Table 1.
Parameters of the treatment head and the incident beam used in the simulations. X and Y denote the crossplane and inplane directions, respectively. Negative Y is away from the gun, and negative X is to the left when facing the gantry. Spot positions, primary collimator and flattening filter lateral positions, and jaw (Y) and MLC (X) positions are relative to the collimator rotation axis, and are the displacement of the object. The jaw and MLC positions are the positions extrapolated to 100 cm SSD. Target position is relative to the manufacturer’s specification. Where two uncertainties are listed, the first applies to the 6 MV beam and the second to the 18 MV beam.
| Nominal energy | 6 (FF out) | 6 (FF in) | 18 (FF out) | 18 (FF in) | Uncertainty | ||||
|---|---|---|---|---|---|---|---|---|---|
| Plane | X | Y | X | Y | X | Y | X | Y | |
| Energy (MeV) | 6.51 | 14.12 | 0.15∕0.2 | ||||||
| Spectral width (FWHM) (%) | 20 | 13.2 | 4 | ||||||
| Divergence (deg) | 0 | 0 | 0.2∕0.1 | ||||||
| Spot size (FWHM) (mm) | 1.4 | 2.1 | 1.4 | 2.1 | 1.2 | 1.6 | 1.2 | 1.6 | 0.1 |
| Beam angle (mrad) | 1.0 | −1.0 | 0.8 | −1.1 | 0.8 | 0.7 | 0.8 | 0.6 | 0.5 |
| Spot position (mm) | −0.1 | 0.5 | 0.0 | 0.6 | 0.0 | 0.3 | 0.0 | 0.4 | 0.5 |
| Target position along beam axis (mm) | −0.4 | −0.5 | −0.3 | −0.4 | 0.1 | ||||
| Primary collimator lateral position (mm) | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.5 |
| Flattening filter lateral position (mm) | ⋯ | ⋯ | 0.0 | 0.6 | ⋯ | ⋯ | 0.1 | 0.4 | 0.1 |
| Flattening filter density (g∕cm3) | 7.84 | 7.84 | ⋯ | ||||||
| Jaw∕MLC positions (cm) | −20.1 | −20.0 | −20.1 | −20.1 | −20.0 | −19.9 | −20.0 | −19.9 | 0.1 |
| Jaw∕MLC positions (cm) | 20.1 | 19.9 | 20.1 | 19.8 | 20.0 | 19.8 | 20.0 | 19.8 | 0.1 |