The stf Data Structure

The stf struct holds all geometric information about the irradiation. The individual fields contain the following information.

Screenshot of the stf structure:

Field	Description
gantry angle	Specification of the gantry angle for each beam in °. Range: 0° - 359°
couch angle	Specification of the couch angle for each beam in °. Range: 0°- 359°
bixel width	Photons: lateral width of each bixel. Particles: lateral spot spacing.
radiation mode	Specification of the radiation mode. Options are: ‘photons’, ‘protons’ or ‘carbon’.
number of Rays	Number of rays for each beam
ray	The ray substructure contains the information about the position and orientation of each ray / bixel for a single beam.
source point	Position of the virtual radiation source in LPS coordinates.
number of bixels per ray	Photons: each ray is a single bixel. Particles: number of bixels / dose spots along each ray.
total number of bixels	Total number of bixels for each beam.

stf.ray substructure

The stf.ray substructure contains the information about the position and orientation of each ray/bixel for a single beam.

Screenshot of the stf.ray substructure:

Field	Code	Description
ray position (beam’s eye view)	`rayPos_bev`	Point where the ray crosses the isocenter plane in the beam’s eye view.
target point (beam’s eye view)	`targetPoint_bev`	Target point of the ray from the beam’s eye view. The target point extends the ray from source to rayPos_bev to behind the patient for use in rayTracing.
ray position (LPS-coordinates)	`rayPos`	rayPos_bev in the LPS coordinate system.
target point (LPS-coordinates)	`targetPoint`	targetPoint_bev in the LPS coordinate system.
energy	`energy`	Photons: Single value (max. LINAC energy). Particles: Energy values of the dose spots along the ray. The number of energies corresponds to the number of bixels per ray.

stf.ray.energy field

The stf.ray.energy field contains all energy values for the spots along the specified ray. If the radiation mode ‘Photons’ was selected, it will be set to NaN.

Screenshot of the stf.ray.energy field:

stf.numOfBixelsPerRay field

The stf.numOfBixelsPerRay field contains the number of bixels / dose spots for every ray of the specified beam. This corresponds to the number of energy values per ray in the stf.ray substructure.

Screenshot of the stf.numOfBixelsPerRay field: