Advanced Physics for Brachytherapy 2018

Geometry for actual measurement of S K

For low energy sources, simulations must also account for the WAFAC - 7.6 o half angle .

• Due to polar angle averaging, S K increases for sources with radioactivity distributed over cyl. ends, leading to Λ WAFAC lower than Λ point results. • This effect depends on the ratio of marker diameter to marker length. • Differences between Λ WAFAC and Λ point range from non-detectable to 3.5%.

Figure from : J. F. Williamson, Med. Phys. 27 (4) 643 2000