Dose Course 2018_Flipping book

Backscatter into the monitor chamber

• The signal from the monitor chamber can be affected from particles which have backscattered from the upper part of the jaws into the chamber (dependent on linac head and monitor chamber design, ) • At narrower collimations there is more backscatter than in larger fields  monitor chamber reaches faster its pre-set value  linac relative output decreases with decreasing field size

Verhaegen & Seuntjens, Phys. Med. Biol, 48 (2003) R107-R164