Gun Aiming Level

During radiation gun current is controlled by the gun servo. At the start of the radiation however there is no input for this servo. To guaranty a smooth start the gun servo is controlled by the Gun Aiming level Item 581. According to Elekta the gun aiming must be equal to the gun Imon Item 417.

This method only works on good (internally) calibrated machines. For older machines use the following method:

• Record the gun I ctrl item 527 part 4 during radiation.
• Set this value in part 1 of the same item.
• (This action is quite useful to see if gun current changes in time, called aging!).
• Now inhibit the radiation (Interrupt button).
• Alter the gun standby current item 580 until part 4 of Gun I ctrl is the same as part 1.
• The current in Gun Standby item 580 is the new Gun Aiming level item 581.
• Reset the old Gun stby value.
• Start radiation and check for a smooth start.

For electrons: Dose rate is controlled and set for 400 mu/minute with item 387 Dose level. (Use Hump Gain Item 386 for fast rise time but watch out for overshoot).

For photons: Photon mode is more complicated. Read TSD for more details.