Physics Administration Settings
This section explains the physics administration settings that are especially relevant for producing VMAT treatment plans that can be successfully delivered by a linear accelerator (i.e., accepted for treatment by the linac console without errors and delivered without any interlock or beam hold). Refer to the general information section in the Physics Administration Software User Guide for further information about the remaining settings.
All parameters depend on the linac’s capabilities and sometimes on the R&V system it is attached to. Therefore, it is difficult to state general values and Brainlab cannot guarantee the correctness of any of the values given below. If in doubt, please contact the linac manufacturer.
Properties/General Parameters/Machine Parameters
|Allowed collimator angles, allowed table (or ring) angles, allowed gantry angles|
Specifies the allowed ranges of collimator angles, table (or ring) angles and gantry angles. Clinical protocols that contain angles outside these ranges are discarded by the software.
|Minimum and maximum gantry speed during dose delivery||A typical value for the minimum gantry speed during dose delivery is 0.5 deg/sec for Varian or Elekta machines, and 0.3 deg/sec for MHI Vero.|
A correct value for the maximum gantry speed is especially important to be able to generate deliverable plans.
|Supported control point spacings|
List of control point spacings supported by the linac. The software is configured to use a spacing of 4 deg between control points, if possible. If 4 deg is not supported by the linac, the closest value from the list of supported ones will be used. Most linacs support a spacing of 4 deg.
Allows specification of the linac’s capability regarding dose rate and gantry speed modulation. Correct settings in this section are especially important to generate deliverable plans. Refer to the Dose Modulation section for further details.
For machines supporting gantry speed modulation, typical Maximum Gantry Speed Change value is 0.75 (deg/sec)/control point.
If plans are not deliverable, the most common cause is a leaf movement that surpasses the technical limits of the MLC controller. Therefore, reducing the values in this section can help create deliverable treatment plans.
Maximum leaf speed: The most important restriction is the maximal leaf speed. A typical value is 25 mm/sec for most of the supported machines. However, Brainlab Novalis classic is limited to 10 mm/sec and Elekta Agility supports 35 mm/sec.
Maximum leaf travel distance per gantry degree: Additionally, the leaf movement is restricted per amount of gantry degree. A typical value for Varian or Elekta machines is 5.5 mm/deg, and a typical value for MHI Vero is 4.4 mm/deg.
Maximum leaf travel distance per monitor unit: Another restriction is the amount of leaf travel per delivered monitor unit. Usually, this restriction is not required for Varian or Elekta machines. MHI Vero machines require a limit of 4.5 mm/MU.
[Per Energy/Modality] Set Parameters/Accelerator Settings/Dose Rates
Supported Dose Rates
Specifies all supported (nominal) dose rates. Depending on the configuration chosen in Dynamic Capabilities, treatment plans use one or many dose rate(s) from this list or dose rates between the minimum and maximum of this list.
Most Varian linacs support 100, 200, 300, 400, 500 and 600 MU/min in Std mode and higher dose rates in SRS or FFF mode.
The recommended values for VMAT deliveries with MHI Vero are 200, 250, 300, 350 and 400 MU/min.
[Per Energy/Modality] Set Parameters/Accelerator Settings/MU and Treatment Limits
There are lower and upper limits on the amount of monitor units that can be delivered per arc and also per arc degree.
If a treatment plan requires more than the upper limit of monitor units for a given arc, the software splits the arc into multiple arcs. The resulting arcs are called portions and must be irradiated one after the other.
Maximum MU per arc: The maximum number of monitor units per individual arc (per portion). An arc surpassing this limit will be split into portions. Refer to your linac’s and/or R&V’s documentation for a suitable value. Typical values for older machines are 999 MU. Newer machines can usually deliver up to 7200 MU in one arc.
Minimum MU per arc degree: The minimum number of monitor units per arc degree of an individual arc (per portion). A typical value for Varian or Elekta machines is 0.30 MU/deg and for MHI Vero is 0.74 MU/deg.
Maximum MU per arc degree: The maximum number of monitor units per arc degree of an individual arc (per portion). An arc surpassing this limit will be split into portions. A typical value for Varian and Elekta machines is 20.00 MU/degs and for MHI Vero is 22.20 MU/deg.