Figure 1.
Measured GRID factor as a function of treatment field size (cm2) at isocenter (d = Dmax) for 6 MV X-rays on a Novalis TX linear accelerator using a brass GRID collimator. For a given field size (in area) and GRID treatment dose, the monitor units are calculated using the GRID factor curve, above. We have explored different formats of GRID field factor as a function of treatment portal sizes, including equivalent square field size, and total area of the field size for a range of field sizes and shapes we anticipated to use for the GRID therapy in dogs. We found that the GRID factor and field size in area capture the most stable relationship, of all tested.