1958-1959 / 3107
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).
Secondary Sources in External Beam RT
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.