The calculation grid resolution/size used affects the accuracy of the dose distribution. In Astroid you have the ablity to vary the grid size dependent on the structure. The calculation grid base resolution is set to the patient. By using a larger grid in areas that are not critical to the calculation you have the ability to speed up the calculation.

1. Open the Calculation Grid block

   

2. The default grid size is set in the site specific configuration settings and is set to the patient. You may make it larger or smaller if needed by typing in the desired number.
3. If you want to use a smaller grid in a target or OAR choose that structure from the dropdown.

   

4. Whatever grid size you set to the patient you may scale down by in powers of 2 in the areas of critical structures and regions of interest by using the +/- on either side of the region spacing setting

   

5. Notice the different size grid in the PTV and the patient

   

6. You may have more than one structure with a different calculation grid spacing set.
7. After you have your calculation grid set hit the OK button
8. You may always come back and adjust your grid if needed