual trays.
Figure C.8.8.25-1 shows an example.
Figure C.8.8.25-1. Virtual Source-Axis Distances
Examples: The use of the above Attributes for snout positioning and block/compensator manufacturing:
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Snout positioning:
The mounting positions as depicted in the drawing are only examples. As the block tray does not really exist in most of the cases, it is only used as a reference position. As some machines use the downstream face of the block as a reference position for their snout positioning, it could make sense to define for example that the block mounting position must be SOURCE_SIDE. In this case, one uses the downstream face of the block as the reference position, which is the same side as used by the machine. This definition is always independent of the actual thickness of the block. The Isocenter-Block Distance is defined and the machine can deduce the position of the snout from this value.
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Scaling of block/compensator data for manufacturing
The Isocenter position is always used as the reference position for all distances measured 'from isocenter'. Real size block and compensator manufacturing should be based on the distance from the Virtual Source (X/Y) to the device, i.e., VirtualSourceToDeviceDistance = VirtualSAD - IsocenterToDeviceDistance.
Section C.8.8.25.10
C.8.8.25.10 Isocenter to Accessory Distance
Snout Position (300A,030D) is defined at the Control Point level and can therefore vary during the beam, causing all the accessories attached to the Snout (Applicator, Block, Compensator, etc.) to move as well.
For each accessory which is attached to the Snout and has its distance to isocenter defined at the Beam level (such as Isocenter to Beam Limiting Device Distance (300A,00BB), Isocenter to Compensator Tray Distance (300A,02E4), Isocenter to Block Tray Distance (300A,00F7) ), the prescribed physical position of the accessory is defined at the first Control Point.
This is consistent with the approach used for Beam Limiting Device Boundaries and Positions (see Section C.8.8.25.3 Leaf Position Boundaries).
For accessories which are attached to the Snout whose distance is defined at the Control Point level, such as Isocenter to Lateral Spreading Device Distance (300A,0374) and Isocenter to Range Modulator Distance (300A,038A), and are attached to the Snout, both the Snout Position (300A,030D) and the accessory distance must change by the same amount.