Physics Bucharest 2017

Secondary Sources in External Beam RT

Secondary barriers are designed to protect individuals beyond the treatment room from:

Leakage: dependent on design, typically limited to 0.1 to 0.2% of the primary beam originates from target - not necessarily via the isocentre. IMRT -> the leakage radiation can be significantly increased (a factor of 10 is often assumed). Scatter: assumed to come from the patient and room walls. Difficult to calculate - use largest field size for measurements the lower the radiation energy, the more of a concern for photon beams.